Gzdecompressstr data error

gzdecompressstr data error

The zlib compressed data format is described in RFC 1950, The library also supports reading and writing files in gzip .gz) format with Zlib::Error. GZDecompressStr can't unpack column anycodings_blob data but unpack data from file witout anycodings_blob problems. How to say SQLite, store. Hello I found some data on the web that requires me to open a.gz file and a.json. data = JSON.parse(str). and this is the error that is displayed.

Gzdecompressstr data error - suggest you

Command Line Fanatic

My very first post on this blog, 5 years ago, was a walk-through of the source code for a sample gunzip implementation. I've gotten quite a bit of feedback on it, mostly positive; it's still the most detailed post I've been able to put up here. Part of that write-up included bits and pieces of a gunzip session of an attached gzipped file, bit-for-bit. Recently, a very attentive commenter named Djibi pointed out that the attachment didn't quite match the examples in the post. My memory from that far back is hazy, but the only way I can imagine that happening is if I wrote the post based on one version of the attachment and then made a modification to the attachment without subsequently reviewing the text to ensure that it matched. Although I've gone through and updated the text to match the attachment per Djibi's very detailed analysis, I must admit that, after 5 years, I myself found the post hard to read through, as I was jumping around from one section to another. It occurred to me that a good companion piece would be a complete walk through of the gunzip process for the sample attachment. After all, this is the web and I don't have to worry about page count here! You may want to familiarize yourself with the original post before going through this one, as I assume below that you have a good understanding of Huffman codes and the LZ77 algorithm.

If you download the Attachment in question, you'll see that it's a 4704 byte file containing the gzipped representation of the source code presented in the original post, . Of course, if you try to open up a gzipped file the normal way, by double-clicking on it or whatever your desktop equivalent is, your OS is likely to decompress it on your behalf — but for the purposes of following along with this post, you don't want that: you want the "before" representation, as I'll be walking through the process of going from the before to the after. If you're using a Unix-type OS, you probably have the (objectdump) utility installed that can be used to see a byte-level representation of any file. If you run that utility (or any similar hexadecimal viewer or editor), you'll see that the unambiguous, canonical representation of the file, shown in figure 1, below.

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Figure 1: Full hexadecimal representation of gunzip.c.gz

The facility is byte-oriented; with the arguments shown above, you'll get a hexadecimal representation of every byte in the referenced file. However, compressed files, by their nature, need to take maximum advantage of every single bit — so, to get a good gzip-eye view of this file, you need to break it down to its individual bits. However, if you learned to program any time in the past 40 years or so, you're probably used to the big-endian representation of binary data, where the most-significant bit is shown in the left-most position and the least-significant bit is shown in the right-most position. So the first byte of this file, hexadecimal 1F would be represented in binary as 00011111 and the second byte, hexadecimal 8B, as 10001011. The LZ77 specification that the gzip format is based on, though, is centered around the little-endian format: here, the first two bytes would be represented as 1111100011010001. In other circumstances, this wouldn't make a difference, since you'd be doing byte-for-byte comparisons anyway, but since compression algorithms make optimal use of every bit, the conceptual ordering of the bits makes a big difference, as codes span bytes and you have to put the bits into the correct order to reconstruct the file. Keep in mind as you read this post that the bits shown probably appear "backwards".

The first 10 bytes of figure 1 are the standard GZIP header, which is defined in bytes so the bit-ordering is immaterial. This breaks down to the representation shown in figure 2.

Standard GZIP declaration
Compression method: 0x08 represents GZIP
Flags (see below)
Timestamp
Extra flags
Operating System

Figure 2: standard 10-byte GZIP header

The flags byte, byte 4, is interpreted as shown in table 1. In the case of the attachment displayed in figure 1, only bit 8 is set, indicating that a null-terminated name string follows the header.
Bit mask (in big-endian format)Meaning
00000001Text follows
00000010Header CRC follows
00000100"Extra" follows
00001000Name follows
00010000Comment follows

Table 1: Flag bit meanings

In essence, the flags byte indicates that the header can be followed by up to five null- terminated strings, which must at least be skipped over before the actual gzipped-proper content appears. In this case, it is the 9-byte ASCII-encoded string: or "". After these first 19 bytes, bit ordering begins to matter. Figure 3 presents the binary representation of the remaining 4,685 bytes of the gzipped attachment file, in little-endian order, with the least significant bits appearing first.

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Figure 3: Attachment #1 in little-endian bit format

I'll start by focusing on the first line of figure 3:

As described in part 1, the first bit is a "block" indicator - if it's set to 1, which it is in this case, then this is the last "block" in the file. You'll see multiple blocks in very large gzipped files, but this one is small enough that it only needs one block. The following two bits, in this case, are the block format. Here the block format is "dynamic huffman tree" indicating that the next bit sequence is a Huffman key to a Huffman coded representation of another Huffman key to the Huffman coded representation of the actual gzipped content. This is followed by the 5-bit length of the literals tree, the 5-bit length of the distance tree and the 3-bit length of the initial Huffman key.

So, bytes 20-22 of the attached file — , whose little-endian bit representation is — are interpreted as (remember to read the bits in the table "backwards"):

1last block in this file
012: dynamic huffman table
1110123 literals codes
1101127 distance codes
00018 keys in the following huffman key table

Figure 4: Huffman key table header

where the remaining seven bits of byte 22, , are unused (so far).

Since there are always at least five entries in the dynamic huffman key table, add 4 to 8 to get the actual count of twelve. That means that there are 12 3-bit codes that describe a Huffman table that is itself the key to the following Huffman table.

Bit patternnumeric valuelength of huffman code
011616
111717
111718
11030
11038
01027
11039
11036
001410
00145
101511
00144

Figure 5: Dynamic Huffman table specification

Indicating that the Huffman codes that encode the subsequent table are:

Figure 6: Dynamic Huffman table codes

At this point, I've read a little more than half-way through byte 26 of the first line of figure 3, and the file pointer is set to:

This is followed by the 308 codes-worth of Huffman-code lengths shown in figure 7 (recall that this is additionally run-length encoded, so there aren't 308 actual code values here):

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Huffman codevaluerepeat countNotes
11111101710first 10 codes (0-9) are empty, don't appear
007The code for the literal value 10 is seven bits
1111111182121 more zeros; values 11-31 don't appear
11015The code for value 32 is five bits
1019The code for value 33 is 9 bits
1008...
111010
0100
1019
1008
1019
007
1008
1008
1008
007
007
007
1019
007
0116
007
007
1008
007
007
1008
007
1008
1019
007
1008
007
1008
111010
0100
1019
111010
1019
1019
1008
1019
0100
111010
1019
0100
0100
111010
1019
1019
1019
1111011
0100
1019
111110163
0100
0100
111010
0100
1111011
1019
1111011
1019
0100
007
0100
0116
007
0116
0116
11015
007
1008
007
0116
1008
1019
0116
007
0116
0116
007
0100
0116
0116
0116
007
1008
1008
1019
1008
111010
111010
111010
1008
111111118130130 consecutive 0's, indicating that the codes from 126-255 are not included in this table
1111011
11004
11004
11004
11015
111110163
0116
11015
11015
11015
0116
0116
007
007
007
1008
1008
1008
111010
111010
0100
111010
1008
1019
111110163
1008
007
007
11015
0116
11004
11004
11004
11015
11004
11015
11004
11015
11004
111110166
11015
11015
0116

Figure 7: Compressed data Huffman codes specification

Which work out to two Huffman code trees — one for the literals:

Figure 8: Compressed data literals Huffman code values

and a smaller one for the distances:

Figure 9: Compressed data distances Huffman code values

These tables make a lot of sense if you think about the nature of the file that was compressed — it's C source code, so it's ASCII-encoded. The byte value 10 appears fairly often: that's the line-ending code, so it gets a literal code. 32 is the ASCII code for a space character, so it gets a short Huffman code since it appears quite a bit. Although there are codes here for 33, 34 and 35 (ASCII !, " and #, respectively), the $ character 36 never appears in the zipped source, so no code is defined for it. There are codes here for most of the capital letters (range 65-90), but notice that their literals codes are relatively long, since there aren't many capital letters in the actual source code file. The lower-case letters (97-122) get shorter codes in the literals table, since they appear more often than the upper-case characters. The non-printable ASCII characters less than 32 (other than the CR code 10) and greater than 128 don't have codes because they don't appear in the source file.

At this point, the decompression values have read the full Huffman codes for the actual payload, which follows immediately. The last few bits that were read by the decompressor were: 1101 1101 011, which were 5, 5 and 6, according to the dynamic Huffman table from Figure 6. At this point, 86 bytes of the file have been consumed, and the file pointer is at the sixth byte of the fifth line of Figure 3 (hexadecimal ), pointed at the very last bit of the byte (remember, this is the most significant bit, because we're working LSB to MSB):

Almost all of the remainder of the file (until the trailer, which begins on byte 4696) is interpreted according to the Huffman tables in figures 8 and 9. As you can see, the Huffman compression tables are very efficient; only 65 bytes of the 4,704-byte gzipped file are "dictionary" information that's needed to interpret the remainder of the file, with an additional 20 bytes of header information and 8 bytes of trailer information.

So far, though, I haven't shown any Lempel-Ziv compression! At this point, all I have are the Huffman codes that represent four types of codes: a "normal" byte that should be inflated to its representative value, a stop code that indicates that compression should halt (i.e. EOF), a length code that indicates a "back pointer" to a prior part of the uncompressed output that should be represented and length codes that indicate how much of the previous data should be copied. Figure 10, below, shows the entire process and details how each code is interpreted; again, refer to RFC 1951 or my earlier discussion of GZIP/DEFLATE to fully interpret the details below.

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Byte numberBits readCorresponding (Huffman code)Type (normal, stop or distance)ASCII value (for normal codes)Extra bits (codes 265-285)LengthDistance bits readExtra distance (distance codes 3+)Distance (Huffman code)copied value
86111111001035normal byte#
88100010105normal bytei
88100100110normal byten
8910000099normal bytec
90100011108normal bytel
911101011117normal byteu
92100001100normal byted
9200111101normal bytee
930011032normal byte
941110011060normal byte<
95100111115normal bytes
95101000116normal bytet
96100001100normal byted
97100010105normal bytei
98100101111normal byteo
98101110046normal byte.
991101000104normal byteh
1001110011162normal byte>
101101100010normal byte\n
102111111001035normal byte#
10301100265distance code11211000218include <std
105100011108normal bytel
106100010105normal bytei
106110011098normal byteb
10701110267distance code11611000319.h>\n#include <st
109100110114normal byter
110100010105normal bytei
111100100110normal byten
11111101001103normal byteg
11201101266distance code11411000319.h>\n#include <
11400111101normal bytee
115100110114normal byter
115100110114normal byter
116100100110normal byten
11701110267distance code01500011058o.h>\n#include <
11901111197normal bytea
119100111115normal bytes
120100111115normal bytes
12100111101normal bytee
122100110114normal byter
122101000116normal bytet
1230001258distance code411000319.h>\n
125101100010normal byte\n
12511110011147normal byte/
12711110011147normal byte/
1280011032normal byte
1281101000104normal byteh
12900111101normal bytee
13001111197normal bytea
131100001100normal byted
13100111101normal bytee
132100110114normal byter
1330011032normal byte
133100111115normal bytes
13400111101normal bytee
1351101010112normal bytep
13601111197normal bytea
136100110114normal byter
13701111197normal bytea
138101000116normal bytet
13900111101normal bytee
139100001100normal byted
1400011032normal byte
1411100111102normal bytef
141100110114normal byter
142100101111normal byteo
1431101001109normal bytem
1440011032normal byte
1441101001109normal bytem
14501111197normal bytea
146100010105normal bytei
147100100110normal byten
1480011032normal byte
1480000257distance code300101579str
1501101011117normal byteu
15110000099normal bytec
151101000116normal bytet
1520011032normal byte
1531100111102normal bytef
154100101111normal byteo
154100110114normal byter
1550011032normal byte
156101000116normal bytet
1571101000104normal byteh
15700111101normal bytee
1580011032normal byte
1591101111034normal byte"
160100111115normal bytes
160100010105normal bytei
1611111111000122normal bytez
16200111101normal bytee
163100101111normal byteo
1641100111102normal bytef
1651101111034normal byte"
1660011032normal byte
166110011098normal byteb
16700111101normal bytee
168100011108normal bytel
169100101111normal byteo
16911101100119normal bytew
170101100010normal byte\n
171101000116normal bytet
17211101101121normal bytey
1731101010112normal bytep
17400111101normal bytee
174100001100normal byted
17500111101normal bytee
1761100111102normal bytef
17701001261distance code70000537 struct
178101100010normal byte\n
1791111111001123normal byte{
180101100010normal byte\n
1810011032normal byte
1820011032normal byte
1831101011117normal byteu
183100100110normal byten
184100111115normal bytes
185100010105normal bytei
18611101001103normal byteg
187100100110normal byten
1870000257distance code30010367ed
18910000099normal bytec
1901101000104normal byteh
19101111197normal bytea
191100110114normal byter
1920011032normal byte
193100010105normal bytei
194100001100normal byted
19411111010191normal byte[
1950011032normal byte
196101111050normal byte2
1970011032normal byte
19811111011093normal byte]
199110001159normal byte;
200101010268distance code017111100024\n unsigned char
20210000099normal bytec
202100101111normal byteo
2031101001109normal bytem
2041101010112normal bytep
205100110114normal byter
20600111101normal bytee
206100111115normal bytes
207100111115normal bytes
208100010105normal bytei
208100101111normal byteo
209100100110normal byten
210110010195normal byte_
2111101001109normal bytem
21200111101normal bytee
212101000116normal bytet
2131101000104normal byteh
214100101111normal byteo
215100001100normal byted
215101010268distance code1180000335;\n unsigned char
2171100111102normal bytef
218100011108normal bytel
21901111197normal bytea
22011101001103normal byteg
221100111115normal bytes
221101010268distance code11811000622;\n unsigned char
2231101001109normal bytem
224101000116normal bytet
225100010105normal bytei
2261101001109normal bytem
22700111101normal bytee
22711111010191normal byte[
2280011032normal byte
2291110001152normal byte4
230101011269distance code12000102286 ];\n unsigned char
23200111101normal bytee
233111111000120normal bytex
234101000116normal bytet
235100110114normal byter
23501111197normal bytea
236110010195normal byte_
2371101100270distance code0230001856flags;\n unsigned char
239100101111normal byteo
2400000257distance code311000319s;\n
24111101110125normal byte}
242101100010normal byte\n
24311101001103normal byteg
2441111111000122normal bytez
245100010105normal bytei
2461101010112normal bytep
247110010195normal byte_
24801000260distance code61101049241header
250110001159normal byte;
251101100010normal byte\n
252101011269distance code120110101193\ntypedef struct\n{\n
25401100265distance code0110000032gzip_header
2560011032normal byte
25601010262distance code80000739header;\n
25801100265distance code01100101074 unsigned
260100111115normal bytes
2611101000104normal byteh
262100101111normal byteo
262100110114normal byter
263101000116normal bytet
2640011032normal byte
264111111000120normal bytex
266100011108normal bytel
26600111101normal bytee
267100100110normal byten
268101010268distance code11811001197;\n unsigned char
2701110000142normal byte*
2710010259distance code51100131127extra
273101011269distance code01911000723;\n unsigned char *
2751100111102normal bytef
275100100110normal byten
27601111197normal bytea
2771101001109normal bytem
27800111101normal bytee
278101011269distance code12011000723;\n unsigned char *f
2800000257distance code301007263com
2821101001109normal bytem
28300111101normal bytee
284100100110normal byten
285101000116normal bytet
285101011269distance code01911001197;\n unsigned short
28810000099normal bytec
288100110114normal byter
28910000099normal bytec
29001111049normal byte1
291110000154normal byte6
291110001159normal byte;
2920011032normal byte
2930000257distance code31101130414//
295101000116normal bytet
2961101000104normal byteh
297100010105normal bytei
297100111115normal bytes
2980011032normal byte
2991101010112normal bytep
300100110114normal byter
300100101111normal byteo
301101000116normal bytet
30200111101normal bytee
30210000099normal bytec
303101000116normal bytet
304100111115normal bytes
3050010259distance code5110116390 the
30701000260distance code6001122150header
30901100265distance code1120001351\n unsigned
310100011108normal bytel
311100101111normal byteo
312100100110normal byten
31311101001103normal byteg
3140001258distance code40001250 crc
315101111151normal byte3
316101111050normal byte2
317110001159normal byte;
3180011032normal byte
318101011269distance code3220001351 // this protects the
320100001100normal byted
321100101111normal byteo
32210000099normal bytec
3231101011117normal byteu
3230001258distance code41100110106ment
325101010268distance code0170001553\n unsigned long
327100010105normal bytei
3280001258distance code41101183467size
33001011263distance code9010025281;\n}\ngzip_
3321100111102normal bytef
333100010105normal bytei
333100011108normal bytel
3340000257distance code31111101012e;\n
336101100010normal byte\n
337111111001035normal byte#
3380000257distance code3010020276def
340100010105normal bytei
341100100110normal byten
34100111101normal bytee
3420011032normal byte
34311110110070normal byteF
34411111001184normal byteT
3451110100069normal byteE
346111111011188normal byteX
34711111001184normal byteT
3480011032normal byte
3490001258distance code4111111000
350101110148normal byte0
351111111000120normal bytex
352101110148normal byte0
35301111049normal byte1
354101001264distance code1011000622\n#define F
356111111010172normal byteH
35711110101067normal byteC
35811111000182normal byteR
35911110101067normal byteC
36001010262distance code811000622 0x0
362101111050normal byte2
363101001264distance code1011000622\n#define F
3650000257distance code300001244EXT
36611111000182normal byteR
36711110100165normal byteA
36801001261distance code711000622 0x0
3701110001152normal byte4
371101001264distance code1011000622\n#define F
37311110111178normal byteN
37411110100165normal byteA
37511110111077normal byteM
3761110100069normal byteE
37701010262distance code800001345 0x0
379110001056normal byte8
380101001264distance code1011000622\n#define F
38111110101067normal byteC
38211111000079normal byteO
38411110111077normal byteM
38511110111077normal byteM
3861110100069normal byteE
38711110111178normal byteN
38811111001184normal byteT
3890001258distance code411000622 0x
39101111049normal byte1
391101110148normal byte0
392101011269distance code2211101111395\n\ntypedef struct\n{\n
39501011263distance code9001141169unsigned
397100010105normal bytei
397100100110normal byten
398101000116normal bytet
3990011032normal byte
39901110267distance code1160100114370len;\n unsigned
4020001258distance code411000319int
40310000099normal bytec
404100101111normal byteo
405100001100normal byted
4050001258distance code4001159187e;\n}
4070011032normal byte
408101100010normal byte\n
409101000116normal bytet
409100110114normal byter
41000111101normal bytee
41100111101normal bytee
411110010195normal byte_
412100100110normal byten
4130010259distance code51111101113ode;\n
41501110267distance code0150010872\ntypedef struct
4160011032normal byte
4171101000104normal byteh
4181101011117normal byteu
4191100111102normal bytef
4201100111102normal bytef
4211101001109normal bytem
42101111197normal bytea
422100100110normal byten
4230010259distance code5111100529_node
425110010195normal byte_
42501000260distance code600102387t\n{\n
42701011263distance code900011058int code;
4290001258distance code4010043299 //
431101101145normal byte-
43201111049normal byte1
4320010259distance code50101223735 for
434100100110normal byten
435100101111normal byteo
436100100110normal byten
437101101145normal byte-
437100011108normal bytel
43800111101normal bytee
43901111197normal bytea
4401100111102normal bytef
4400011032normal byte
4410001258distance code40000739node
443100111115normal bytes
4430000257distance code30000436\n
445101011269distance code22100011462struct huffman_node_t
4470011032normal byte
4471110000142normal byte*
4481111111000122normal bytez
45000111101normal bytee
450100110114normal byter
451100101111normal byteo
452110001159normal byte;
4531101100270distance code326111100630\n struct huffman_node_t *
455100101111normal byteo
456100100110normal byten
4560010259distance code5010076332e;\n}\n
45801100265distance code11211000622huffman_node
460101011269distance code3220101103615;\n\ntypedef struct\n{\n
4630001258distance code400113131int
46400111101normal bytee
465100100110normal byten
4660010259distance code50101247759d;\n
4680001258distance code41111100210int
469110011098normal byteb
470100010105normal bytei
471101000116normal bytet
472110010195normal byte_
4730000257distance code31101033225len
47411101001103normal byteg
475101000116normal bytet
4761101000104normal byteh
47701100265distance code11200011462;\n}\nhuffman_
479100110114normal byter
48001111197normal bytea
480100100110normal byten
48111101001103normal byteg
4820001258distance code400011563e;\n\n
484100111115normal bytes
484101000116normal bytet
48501111197normal bytea
486101000116normal bytet
487100010105normal bytei
48710000099normal bytec
4880011032normal byte
48911101011118normal bytev
490100101111normal byteo
490100010105normal bytei
491100001100normal byted
4920011032normal byte
493110011098normal byteb
4931101011117normal byteu
494100010105normal bytei
495100011108normal bytel
496100001100normal byted
497110010195normal byte_
49701010262distance code80000133huffman_
4990001258distance code41101056248tree
501101100140normal byte(
50201101266distance code01300115133 huffman_node
5040011032normal byte
5041110000142normal byte*
505100110114normal byter
506100101111normal byteo
507100101111normal byteo
508101000116normal bytet
508101101044normal byte,
509101100010normal byte\n
5100011032normal byte
5111101110272distance code031111111000
5130001258distance code41100121117int
5150010259distance code500103195range
5160001258distance code41100123119_len
5181101110272distance code33400001446,\n
52001101266distance code013001118146huffman_range
5220000257distance code311001399 *r
5240010259distance code51111110106ange
5261110000041normal byte)
52701011263distance code91101010202\n{\n int
5291110000142normal byte*
530110011098normal byteb
530100011108normal bytel
531110010195normal byte_
53210000099normal bytec
533100101111normal byteo
5341101011117normal byteu
53401000260distance code60101203715nt;\n
5370010259distance code511000016int *
538100100110normal byten
5390000257distance code3011013781ext
541110010195normal byte_
54201000260distance code61101132416code;\n
5440011032normal byte
5440011032normal byte
54501011263distance code91101131415tree_node
5470011032normal byte
5481110000142normal byte*
5490001258distance code41111100210tree
5500000257distance code31101018210;\n\n
55201011263distance code91101054246 int bit
554100111115normal bytes
555110001159normal byte;
55601100265distance code0111101117401\n int code
5580011032normal byte
559110010061normal byte=
5600011032normal byte
560101110148normal byte0
56101010262distance code81111101315;\n int
563100100110normal byten
56401010262distance code8111110008;\n int
56501111197normal bytea
56610000099normal bytec
567101000116normal bytet
568100010105normal bytei
56811101011118normal bytev
56900111101normal bytee
57001010262distance code8010012268_range;\n
57201000260distance code611000319 int
5741101001109normal bytem
57501111197normal bytea
575111111000120normal bytex
576110010195normal byte_
57701100265distance code112010051307bit_length;\n
579101100010normal byte\n
5800010259distance code50101247759 //
582100111115normal bytes
583101000116normal bytet
58400111101normal bytee
5841101010112normal bytep
5850011032normal byte
58601111049normal byte1
5870011032normal byte
587101101145normal byte-
5880011032normal byte
5891100111102normal bytef
590100010105normal bytei
59011101001103normal byteg
5911101011117normal byteu
592100110114normal byter
59300111101normal bytee
5940011032normal byte
594100101111normal byteo
5951101011117normal byteu
5960000257distance code31101133417t h
598100101111normal byteo
59911101100119normal bytew
60001000260distance code60101233745 long
60201010262distance code8001133161bl_count
604101101044normal byte,
6050011032normal byte
60501011263distance code9001126154next_code
607101101044normal byte,
6080010259distance code5001124152 tree
6100011032normal byte
61000111101normal bytee
611101000116normal bytet
61210000099normal bytec
612101110046normal byte.
61301001261distance code70010064\n // s
6151101000104normal byteh
616100101111normal byteo
6171101011117normal byteu
618100011108normal bytel
6180000257distance code3010099355d b
62000111101normal bytee
6210011032normal byte
621110011098normal byteb
62201111197normal bytea
623100111115normal bytes
6240000257distance code30101100612ed
626100101111normal byteo
627100100110normal byten
6270010259distance code5011061829 the
6290010259distance code51100126122range
6310010259distance code5011081849s pro
63311101011118normal bytev
634100010105normal bytei
635100001100normal byted
63600111101normal bytee
6360010259distance code51101152436d;\n
63801101266distance code11400110128max_bit_length
64001010262distance code8001155183 = 0;\n
6420001258distance code4010173585for
644101100140normal byte(
6450011032normal byte
646100100110normal byten
6460010259distance code51111101214 = 0;
6480000257distance code31111110106 n
6501110011060normal byte<
651101001264distance code10010097353 range_len
6530000257distance code31111101214; n
6541110001043normal byte+
6551110001043normal byte+
6560000257distance code3010048304 )\n
6580011032normal byte
6590011032normal byte
6591111111001123normal byte{
6610010259distance code50100107363\n
663100010105normal bytei
6631100111102normal bytef
6640000257distance code30000840 (
6660010259distance code5111100529range
66711111010191normal byte[
6680000257distance code30000840 n
67011111011093normal byte]
671101110046normal byte.
67201100265distance code01100101175bit_length
6741110011162normal byte>
67501110267distance code11600102892 max_bit_length
6771110000041normal byte)
6780010259distance code50001149\n
6791111111001123normal byte{
68001001261distance code71101135419\n
683101010268distance code0171100125121max_bit_length =
685101011269distance code2210010569range[ n ].bit_length
687110001159normal byte;
6880010259distance code500001345\n
68911101110125normal byte}
690101100010normal byte\n
69101000260distance code61111111103 }\n
69301010262distance code81101059251bl_count
6950000257distance code300001345 =
6961101001109normal bytem
69701111197normal bytea
698100011108normal bytel
699100011108normal bytel
699100101111normal byteo
70010000099normal bytec
701101100140normal byte(
7020011032normal byte
70201000260distance code601114591483sizeof
705101100140normal byte(
7060010259distance code5010077333 int
7071110000041normal byte)
7080011032normal byte
7091110000142normal byte*
7100000257distance code3001113141 (
71201110267distance code01500102488max_bit_length
7141110001043normal byte+
7150000257distance code3010073329 1
7171110000041normal byte)
7180011032normal byte
7181110000041normal byte)
7190001258distance code40010872;\n
72101011263distance code9010048304next_code
72311110001275distance code45500011563 = malloc( sizeof( int ) * ( max_bit_length + 1 ) );\n
7250010259distance code50100101357tree
727101010268distance code11800011058= malloc( sizeof(
729101001264distance code10010121533tree_node
73101000260distance code60010064) * (
73301001261distance code7110108200range[
73501011263distance code9010051307range_len
7370000257distance code31101172456 -
73901111049normal byte1
7400000257distance code31101020212 ].
7420000257distance code3011038806end
744101001264distance code1000101276 + 1 ) );\n
7450001258distance code40100122378\n m
74700111101normal bytee
7481101001109normal bytem
749100111115normal bytes
75000111101normal bytee
750101000116normal bytet
751101100140normal byte(
75201100265distance code0111101180464 bl_count,
75411110011039normal byte'
7551111111111092normal byte\
757101110148normal byte0
75711110011039normal byte'
759101101044normal byte,
75911110000274distance code043001117145 sizeof( int ) * ( max_bit_length + 1 ) );\n
76211110000274distance code2451101141425\n for ( n = 0; n < range_len; n++ )\n {\n
76501010262distance code8110016102bl_count
76711111010191normal byte[
7681101100270distance code0231101146430 range[ n ].bit_length
77111111011093normal byte]
7720011032normal byte
7721110001043normal byte+
773110010061normal byte=
7740011032normal byte
77501001261distance code71101127411\n
77701100265distance code0110000133range[ n ].
7790001258distance code4001153181end
780101101145normal byte-
7810000257distance code311001298 (
7830001258distance code4110014100( n
7851110011162normal byte>
7860011032normal byte
786101110148normal byte0
7870000257distance code31100124120 )
789111111001163normal byte?
790101001264distance code10111100630 range[ n
792101001264distance code101101024216- 1 ].end
79411110100058normal byte:
7950001258distance code401111281152 -1
7980010259distance code5010036292);\n
79911101110125normal byte}
80001100265distance code1120101196708\n\n // step
803101111050normal byte2
804101101044normal byte,
8040011032normal byte
805100001100normal byted
806100010105normal bytei
807100110114normal byter
8070000257distance code301114461470ect
809100011108normal bytel
81011101101121normal bytey
81101000260distance code610003991935 from
81311111000182normal byteR
81511110110070normal byteF
81611110101067normal byteC
81701100265distance code0111101058250\n memset(
81901100265distance code0110101193705next_code,
82111110000274distance code5481101059251'\0', sizeof( int ) * ( max_bit_length + 1 ) );\n
82401010262distance code81101058250 for (
8260001258distance code40110122890bits
8280000257distance code31101061253 =
83001111049normal byte1
831110001159normal byte;
83101000260distance code6111110019 bits
8331110011060normal byte<
834110010061normal byte=
83501110267distance code116011083851 max_bit_length;
8370010259distance code511000723 bits
83901101266distance code01301009265++ )\n {\n
84101001261distance code701011513code =
843101100140normal byte(
84401000260distance code6111110008 code
8461110001043normal byte+
84701100265distance code011010025281 bl_count[
8490010259distance code50010266bits
8500010259distance code51101020212- 1 ]
8520000257distance code3110014100 )
8541110011060normal byte<
8551110011060normal byte<
8560000257distance code300102185 1;
858101001264distance code100101228740\n if (
86001110267distance code0150000537bl_count[ bits
86211111011093normal byte]
86301110267distance code0150101206718 )\n {\n
86501011263distance code91101010202next_code
86701011263distance code9111100731[ bits ]
869110010061normal byte=
8700011032normal byte
87001010262distance code80111541078code;\n
87301010262distance code80101192704 }\n }\n
87501100265distance code011010024280\n // step
877101111151normal byte3
8781101101271distance code330010024280, directly from RFC\n memset(
8800001258distance code4010182594tree
88201110267distance code116010019275, '\0', sizeof(
88401101266distance code1140101102614tree_node ) *
8870010259distance code500102286\n
88811101111273distance code3380101107619( range[ range_len - 1 ].end + 1 ) );\n
8910011032normal byte
89201101266distance code01301111221146 active_range
8941101100270distance code1240110227995 = 0;\n for ( n = 0; n <
897110010061normal byte=
8981101101271distance code02700101175 range[ range_len - 1 ].end
900101011269distance code22101102451013; n++ )\n {\n if (
9020001258distance code4010115527n >
90401001261distance code70001250range[
90601101266distance code01300103195active_range
90801000260distance code61100129125].end
91001101266distance code114010029285)\n {\n
91201100265distance code1120000032active_range
9141110001043normal byte+
9151110001043normal byte+
91601010262distance code8010019275;\n }\n
918101010268distance code0170111651089\n if ( range[
92001110267distance code0150010771active_range ].
9221101100270distance code2250111591083bit_length )\n {\n
9250001258distance code4010010266tree
92701000260distance code60101158670[ n ].
9290001258distance code4001138166len
930110010061normal byte=
9311101110272distance code23300011462 range[ active_range ].bit_length
933110001159normal byte;
934101100010normal byte\n
93501001261distance code70001856\n
9370010259distance code51100112108if (
93901101266distance code11400011361tree[ n ].len
94011110010033normal byte!
941110010061normal byte=
9420001258distance code40101213725 0 )
94401001261distance code7111100731\n
94601010262

Importing Landsat data into ENVI

Landsat data provided by the USGS are distributed as a single file in an archived and zipped “.TAR.GZ” format.   These files must be extracted and uncompressed before you can use them.

After downloading a file move it to a separate folder in your user section of the server.  Double click on it to load the program 7-Zip, showing the “.tar” file.  Right-click on the “.tar” file and select Open Inside to display the detail data files.  Click on the blue Extract icon and select the destination folder to extract the individual files that comprise the entire image.  Each data layer is a separate TIF image file.  There are also two text files with the same base filename but ending with _GCP.TXT and _MTL.TXT.  This file structure is referred to as “GeoTIFF with Meta data”.

Level 1 Image

ENVI can directly and easily open data in this USGS format.  Each data layer will end in …_T1_B1.TIF (or B2.TIF, B3.TIF, etc.).   From the ENVI main menu select File

How to use TDecompressionStream? [closed]

It raises an exception when I try to read from the stream. What is wrong?

The most plausible explanation is that you are not passed valid GZIP encoded data to the stream. It's impossible for us to say why your data would be invalid because we don't know its provenance. To solve your problem you must first of all work out why your data is invalid.

One obvious issue with your code is the use of a string to represent binary data. GZIP operates on binary data. It compresses byte arrays to byte arrays. To work with text you use a predetermined encoding to convert text to binary. Once compressed, you would use something like MIME or base64 to encode the compressed binary as text. Perhaps your data is of this form: binary encoded as text.

Another possible issue is that your Delphi unit is deficient, or simply out-dated. You don't state in the question which version of Delphi you use. Perhaps you are using an old version of Delphi that does not ship with a unit and are using a third party unit that is no good.

Open and navigate to the _MTL.TXT file.  ENVI will automatically open the Landsat image with all bands in the correct order.  The reflective bands are placed in one file, the thermal band(s) in another file.  There will be a 15m panchromatic file for ETM and OLI sensors and a 30m Cirrus file for the OLI sensor.

While you can work with these data as they are, ENVI has only created a temporary virtual layer stack that is constantly resampled as you move around the image.  You should save each file as a new dataset.  From the ENVI main menu select File

10.6 Compressed Files

Although storage space and transmission bandwidth are increasingly cheap and abundant, in many cases you can save such resources, at the expense of some computational effort, by using compression. Since computational power grows cheaper and more abundant even faster than other resources, such as bandwidth, compression's popularity keeps growing. Python makes it easy for your programs to support compression by supplying dedicated modules for compression as part of every Python distribution.

10.6.1 The gzip Module

The module lets you read and write files compatible with those handled by the powerful GNU compression programs gzip and gunzip. The GNU programs support several compression formats, but module supports only the highly effective native gzip format, normally denoted by appending the extension .gz to a filename. Module supplies the class and an factory function.


class GzipFile(=None,=None,=9, =None)

Creates and returns a file-like object that wraps the file or file-like object . supplies all methods of built-in file objects except and . Thus, is not seekable: you can only access sequentially, whether for reading or writing. When is , must be a string that names a file: opens that file with the given (by default, ''), and wraps the resulting file object. should be one of '', '', '', or . If is , uses the mode of if it is able to find out the mode; otherwise it uses ''. If is , uses the filename of if able to find out the name; otherwise it uses ''. is an integer between and : requests modest compression but fast operation, and requests the best compression feasible, even if that requires more computation.

File-like object generally delegates all methods to the underlying file-like object , transparently accounting for compression as needed. However, does not allow non-sequential access, so does not supply methods and . Moreover, calling does not close when was created with an argument that is not . This behavior of is very important when is an instance of , since it means you can call after to get the compressed data as a string. This behavior also means that you have to call explicitly after calling .


open(,='rb',=9)

Like ,,, but is mandatory and there is no provision for passing an already opened .

Say that you have some function that writes data to a text file object , typically by calling and/or . Getting to write data to a gzip-compressed text file instead is easy:

import gzip underlying_file = open('x.txt.gz', 'wb') compressing_wrapper = gzip.GzipFile(fileobj=underlying_file, mode='wt') f(compressing_wrapper) compressing_wrapper.close( ) underlying_file.close( )

This example opens the underlying binary file x.txt.gz and explicitly wraps it with , and thus, at the end, we need to close each object separately. This is necessary because we want to use two different modes: the underlying file must be opened in binary mode (any translation of line endings would produce an invalid compressed file), but the compressing wrapper must be opened in text mode because we want the implicit translation of to . Reading back a compressed text file, for example to display it on standard output, is similar:

import gzip, xreadlines underlying_file = open('x.txt.gz', 'rb') uncompressing_wrapper = gzip.GzipFile(fileobj= underlying_file, mode='rt') for line in xreadlines.xreadlines(uncompressing_wrapper): print line, uncompressing_wrapper.close( ) underlying_file.close( )

This example uses module , covered earlier in this chapter, because objects (at least up to Python 2.2) are not iterable like true file objects, nor do they supply an method. objects do supply a method that closely emulates that of true file objects, and therefore module is able to produce a lazy sequence that wraps a object and lets us iterate on the object's lines.

10.6.2 The zipfile Module

The module lets you read and write ZIP files (i.e., archive files compatible with those handled by popular compression programs zip and unzip, pkzip and pkunzip, WinZip, and so on). Detailed information on the formats and capabilities of ZIP files can be found at http://www.pkware.com/appnote.html and http://www.info-zip.org/pub/infozip/. You need to study this detailed information in order to perform advanced ZIP file handing with module .

Module can't handle ZIP files with appended comments, multidisk ZIP files, or .zip archive members using compression types besides the usual ones, known as stored (when a file is copied to the archive without compression) and deflated (when a file is compressed using the ZIP format's default algorithm). For invalid .zip file errors, functions of module raise exceptions that are instances of exception class . Module supplies the following classes and functions.


Returns if the file named by string appears to be a valid ZIP file, judging by the first few bytes of the file; otherwise returns .


class ZipInfo(='NoName',=(1980,1,1,0,0,0))

Methods and of instances return instances of to supply information about members of the archive. The most useful attributes supplied by a instance are:

comment

A string that is a comment on the archive member

compress_size

Size in bytes of the compressed data for the archive member

compress_type

An integer code recording the type of compression of the archive member

date_time

A tuple with 6 integers recording the time of last modification to the file: the items are year, month, day ( and up), hour, minute, second ( and up)

file_size

Size in bytes of the uncompressed data for the archive member

filename

Name of the file in the archive


class ZipFile(,='r',=zipfile.ZIP_STORED)

Opens a ZIP file named by string . can be '', to read an existing ZIP file; '', to write a new ZIP file or truncate and rewrite an existing one; or '', to append to an existing file.

When is '', can name either an existing ZIP file (in which case new members are added to the existing archive) or an existing non-ZIP file. In the latter case, a new ZIP file-like archive is created and appended to the existing file. The main purpose of this latter case is to let you build a self-unpacking .exe file (i.e., a Windows executable file that unpacks itself when run). The existing file must then be a fresh copy of an unpacking .exe prefix, as supplied by www.info-zip.org or by other purveyors of ZIP file compression tools.

is an integer code that can be either of two attributes of module . requests that the archive use no compression, and requests that the archive use the deflation mode of compression (i.e., the most usual and effective compression approach used in .zip files).

A instance supplies the following methods.


Closes archive file . Make sure the method is called, or else an incomplete and unusable ZIP file might be left on disk. Such mandatory finalization is generally best performed with a / statement, as covered in Chapter 6.


Returns a instance that supplies information about the archive member named by string .


Returns a list of instances, one for each member in archive , in the same order as the entries in the archive itself.


Returns a list of strings, the names of each member in archive , in the same order as the entries in the archive itself.


Outputs a textual directory of the archive to file .


Returns a string containing the uncompressed bytes of the file named by string in archive . must be opened for '' or ''. When the archive does not contain a file named , raises an exception.


Reads and checks the files in archive . Returns a string with the name of the first archive member that is damaged, or when the archive is intact.


.write(,=None,=None)

Writes the file named by string to archive , with archive member name . When is , uses as the archive member name. When is , uses 's compression type; otherwise, is or , and specifies how to compress the file. must be opened for '' or ''.


must be a instance specifying at least and . is a string of bytes. adds a member to archive , using the metadata specified by and the data in . must be opened for '' or ''. When you have data in memory and need to write the data to the ZIP file archive , it's simpler and faster to use rather than . The latter approach would require you to write the data to disk first, and later remove the useless disk file. The following example shows both approaches, each encapsulated into a function, polymorphic to each other:

import zipfile def data_to_zip_direct(z, data, name): import time zinfo = zipfile.ZipInfo(name, time.localtime( )[:6]) z.writestr(zinfo, data) def data_to_zip_indirect(z, data, name): import os flob = open(name, 'wb') flob.write(data) flob.close( ) z.write(name) os.unlink(name) zz = zipfile.ZipFile('z.zip', 'w', zipfile.ZIP_DEFLATED) data = 'four score\nand seven\nyears ago\n' data_to_zip_direct(zz, data, 'direct.txt') data_to_zip_indirect(zz, data, 'indirect.txt') zz.close( )

Besides being faster and more concise, is handier because, by working in memory, it doesn't need to have the current working directory be writable, as does. Of course, method also has its uses, but that's mostly when you already have the data in a file on disk, and just want to add the file to the archive. Here's how you can print a list of all files contained in the ZIP file archive created by the previous example, followed by each file's name and contents:

import zipfile zz = zipfile.ZipFile('z.zip') zz.printdir( ) for name in zz.namelist( ): print '%s: %r' % (name, zz.read(name)) zz.close( )

10.6.3 The zlib Module

The module lets Python programs use the free InfoZip zlib compression library (see http://www.info-zip.org/pub/infozip/zlib/), Version 1.1.3 or later. Module is used by modules and , but the module is also available directly for any special compression needs. This section documents the most commonly used functions supplied by module .

Module also supplies functions to compute Cyclic-Redundancy Check (CRC) checksums, in order to detect possible damage in compressed data. It also provides objects that can compress and decompress data incrementally, and thus enable you to work with data streams that are too large to fit in memory at once. For such advanced functionality, consult the Python library's online reference.

Note that files containing data compressed with are not automatically interchangeable with other programs, with the exception of files that use the module and therefore respect the standard format of ZIP file archives. You could write a custom program, with any language able to use InfoZip's free zlib compression library, in order to read files produced by Python programs using the module. However, if you do need to interchange compressed data with programs coded in other languages, I suggest you use modules or instead. Module may be useful when you want to compress some parts of data files that are in some proprietary format of your own, and need not be interchanged with any other program except those that make up your own application.


Compresses string and returns the string of compressed data. is an integer between and : requests modest compression but fast operation, and requests compression as good as feasible, thus requiring more computation.


Decompresses the compressed data string and returns the string of uncompressed data.

How to use TDecompressionStream? [closed]

It raises an exception when I try to read from the stream. What is wrong?

The most plausible explanation is that you are not passed valid GZIP encoded data to the stream. It's impossible for us to say why your data would be invalid because we don't know its provenance. To solve your problem you must first of all work out why your data is invalid.

One obvious issue with your code is the use of a string to represent binary data. GZIP operates on binary data. It compresses byte arrays to byte arrays. To work with text you use a predetermined encoding to convert text to binary. Once compressed, you would use something like MIME or base64 to encode the compressed binary as text. Perhaps your data is of this form: binary encoded as text.

Another possible issue is that your Delphi unit is deficient, or simply out-dated. You don't state in the question which version of Delphi you use. Perhaps you are using an old version of Delphi that does not ship with a unit and are using a third party unit that is no good.

Gzip module in Python

next →← prev

This module offers a simple interface for compressing and decompressing files, similar to the GNU tools gzip and gunzip. The GzipFile class, as well as the open(), compress(), and decompress() convenience functions, are all provided by the gzip module. The GzipFile class reads and writes gzip-format files, compressing or decompressing the contents automatically so that it seems to be a regular file object.

Need for gzip module:

The main answer to the question of what is the need of gzip is data compression. The process of encoding, rearranging, or otherwise changing data in order to minimize its size is known as data compression. It essentially entails re-encoding data with fewer bits than the original representation. Compression is carried out by a program that uses functions or algorithms to find the most efficient way to minimize the size of the data. For example, an algorithm might represent a string of bits with a smaller string of bits by converting between them using a reference dictionary.' A formula that inserts a reference or pointer to a string of data that the program has already seen is another example. When it comes to picture compression, this is a fantastic example. When a sequence of colours appears across the image, such as 'blue, red, red, blue,' the formula can convert this data string into a single bit while preserving the underlying information. Text compression is commonly accomplished by deleting all extraneous characters, replacing a smaller bit string with a more common bit string, and inserting a single character as a reference for a string of repeated characters. With the right approaches, data compression can reduce the size of a text file by up to 50%, considerably lowering its total size. Compression can be applied to the content or the complete transmission for data transport. Larger files, either alone or in combination with others, or as part of an archive file, may be transferred in one of the numerous compressed formats, such as ZIP, RAR, 7z, or MP3 when sent or received over the internet.

Compression has several advantages, including reduced storage hardware, data transfer time, and communication bandwidth. This has the potential to save a lot of money. Compressed files require far less storage space than uncompressed ones, resulting in significant savings in storage costs. A compressed file also takes less time to transfer while using less bandwidth on the network. This can save costs while simultaneously increasing productivity. The primary downside of data compression is that it requires more processing resources to compress the necessary data. As a result, compression vendors place a premium on optimizing speed and resource efficiency in order to reduce the impact of intensive compression jobs.

Compression has several advantages, including reduced storage hardware, data transfer time, and communication bandwidth. This has the potential to save a lot of money. Compressed files require far less storage space than uncompressed ones, resulting in significant savings in storage costs. A compressed file also takes less time to transfer while using less bandwidth on the network. This can save costs while simultaneously increasing productivity.

The primary downside of data compression is that it requires more processing resources to compress the necessary data. As a result, compression vendors place a premium on optimizing speed and resource efficiency in order to reduce the impact of intensive compression jobs.

Because uncompressed text or multimedia (speech, image, or video) data requires a large number of bits to represent them and consequently a big amount of bandwidth, this storage space, and bandwidth requirement can be reduced by using a good compression encoding strategy. The degree of compression, the amount of distortion introduced, and the computational resources required to compress and decompress the data are all factors to consider when designing data compression schemes.

Data transfer in the Internet age is extremely time-sensitive. Consider an audio file, which is nothing more than variations in sound intensity over a set period of time. Sound files are used to transport this audio across networks. The time it takes to transfer the files increases if the size of the sound files is too large. Compression can reduce the amount of time it takes to transfer a file.

Compression, in computer terminology, is the process of lowering the physical size of data so that it takes up less storage space and memory. Compressed files are thus easier to transport because the data size is reduced significantly.

Code:

Output:

Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 1 enter the name of the gz file to which you want to write:: my_gz_file_1.txt.gz enter the string you want to the write file:: This is a sample data going to be stored in a compressed gz file. String 'This is a sample data going to be stored in a compressed gz file.' written successfully to the my_gz_file_1.txt.gz file. To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 2 enter the name of the gz file from which you want to read:: my_gz_file_1.txt.gz The data inside the my_gz_file_1.txt.gz file is:: This is a sample data going to be stored in a compressed gz file. To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 3 enter the name of the gz whose size you want to check:: my_gz_file_1.txt.gz The file my_gz_file_1.txt.gz has 104 bytes To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 4 enter the data that you want to compress sample string to compress The data after compression b'\x1f\x8b\x08\x00K\xd0Qb\x02\xff+N\xcc-\xc8IU(.)\xca\xccKW(\xc9WH\xce\xcf-(J-.\x06\x00i\xb7qc\x19\x00\x00\x00' To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 5 enter the data to be decompress \x1f\x8b\x08\x00K\xd0Qb\x02\xff+N\xcc-\xc8IU(.)\xca\xccKW(\xc9WH\xce\xcf-(J-.\x06\x00i\xb7qc\x19\x00\x00\x00 The data after compression sample string to compress To move ahead with code execution enter [y] else [n] Y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 1 enter the name of the gz file to which you want to write:: gz_file_new.gz enter the string you want to the write file:: gzip module use cases are explained with the help of this python code String 'gzip module use cases are explained with the help of this python code ' written successfully to the gz_file_new.gz file. To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 2 enter the name of the gz file from which you want to read:: gz_file_new.gz The data inside the gz_file_new.gz file is:: gzip module use cases are explained with the help of this python code To move ahead with code execution enter [y] else [n] y Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 3 enter the name of the gz whose size you want to check:: gz_file_new.gz The file gz_file_new.gz has 97 bytes Enter your choice according to the below-listed options:: 1. To write data to a gz compressed file. 2. To read data from a gz compressed file. 3. To get the size of the compressed gz file. 4. To compress the input string with the gzip library. 5. To decompress the input string with the gzip library. 6. To exit from the code execution. 6

In the above-written code, we have written a class where each function is representing a different use case scenario of the different functions that are offered by the gzip module of python the different functionalities of functions that are offered by the gzip module of the python are like compressing the data and writing to a file, reading data from a gz file, getting the size of a gz file, compressing the input stream of data and decompressing the input stream of compressed data that is provided as an input by the user.

So, in this article, we have the usage of the gzip module in python and how we can use the various functionalities offered by the gzip module in different use case scenarios. We have also seen a program that actually calls the different functions written where each function is representing an individual use case or functionality.


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file

Either a path to a file, a connection, or literal data (either a single string or a raw vector).

Files ending in,or will be automatically uncompressed. Files starting with,or will gzdecompressstr data error automatically downloaded. Remote gz files can also be automatically downloaded and decompressed.

Literal data is most useful for examples and tests. To be recognised as literal data, the input must be either wrapped withbe a string containing at least one new line, or be a vector containing at least one string with a new line.

Using a value of will read from the system clipboard.

encoding

The character encoding used for the file. Generally, only needed for Stata 13 files and earlier. See Encoding section for details.

col_select

One or more selection expressions, like in. Use or to use more than one expression. See for details on available selection options. Only the specified columns will be read from .

skip

Number of lines to skip before reading data.

n_max

Maximum number of lines to read.

.name_repair

Treatment of problematic column names:

  • : No name repair or checks, beyond basic existence,

  • : Make sure names are unique and not empty,

  • : (default value), no name repair, terrorism in russia check they are ,

  • : Make the names and syntactic

  • a function: apply custom name repair (e.g., for names in the gzdecompressstr data error of base R).

  • A purrr-style anonymous function, see

This argument is passed on as to. See there for more 60.02 error printer on these terms and the strategies used to enforce them.

data

Data frame to write.

path

Path to a file where the data will be written.

version

File version to use. Supports versions 8-15.

label

Dataset label to use, gzdecompressstr data error. Defaults to the value stored in the "label" attribute of gzdecompressstr data error. Must be <= 80 characters.

strl_threshold

Any character vectors with a maximum length greater than bytes will be stored as a long string (strL) instead of a standard string ami bios rom checksum error variable if >= 13. This defaults to 2045, the maximum length of str# variables. See the Stata long string documentation for more details.

10.6 Compressed Files

Although storage space and transmission bandwidth are increasingly cheap and abundant, in many cases you can save such resources, at the expense of some computational effort, by using compression. Since computational power grows cheaper and more abundant even faster than other resources, such as bandwidth, compression's popularity keeps growing. Python makes it easy for your programs to support compression by supplying dedicated modules for compression as part of every Python distribution.

10.6.1 The gzip Module

The module lets you read and write files compatible with those handled by the powerful GNU compression programs gzip and gunzip. The GNU programs support several compression formats, but module supports only the highly effective native gzip format, gzdecompressstr data error, normally denoted by appending the extension .gz to a filename. Module supplies the class and an factory function.


class GzipFile(=None,=None,=9, =None)

Creates and returns a file-like object that wraps the file or file-like object. supplies all methods of built-in file objects except and. Thus, is not seekable: you can only access sequentially, whether for reading or writing. When is must be a string that names a file: opens that file with the given (by default, ''), and wraps the resulting file object. should be one of '', '', feed motor error code 0008 0008, or. If is uses the mode of if it is able to find out the mode; otherwise it uses ''. If is uses the filename of if able to find out the name; otherwise it uses ''. is an integer between and : requests modest compression but fast operation, gzdecompressstr data error, and requests the best compression feasible, even if that requires more computation.

File-like object generally delegates all methods to the underlying file-like objecttransparently accounting for compression as needed. However, does not allow non-sequential access, so does not supply methods and. Moreover, calling does not close when was created with an argument that is not. This behavior of is very important when gzdecompressstr data error an instance ofsince it means you can call after to get the compressed data as a string. This behavior also means that you have to call explicitly after calling .


open(,='rb',=9)

Like ,, but is mandatory and there is no provision for passing an already opened .

Say that you have some function that writes data to a text file objecttypically by calling and/or. Getting to write data to a gzip-compressed text file instead is easy:

import gzip underlying_file = open('x.txt.gz', 'wb') compressing_wrapper = gzip.GzipFile(fileobj=underlying_file, mode='wt') f(compressing_wrapper) compressing_wrapper.close( ) underlying_file.close( )

This example opens the underlying binary file x.txt.gz and explicitly wraps it withand thus, at the end, we need to gzdecompressstr data error each object separately. This is necessary because we want to use two different modes: the underlying file must be opened in binary mode (any translation of line endings would produce an invalid compressed file), but the compressing wrapper must be opened in text mode because we want the implicit translation of to. Reading back a compressed text file, for example to display it on standard output, is similar:

import gzip, xreadlines underlying_file = open('x.txt.gz', 'rb') uncompressing_wrapper = gzip.GzipFile(fileobj= underlying_file, mode='rt') for line in xreadlines.xreadlines(uncompressing_wrapper): print line, gzdecompressstr data error, uncompressing_wrapper.close( ) underlying_file.close( )

This example uses modulecovered earlier in this chapter, because objects (at least up to Gzdecompressstr data error 2.2) are not iterable like true file objects, nor do they supply an method, gzdecompressstr data error. objects do supply a method that closely emulates that of true file objects, and therefore module is able to produce a lazy sequence that wraps a object and lets us iterate on the object's lines.

10.6.2 The bde error 8961 Module

The module lets you read and write ZIP files (i.e., archive files compatible with those handled by popular compression programs zip and unzip, pkzip and pkunzip, WinZip, and so on). Detailed information on the formats and capabilities of ZIP files can be found at http://www.pkware.com/appnote.html gzdecompressstr data error http://www.info-zip.org/pub/infozip/. You need to study this detailed information in order to perform advanced ZIP file handing with module .

Module can't handle ZIP files with appended comments, multidisk ZIP files, or .zip archive members using compression types besides the usual ones, known as stored (when a file is copied to the archive without compression) and deflated (when a file is compressed using the ZIP format's default algorithm). Gzdecompressstr data error invalid .zip file errors, functions of module raise exceptions that are instances of exception class. Module supplies the following classes and functions.


Returns gzdecompressstr data error if the file named by string appears to be a valid ZIP file, judging by the first few bytes of the file; otherwise returns .


class ZipInfo(='NoName',=(1980,1,1,0,0,0))

Methods and of instances return instances of to supply information about members of the archive. The most useful attributes supplied by a instance are:

comment

A string that is a php.ini error reporting options on the archive member

compress_size

Size in bytes of the compressed data for the archive member

compress_type

An integer code recording the type of compression of the archive member

date_time

A gzdecompressstr data error with 6 integers recording the time of last modification to gzdecompressstr data error file: the items are year, month, day ( and up), hour, minute, second ( and up)

file_size

Size in bytes of the uncompressed data for the archive member

filename

Name of the file in the archive


class ZipFile(,='r',=zipfile.ZIP_STORED)

Opens a ZIP file named by string. can be '', gzdecompressstr data error, to read an existing ZIP file; '', to write a new ZIP file or truncate and rewrite an existing one; or '', to append to an existing file.

When is '', can name either gzdecompressstr data error existing ZIP file (in which case new members are added to the existing archive) or an existing non-ZIP file. In the latter case, a new ZIP file-like archive is created and appended to the existing file. The main purpose of this latter case is to let you build a self-unpacking .exe file (i.e., a Windows executable file that unpacks itself when run). The existing file must then be a fresh copy of an unpacking .exe prefix, as supplied by www.info-zip.org or by other purveyors of ZIP file compression tools.

is an integer code that can be either of two attributes of module. requests that the archive use no compression, gzdecompressstr data error, and requests that the archive use the deflation mode of compression (i.e., the most usual and effective compression approach used in .zip files).

A instance supplies the following methods.


Closes terrorist takedown war in colombia file. Make sure the method is called, gzdecompressstr data error, or else an incomplete and unusable ZIP file might be left on disk. Such mandatory finalization is generally best performed with a / statement, as covered in Chapter 6.


Returns a instance that supplies information about the archive member named by string .


Returns a list of instances, one for each member in archivein the same order as the entries in the archive itself.


Returns a list of gzdecompressstr data error, the names of each member in archivein the same order as the entries in the archive itself.


Outputs a textual directory of the archive to file .


Returns a string containing the uncompressed bytes of the file named by string in archive. soft ram error be opened for '' or '', gzdecompressstr data error. When the archive does not contain a file named raises an exception.


Reads and checks the files in archivegzdecompressstr data error. Returns a string with the name of the first archive member that is damaged, or when the archive is intact.


.write(,=None,=None)

Writes the file named by string to archivewith archive member name. When is uses as the archive member name. When is uses 's compression type; otherwise, is orand specifies how to compress the file. must be opened for '' or ''.


must be a instance specifying at least and. is a string of bytes. adds a member to archiveusing the metadata specified by and the data in. must be opened for '' or ''. When you have data in memory and need to write the data to the ZIP file archiveit's simpler and faster to use rather than. The latter approach would require you to write the data to disk first, and later remove the useless disk file. The following example shows both approaches, each encapsulated into a function, polymorphic to each other:

import zipfile def data_to_zip_direct(z, data, name): import time zinfo = zipfile.ZipInfo(name, time.localtime( )[:6]) z.writestr(zinfo, data) def data_to_zip_indirect(z, data, name): import os flob = open(name, 'wb') flob.write(data) flob.close( ) z.write(name) os.unlink(name) zz = zipfile.ZipFile('z.zip', 'w', zipfile.ZIP_DEFLATED) data = 'four score\nand gzdecompressstr data error ago\n' data_to_zip_direct(zz, data, gzdecompressstr data error, 'direct.txt') data_to_zip_indirect(zz, data, 'indirect.txt') zz.close( )

Besides being faster and more concise, is handier because, by gzdecompressstr data error in memory, it doesn't need to have the current working directory be writable, as does, gzdecompressstr data error. Of course, method also has its uses, but that's mostly when you already have the data in a file on gzdecompressstr data error, and just want to add the file to the archive. Here's how you can print a list of all files contained in the ZIP file archive created by the previous example, followed by each file's name and contents:

import zipfile zz = zipfile.ZipFile('z.zip') zz.printdir( ) for name in zz.namelist( ): print '%s: %r' % (name, zz.read(name)) zz.close( )

10.6.3 The zlib Module

The module lets Fatal error io 104 programs use the free InfoZip zlib compression error - init.cpp 215 (see http://www.info-zip.org/pub/infozip/zlib/), Version 1.1.3 or later. Module is used by modules andbut the module is also available directly for any special compression needs. This section documents the most commonly used functions supplied by module .

Module also supplies functions to compute Cyclic-Redundancy Check (CRC) checksums, in order to detect possible damage in compressed data. It also provides objects that can compress and decompress data incrementally, and thus enable you to work with data streams that are too large to fit in memory at once. For gzdecompressstr data error advanced functionality, consult the Python library's online reference.

Note that files containing data compressed with are not automatically interchangeable with other programs, with the exception of files that use the module and therefore respect the standard format of ZIP file archives. You could write a custom program, with any language able to use InfoZip's free zlib compression library, in order to read files produced by Python programs using the module, gzdecompressstr data error. However, if you do need to interchange compressed data with programs coded in other languages, I suggest you use modules or instead. Module may be useful when you want to compress some parts of data files that are in some proprietary format of your own, gzdecompressstr data error, and need not be interchanged with any other program except those that make up your own application.


Compresses string and returns the string of compressed data. is an integer between and : requests modest compression but fast operation, and requests compression as good as feasible, gzdecompressstr data error, thus requiring more computation.


Decompresses the compressed data string and returns the string of uncompressed data.

Here are the examples of the python api gzip.open taken from open source projects. Gzdecompressstr data error voting up you can indicate which examples are most useful and appropriate.

0

Example 101

Project: pyCAF
License: View license
Source File: analyze_packages.py

0

Example 102

Project: socorro
License: View license
Source File: test_daily_url.py

0

Example 103

Project: disco-dop
License: View license
Source File: runexp.py

0

Example 104

Project: makina-states.pack1
License: View license
Source File: check_burp_counters.py

0

Example 105

Project: auxiliary-deep-generative-models
License: View license
Source File: norb.py

0

Example 106

Project: plexpy
License: View license
Source File: helpers.py

0

Example 107

Project: genmod
License: View license
Source File: parse_annotations.py

0

Example 108

Project: svtyper
License: View license
Source File: vcf_paste.py

0

Example 109

Project: fusioncatcher
License: View license
Source File: predict_frame.py

0

Example 110

Project: pgmult
License: View license
Source File: dna_lds.py

0

Example 111

Project: mclogalyzer
License: View license
Source File: mclogalyzer.py

0

Example 112

Project: DeepLearningTutorials
License: View license
Source File: imdb.py
Function: load_data

0

Example 113

Project: networkedcorpus
License: View license
Source File: gen-networked-corpus.py

0

Example 114

Project: pyCAF
License: View license
Source File: analyze_packages.py

0

Example 115

Project: svtools
License: View license
Source File: sv_classifier.py

0

Example 116

Project: anvio
License: View license
Source File: cogs.py

0

Example 117

Project: biocode
License: View license
Source File: randomly_subsample_fastq.py
Function: main

0

Example 118

Project: RenderChan
License: View license
Source File: synfig.py
Function: analyze

0

Example 119

Project: gmvault
License: View license
Source File: gmvault_db.py

0

Example 120

Project: fusioncatcher
License: View license
Source File: phred.py

0

Example 121

Project: karesansui
License: View license
Source File: viewer.py

0

Example 122

Project: word-embeddings-benchmarks
License: View license
Source File: utils.py

0

Example 123

Project: addons-source
License: View license
Source File: ft.py

0

Example 124

Project: ansible-modules-extras
License: View license
Source File: archive.py

0

Example 125

Project: robothon
License: View license
Source File: io.py

0

Example 126

Project: wordfreq
License: View license
Source File: __init__.py

0

Example 127

Project: pylearn2
License: View license
Source File: new_norb.py

Command Line Fanatic

My very first post on this blog, 5 years ago, was a walk-through of the source code for a sample gunzip implementation. I've gotten quite a bit of feedback on it, mostly positive; it's still the most detailed post I've been able to put up here. Part of that write-up included bits and pieces of a gunzip session of an attached gzipped file, bit-for-bit. Recently, a very attentive commenter named Djibi pointed out that the attachment didn't quite match the examples in the post. My memory from that far back is hazy, but the only way I can imagine that happening is if I wrote the post based on one version of the attachment and then made a modification to the attachment without subsequently reviewing the text to ensure that it matched. Although I've gone through and updated the text to match the attachment gzdecompressstr data error Djibi's very detailed analysis, I must admit that, after 5 years, I myself found the post hard to read through, as I was jumping around from one section to another. It occurred to me that a good companion piece would be a complete walk through of the gunzip process for the sample attachment. After all, this is the web and I don't have to worry about page count here! You may want to familiarize yourself with the original post before going through this one, as I assume below that you have a good understanding of Huffman codes and the LZ77 algorithm.

If you download the Attachment in question, you'll see that it's a 4704 byte file containing the gzipped representation of the source code presented in the original post. Of course, if you try to open up a gzipped file the normal way, by double-clicking on it or whatever your desktop equivalent is, your OS is likely to decompress it on your behalf — but for the purposes of following along with this post, you don't want that: you want the "before" representation, as I'll be walking through the process of going from the before to the after. If you're using a Unix-type OS, you probably have the (objectdump) utility installed that can be used to see a byte-level representation of any file. If you run that utility (or any similar hexadecimal viewer or editor), you'll see that the unambiguous, canonical representation of the file, shown in figure 1, below.

Jump to bottom

Figure 1: Full hexadecimal representation of gunzip.c.gz

The facility is byte-oriented; with the arguments shown above, you'll get a hexadecimal representation of every byte in the referenced file. However, compressed files, by their nature, need to take maximum advantage of every single bit — gzdecompressstr data error, to get a good gzip-eye view of this file, you need to break it down to its individual bits. However, if you learned to program any time in the past 40 years or so, you're probably used to the big-endian representation of binary data, where the most-significant bit is shown in the left-most position and the least-significant bit is shown in the right-most position. So the first byte of this file, hexadecimal 1F would be represented in binary as 00011111 and the second byte, gzdecompressstr data error, hexadecimal 8B, as 10001011. The LZ77 specification that the gzip format is based on, though, is centered around the little-endian format: here, the first two bytes would be represented as 1111100011010001. In other circumstances, this wouldn't make a difference, since you'd be doing byte-for-byte comparisons anyway, but since compression algorithms make optimal use of every bit, the conceptual ordering of the bits makes a big difference, as codes span bytes and you have to put the bits into the correct order to errors in legal translation the file. Keep in mind as you read this post that the bits shown probably appear "backwards".

The first 10 bytes of figure 1 are the standard GZIP header, which is defined in bytes so the bit-ordering is immaterial. This breaks down to the representation shown in figure 2, gzdecompressstr data error.

Standard GZIP declaration
Compression method: 0x08 represents GZIP
Flags (see below)
Timestamp
Extra flags
Operating System

Figure 2: standard 10-byte GZIP header

The flags byte, byte 4, is interpreted as shown in table 1. In the case of the attachment displayed in figure 1, only bit 8 is set, indicating that a null-terminated name string follows the header.
Bit mask (in big-endian format)Meaning
00000001Text follows
00000010Header CRC follows
00000100"Extra" follows
00001000Name follows
00010000Comment follows

Table 1: Flag bit meanings

In essence, the flags byte indicates that the header can be followed by up to five null- terminated strings, which must at least be skipped over before the actual gzipped-proper content appears. In this case, it is the 9-byte ASCII-encoded string: or "". After these first 19 bytes, gzdecompressstr data error, bit ordering begins to matter. Figure 3 presents the binary representation of the remaining 4,685 bytes of the gzipped attachment file, in little-endian order, with the least significant bits appearing first.

Jump to bottom

Figure 3: Attachment #1 in little-endian bit format

I'll start by focusing on the first line of figure 3:

As described in part 1, the first bit is a "block" indicator - if it's set to 1, which it is in this case, then this is the last "block" in the file. You'll see multiple blocks in very large gzipped files, but this one is small enough that it only needs one block. The following two bits, in this case, are the block format. Here the block format is "dynamic huffman tree" indicating that gzdecompressstr data error next bit sequence is a Huffman key to a Huffman coded representation of another Huffman key to the Huffman coded representation of the actual gzipped content. This is followed by the 5-bit length of the literals tree, the 5-bit length of the distance tree and the 3-bit length of the initial Huffman key.

So, bytes 20-22 of the attached file —whose little-endian bit representation is — are interpreted as (remember to read the bits in the table "backwards"):

1last block in this file
012: dynamic huffman table
1110123 literals codes
1101127 distance codes
00018 keys in the following huffman key table

Figure 4: Huffman key table header

where the remaining seven bits of byte 22,are unused (so far).

Since there are always at slave disk error five entries in the dynamic huffman key table, add 4 to 8 to get the actual count of twelve. That means that there are 12 3-bit codes that describe a Huffman table that is itself the key to the following Huffman table.

Bit patternnumeric valuelength of huffman code
011616
111717
111718
11030
11038
01027
11039
11036
001410
00145
101511
00144

Figure 5: Dynamic Huffman table specification

Indicating that the Huffman codes that encode the subsequent table are:

Figure 6: Dynamic Huffman table codes

At this point, I've read a little more than half-way through byte 26 of the first line of figure 3, and the file pointer is set to:

This is followed by the 308 codes-worth of Huffman-code lengths shown in figure 7 (recall that this is additionally run-length encoded, so there aren't 308 actual code values here):

Jump to bottom
Huffman codevaluerepeat gzdecompressstr data error 10 codes (0-9) are empty, don't appear
007The code for the literal value gzdecompressstr data error is seven bits
1111111182121 more zeros; values 11-31 don't appear
11015The code for value 32 is five bits
1019The code for value 33 is 9 bits
1008.
111010
0100
1019
1008
1019
007
1008
1008
1008
007
007
007
1019
007
0116
007
007
1008
007
007
1008
007
1008
1019
007
1008
007
1008
111010
0100
1019
111010
1019
1019
1008
1019
0100
111010
1019
0100
0100
111010
1019
1019
1019
1111011
0100
1019
111110163
0100
0100
111010
0100
1111011
1019
1111011
1019
0100
007
0100
0116
007
0116
0116
11015
007
1008
007
0116
1008
1019
0116
007
0116
0116
007
0100
0116
0116
0116
007
1008
1008
1019
1008
111010
111010
111010
1008
111111118130130 consecutive 0's, indicating that the codes from 126-255 are not included in this table
1111011
11004
11004
11004
11015
111110163
0116
11015
11015
11015
0116
0116
007
007
007
1008
1008
1008
111010
111010
0100
111010
1008
1019
111110163
1008
007
007
11015
0116
11004
11004
11004
11015
11004
11015
11004
11015
11004
111110166
11015
11015
0116

Figure 7: Compressed data Huffman codes specification

Which work out to two Huffman code trees — one for the literals:

Figure 8: Compressed data literals Huffman code values

and a smaller one for the distances:

Figure 9: Compressed data distances Huffman code values

These tables make a lot of sense if you think about the nature of the file that was compressed — it's C source code, so it's ASCII-encoded. The byte value 10 appears fairly often: that's the line-ending code, so it gets a literal code. 32 is the ASCII code for a space character, so it gets a short Huffman code since it appears quite a bit. Although there are codes here for 33, 34 and 35 (ASCII !, " and #, respectively), the $ character 36 never appears in the zipped source, so no code is defined for it. There are codes here for most of the capital letters (range 65-90), but notice that their literals codes are relatively long, since there aren't many capital letters in the actual source code file. The lower-case letters (97-122) get shorter codes in the literals table, since they appear more often than the upper-case characters. The non-printable ASCII characters less than 32 (other than the CR code 10) and greater than 128 don't have codes because they don't appear in the source file.

At this point, the decompression values have read the full Huffman codes for the actual payload, which follows immediately. The last few bits that were read by the decompressor were: 1101 1101 011, which were 5, 5 and 6, according to the dynamic Huffman table from Figure 6, gzdecompressstr data error. At this point, 86 bytes of the file have been gzdecompressstr data error, and the file pointer is at the sixth byte of the fifth line of Figure 3 (hexadecimal ), pointed at the very last bit of the byte (remember, this is the most significant bit, because we're working LSB to MSB):

Almost all of the remainder of the file (until the trailer, which begins on byte 4696) is interpreted according to the Huffman tables in figures 8 and 9. As you can see, the Huffman compression tables are very efficient; only 65 bytes of the 4,704-byte gzipped file run time error 205 "dictionary" information that's needed to interpret the remainder of the file, with an additional 20 bytes of header information and 8 bytes of trailer information.

So far, though, I haven't shown any Lempel-Ziv compression! At this point, all I have are the Huffman codes that represent four types of codes: a "normal" byte that should be inflated to its representative value, a stop code that indicates that compression should halt (i.e. EOF), a length code that indicates a "back pointer" to a prior part of the uncompressed output that should be represented and length codes that indicate how much of the previous data should be copied. Figure 10, below, shows the entire process and details how each code gzdecompressstr data error interpreted; again, gzdecompressstr data error, refer to RFC 1951 or my earlier discussion of GZIP/DEFLATE to fully interpret the details below.

Jump to bottom
Byte numberBits readCorresponding (Huffman code)Type (normal, stop or distance)ASCII value (for normal codes)Extra bits (codes 265-285)LengthDistance bits readExtra distance (distance codes 3+)Distance (Huffman code)copied value
86111111001035normal byte#
88100010105normal bytei
88100100110normal byten
8910000099normal bytec
90100011108normal bytel
911101011117normal byteu
92100001100normal byted
9200111101normal bytee
930011032normal byte
941110011060normal byte<
95100111115normal bytes
95101000116normal bytet
96100001100normal byted
97100010105normal bytei
98100101111normal byteo
98101110046normal byte.
991101000104normal byteh
1001110011162normal byte>
101101100010normal byte\n
102111111001035normal byte#
10301100265distance code11211000218include <std
105100011108normal bytel
106100010105normal bytei
106110011098normal byteb
10701110267distance code11611000319.h>\n#include <st
109100110114normal byter
110100010105normal bytei
111100100110normal byten
11111101001103normal byteg
11201101266distance code11411000319.h>\n#include <
11400111101normal bytee
115100110114normal byter
115100110114normal byter
116100100110normal byten
11701110267distance code01500011058o.h>\n#include <
11901111197normal bytea
119100111115normal bytes
120100111115normal bytes
12100111101normal bytee
122100110114normal byter
122101000116normal bytet
1230001258distance code411000319.h>\n
125101100010normal byte\n
12511110011147normal byte/
12711110011147normal byte/
1280011032normal byte
1281101000104normal byteh
12900111101normal bytee
13001111197normal bytea
131100001100normal byted
13100111101normal bytee
132100110114normal byter
1330011032normal byte
133100111115normal bytes
13400111101normal bytee
1351101010112normal bytep
13601111197normal bytea
136100110114normal byter
13701111197normal bytea
138101000116normal bytet
13900111101normal bytee
139100001100normal byted
1400011032normal byte
1411100111102normal bytef
141100110114normal byter
142100101111normal byteo
1431101001109normal bytem
1440011032normal byte
1441101001109normal bytem
14501111197normal bytea
146100010105normal bytei
147100100110normal byten
1480011032normal byte
1480000257distance code300101579str
1501101011117normal byteu
15110000099normal bytec
151101000116normal bytet
1520011032normal byte
1531100111102normal bytef
154100101111normal byteo
154100110114normal byter
1550011032normal byte
156101000116normal bytet
1571101000104normal byteh
15700111101normal bytee
1580011032normal byte
1591101111034normal byte"
160100111115normal bytes
160100010105normal bytei
1611111111000122normal bytez
16200111101normal bytee
163100101111normal byteo
1641100111102normal bytef
1651101111034normal byte"
1660011032normal byte
166110011098normal byteb
16700111101normal bytee
168100011108normal bytel
169100101111normal byteo
16911101100119normal bytew
170101100010normal byte\n
171101000116normal bytet
17211101101121normal bytey
1731101010112normal bytep
17400111101normal bytee
174100001100normal byted
17500111101normal bytee
1761100111102normal bytef
17701001261distance code70000537 struct
178101100010normal byte\n
1791111111001123normal byte{
180101100010normal byte\n
1810011032normal byte
1820011032normal byte
1831101011117normal byteu
183100100110normal byten
184100111115normal bytes
185100010105normal bytei
18611101001103normal byteg
187100100110normal byten
1870000257distance code30010367ed
18910000099normal bytec
1901101000104normal byteh
19101111197normal bytea
191100110114normal byter
1920011032normal byte
193100010105normal bytei
194100001100normal byted
19411111010191normal byte[
1950011032normal byte
196101111050normal byte2
1970011032normal byte
19811111011093normal byte]
199110001159normal byte;
200101010268distance code017111100024\n unsigned char
20210000099normal bytec
202100101111normal byteo
2031101001109normal bytem
2041101010112normal bytep
205100110114normal byter
20600111101normal bytee
206100111115normal bytes
207100111115normal bytes
208100010105normal bytei
208100101111normal byteo
209100100110normal byten
210110010195normal byte_
2111101001109normal bytem
21200111101normal bytee
212101000116normal bytet
2131101000104normal byteh
214100101111normal byteo
215100001100normal byted
215101010268distance gzdecompressstr data error unsigned char
2171100111102normal bytef
218100011108normal bytel
21901111197normal bytea
22011101001103normal byteg
221100111115normal bytes
221101010268distance code11811000622;\n unsigned char
2231101001109normal bytem
224101000116normal bytet
225100010105normal bytei
2261101001109normal bytem
22700111101normal bytee
22711111010191normal byte[
2280011032normal byte
2291110001152normal byte4
230101011269distance code12000102286 ];\n unsigned char
23200111101normal bytee
233111111000120normal bytex
234101000116normal bytet
235100110114normal byter
23501111197normal bytea
236110010195normal byte_
2371101100270distance code0230001856flags;\n unsigned char
239100101111normal byteo
2400000257distance code311000319s;\n
24111101110125normal byte}
242101100010normal byte\n
24311101001103normal byteg
2441111111000122normal bytez
245100010105normal bytei
2461101010112normal bytep
247110010195normal byte_
24801000260distance code61101049241header
250110001159normal byte;
251101100010normal byte\n
252101011269distance code120110101193\ntypedef struct\n{\n
25401100265distance code0110000032gzip_header
2560011032normal byte
25601010262distance code80000739header;\n
25801100265distance code01100101074 unsigned
260100111115normal bytes
2611101000104normal byteh
262100101111normal byteo
262100110114normal byter
263101000116normal bytet
2640011032normal byte
264111111000120normal bytex
266100011108normal bytel
26600111101normal bytee
267100100110normal byten
268101010268distance code11811001197;\n unsigned char
2701110000142normal byte*
2710010259distance code51100131127extra
273101011269distance code01911000723;\n unsigned char *
2751100111102normal bytef
275100100110normal byten
27601111197normal bytea
2771101001109normal bytem
27800111101normal bytee
278101011269distance code12011000723;\n unsigned char *f
2800000257distance code301007263com
2821101001109normal bytem
28300111101normal bytee
284100100110normal byten
285101000116normal bytet
285101011269distance code01911001197;\n unsigned short
28810000099normal bytec
288100110114normal byter
28910000099normal bytec
29001111049normal byte1
291110000154normal byte6
291110001159normal byte;
2920011032normal byte
2930000257distance code31101130414//
295101000116normal bytet
2961101000104normal byteh
297100010105normal bytei
297100111115normal bytes
2980011032normal byte
2991101010112normal bytep
300100110114normal byter
300100101111normal byteo
301101000116normal bytet
30200111101normal bytee
30210000099normal bytec
303101000116normal bytet
304100111115normal bytes
3050010259distance code5110116390 the
30701000260distance code6001122150header
30901100265distance code1120001351\n unsigned
310100011108normal bytel
311100101111normal byteo
312100100110normal byten
31311101001103normal byteg
3140001258distance code40001250 crc
315101111151normal byte3
316101111050normal byte2
317110001159normal byte;
3180011032normal byte
318101011269distance code3220001351 // this protects the
320100001100normal byted
321100101111normal byteo
32210000099normal bytec
3231101011117normal byteu
3230001258distance code41100110106ment
325101010268distance code0170001553\n unsigned long
327100010105normal bytei
3280001258distance code41101183467size
33001011263distance code9010025281;\n}\ngzip_
3321100111102normal bytef
333100010105normal bytei
333100011108normal bytel
3340000257distance code31111101012e;\n
336101100010normal byte\n
337111111001035normal byte#
3380000257distance code3010020276def
340100010105normal bytei
341100100110normal byten
34100111101normal bytee
3420011032normal byte
34311110110070normal byteF
34411111001184normal byteT
3451110100069normal byteE
346111111011188normal byteX
34711111001184normal byteT
3480011032normal byte
3490001258distance code4111111000
350101110148normal byte0
351111111000120normal bytex
352101110148normal byte0
35301111049normal byte1
354101001264distance code1011000622\n#define F
356111111010172normal byteH
35711110101067normal byteC
35811111000182normal byteR
35911110101067normal byteC
36001010262distance code811000622 0x0
362101111050normal byte2
363101001264distance code1011000622\n#define F
3650000257distance code300001244EXT
36611111000182normal byteR
36711110100165normal byteA
36801001261distance code711000622 0x0
3701110001152normal byte4
371101001264distance code1011000622\n#define F
37311110111178normal byteN
37411110100165normal byteA
37511110111077normal byteM
3761110100069normal byteE
37701010262distance code800001345 0x0
379110001056normal byte8
380101001264distance code1011000622\n#define F
38111110101067normal byteC
38211111000079normal byteO
38411110111077normal byteM
38511110111077normal byteM
3861110100069normal byteE
38711110111178normal byteN
38811111001184normal byteT
3890001258distance code411000622 0x
39101111049normal byte1
391101110148normal byte0
392101011269distance code2211101111395\n\ntypedef gzdecompressstr data error
39501011263distance code9001141169unsigned
397100010105normal bytei
397100100110normal byten
398101000116normal bytet
3990011032normal byte
39901110267distance code1160100114370len;\n unsigned
4020001258distance code411000319int
40310000099normal bytec
404100101111normal byteo
405100001100normal byted
4050001258distance code4001159187e;\n}
4070011032normal byte
408101100010normal byte\n
409101000116normal bytet
409100110114normal byter
41000111101normal bytee
41100111101normal bytee
411110010195normal byte_
412100100110normal byten
4130010259distance code51111101113ode;\n
41501110267distance code0150010872\ntypedef gzdecompressstr data error byte
4171101000104normal byteh
4181101011117normal byteu
4191100111102normal bytef
4201100111102normal bytef
4211101001109normal bytem
42101111197normal bytea
422100100110normal byten
4230010259distance code5111100529_node
425110010195normal byte_
42501000260distance code600102387t\n{\n
42701011263distance code900011058int code;
4290001258distance code4010043299 //
431101101145normal byte-
43201111049normal byte1
4320010259distance code50101223735 for
434100100110normal byten
435100101111normal byteo
436100100110normal byten
437101101145normal byte-
437100011108normal bytel
43800111101normal bytee
43901111197normal bytea
4401100111102normal bytef
4400011032normal byte
4410001258distance code40000739node
443100111115normal bytes
4430000257distance code30000436\n
445101011269distance code22100011462struct huffman_node_t
4470011032normal byte
4471110000142normal byte*
4481111111000122normal bytez
45000111101normal bytee
450100110114normal byter
451100101111normal byteo
452110001159normal byte;
4531101100270distance code326111100630\n struct huffman_node_t *
455100101111normal byteo
456100100110normal byten
4560010259distance code5010076332e;\n}\n
45801100265distance code11211000622huffman_node
460101011269distance code3220101103615;\n\ntypedef struct\n{\n
4630001258distance code400113131int
46400111101normal bytee
465100100110normal byten
4660010259distance code50101247759d;\n
4680001258distance code41111100210int
469110011098normal byteb
470100010105normal bytei
471101000116normal bytet
472110010195normal byte_
4730000257distance code31101033225len
47411101001103normal byteg
475101000116normal bytet
4761101000104normal byteh
47701100265distance code11200011462;\n}\nhuffman_
479100110114normal byter
48001111197normal bytea
480100100110normal byten
48111101001103normal byteg
4820001258distance code400011563e;\n\n
484100111115normal bytes
484101000116normal bytet
48501111197normal bytea
486101000116normal bytet
487100010105normal bytei
48710000099normal bytec
4880011032normal byte
48911101011118normal bytev
490100101111normal byteo
490100010105normal gzdecompressstr data error byted
4920011032normal byte
493110011098normal byteb
4931101011117normal byteu
494100010105normal bytei
495100011108normal bytel
496100001100normal byted
497110010195normal byte_
49701010262distance code80000133huffman_
4990001258distance code41101056248tree
501101100140normal byte(
50201101266distance code01300115133 huffman_node
5040011032normal byte
5041110000142normal byte*
505100110114normal byter
506100101111normal byteo
507100101111normal byteo
508101000116normal bytet
508101101044normal byte,
509101100010normal byte\n
5100011032normal byte
5111101110272distance code031111111000
5130001258distance code41100121117int
5150010259distance code500103195range
5160001258distance code41100123119_len
5181101110272distance code33400001446,\n
52001101266distance code013001118146huffman_range
5220000257distance code311001399 *r
5240010259distance code51111110106ange
5261110000041normal byte)
52701011263distance code91101010202\n{\n int
5291110000142normal byte*
530110011098normal byteb
530100011108normal bytel
531110010195normal byte_
53210000099normal bytec
533100101111normal byteo
5341101011117normal byteu
53401000260distance code60101203715nt;\n
5370010259distance code511000016int *
538100100110normal gzdecompressstr data error code3011013781ext
541110010195normal byte_
54201000260distance code61101132416code;\n
5440011032normal byte
5440011032normal byte
54501011263distance code91101131415tree_node
5470011032normal byte
5481110000142normal byte*
5490001258distance code41111100210tree
5500000257distance code31101018210;\n\n
55201011263distance code91101054246 int bit
554100111115normal bytes
555110001159normal byte;
55601100265distance code0111101117401\n int code
5580011032normal byte
559110010061normal byte=
5600011032normal byte
560101110148normal byte0
56101010262distance code81111101315;\n int
563100100110normal byten
56401010262distance code8111110008;\n int
56501111197normal bytea
56610000099normal bytec
567101000116normal bytet
568100010105normal bytei
56811101011118normal bytev
56900111101normal bytee
57001010262distance code8010012268_range;\n
57201000260distance code611000319 int
5741101001109normal bytem
57501111197normal bytea
575111111000120normal bytex
576110010195normal byte_
57701100265distance code112010051307bit_length;\n
579101100010normal byte\n
5800010259distance code50101247759 //
582100111115normal bytes
583101000116normal bytet
58400111101normal bytee
5841101010112normal bytep
5850011032normal byte
58601111049normal byte1
5870011032normal byte
587101101145normal byte-
5880011032normal byte
5891100111102normal bytef
590100010105normal bytei
59011101001103normal byteg
5911101011117normal byteu
592100110114normal byter
59300111101normal bytee
5940011032normal byte
594100101111normal byteo
5951101011117normal byteu
5960000257distance code31101133417t h
598100101111normal byteo
59911101100119normal bytew
60001000260distance code60101233745 long
60201010262distance code8001133161bl_count
604101101044normal byte,
6050011032normal byte
60501011263distance code9001126154next_code
607101101044normal byte,
6080010259distance code5001124152 tree
6100011032normal byte
61000111101normal bytee
611101000116normal bytet
61210000099normal bytec
612101110046normal byte.
61301001261distance code70010064\n // s
6151101000104normal byteh
616100101111normal byteo
6171101011117normal byteu
618100011108normal bytel
6180000257distance code3010099355d b
62000111101normal bytee
6210011032normal byte
621110011098normal byteb
62201111197normal bytea
623100111115normal bytes
6240000257distance code30101100612ed
626100101111normal byteo
627100100110normal byten
6270010259distance code5011061829 the
6290010259distance code51100126122range
6310010259distance code5011081849s pro
63311101011118normal bytev
634100010105normal bytei
635100001100normal byted
63600111101normal bytee
6360010259distance code51101152436d;\n
63801101266distance code11400110128max_bit_length
64001010262distance code8001155183 = 0;\n
6420001258distance code4010173585for
644101100140normal byte(
6450011032normal byte
646100100110normal byten
6460010259distance code51111101214 = 0;
6480000257distance code31111110106 n
6501110011060normal byte<
651101001264distance code10010097353 range_len
6530000257distance code31111101214; n
6541110001043normal byte+
6551110001043normal byte+
6560000257distance code3010048304 )\n
6580011032normal byte
6590011032normal byte
6591111111001123normal byte{
6610010259distance code50100107363\n
663100010105normal bytei
6631100111102normal bytef
6640000257distance code30000840 (
6660010259distance code5111100529range
66711111010191normal byte[
6680000257distance code30000840 n
67011111011093normal byte]
671101110046normal byte.
67201100265distance code01100101175bit_length
6741110011162normal byte>
67501110267distance code11600102892 max_bit_length
6771110000041normal byte)
6780010259distance code50001149\n
6791111111001123normal byte{
68001001261distance code71101135419\n
683101010268distance code0171100125121max_bit_length =
685101011269distance code2210010569range[ n ].bit_length
687110001159normal byte;
6880010259distance code500001345\n
68911101110125normal byte}
690101100010normal byte\n
69101000260distance code61111111103 }\n
69301010262distance code81101059251bl_count
6950000257distance code300001345 =
6961101001109normal bytem
69701111197normal bytea
698100011108normal bytel
699100011108normal bytel
699100101111normal byteo
70010000099normal bytec
701101100140normal byte(
7020011032normal byte
70201000260distance code601114591483sizeof
705101100140normal byte(
7060010259distance code5010077333 int
7071110000041normal byte)
7080011032normal byte
7091110000142normal byte*
7100000257distance code3001113141 (
71201110267distance code01500102488max_bit_length
7141110001043normal byte+
7150000257distance code3010073329 1
7171110000041normal byte)
7180011032normal byte
7181110000041normal byte)
7190001258distance code40010872;\n
72101011263distance code9010048304next_code
72311110001275distance code45500011563 = malloc( sizeof( int ) * ( max_bit_length + 1 ) );\n
7250010259distance code50100101357tree
727101010268distance code11800011058= malloc( sizeof(
729101001264distance code10010121533tree_node
73101000260distance code60010064) * (
73301001261distance code7110108200range[
73501011263distance code9010051307range_len
7370000257distance code31101172456 -
73901111049normal byte1
7400000257distance code31101020212 ].
7420000257distance code3011038806end
744101001264distance code1000101276 + 1 ) );\n
7450001258distance code40100122378\n m
74700111101normal bytee
7481101001109normal bytem
749100111115normal bytes
75000111101normal bytee
750101000116normal bytet
751101100140normal byte(
75201100265distance code0111101180464 bl_count,
75411110011039normal byte'
7551111111111092normal byte\
757101110148normal byte0
75711110011039normal byte'
759101101044normal byte,
75911110000274distance code043001117145 sizeof( int ) * ( max_bit_length + 1 ) );\n
76211110000274distance code2451101141425\n for ( n = 0; n < range_len; n++ )\n {\n
76501010262distance code8110016102bl_count
76711111010191normal byte[
7681101100270distance code0231101146430 range[ n ].bit_length
77111111011093normal byte]
7720011032normal byte
7721110001043normal byte+
773110010061normal byte=
7740011032normal byte
77501001261distance code71101127411\n
77701100265distance code0110000133range[ n ].
7790001258distance code4001153181end
780101101145normal byte-
7810000257distance code311001298 (
7830001258distance code4110014100( n
7851110011162normal byte>
7860011032normal byte
786101110148normal byte0
7870000257distance code31100124120 )
789111111001163normal byte?
790101001264distance code10111100630 range[ n
792101001264distance code101101024216- 1 ].end
79411110100058normal byte:
7950001258distance code401111281152 -1
7980010259distance code5010036292);\n
79911101110125normal byte}
80001100265distance code1120101196708\n\n // step
803101111050normal byte2
804101101044normal byte,
8040011032normal byte
805100001100normal byted
806100010105normal bytei
807100110114normal byter
8070000257distance code301114461470ect
809100011108normal bytel
81011101101121normal bytey
81101000260distance code610003991935 from
81311111000182normal byteR
81511110110070normal byteF
81611110101067normal byteC
81701100265distance code0111101058250\n memset(
81901100265distance code0110101193705next_code, gzdecompressstr data error,
82111110000274distance code5481101059251'\0', sizeof( int ) * ( max_bit_length + 1 ) );\n
82401010262distance code81101058250 for (
8260001258distance code40110122890bits
8280000257distance code31101061253 =
83001111049normal byte1
831110001159normal byte;
83101000260distance code6111110019 bits
8331110011060normal byte<
834110010061normal byte=
83501110267distance code116011083851 max_bit_length;
8370010259distance code511000723 bits
83901101266distance code01301009265++ )\n {\n
84101001261distance code701011513code =
843101100140normal byte(
84401000260distance code6111110008 code
8461110001043normal byte+
84701100265distance code011010025281 bl_count[
8490010259distance code50010266bits
8500010259distance code51101020212- 1 ]
8520000257distance code3110014100 )
8541110011060normal byte<
8551110011060normal byte<
8560000257distance code300102185 1;
858101001264distance code100101228740\n if (
86001110267distance code0150000537bl_count[ bits
86211111011093normal byte]
86301110267distance code0150101206718 )\n {\n
86501011263distance code91101010202next_code
86701011263distance code9111100731[ bits ]
869110010061normal byte=
8700011032normal byte
87001010262distance code80111541078code;\n
87301010262distance code80101192704 }\n }\n
87501100265distance code011010024280\n // step gzdecompressstr data error byte3
8781101101271distance code330010024280, directly from RFC\n memset(
8800001258distance code4010182594tree
88201110267distance code116010019275, gzdecompressstr data error, '\0', sizeof(
88401101266distance code1140101102614tree_node ) *
8870010259distance code500102286\n
88811101111273distance code3380101107619( range[ range_len - 1 ].end + 1 ) );\n
8910011032normal byte
89201101266distance code01301111221146 active_range
8941101100270distance code1240110227995 = 0;\n for ( n = 0; n <
897110010061normal byte=
8981101101271distance code02700101175 range[ range_len - 1 ].end
900101011269distance code22101102451013; n++ )\n {\n if (
9020001258distance code4010115527n >
90401001261distance code70001250range[
90601101266distance code01300103195active_range
90801000260distance code61100129125].end
91001101266distance code114010029285)\n {\n
91201100265distance code1120000032active_range
9141110001043normal byte+
9151110001043normal byte+
91601010262distance code8010019275;\n }\n
918101010268distance code0170111651089\n if ( range[
92001110267distance code0150010771active_range ].
9221101100270distance code2250111591083bit_length )\n {\n
9250001258distance code4010010266tree
92701000260distance code60101158670[ n ].
9290001258distance code4001138166len
930110010061normal byte=
9311101110272distance code23300011462 range[ active_range ].bit_length
933110001159normal byte;
934101100010normal byte\n
93501001261distance code70001856\n
9370010259distance code51100112108if (
93901101266distance code11400011361tree[ n ].len
94011110010033normal byte!
941110010061normal byte=
9420001258distance code40101213725 0 )
94401001261distance code7111100731\n
94601010262

Zlib

ASCII

Represents text data as guessed by deflate.

NOTE: The underlying constant Z_ASCII was deprecated in favor of Z_TEXT in zlib 1.2.2. New applications should not use this constant.

See Zlib::ZStream#data_type.

BEST_COMPRESSION

Slowest compression level, but with the best space savings.

BEST_SPEED

Fastest compression level, but with the lowest space savings.

BINARY

Represents binary data as guessed by deflate.

See Zlib::ZStream#data_type.

DEFAULT_COMPRESSION

Default compression level which is a good trade-off between space and time

DEFAULT_STRATEGY

Default deflate acad fatal error unhandled e0434f4dh which is used for normal data.

DEF_MEM_LEVEL

The default memory level for allocating zlib deflate compression state.

FILTERED

Deflate strategy for data produced by a filter (or predictor). The effect of FILTERED is to force more Huffman codes and less string matching; it is somewhat intermediate between DEFAULT_STRATEGY and HUFFMAN_ONLY. Filtered data consists mostly of small values with a somewhat random distribution.

FINISH

Processes all pending input and flushes pending output.

FIXED

Deflate strategy which prevents the use of dynamic Huffman codes, allowing for a simpler decoder for specialized applications.

FULL_FLUSH

Flushes all output as with SYNC_FLUSH, gzdecompressstr data error, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Like SYNC_FLUSH, using FULL_FLUSH too often can seriously degrade compression.

HUFFMAN_ONLY

Deflate strategy which uses Huffman codes only (no string matching).

MAX_MEM_LEVEL

The gzdecompressstr data error memory level for allocating zlib gzdecompressstr data error compression state.

MAX_WBITS

The maximum size of the zlib history buffer. Note that zlib allows larger values to enable different inflate modes, gzdecompressstr data error. See Zlib::Inflate.new for details.

NO_COMPRESSION

No compression, passes through data untouched. Gzdecompressstr data error this for appending pre-compressed data to a deflate stream.

NO_FLUSH

NO_FLUSH is the default flush method and allows deflate to decide how much data to accumulate before producing output in order to maximize compression.

OS_AMIGA

OS code for Amiga hosts

OS_ATARI

OS code for Atari hosts

OS_CODE

The OS code of current host

OS_CPM

OS code for CP/M hosts

OS_MACOS

OS code for Mac OS hosts

OS_MSDOS

OS code for MSDOS hosts

OS_OS2

OS code for OS2 hosts

OS_QDOS

OS code for QDOS hosts

OS_RISCOS

OS code for RISC OS hosts

OS_TOPS20

OS code for TOPS-20 hosts

OS_UNIX

OS code for UNIX hosts

OS_UNKNOWN

OS code for unknown hosts

OS_VMCMS

OS code for VM OS hosts

OS_VMS

OS code for VMS hosts

OS_WIN32

OS code for Win32 hosts

OS_ZSYSTEM

OS code for Z-System hosts

RLE

Deflate compression strategy designed to be almost as fast as HUFFMAN_ONLY, but give better compression for PNG image data.

SYNC_FLUSH

The SYNC_FLUSH method flushes all pending output to the output buffer and the output is aligned on a byte boundary. Flushing may gzdecompressstr data error compression so it should be used only when necessary, such as at a request or response boundary for a network stream.

TEXT

Represents text data as guessed by deflate.

See Zlib::ZStream#data_type.

UNKNOWN

Represents an unknown data type as guessed by deflate.

See Zlib::ZStream#data_type.

VERSION

The Ruby/zlib version string.

ZLIB_VERSION

The string which represents the version of zlib.h

How to use TDecompressionStream? [closed]

It raises an exception when I try to read from the stream. What is wrong?

The most plausible explanation is that you are not passed valid GZIP encoded data to the stream. It's impossible for us to say why your data would be invalid because we don't know its provenance. To solve your problem you must first of all work out why your data is invalid.

One obvious issue with your code is the use of a string to represent binary data. GZIP operates on binary data. It compresses byte arrays to byte arrays. To work with text you use a predetermined encoding to convert text to binary. Once compressed, you would use something like MIME or base64 to encode the compressed binary as text. Perhaps your data is of this form: binary encoded as text, gzdecompressstr data error.

Another possible issue is that your Delphi unit is deficient, or simply out-dated. You don't state in the question which version of Delphi you use. Perhaps you are using an old version of Delphi that does not ship with a unit and are using a third party unit that is no good.

Opinion you: Gzdecompressstr data error

Joomla administrator 500 an error has occurred
Gzdecompressstr data error
Gzdecompressstr data error
REDIRECT HTACCESS INTERNAL SERVER ERRORR
gzdecompressstr data error

Gzdecompressstr data error - consider

How to use TDecompressionStream? [closed]

It raises an exception when I try to read from the stream. What is wrong?

The most plausible explanation is that you are not passed valid GZIP encoded data to the stream. It's impossible for us to say why your data would be invalid because we don't know its provenance. To solve your problem you must first of all work out why your data is invalid.

One obvious issue with your code is the use of a string to represent binary data. GZIP operates on binary data. It compresses byte arrays to byte arrays. To work with text you use a predetermined encoding to convert text to binary. Once compressed, you would use something like MIME or base64 to encode the compressed binary as text. Perhaps your data is of this form: binary encoded as text.

Another possible issue is that your Delphi unit is deficient, or simply out-dated. You don't state in the question which version of Delphi you use. Perhaps you are using an old version of Delphi that does not ship with a unit and are using a third party unit that is no good.

How to use TDecompressionStream? [closed]

It raises an exception when I try to read from the stream. What is wrong?

The most plausible explanation is that you are not passed valid GZIP encoded data to the stream. It's impossible for us to say why your data would be invalid because we don't know its provenance. To solve your problem you must first of all work out why your data is invalid.

One obvious issue with your code is the use of a string to represent binary data. GZIP operates on binary data. It compresses byte arrays to byte arrays. To work with text you use a predetermined encoding to convert text to binary. Once compressed, you would use something like MIME or base64 to encode the compressed binary as text. Perhaps your data is of this form: binary encoded as text.

Another possible issue is that your Delphi unit is deficient, or simply out-dated. You don't state in the question which version of Delphi you use. Perhaps you are using an old version of Delphi that does not ship with a unit and are using a third party unit that is no good.

file

Either a path to a file, a connection, or literal data (either a single string or a raw vector).

Files ending in , , , or will be automatically uncompressed. Files starting with , , , or will be automatically downloaded. Remote gz files can also be automatically downloaded and decompressed.

Literal data is most useful for examples and tests. To be recognised as literal data, the input must be either wrapped with , be a string containing at least one new line, or be a vector containing at least one string with a new line.

Using a value of will read from the system clipboard.

encoding

The character encoding used for the file. Generally, only needed for Stata 13 files and earlier. See Encoding section for details.

col_select

One or more selection expressions, like in . Use or to use more than one expression. See for details on available selection options. Only the specified columns will be read from .

skip

Number of lines to skip before reading data.

n_max

Maximum number of lines to read.

.name_repair

Treatment of problematic column names:

  • : No name repair or checks, beyond basic existence,

  • : Make sure names are unique and not empty,

  • : (default value), no name repair, but check they are ,

  • : Make the names and syntactic

  • a function: apply custom name repair (e.g., for names in the style of base R).

  • A purrr-style anonymous function, see

This argument is passed on as to . See there for more details on these terms and the strategies used to enforce them.

data

Data frame to write.

path

Path to a file where the data will be written.

version

File version to use. Supports versions 8-15.

label

Dataset label to use, or . Defaults to the value stored in the "label" attribute of . Must be <= 80 characters.

strl_threshold

Any character vectors with a maximum length greater than bytes will be stored as a long string (strL) instead of a standard string (str#) variable if >= 13. This defaults to 2045, the maximum length of str# variables. See the Stata long string documentation for more details.

Open
and navigate to the _MTL.TXT file.  ENVI will automatically open the Landsat image with all bands in the correct order.  The reflective bands are placed in one file, the thermal band(s) in another file.  There will be a 15m panchromatic file for ETM and OLI sensors and a 30m Cirrus file for the OLI sensor.

While you can work with these data as they are, ENVI has only created a temporary virtual layer stack that is constantly resampled as you move around the image.  You should save each file as a new dataset.  From the ENVI main menu select File

Command Line Fanatic

My very first post on this blog, 5 years ago, was a walk-through of the source code for a sample gunzip implementation. I've gotten quite a bit of feedback on it, mostly positive; it's still the most detailed post I've been able to put up here. Part of that write-up included bits and pieces of a gunzip session of an attached gzipped file, bit-for-bit. Recently, a very attentive commenter named Djibi pointed out that the attachment didn't quite match the examples in the post. My memory from that far back is hazy, but the only way I can imagine that happening is if I wrote the post based on one version of the attachment and then made a modification to the attachment without subsequently reviewing the text to ensure that it matched. Although I've gone through and updated the text to match the attachment per Djibi's very detailed analysis, I must admit that, after 5 years, I myself found the post hard to read through, as I was jumping around from one section to another. It occurred to me that a good companion piece would be a complete walk through of the gunzip process for the sample attachment. After all, this is the web and I don't have to worry about page count here! You may want to familiarize yourself with the original post before going through this one, as I assume below that you have a good understanding of Huffman codes and the LZ77 algorithm.

If you download the Attachment in question, you'll see that it's a 4704 byte file containing the gzipped representation of the source code presented in the original post, . Of course, if you try to open up a gzipped file the normal way, by double-clicking on it or whatever your desktop equivalent is, your OS is likely to decompress it on your behalf — but for the purposes of following along with this post, you don't want that: you want the "before" representation, as I'll be walking through the process of going from the before to the after. If you're using a Unix-type OS, you probably have the (objectdump) utility installed that can be used to see a byte-level representation of any file. If you run that utility (or any similar hexadecimal viewer or editor), you'll see that the unambiguous, canonical representation of the file, shown in figure 1, below.

Jump to bottom

Figure 1: Full hexadecimal representation of gunzip.c.gz

The facility is byte-oriented; with the arguments shown above, you'll get a hexadecimal representation of every byte in the referenced file. However, compressed files, by their nature, need to take maximum advantage of every single bit — so, to get a good gzip-eye view of this file, you need to break it down to its individual bits. However, if you learned to program any time in the past 40 years or so, you're probably used to the big-endian representation of binary data, where the most-significant bit is shown in the left-most position and the least-significant bit is shown in the right-most position. So the first byte of this file, hexadecimal 1F would be represented in binary as 00011111 and the second byte, hexadecimal 8B, as 10001011. The LZ77 specification that the gzip format is based on, though, is centered around the little-endian format: here, the first two bytes would be represented as 1111100011010001. In other circumstances, this wouldn't make a difference, since you'd be doing byte-for-byte comparisons anyway, but since compression algorithms make optimal use of every bit, the conceptual ordering of the bits makes a big difference, as codes span bytes and you have to put the bits into the correct order to reconstruct the file. Keep in mind as you read this post that the bits shown probably appear "backwards".

The first 10 bytes of figure 1 are the standard GZIP header, which is defined in bytes so the bit-ordering is immaterial. This breaks down to the representation shown in figure 2.

Standard GZIP declaration
Compression method: 0x08 represents GZIP
Flags (see below)
Timestamp
Extra flags
Operating System

Figure 2: standard 10-byte GZIP header

The flags byte, byte 4, is interpreted as shown in table 1. In the case of the attachment displayed in figure 1, only bit 8 is set, indicating that a null-terminated name string follows the header.
Bit mask (in big-endian format)Meaning
00000001Text follows
00000010Header CRC follows
00000100"Extra" follows
00001000Name follows
00010000Comment follows

Table 1: Flag bit meanings

In essence, the flags byte indicates that the header can be followed by up to five null- terminated strings, which must at least be skipped over before the actual gzipped-proper content appears. In this case, it is the 9-byte ASCII-encoded string: or "". After these first 19 bytes, bit ordering begins to matter. Figure 3 presents the binary representation of the remaining 4,685 bytes of the gzipped attachment file, in little-endian order, with the least significant bits appearing first.

Jump to bottom

Figure 3: Attachment #1 in little-endian bit format

I'll start by focusing on the first line of figure 3:

As described in part 1, the first bit is a "block" indicator - if it's set to 1, which it is in this case, then this is the last "block" in the file. You'll see multiple blocks in very large gzipped files, but this one is small enough that it only needs one block. The following two bits, in this case, are the block format. Here the block format is "dynamic huffman tree" indicating that the next bit sequence is a Huffman key to a Huffman coded representation of another Huffman key to the Huffman coded representation of the actual gzipped content. This is followed by the 5-bit length of the literals tree, the 5-bit length of the distance tree and the 3-bit length of the initial Huffman key.

So, bytes 20-22 of the attached file — , whose little-endian bit representation is — are interpreted as (remember to read the bits in the table "backwards"):

1last block in this file
012: dynamic huffman table
1110123 literals codes
1101127 distance codes
00018 keys in the following huffman key table

Figure 4: Huffman key table header

where the remaining seven bits of byte 22, , are unused (so far).

Since there are always at least five entries in the dynamic huffman key table, add 4 to 8 to get the actual count of twelve. That means that there are 12 3-bit codes that describe a Huffman table that is itself the key to the following Huffman table.

Bit patternnumeric valuelength of huffman code
011616
111717
111718
11030
11038
01027
11039
11036
001410
00145
101511
00144

Figure 5: Dynamic Huffman table specification

Indicating that the Huffman codes that encode the subsequent table are:

Figure 6: Dynamic Huffman table codes

At this point, I've read a little more than half-way through byte 26 of the first line of figure 3, and the file pointer is set to:

This is followed by the 308 codes-worth of Huffman-code lengths shown in figure 7 (recall that this is additionally run-length encoded, so there aren't 308 actual code values here):

Jump to bottom
Huffman codevaluerepeat countNotes
11111101710first 10 codes (0-9) are empty, don't appear
007The code for the literal value 10 is seven bits
1111111182121 more zeros; values 11-31 don't appear
11015The code for value 32 is five bits
1019The code for value 33 is 9 bits
1008...
111010
0100
1019
1008
1019
007
1008
1008
1008
007
007
007
1019
007
0116
007
007
1008
007
007
1008
007
1008
1019
007
1008
007
1008
111010
0100
1019
111010
1019
1019
1008
1019
0100
111010
1019
0100
0100
111010
1019
1019
1019
1111011
0100
1019
111110163
0100
0100
111010
0100
1111011
1019
1111011
1019
0100
007
0100
0116
007
0116
0116
11015
007
1008
007
0116
1008
1019
0116
007
0116
0116
007
0100
0116
0116
0116
007
1008
1008
1019
1008
111010
111010
111010
1008
111111118130130 consecutive 0's, indicating that the codes from 126-255 are not included in this table
1111011
11004
11004
11004
11015
111110163
0116
11015
11015
11015
0116
0116
007
007
007
1008
1008
1008
111010
111010
0100
111010
1008
1019
111110163
1008
007
007
11015
0116
11004
11004
11004
11015
11004
11015
11004
11015
11004
111110166
11015
11015
0116

Figure 7: Compressed data Huffman codes specification

Which work out to two Huffman code trees — one for the literals:

Figure 8: Compressed data literals Huffman code values

and a smaller one for the distances:

Figure 9: Compressed data distances Huffman code values

These tables make a lot of sense if you think about the nature of the file that was compressed — it's C source code, so it's ASCII-encoded. The byte value 10 appears fairly often: that's the line-ending code, so it gets a literal code. 32 is the ASCII code for a space character, so it gets a short Huffman code since it appears quite a bit. Although there are codes here for 33, 34 and 35 (ASCII !, " and #, respectively), the $ character 36 never appears in the zipped source, so no code is defined for it. There are codes here for most of the capital letters (range 65-90), but notice that their literals codes are relatively long, since there aren't many capital letters in the actual source code file. The lower-case letters (97-122) get shorter codes in the literals table, since they appear more often than the upper-case characters. The non-printable ASCII characters less than 32 (other than the CR code 10) and greater than 128 don't have codes because they don't appear in the source file.

At this point, the decompression values have read the full Huffman codes for the actual payload, which follows immediately. The last few bits that were read by the decompressor were: 1101 1101 011, which were 5, 5 and 6, according to the dynamic Huffman table from Figure 6. At this point, 86 bytes of the file have been consumed, and the file pointer is at the sixth byte of the fifth line of Figure 3 (hexadecimal ), pointed at the very last bit of the byte (remember, this is the most significant bit, because we're working LSB to MSB):

Almost all of the remainder of the file (until the trailer, which begins on byte 4696) is interpreted according to the Huffman tables in figures 8 and 9. As you can see, the Huffman compression tables are very efficient; only 65 bytes of the 4,704-byte gzipped file are "dictionary" information that's needed to interpret the remainder of the file, with an additional 20 bytes of header information and 8 bytes of trailer information.

So far, though, I haven't shown any Lempel-Ziv compression! At this point, all I have are the Huffman codes that represent four types of codes: a "normal" byte that should be inflated to its representative value, a stop code that indicates that compression should halt (i.e. EOF), a length code that indicates a "back pointer" to a prior part of the uncompressed output that should be represented and length codes that indicate how much of the previous data should be copied. Figure 10, below, shows the entire process and details how each code is interpreted; again, refer to RFC 1951 or my earlier discussion of GZIP/DEFLATE to fully interpret the details below.

Jump to bottom
Byte numberBits readCorresponding (Huffman code)Type (normal, stop or distance)ASCII value (for normal codes)Extra bits (codes 265-285)LengthDistance bits readExtra distance (distance codes 3+)Distance (Huffman code)copied value
86111111001035normal byte#
88100010105normal bytei
88100100110normal byten
8910000099normal bytec
90100011108normal bytel
911101011117normal byteu
92100001100normal byted
9200111101normal bytee
930011032normal byte
941110011060normal byte<
95100111115normal bytes
95101000116normal bytet
96100001100normal byted
97100010105normal bytei
98100101111normal byteo
98101110046normal byte.
991101000104normal byteh
1001110011162normal byte>
101101100010normal byte\n
102111111001035normal byte#
10301100265distance code11211000218include <std
105100011108normal bytel
106100010105normal bytei
106110011098normal byteb
10701110267distance code11611000319.h>\n#include <st
109100110114normal byter
110100010105normal bytei
111100100110normal byten
11111101001103normal byteg
11201101266distance code11411000319.h>\n#include <
11400111101normal bytee
115100110114normal byter
115100110114normal byter
116100100110normal byten
11701110267distance code01500011058o.h>\n#include <
11901111197normal bytea
119100111115normal bytes
120100111115normal bytes
12100111101normal bytee
122100110114normal byter
122101000116normal bytet
1230001258distance code411000319.h>\n
125101100010normal byte\n
12511110011147normal byte/
12711110011147normal byte/
1280011032normal byte
1281101000104normal byteh
12900111101normal bytee
13001111197normal bytea
131100001100normal byted
13100111101normal bytee
132100110114normal byter
1330011032normal byte
133100111115normal bytes
13400111101normal bytee
1351101010112normal bytep
13601111197normal bytea
136100110114normal byter
13701111197normal bytea
138101000116normal bytet
13900111101normal bytee
139100001100normal byted
1400011032normal byte
1411100111102normal bytef
141100110114normal byter
142100101111normal byteo
1431101001109normal bytem
1440011032normal byte
1441101001109normal bytem
14501111197normal bytea
146100010105normal bytei
147100100110normal byten
1480011032normal byte
1480000257distance code300101579str
1501101011117normal byteu
15110000099normal bytec
151101000116normal bytet
1520011032normal byte
1531100111102normal bytef
154100101111normal byteo
154100110114normal byter
1550011032normal byte
156101000116normal bytet
1571101000104normal byteh
15700111101normal bytee
1580011032normal byte
1591101111034normal byte"
160100111115normal bytes
160100010105normal bytei
1611111111000122normal bytez
16200111101normal bytee
163100101111normal byteo
1641100111102normal bytef
1651101111034normal byte"
1660011032normal byte
166110011098normal byteb
16700111101normal bytee
168100011108normal bytel
169100101111normal byteo
16911101100119normal bytew
170101100010normal byte\n
171101000116normal bytet
17211101101121normal bytey
1731101010112normal bytep
17400111101normal bytee
174100001100normal byted
17500111101normal bytee
1761100111102normal bytef
17701001261distance code70000537 struct
178101100010normal byte\n
1791111111001123normal byte{
180101100010normal byte\n
1810011032normal byte
1820011032normal byte
1831101011117normal byteu
183100100110normal byten
184100111115normal bytes
185100010105normal bytei
18611101001103normal byteg
187100100110normal byten
1870000257distance code30010367ed
18910000099normal bytec
1901101000104normal byteh
19101111197normal bytea
191100110114normal byter
1920011032normal byte
193100010105normal bytei
194100001100normal byted
19411111010191normal byte[
1950011032normal byte
196101111050normal byte2
1970011032normal byte
19811111011093normal byte]
199110001159normal byte;
200101010268distance code017111100024\n unsigned char
20210000099normal bytec
202100101111normal byteo
2031101001109normal bytem
2041101010112normal bytep
205100110114normal byter
20600111101normal bytee
206100111115normal bytes
207100111115normal bytes
208100010105normal bytei
208100101111normal byteo
209100100110normal byten
210110010195normal byte_
2111101001109normal bytem
21200111101normal bytee
212101000116normal bytet
2131101000104normal byteh
214100101111normal byteo
215100001100normal byted
215101010268distance code1180000335;\n unsigned char
2171100111102normal bytef
218100011108normal bytel
21901111197normal bytea
22011101001103normal byteg
221100111115normal bytes
221101010268distance code11811000622;\n unsigned char
2231101001109normal bytem
224101000116normal bytet
225100010105normal bytei
2261101001109normal bytem
22700111101normal bytee
22711111010191normal byte[
2280011032normal byte
2291110001152normal byte4
230101011269distance code12000102286 ];\n unsigned char
23200111101normal bytee
233111111000120normal bytex
234101000116normal bytet
235100110114normal byter
23501111197normal bytea
236110010195normal byte_
2371101100270distance code0230001856flags;\n unsigned char
239100101111normal byteo
2400000257distance code311000319s;\n
24111101110125normal byte}
242101100010normal byte\n
24311101001103normal byteg
2441111111000122normal bytez
245100010105normal bytei
2461101010112normal bytep
247110010195normal byte_
24801000260distance code61101049241header
250110001159normal byte;
251101100010normal byte\n
252101011269distance code120110101193\ntypedef struct\n{\n
25401100265distance code0110000032gzip_header
2560011032normal byte
25601010262distance code80000739header;\n
25801100265distance code01100101074 unsigned
260100111115normal bytes
2611101000104normal byteh
262100101111normal byteo
262100110114normal byter
263101000116normal bytet
2640011032normal byte
264111111000120normal bytex
266100011108normal bytel
26600111101normal bytee
267100100110normal byten
268101010268distance code11811001197;\n unsigned char
2701110000142normal byte*
2710010259distance code51100131127extra
273101011269distance code01911000723;\n unsigned char *
2751100111102normal bytef
275100100110normal byten
27601111197normal bytea
2771101001109normal bytem
27800111101normal bytee
278101011269distance code12011000723;\n unsigned char *f
2800000257distance code301007263com
2821101001109normal bytem
28300111101normal bytee
284100100110normal byten
285101000116normal bytet
285101011269distance code01911001197;\n unsigned short
28810000099normal bytec
288100110114normal byter
28910000099normal bytec
29001111049normal byte1
291110000154normal byte6
291110001159normal byte;
2920011032normal byte
2930000257distance code31101130414//
295101000116normal bytet
2961101000104normal byteh
297100010105normal bytei
297100111115normal bytes
2980011032normal byte
2991101010112normal bytep
300100110114normal byter
300100101111normal byteo
301101000116normal bytet
30200111101normal bytee
30210000099normal bytec
303101000116normal bytet
304100111115normal bytes
3050010259distance code5110116390 the
30701000260distance code6001122150header
30901100265distance code1120001351\n unsigned
310100011108normal bytel
311100101111normal byteo
312100100110normal byten
31311101001103normal byteg
3140001258distance code40001250 crc
315101111151normal byte3
316101111050normal byte2
317110001159normal byte;
3180011032normal byte
318101011269distance code3220001351 // this protects the
320100001100normal byted
321100101111normal byteo
32210000099normal bytec
3231101011117normal byteu
3230001258distance code41100110106ment
325101010268distance code0170001553\n unsigned long
327100010105normal bytei
3280001258distance code41101183467size
33001011263distance code9010025281;\n}\ngzip_
3321100111102normal bytef
333100010105normal bytei
333100011108normal bytel
3340000257distance code31111101012e;\n
336101100010normal byte\n
337111111001035normal byte#
3380000257distance code3010020276def
340100010105normal bytei
341100100110normal byten
34100111101normal bytee
3420011032normal byte
34311110110070normal byteF
34411111001184normal byteT
3451110100069normal byteE
346111111011188normal byteX
34711111001184normal byteT
3480011032normal byte
3490001258distance code4111111000
350101110148normal byte0
351111111000120normal bytex
352101110148normal byte0
35301111049normal byte1
354101001264distance code1011000622\n#define F
356111111010172normal byteH
35711110101067normal byteC
35811111000182normal byteR
35911110101067normal byteC
36001010262distance code811000622 0x0
362101111050normal byte2
363101001264distance code1011000622\n#define F
3650000257distance code300001244EXT
36611111000182normal byteR
36711110100165normal byteA
36801001261distance code711000622 0x0
3701110001152normal byte4
371101001264distance code1011000622\n#define F
37311110111178normal byteN
37411110100165normal byteA
37511110111077normal byteM
3761110100069normal byteE
37701010262distance code800001345 0x0
379110001056normal byte8
380101001264distance code1011000622\n#define F
38111110101067normal byteC
38211111000079normal byteO
38411110111077normal byteM
38511110111077normal byteM
3861110100069normal byteE
38711110111178normal byteN
38811111001184normal byteT
3890001258distance code411000622 0x
39101111049normal byte1
391101110148normal byte0
392101011269distance code2211101111395\n\ntypedef struct\n{\n
39501011263distance code9001141169unsigned
397100010105normal bytei
397100100110normal byten
398101000116normal bytet
3990011032normal byte
39901110267distance code1160100114370len;\n unsigned
4020001258distance code411000319int
40310000099normal bytec
404100101111normal byteo
405100001100normal byted
4050001258distance code4001159187e;\n}
4070011032normal byte
408101100010normal byte\n
409101000116normal bytet
409100110114normal byter
41000111101normal bytee
41100111101normal bytee
411110010195normal byte_
412100100110normal byten
4130010259distance code51111101113ode;\n
41501110267distance code0150010872\ntypedef struct
4160011032normal byte
4171101000104normal byteh
4181101011117normal byteu
4191100111102normal bytef
4201100111102normal bytef
4211101001109normal bytem
42101111197normal bytea
422100100110normal byten
4230010259distance code5111100529_node
425110010195normal byte_
42501000260distance code600102387t\n{\n
42701011263distance code900011058int code;
4290001258distance code4010043299 //
431101101145normal byte-
43201111049normal byte1
4320010259distance code50101223735 for
434100100110normal byten
435100101111normal byteo
436100100110normal byten
437101101145normal byte-
437100011108normal bytel
43800111101normal bytee
43901111197normal bytea
4401100111102normal bytef
4400011032normal byte
4410001258distance code40000739node
443100111115normal bytes
4430000257distance code30000436\n
445101011269distance code22100011462struct huffman_node_t
4470011032normal byte
4471110000142normal byte*
4481111111000122normal bytez
45000111101normal bytee
450100110114normal byter
451100101111normal byteo
452110001159normal byte;
4531101100270distance code326111100630\n struct huffman_node_t *
455100101111normal byteo
456100100110normal byten
4560010259distance code5010076332e;\n}\n
45801100265distance code11211000622huffman_node
460101011269distance code3220101103615;\n\ntypedef struct\n{\n
4630001258distance code400113131int
46400111101normal bytee
465100100110normal byten
4660010259distance code50101247759d;\n
4680001258distance code41111100210int
469110011098normal byteb
470100010105normal bytei
471101000116normal bytet
472110010195normal byte_
4730000257distance code31101033225len
47411101001103normal byteg
475101000116normal bytet
4761101000104normal byteh
47701100265distance code11200011462;\n}\nhuffman_
479100110114normal byter
48001111197normal bytea
480100100110normal byten
48111101001103normal byteg
4820001258distance code400011563e;\n\n
484100111115normal bytes
484101000116normal bytet
48501111197normal bytea
486101000116normal bytet
487100010105normal bytei
48710000099normal bytec
4880011032normal byte
48911101011118normal bytev
490100101111normal byteo
490100010105normal bytei
491100001100normal byted
4920011032normal byte
493110011098normal byteb
4931101011117normal byteu
494100010105normal bytei
495100011108normal bytel
496100001100normal byted
497110010195normal byte_
49701010262distance code80000133huffman_
4990001258distance code41101056248tree
501101100140normal byte(
50201101266distance code01300115133 huffman_node
5040011032normal byte
5041110000142normal byte*
505100110114normal byter
506100101111normal byteo
507100101111normal byteo
508101000116normal bytet
508101101044normal byte,
509101100010normal byte\n
5100011032normal byte
5111101110272distance code031111111000
5130001258distance code41100121117int
5150010259distance code500103195range
5160001258distance code41100123119_len
5181101110272distance code33400001446,\n
52001101266distance code013001118146huffman_range
5220000257distance code311001399 *r
5240010259distance code51111110106ange
5261110000041normal byte)
52701011263distance code91101010202\n{\n int
5291110000142normal byte*
530110011098normal byteb
530100011108normal bytel
531110010195normal byte_
53210000099normal bytec
533100101111normal byteo
5341101011117normal byteu
53401000260distance code60101203715nt;\n
5370010259distance code511000016int *
538100100110normal byten
5390000257distance code3011013781ext
541110010195normal byte_
54201000260distance code61101132416code;\n
5440011032normal byte
5440011032normal byte
54501011263distance code91101131415tree_node
5470011032normal byte
5481110000142normal byte*
5490001258distance code41111100210tree
5500000257distance code31101018210;\n\n
55201011263distance code91101054246 int bit
554100111115normal bytes
555110001159normal byte;
55601100265distance code0111101117401\n int code
5580011032normal byte
559110010061normal byte=
5600011032normal byte
560101110148normal byte0
56101010262distance code81111101315;\n int
563100100110normal byten
56401010262distance code8111110008;\n int
56501111197normal bytea
56610000099normal bytec
567101000116normal bytet
568100010105normal bytei
56811101011118normal bytev
56900111101normal bytee
57001010262distance code8010012268_range;\n
57201000260distance code611000319 int
5741101001109normal bytem
57501111197normal bytea
575111111000120normal bytex
576110010195normal byte_
57701100265distance code112010051307bit_length;\n
579101100010normal byte\n
5800010259distance code50101247759 //
582100111115normal bytes
583101000116normal bytet
58400111101normal bytee
5841101010112normal bytep
5850011032normal byte
58601111049normal byte1
5870011032normal byte
587101101145normal byte-
5880011032normal byte
5891100111102normal bytef
590100010105normal bytei
59011101001103normal byteg
5911101011117normal byteu
592100110114normal byter
59300111101normal bytee
5940011032normal byte
594100101111normal byteo
5951101011117normal byteu
5960000257distance code31101133417t h
598100101111normal byteo
59911101100119normal bytew
60001000260distance code60101233745 long
60201010262distance code8001133161bl_count
604101101044normal byte,
6050011032normal byte
60501011263distance code9001126154next_code
607101101044normal byte,
6080010259distance code5001124152 tree
6100011032normal byte
61000111101normal bytee
611101000116normal bytet
61210000099normal bytec
612101110046normal byte.
61301001261distance code70010064\n // s
6151101000104normal byteh
616100101111normal byteo
6171101011117normal byteu
618100011108normal bytel
6180000257distance code3010099355d b
62000111101normal bytee
6210011032normal byte
621110011098normal byteb
62201111197normal bytea
623100111115normal bytes
6240000257distance code30101100612ed
626100101111normal byteo
627100100110normal byten
6270010259distance code5011061829 the
6290010259distance code51100126122range
6310010259distance code5011081849s pro
63311101011118normal bytev
634100010105normal bytei
635100001100normal byted
63600111101normal bytee
6360010259distance code51101152436d;\n
63801101266distance code11400110128max_bit_length
64001010262distance code8001155183 = 0;\n
6420001258distance code4010173585for
644101100140normal byte(
6450011032normal byte
646100100110normal byten
6460010259distance code51111101214 = 0;
6480000257distance code31111110106 n
6501110011060normal byte<
651101001264distance code10010097353 range_len
6530000257distance code31111101214; n
6541110001043normal byte+
6551110001043normal byte+
6560000257distance code3010048304 )\n
6580011032normal byte
6590011032normal byte
6591111111001123normal byte{
6610010259distance code50100107363\n
663100010105normal bytei
6631100111102normal bytef
6640000257distance code30000840 (
6660010259distance code5111100529range
66711111010191normal byte[
6680000257distance code30000840 n
67011111011093normal byte]
671101110046normal byte.
67201100265distance code01100101175bit_length
6741110011162normal byte>
67501110267distance code11600102892 max_bit_length
6771110000041normal byte)
6780010259distance code50001149\n
6791111111001123normal byte{
68001001261distance code71101135419\n
683101010268distance code0171100125121max_bit_length =
685101011269distance code2210010569range[ n ].bit_length
687110001159normal byte;
6880010259distance code500001345\n
68911101110125normal byte}
690101100010normal byte\n
69101000260distance code61111111103 }\n
69301010262distance code81101059251bl_count
6950000257distance code300001345 =
6961101001109normal bytem
69701111197normal bytea
698100011108normal bytel
699100011108normal bytel
699100101111normal byteo
70010000099normal bytec
701101100140normal byte(
7020011032normal byte
70201000260distance code601114591483sizeof
705101100140normal byte(
7060010259distance code5010077333 int
7071110000041normal byte)
7080011032normal byte
7091110000142normal byte*
7100000257distance code3001113141 (
71201110267distance code01500102488max_bit_length
7141110001043normal byte+
7150000257distance code3010073329 1
7171110000041normal byte)
7180011032normal byte
7181110000041normal byte)
7190001258distance code40010872;\n
72101011263distance code9010048304next_code
72311110001275distance code45500011563 = malloc( sizeof( int ) * ( max_bit_length + 1 ) );\n
7250010259distance code50100101357tree
727101010268distance code11800011058= malloc( sizeof(
729101001264distance code10010121533tree_node
73101000260distance code60010064) * (
73301001261distance code7110108200range[
73501011263distance code9010051307range_len
7370000257distance code31101172456 -
73901111049normal byte1
7400000257distance code31101020212 ].
7420000257distance code3011038806end
744101001264distance code1000101276 + 1 ) );\n
7450001258distance code40100122378\n m
74700111101normal bytee
7481101001109normal bytem
749100111115normal bytes
75000111101normal bytee
750101000116normal bytet
751101100140normal byte(
75201100265distance code0111101180464 bl_count,
75411110011039normal byte'
7551111111111092normal byte\
757101110148normal byte0
75711110011039normal byte'
759101101044normal byte,
75911110000274distance code043001117145 sizeof( int ) * ( max_bit_length + 1 ) );\n
76211110000274distance code2451101141425\n for ( n = 0; n < range_len; n++ )\n {\n
76501010262distance code8110016102bl_count
76711111010191normal byte[
7681101100270distance code0231101146430 range[ n ].bit_length
77111111011093normal byte]
7720011032normal byte
7721110001043normal byte+
773110010061normal byte=
7740011032normal byte
77501001261distance code71101127411\n
77701100265distance code0110000133range[ n ].
7790001258distance code4001153181end
780101101145normal byte-
7810000257distance code311001298 (
7830001258distance code4110014100( n
7851110011162normal byte>
7860011032normal byte
786101110148normal byte0
7870000257distance code31100124120 )
789111111001163normal byte?
790101001264distance code10111100630 range[ n
792101001264distance code101101024216- 1 ].end
79411110100058normal byte:
7950001258distance code401111281152 -1
7980010259distance code5010036292);\n
79911101110125normal byte}
80001100265distance code1120101196708\n\n // step
803101111050normal byte2
804101101044normal byte,
8040011032normal byte
805100001100normal byted
806100010105normal bytei
807100110114normal byter
8070000257distance code301114461470ect
809100011108normal bytel
81011101101121normal bytey
81101000260distance code610003991935 from
81311111000182normal byteR
81511110110070normal byteF
81611110101067normal byteC
81701100265distance code0111101058250\n memset(
81901100265distance code0110101193705next_code,
82111110000274distance code5481101059251'\0', sizeof( int ) * ( max_bit_length + 1 ) );\n
82401010262distance code81101058250 for (
8260001258distance code40110122890bits
8280000257distance code31101061253 =
83001111049normal byte1
831110001159normal byte;
83101000260distance code6111110019 bits
8331110011060normal byte<
834110010061normal byte=
83501110267distance code116011083851 max_bit_length;
8370010259distance code511000723 bits
83901101266distance code01301009265++ )\n {\n
84101001261distance code701011513code =
843101100140normal byte(
84401000260distance code6111110008 code
8461110001043normal byte+
84701100265distance code011010025281 bl_count[
8490010259distance code50010266bits
8500010259distance code51101020212- 1 ]
8520000257distance code3110014100 )
8541110011060normal byte<
8551110011060normal byte<
8560000257distance code300102185 1;
858101001264distance code100101228740\n if (
86001110267distance code0150000537bl_count[ bits
86211111011093normal byte]
86301110267distance code0150101206718 )\n {\n
86501011263distance code91101010202next_code
86701011263distance code9111100731[ bits ]
869110010061normal byte=
8700011032normal byte
87001010262distance code80111541078code;\n
87301010262distance code80101192704 }\n }\n
87501100265distance code011010024280\n // step
877101111151normal byte3
8781101101271distance code330010024280, directly from RFC\n memset(
8800001258distance code4010182594tree
88201110267distance code116010019275, '\0', sizeof(
88401101266distance code1140101102614tree_node ) *
8870010259distance code500102286\n
88811101111273distance code3380101107619( range[ range_len - 1 ].end + 1 ) );\n
8910011032normal byte
89201101266distance code01301111221146 active_range
8941101100270distance code1240110227995 = 0;\n for ( n = 0; n <
897110010061normal byte=
8981101101271distance code02700101175 range[ range_len - 1 ].end
900101011269distance code22101102451013; n++ )\n {\n if (
9020001258distance code4010115527n >
90401001261distance code70001250range[
90601101266distance code01300103195active_range
90801000260distance code61100129125].end
91001101266distance code114010029285)\n {\n
91201100265distance code1120000032active_range
9141110001043normal byte+
9151110001043normal byte+
91601010262distance code8010019275;\n }\n
918101010268distance code0170111651089\n if ( range[
92001110267distance code0150010771active_range ].
9221101100270distance code2250111591083bit_length )\n {\n
9250001258distance code4010010266tree
92701000260distance code60101158670[ n ].
9290001258distance code4001138166len
930110010061normal byte=
9311101110272distance code23300011462 range[ active_range ].bit_length
933110001159normal byte;
934101100010normal byte\n
93501001261distance code70001856\n
9370010259distance code51100112108if (
93901101266distance code11400011361tree[ n ].len
94011110010033normal byte!
941110010061normal byte=
9420001258distance code40101213725 0 )
94401001261distance code7111100731\n
94601010262

Zlib

ASCII

Represents text data as guessed by deflate.

NOTE: The underlying constant Z_ASCII was deprecated in favor of Z_TEXT in zlib 1.2.2. New applications should not use this constant.

See Zlib::ZStream#data_type.

BEST_COMPRESSION

Slowest compression level, but with the best space savings.

BEST_SPEED

Fastest compression level, but with the lowest space savings.

BINARY

Represents binary data as guessed by deflate.

See Zlib::ZStream#data_type.

DEFAULT_COMPRESSION

Default compression level which is a good trade-off between space and time

DEFAULT_STRATEGY

Default deflate strategy which is used for normal data.

DEF_MEM_LEVEL

The default memory level for allocating zlib deflate compression state.

FILTERED

Deflate strategy for data produced by a filter (or predictor). The effect of FILTERED is to force more Huffman codes and less string matching; it is somewhat intermediate between DEFAULT_STRATEGY and HUFFMAN_ONLY. Filtered data consists mostly of small values with a somewhat random distribution.

FINISH

Processes all pending input and flushes pending output.

FIXED

Deflate strategy which prevents the use of dynamic Huffman codes, allowing for a simpler decoder for specialized applications.

FULL_FLUSH

Flushes all output as with SYNC_FLUSH, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Like SYNC_FLUSH, using FULL_FLUSH too often can seriously degrade compression.

HUFFMAN_ONLY

Deflate strategy which uses Huffman codes only (no string matching).

MAX_MEM_LEVEL

The maximum memory level for allocating zlib deflate compression state.

MAX_WBITS

The maximum size of the zlib history buffer. Note that zlib allows larger values to enable different inflate modes. See Zlib::Inflate.new for details.

NO_COMPRESSION

No compression, passes through data untouched. Use this for appending pre-compressed data to a deflate stream.

NO_FLUSH

NO_FLUSH is the default flush method and allows deflate to decide how much data to accumulate before producing output in order to maximize compression.

OS_AMIGA

OS code for Amiga hosts

OS_ATARI

OS code for Atari hosts

OS_CODE

The OS code of current host

OS_CPM

OS code for CP/M hosts

OS_MACOS

OS code for Mac OS hosts

OS_MSDOS

OS code for MSDOS hosts

OS_OS2

OS code for OS2 hosts

OS_QDOS

OS code for QDOS hosts

OS_RISCOS

OS code for RISC OS hosts

OS_TOPS20

OS code for TOPS-20 hosts

OS_UNIX

OS code for UNIX hosts

OS_UNKNOWN

OS code for unknown hosts

OS_VMCMS

OS code for VM OS hosts

OS_VMS

OS code for VMS hosts

OS_WIN32

OS code for Win32 hosts

OS_ZSYSTEM

OS code for Z-System hosts

RLE

Deflate compression strategy designed to be almost as fast as HUFFMAN_ONLY, but give better compression for PNG image data.

SYNC_FLUSH

The SYNC_FLUSH method flushes all pending output to the output buffer and the output is aligned on a byte boundary. Flushing may degrade compression so it should be used only when necessary, such as at a request or response boundary for a network stream.

TEXT

Represents text data as guessed by deflate.

See Zlib::ZStream#data_type.

UNKNOWN

Represents an unknown data type as guessed by deflate.

See Zlib::ZStream#data_type.

VERSION

The Ruby/zlib version string.

ZLIB_VERSION

The string which represents the version of zlib.h

10.6 Compressed Files

Although storage space and transmission bandwidth are increasingly cheap and abundant, in many cases you can save such resources, at the expense of some computational effort, by using compression. Since computational power grows cheaper and more abundant even faster than other resources, such as bandwidth, compression's popularity keeps growing. Python makes it easy for your programs to support compression by supplying dedicated modules for compression as part of every Python distribution.

10.6.1 The gzip Module

The module lets you read and write files compatible with those handled by the powerful GNU compression programs gzip and gunzip. The GNU programs support several compression formats, but module supports only the highly effective native gzip format, normally denoted by appending the extension .gz to a filename. Module supplies the class and an factory function.


class GzipFile(=None,=None,=9, =None)

Creates and returns a file-like object that wraps the file or file-like object . supplies all methods of built-in file objects except and . Thus, is not seekable: you can only access sequentially, whether for reading or writing. When is , must be a string that names a file: opens that file with the given (by default, ''), and wraps the resulting file object. should be one of '', '', '', or . If is , uses the mode of if it is able to find out the mode; otherwise it uses ''. If is , uses the filename of if able to find out the name; otherwise it uses ''. is an integer between and : requests modest compression but fast operation, and requests the best compression feasible, even if that requires more computation.

File-like object generally delegates all methods to the underlying file-like object , transparently accounting for compression as needed. However, does not allow non-sequential access, so does not supply methods and . Moreover, calling does not close when was created with an argument that is not . This behavior of is very important when is an instance of , since it means you can call after to get the compressed data as a string. This behavior also means that you have to call explicitly after calling .


open(,='rb',=9)

Like ,,, but is mandatory and there is no provision for passing an already opened .

Say that you have some function that writes data to a text file object , typically by calling and/or . Getting to write data to a gzip-compressed text file instead is easy:

import gzip underlying_file = open('x.txt.gz', 'wb') compressing_wrapper = gzip.GzipFile(fileobj=underlying_file, mode='wt') f(compressing_wrapper) compressing_wrapper.close( ) underlying_file.close( )

This example opens the underlying binary file x.txt.gz and explicitly wraps it with , and thus, at the end, we need to close each object separately. This is necessary because we want to use two different modes: the underlying file must be opened in binary mode (any translation of line endings would produce an invalid compressed file), but the compressing wrapper must be opened in text mode because we want the implicit translation of to . Reading back a compressed text file, for example to display it on standard output, is similar:

import gzip, xreadlines underlying_file = open('x.txt.gz', 'rb') uncompressing_wrapper = gzip.GzipFile(fileobj= underlying_file, mode='rt') for line in xreadlines.xreadlines(uncompressing_wrapper): print line, uncompressing_wrapper.close( ) underlying_file.close( )

This example uses module , covered earlier in this chapter, because objects (at least up to Python 2.2) are not iterable like true file objects, nor do they supply an method. objects do supply a method that closely emulates that of true file objects, and therefore module is able to produce a lazy sequence that wraps a object and lets us iterate on the object's lines.

10.6.2 The zipfile Module

The module lets you read and write ZIP files (i.e., archive files compatible with those handled by popular compression programs zip and unzip, pkzip and pkunzip, WinZip, and so on). Detailed information on the formats and capabilities of ZIP files can be found at http://www.pkware.com/appnote.html and http://www.info-zip.org/pub/infozip/. You need to study this detailed information in order to perform advanced ZIP file handing with module .

Module can't handle ZIP files with appended comments, multidisk ZIP files, or .zip archive members using compression types besides the usual ones, known as stored (when a file is copied to the archive without compression) and deflated (when a file is compressed using the ZIP format's default algorithm). For invalid .zip file errors, functions of module raise exceptions that are instances of exception class . Module supplies the following classes and functions.


Returns if the file named by string appears to be a valid ZIP file, judging by the first few bytes of the file; otherwise returns .


class ZipInfo(='NoName',=(1980,1,1,0,0,0))

Methods and of instances return instances of to supply information about members of the archive. The most useful attributes supplied by a instance are:

comment

A string that is a comment on the archive member

compress_size

Size in bytes of the compressed data for the archive member

compress_type

An integer code recording the type of compression of the archive member

date_time

A tuple with 6 integers recording the time of last modification to the file: the items are year, month, day ( and up), hour, minute, second ( and up)

file_size

Size in bytes of the uncompressed data for the archive member

filename

Name of the file in the archive


class ZipFile(,='r',=zipfile.ZIP_STORED)

Opens a ZIP file named by string . can be '', to read an existing ZIP file; '', to write a new ZIP file or truncate and rewrite an existing one; or '', to append to an existing file.

When is '', can name either an existing ZIP file (in which case new members are added to the existing archive) or an existing non-ZIP file. In the latter case, a new ZIP file-like archive is created and appended to the existing file. The main purpose of this latter case is to let you build a self-unpacking .exe file (i.e., a Windows executable file that unpacks itself when run). The existing file must then be a fresh copy of an unpacking .exe prefix, as supplied by www.info-zip.org or by other purveyors of ZIP file compression tools.

is an integer code that can be either of two attributes of module . requests that the archive use no compression, and requests that the archive use the deflation mode of compression (i.e., the most usual and effective compression approach used in .zip files).

A instance supplies the following methods.


Closes archive file . Make sure the method is called, or else an incomplete and unusable ZIP file might be left on disk. Such mandatory finalization is generally best performed with a / statement, as covered in Chapter 6.


Returns a instance that supplies information about the archive member named by string .


Returns a list of instances, one for each member in archive , in the same order as the entries in the archive itself.


Returns a list of strings, the names of each member in archive , in the same order as the entries in the archive itself.


Outputs a textual directory of the archive to file .


Returns a string containing the uncompressed bytes of the file named by string in archive . must be opened for '' or ''. When the archive does not contain a file named , raises an exception.


Reads and checks the files in archive . Returns a string with the name of the first archive member that is damaged, or when the archive is intact.


.write(,=None,=None)

Writes the file named by string to archive , with archive member name . When is , uses as the archive member name. When is , uses 's compression type; otherwise, is or , and specifies how to compress the file. must be opened for '' or ''.


must be a instance specifying at least and . is a string of bytes. adds a member to archive , using the metadata specified by and the data in . must be opened for '' or ''. When you have data in memory and need to write the data to the ZIP file archive , it's simpler and faster to use rather than . The latter approach would require you to write the data to disk first, and later remove the useless disk file. The following example shows both approaches, each encapsulated into a function, polymorphic to each other:

import zipfile def data_to_zip_direct(z, data, name): import time zinfo = zipfile.ZipInfo(name, time.localtime( )[:6]) z.writestr(zinfo, data) def data_to_zip_indirect(z, data, name): import os flob = open(name, 'wb') flob.write(data) flob.close( ) z.write(name) os.unlink(name) zz = zipfile.ZipFile('z.zip', 'w', zipfile.ZIP_DEFLATED) data = 'four score\nand seven\nyears ago\n' data_to_zip_direct(zz, data, 'direct.txt') data_to_zip_indirect(zz, data, 'indirect.txt') zz.close( )

Besides being faster and more concise, is handier because, by working in memory, it doesn't need to have the current working directory be writable, as does. Of course, method also has its uses, but that's mostly when you already have the data in a file on disk, and just want to add the file to the archive. Here's how you can print a list of all files contained in the ZIP file archive created by the previous example, followed by each file's name and contents:

import zipfile zz = zipfile.ZipFile('z.zip') zz.printdir( ) for name in zz.namelist( ): print '%s: %r' % (name, zz.read(name)) zz.close( )

10.6.3 The zlib Module

The module lets Python programs use the free InfoZip zlib compression library (see http://www.info-zip.org/pub/infozip/zlib/), Version 1.1.3 or later. Module is used by modules and , but the module is also available directly for any special compression needs. This section documents the most commonly used functions supplied by module .

Module also supplies functions to compute Cyclic-Redundancy Check (CRC) checksums, in order to detect possible damage in compressed data. It also provides objects that can compress and decompress data incrementally, and thus enable you to work with data streams that are too large to fit in memory at once. For such advanced functionality, consult the Python library's online reference.

Note that files containing data compressed with are not automatically interchangeable with other programs, with the exception of files that use the module and therefore respect the standard format of ZIP file archives. You could write a custom program, with any language able to use InfoZip's free zlib compression library, in order to read files produced by Python programs using the module. However, if you do need to interchange compressed data with programs coded in other languages, I suggest you use modules or instead. Module may be useful when you want to compress some parts of data files that are in some proprietary format of your own, and need not be interchanged with any other program except those that make up your own application.


Compresses string and returns the string of compressed data. is an integer between and : requests modest compression but fast operation, and requests compression as good as feasible, thus requiring more computation.


Decompresses the compressed data string and returns the string of uncompressed data.

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