NAME
compress
—
zlib general purpose compression
library
SYNOPSIS
#include <zlib.h>
Basic functions
const char *
zlibVersion
(void);
int
deflateInit
(z_streamp
strm, int
level);
int
deflate
(z_streamp
strm, int
flush);
int
deflateEnd
(z_streamp
strm);
int
inflateInit
(z_streamp
strm);
int
inflate
(z_streamp
strm, int
flush);
int
inflateEnd
(z_streamp
strm);
Advanced functions
int
deflateInit2
(z_streamp
strm, int level,
int method,
int windowBits,
int memLevel,
int strategy);
int
deflateSetDictionary
(z_streamp
strm, const Bytef
*dictionary, uInt
dictLength);
int
deflateCopy
(z_streamp
dest, z_streamp
source);
int
deflateReset
(z_streamp
strm);
int
deflateParams
(z_streamp
strm, int level,
int strategy);
int
deflateTune
(z_streamp
strm, int
good_length, int
max_lazy, int
nice_length, int
max_chain);
uLong
deflateBound
(z_streamp
strm, uLong
sourceLen);
int
deflatePrime
(z_streamp
strm, int bits,
int value);
int
deflateSetHeader
(z_streamp
strm, gz_headerp
head);
int
inflateInit2
(z_streamp
strm, int
windowBits);
int
inflateSetDictionary
(z_streamp
strm, const Bytef
*dictionary, uInt
dictLength);
int
inflateSync
(z_streamp
strm);
int
inflateCopy
(z_streamp
dst, z_streamp
source);
int
inflateReset
(z_streamp
strm);
int
inflatePrime
(z_streamp
strm, int bits,
int value);
int
inflateGetHeader
(z_streamp
strm, gz_headerp
head);
int
inflateBackInit
(z_stream
*strm, int
windowBits, unsigned char
FAR *window);
int
inflateBack
(z_stream
*strm, in_func in,
void FAR *in_desc,
out_func out,
void FAR *out_desc);
int
inflateBackEnd
(z_stream
*strm);
uLong
zlibCompileFlags
(void);
Utility functions
typedef voidp gzFile;
int
compress
(Bytef
*dest, uLongf
*destLen, const Bytef
*source, uLong
sourceLen);
int
compress2
(Bytef
*dest, uLongf
*destLen, const Bytef
*source, uLong
sourceLen, int
level);
uLong
compressBound
(uLong
sourceLen);
int
uncompress
(Bytef
*dest, uLongf
*destLen, const Bytef
*source, uLong
sourceLen);
gzFile
gzopen
(const
char *path, const char
*mode);
gzFile
gzdopen
(int
fd, const char
*mode);
int
gzsetparams
(gzFile
file, int level,
int strategy);
int
gzread
(gzFile
file, voidp buf,
unsigned len);
int
gzwrite
(gzFile
file, voidpc buf,
unsigned len);
int
gzprintf
(gzFile
file, const char
*format, ...);
int
gzputs
(gzFile
file, const char
*s);
char *
gzgets
(gzFile
file, char *buf,
int len);
int
gzputc
(gzFile
file, int c);
int
gzgetc
(gzFile
file);
int
gzungetc
(int
c, gzFile
file);
int
gzflush
(gzFile
file, int
flush);
z_off_t
gzseek
(gzFile
file, z_off_t
offset, int
whence);
int
gzrewind
(gzFile
file);
z_off_t
gztell
(gzFile
file);
int
gzeof
(gzFile
file);
int
gzdirect
(gzFile
file);
int
gzclose
(gzFile
file);
const char *
gzerror
(gzFile
file, int
*errnum);
void
gzclearerr
(gzFile
file);
Checksum functions
uLong
adler32
(uLong
adler, const Bytef
*buf, uInt
len);
uLong
adler32_combine
(uLong
adler1, uLong
adler2, z_off_t
len2);
uLong
crc32
(uLong
crc, const Bytef
*buf, uInt
len);
uLong
crc32_combine
(uLong
crc1, uLong crc2,
z_off_t len2);
DESCRIPTION
This manual page describes the zlib
general purpose compression library, version 1.2.3.
The zlib
compression library provides
in-memory compression and decompression functions, including integrity
checks of the uncompressed data. This version of the library supports only
one compression method (deflation) but other algorithms will be added later
and will have the same stream interface.
Compression can be done in a single step if the buffers are large enough (for example if an input file is mmap'ed), or can be done by repeated calls of the compression function. In the latter case, the application must provide more input and/or consume the output (providing more output space) before each call.
The compressed data format used by default by the in-memory
functions is the zlib
format, which is a zlib
wrapper documented in RFC 1950, wrapped around a deflate stream, which is
itself documented in RFC 1951.
The library also supports reading and writing files in gzip(1) (.gz) format with an interface similar to that of stdio(3) using the functions that start with "gz". The gzip format is different from the zlib format. gzip is a gzip wrapper, documented in RFC 1952, wrapped around a deflate stream. This library can optionally read and write gzip streams in memory as well.
The zlib format was designed to be compact and fast for use in memory and on communications channels. The gzip format was designed for single-file compression on file systems, has a larger header than zlib to maintain directory information, and uses a different, slower, check method than zlib.
The library does not install any signal handler. The decoder checks the consistency of the compressed data, so the library should never crash even in case of corrupted input.
The functions within the library are divided into the following sections:
- Basic functions
- Advanced functions
- Utility functions
- Checksum functions
BASIC FUNCTIONS
- const char *
zlibVersion
(void); -
The application can compare
zlibVersion
() andZLIB_VERSION
for consistency. If the first character differs, the library code actually used is not compatible with the ⟨zlib.h⟩ header file used by the application. This check is automatically made bydeflateInit
() andinflateInit
(). - int
deflateInit
(z_streamp strm, int level); -
The
deflateInit
() function initializes the internal stream state for compression. The fields zalloc, zfree, and opaque must be initialized before by the caller. If zalloc and zfree are set toZ_NULL
,deflateInit
() updates them to use default allocation functions.The compression level must be
Z_DEFAULT_COMPRESSION
, or between 0 and 9: 1 gives best speed, 9 gives best compression, 0 gives no compression at all (the input data is simply copied a block at a time).Z_DEFAULT_COMPRESSION
requests a default compromise between speed and compression (currently equivalent to level 6).deflateInit
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_STREAM_ERROR
if level is not a valid compression level,Z_VERSION_ERROR
if thezlib
library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION). msg is set to null if there is no error message.deflateInit
() does not perform any compression: this will be done bydeflate
(). - int
deflate
(z_streamp strm, int flush); -
deflate
() compresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency (reading input without producing any output) except when forced to flush.The detailed semantics are as follows.
deflate
() performs one or both of the following actions:Compress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in and avail_in are updated and processing will resume at this point for the next call to
deflate
().Provide more output starting at next_out and update next_out and avail_out accordingly. This action is forced if the parameter flush is non-zero. Forcing flush frequently degrades the compression ratio, so this parameter should be set only when necessary (in interactive applications). Some output may be provided even if flush is not set.
Before the call to
deflate
(), the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating avail_in or avail_out accordingly; avail_out should never be zero before the call. The application can consume the compressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call todeflate
(). Ifdeflate
() returnsZ_OK
and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.Normally the parameter flush is set to
Z_NO_FLUSH
, which allowsdeflate
() to decide how much data to accumulate before producing output, in order to maximise compression.If the parameter flush is set to
Z_SYNC_FLUSH
, all pending output is flushed to the output buffer and the output is aligned on a byte boundary, so that the decompressor can get all input data available so far. (In particular, avail_in is zero after the call if enough output space has been provided before the call.) Flushing may degrade compression for some compression algorithms and so it should be used only when necessary.If flush is set to
Z_FULL_FLUSH
, all output is flushed as withZ_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. UsingZ_FULL_FLUSH
too often can seriously degrade compression.If
deflate
() returns with avail_out == 0, this function must be called again with the same value of the flush parameter and more output space (updated avail_out), until the flush is complete (deflate
() returns with non-zero avail_out). In the case of aZ_FULL_FLUSH
or aZ_SYNC_FLUSH
, make sure that avail_out is greater than six to avoid repeated flush markers due to avail_out == 0 on return.If the parameter flush is set to
Z_FINISH
, pending input is processed, pending output is flushed anddeflate
() returns withZ_STREAM_END
if there was enough output space; ifdeflate
() returns withZ_OK
, this function must be called again withZ_FINISH
and more output space (updated avail_out but no more input data, until it returns withZ_STREAM_END
or an error. Afterdeflate
() has returnedZ_STREAM_END
, the only possible operations on the stream aredeflateReset
() ordeflateEnd
().Z_FINISH
can be used immediately afterdeflateInit
() if all the compression is to be done in a single step. In this case, avail_out must be at least the value returned bydeflateBound
() (see below). Ifdeflate
() does not returnZ_STREAM_END
, then it must be called again as described above.deflate
() sets strm->adler to the Adler-32 checksum of all input read so far (that is, total_in bytes).deflate
() may update strm->data_type if it can make a good guess about the input data type (Z_BINARY or Z_TEXT). If in doubt, the data is considered binary. This field is only for information purposes and does not affect the compression algorithm in any manner.deflate
() returnsZ_OK
if some progress has been made (more input processed or more output produced),Z_STREAM_END
if all input has been consumed and all output has been produced (only when flush is set toZ_FINISH
),Z_STREAM_ERROR
if the stream state was inconsistent (for example, if next_in or next_out wasNULL
),Z_BUF_ERROR
if no progress is possible (for example, avail_in or avail_out was zero). Note thatZ_BUF_ERROR
is not fatal, anddeflate
() can be called again with more input and more output space to continue processing. - int
deflateEnd
(z_streamp strm); -
All dynamically allocated data structures for this stream are freed. This function discards any unprocessed input and does not flush any pending output.
deflateEnd
() returnsZ_OK
if successful,Z_STREAM_ERROR
if the stream state was inconsistent,Z_DATA_ERROR
if the stream was freed prematurely (some input or output was discarded). In the error case, msg may be set but then points to a static string (which must not be deallocated). - int
inflateInit
(z_streamp strm); - The
inflateInit
() function initializes the internal stream state for decompression. The fields next_in, avail_in, zalloc, zfree, and opaque must be initialized before by the caller. If next_in is notZ_NULL
and avail_in is large enough (the exact value depends on the compression method),inflateInit
() determines the compression method from thezlib
header and allocates all data structures accordingly; otherwise the allocation will be deferred to the first call toinflate
(). If zalloc and zfree are set toZ_NULL
,inflateInit
() updates them to use default allocation functions.inflateInit
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_VERSION_ERROR
if thezlib
library version is incompatible with the version assumed by the caller. msg is set to null if there is no error message.inflateInit
() does not perform any decompression apart from reading thezlib
header if present: this will be done byinflate
(). (So next_in and avail_in may be modified, but next_out and avail_out are unchanged.) - int
inflate
(z_streamp strm, int flush); inflate
() decompresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency (reading input without producing any output) except when forced to flush.The detailed semantics are as follows.
inflate
() performs one or both of the following actions:Decompress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in is updated and processing will resume at this point for the next call to
inflate
().Provide more output starting at next_out and update next_out and avail_out accordingly.
inflate
() provides as much output as possible, until there is no more input data or no more space in the output buffer (see below about the flush parameter).Before the call to
inflate
(), the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating the next_* and avail_* values accordingly. The application can consume the uncompressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call toinflate
(). Ifinflate
() returnsZ_OK
and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.The flush parameter of
inflate
() can beZ_NO_FLUSH
,Z_SYNC_FLUSH
,Z_FINISH
, orZ_BLOCK
.Z_SYNC_FLUSH
requests thatinflate
() flush as much output as possible to the output buffer.Z_BLOCK
requests thatinflate
() stop if and when it gets to the next deflate block boundary. When decoding the zlib or gzip format, this will causeinflate
() to return immediately after the header and before the first block. When doing a raw inflate,inflate
() will go ahead and process the first block, and will return when it gets to the end of that block, or when it runs out of data.The
Z_BLOCK
option assists in appending to or combining deflate streams. Also to assist in this, on returninflate
() will set strm->data_type to the number of unused bits in the last byte taken from strm->next_in, plus 64 ifinflate
() is currently decoding the last block in the deflate stream, plus 128 ifinflate
() returned immediately after decoding an end-of-block code or decoding the complete header up to just before the first byte of the deflate stream. The end-of-block will not be indicated until all of the uncompressed data from that block has been written to strm->next_out. The number of unused bits may in general be greater than seven, except when bit 7 of data_type is set, in which case the number of unused bits will be less than eight.inflate
() should normally be called until it returnsZ_STREAM_END
or an error. However if all decompression is to be performed in a single step (a single call to inflate), the parameter flush should be set toZ_FINISH
. In this case all pending input is processed and all pending output is flushed; avail_out must be large enough to hold all the uncompressed data. (The size of the uncompressed data may have been saved by the compressor for this purpose.) The next operation on this stream must beinflateEnd
() to deallocate the decompression state. The use ofZ_FINISH
is never required, but can be used to informinflate
() that a faster approach may be used for the singleinflate
() call.In this implementation,
inflate
() always flushes as much output as possible to the output buffer, and always uses the faster approach on the first call. So the only effect of the flush parameter in this implementation is on the return value ofinflate
(), as noted below, or when it returns early becauseZ_BLOCK
is used.If a preset dictionary is needed after this call (see
inflateSetDictionary
() below),inflate
() sets strm->adler to the Adler-32 checksum of the dictionary chosen by the compressor and returns Z_NEED_DICT; otherwise it sets strm->adler to the Adler-32 checksum of all output produced so far (that is, total_out bytes) and returnsZ_OK
,Z_STREAM_END
or an error code as described below. At the end of the stream,inflate
() checks that its computed Adler-32 checksum is equal to that saved by the compressor and returnsZ_STREAM_END
only if the checksum is correct.inflate
() will decompress and check either zlib-wrapped or gzip-wrapped deflate data. The header type is detected automatically. Any information contained in the gzip header is not retained, so applications that need that information should instead use raw inflate; seeinflateInit2
() below, orinflateBack
() and perform their own processing of the gzip header and trailer.inflate
() returnsZ_OK
if some progress has been made (more input processed or more output produced),Z_STREAM_END
if the end of the compressed data has been reached and all uncompressed output has been produced,Z_NEED_DICT
if a preset dictionary is needed at this point,Z_DATA_ERROR
if the input data was corrupted (input stream not conforming to thezlib
format or incorrect check value),Z_STREAM_ERROR
if the stream structure was inconsistent (for example, if next_in or next_out wasNULL
),Z_MEM_ERROR
if there was not enough memory,Z_BUF_ERROR
if no progress is possible or if there was not enough room in the output buffer whenZ_FINISH
is used. Note thatZ_BUF_ERROR
is not fatal, andinflate
() can be called again with more input and more output space to continue compressing. IfZ_DATA_ERROR
is returned, the application may then callinflateSync
() to look for a good compression block if a partial recovery of the data is desired.- int
inflateEnd
(z_streamp strm); - All dynamically allocated data structures for this stream are freed. This
function discards any unprocessed input and does not flush any pending
output.
inflateEnd
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the stream state was inconsistent. In the error case, msg may be set but then points to a static string (which must not be deallocated).
ADVANCED FUNCTIONS
The following functions are needed only in some special applications.
- int
deflateInit2
(z_streamp strm, int level, int method, int windowBits, int memLevel, int strategy); -
This is another version of
deflateInit
() with more compression options. The fields next_in, zalloc, zfree, and opaque must be initialized before by the caller.The method parameter is the compression method. It must be
Z_DEFLATED
in this version of the library.The windowBits parameter is the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage. The default value is 15 if
deflateInit
() is used instead.windowBits can also be -8..-15 for raw deflate. In this case, -windowBits determines the window size.
deflate
() will then generate raw deflate data with no zlib header or trailer, and will not compute an Adler-32 check value.windowBits can also be greater than 15 for optional gzip encoding. Add 16 to windowBits to write a simple gzip header and trailer around the compressed data instead of a zlib wrapper. The gzip header will have no file name, no extra data, no comment, no modification time (set to zero), no header crc, and the operating system will be set to 255 (unknown). If a gzip stream is being written, strm->adler is a crc32 instead of an adler32.
The memLevel parameter specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed. The default value is 8. See ⟨zconf.h⟩ for total memory usage as a function of windowBits and memLevel.
The strategy parameter is used to tune the compression algorithm. Use the value
Z_DEFAULT_STRATEGY
for normal data;Z_FILTERED
for data produced by a filter (or predictor);Z_HUFFMAN_ONLY
to force Huffman encoding only (no string match), orZ_RLE
to limit match distances to one (run-length encoding). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect ofZ_FILTERED
is to force more Huffman coding and less string matching; it is somewhat intermediate betweenZ_DEFAULT
andZ_HUFFMAN_ONLY
.Z_RLE
is designed to be almost as fast asZ_HUFFMAN_ONLY
, but gives better compression for PNG image data. The strategy parameter only affects the compression ratio but not the correctness of the compressed output, even if it is not set appropriately.Z_FIXED
prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.deflateInit2
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_STREAM_ERROR
if a parameter is invalid (such as an invalid method). msg is set to null if there is no error message.deflateInit2
() does not perform any compression: this will be done bydeflate
(). - int
deflateSetDictionary
(z_streamp strm, const Bytef *dictionary, uInt dictLength); -
Initializes the compression dictionary from the given byte sequence without producing any compressed output. This function must be called immediately after
deflateInit
(),deflateInit2
(), ordeflateReset
(), before any call todeflate
(). The compressor and decompressor must use exactly the same dictionary (seeinflateSetDictionary
()).The dictionary should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary.
Depending on the size of the compression data structures selected by
deflateInit
() ordeflateInit2
(), a part of the dictionary may in effect be discarded, for example if the dictionary is larger than the window size indeflate
() ordeflate2
(). Thus the strings most likely to be useful should be put at the end of the dictionary, not at the front. In addition, the current implementation ofdeflate
() will use at most the window size minus 262 bytes of the provided dictionary.Upon return of this function, strm->adler is set to the Adler-32 value of the dictionary; the decompressor may later use this value to determine which dictionary has been used by the compressor. (The Adler-32 value applies to the whole dictionary even if only a subset of the dictionary is actually used by the compressor.) If a raw deflate was requested, then the Adler-32 value is not computed and strm->adler is not set.
deflateSetDictionary
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent (for example ifdeflate
() has already been called for this stream or if the compression method is bsort).deflateSetDictionary
() does not perform any compression: this will be done bydeflate
(). - int
deflateCopy
(z_streamp dest, z_streamp source); -
The
deflateCopy
() function sets the destination stream as a complete copy of the source stream.This function can be useful when several compression strategies will be tried, for example when there are several ways of pre-processing the input data with a filter. The streams that will be discarded should then be freed by calling
deflateEnd
(). Note thatdeflateCopy
() duplicates the internal compression state which can be quite large, so this strategy is slow and can consume lots of memory.deflateCopy
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_STREAM_ERROR
if the source stream state was inconsistent (such as zalloc being NULL). msg is left unchanged in both source and destination. - int
deflateReset
(z_streamp strm); -
This function is equivalent to
deflateEnd
() followed bydeflateInit
(), but does not free and reallocate all the internal compression state. The stream will keep the same compression level and any other attributes that may have been set bydeflateInit2
().deflateReset
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent (such as zalloc or state being NULL). - int
deflateParams
(z_streamp strm, int level, int strategy); -
The
deflateParams
() function dynamically updates the compression level and compression strategy. The interpretation of level and strategy is as indeflateInit2
(). This can be used to switch between compression and straight copy of the input data, or to switch to a different kind of input data requiring a different strategy. If the compression level is changed, the input available so far is compressed with the old level (and may be flushed); the new level will take effect only at the next call todeflate
().Before the call to
deflateParams
(), the stream state must be set as for a call todeflate
(), since the currently available input may have to be compressed and flushed. In particular, strm->avail_out must be non-zero.deflateParams
() returnsZ_OK
if successful,Z_STREAM_ERROR
if the source stream state was inconsistent or if a parameter was invalid, orZ_BUF_ERROR
if strm->avail_out was zero. - int
deflateTune
(z_streamp strm, int good_length, int max_lazy, int nice_length, int max_chain) -
Fine tune
deflate
()'s internal compression parameters. This should only be used by someone who understands the algorithm used by zlib's deflate for searching for the best matching string, and even then only by the most fanatic optimizer trying to squeeze out the last compressed bit for their specific input data. Read the deflate.c source code for the meaning of the max_lazy, good_length, nice_length, and max_chain parameters.deflateTune
() can be called afterdeflateInit
() ordeflateInit2
(), and returnsZ_OK
on success, orZ_STREAM_ERROR
for an invalid deflate stream. - uLong
deflateBound
(z_streamp strm, uLong sourceLen) -
deflateBound
() returns an upper bound on the compressed size after deflation of sourceLen bytes. It must be called afterdeflateInit
() ordeflateInit2
(). This would be used to allocate an output buffer for deflation in a single pass, and so would be called beforedeflate
(). - int
deflatePrime
(z_streamp strm, int bits, int value) -
deflatePrime
() inserts bits in the deflate output stream. The intent is that this function is used to start off the deflate output with the bits leftover from a previous deflate stream when appending to it. As such, this function can only be used for raw deflate, and must be used before the firstdeflate
() call after adeflateInit2
() ordeflateReset
(). bits must be less than or equal to 16, and that many of the least significant bits of value will be inserted in the output.deflatePrime
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent. - int
deflateSetHeader
(z_streamp strm, gz_headerp head) -
deflateSetHeader
() provides gzip header information for when a gzip stream is requested bydeflateInit2
().deflateSetHeader
() may be called afterdeflateInit2
() ordeflateReset
() and before the first call ofdeflate
(). The text, time, os, extra field, name, and comment information in the provided gz_header structure are written to the gzip header (xflag is ignored - the extra flags are set according to the compression level). The caller must assure that, if notZ_NULL
, name and comment are terminated with a zero byte, and that if extra is notZ_NULL
, that extra_len bytes are available there. If hcrc is true, a gzip header CRC is included. Note that the current versions of the command-line version of gzip(1) do not support header CRCs, and will report that it is a “multi-part gzip file” and give up.If
deflateSetHeader
() is not used, the default gzip header has text false, the time set to zero, and os set to 255, with no extra, name, or comment fields. The gzip header is returned to the default state bydeflateReset
().deflateSetHeader
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent. - int
inflateInit2
(z_streamp strm, int windowBits); -
This is another version of
inflateInit
() with an extra parameter. The fields next_in, avail_in, zalloc, zfree, and opaque must be initialized before by the caller.The windowBits parameter is the base two logarithm of the maximum window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. The default value is 15 if
inflateInit
() is used instead. windowBits must be greater than or equal to the windowBits value provided todeflateInit2
() while compressing, or it must be equal to 15 ifdeflateInit2
() was not used. If a compressed stream with a larger window size is given as input,inflate
() will return with the error codeZ_DATA_ERROR
instead of trying to allocate a larger window.windowBits can also be -8..-15 for raw inflate. In this case, -windowBits determines the window size.
inflate
() will then process raw deflate data, not looking for a zlib or gzip header, not generating a check value, and not looking for any check values for comparison at the end of the stream. This is for use with other formats that use the deflate compressed data format such as zip. Those formats provide their own check values. If a custom format is developed using the raw deflate format for compressed data, it is recommended that a check value such as an Adler-32 or a crc32 be applied to the uncompressed data as is done in the zlib, gzip, and zip formats. For most applications, the zlib format should be used as is. Note that comments above on the use indeflateInit2
() applies to the magnitude of windowBits.windowBits can also be greater than 15 for optional gzip decoding. Add 32 to windowBits to enable zlib and gzip decoding with automatic header detection, or add 16 to decode only the gzip format (the zlib format will return a
Z_DATA_ERROR
). If a gzip stream is being decoded, strm->adler is a crc32 instead of an adler32.inflateInit2
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_STREAM_ERROR
if a parameter is invalid (such as a null strm). msg is set to null if there is no error message.inflateInit2
() does not perform any decompression apart from reading thezlib
header if present: this will be done byinflate
(). (So next_in and avail_in may be modified, but next_out and avail_out are unchanged.) - int
inflateSetDictionary
(z_streamp strm, const Bytef *dictionary, uInt dictLength); -
Initializes the decompression dictionary from the given uncompressed byte sequence. This function must be called immediately after a call to
inflate
() if that call returnedZ_NEED_DICT
. The dictionary chosen by the compressor can be determined from the Adler-32 value returned by that call toinflate
(). The compressor and decompressor must use exactly the same dictionary (seedeflateSetDictionary
()). For raw inflate, this function can be called immediately afterinflateInit2
() orinflateReset
() and before any call toinflate
() to set the dictionary. The application must ensure that the dictionary that was used for compression is provided.inflateSetDictionary
() returnsZ_OK
if successful,Z_STREAM_ERROR
if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent,Z_DATA_ERROR
if the given dictionary doesn't match the expected one (incorrect Adler-32 value).inflateSetDictionary
() does not perform any decompression: this will be done by subsequent calls ofinflate
(). - int
inflateSync
(z_streamp strm); -
Skips invalid compressed data until a full flush point (see above the description of
deflate
() withZ_FULL_FLUSH
) can be found, or until all available input is skipped. No output is provided.inflateSync
() returnsZ_OK
if a full flush point has been found,Z_BUF_ERROR
if no more input was provided,Z_DATA_ERROR
if no flush point has been found, orZ_STREAM_ERROR
if the stream structure was inconsistent. In the success case, the application may save the current value of total_in which indicates where valid compressed data was found. In the error case, the application may repeatedly callinflateSync
(), providing more input each time, until success or end of the input data. - int
inflateCopy
(z_streamp dest, z_streamp source) -
Sets the destination stream as a complete copy of the source stream.
This function can be useful when randomly accessing a large stream. The first pass through the stream can periodically record the inflate state, allowing restarting inflate at those points when randomly accessing the stream.
inflateCopy
() returnsZ_OK
if success,Z_MEM_ERROR
if there was not enough memory,Z_STREAM_ERROR
if the source stream state was inconsistent (such as zalloc being NULL). msg is left unchanged in both source and dest. - int
inflateReset
(z_streamp strm); -
This function is equivalent to
inflateEnd
() followed byinflateInit
(), but does not free and reallocate all the internal decompression state. The stream will keep attributes that may have been set byinflateInit2
().inflateReset
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent (such as zalloc or state being NULL). - int
inflatePrime
(z_stream strm, int bits, int value) -
This function inserts bits in the inflate input stream. The intent is that this function is used to start inflating at a bit position in the middle of a byte. The provided bits will be used before any bytes are used from next_in. This function should only be used with raw inflate, and should be used before the first
inflate
() call afterinflateInit2
() orinflateReset
(). bits must be less than or equal to 16, and that many of the least significant bits of value will be inserted in the input.inflatePrime
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent. - int
inflateGetHeader
(z_streamp strm, gz_headerp head) -
inflateGetHeader
() requests that gzip header information be stored in the provided gz_header structure.inflateGetHeader
() may be called afterinflateInit2
() orinflateReset
(), and before the first call ofinflate
(). Asinflate
() processes the gzip stream, head->done is zero until the header is completed, at which time head->done is set to one. If a zlib stream is being decoded, then head->done is set to -1 to indicate that there will be no gzip header information forthcoming. Note thatZ_BLOCK
can be used to forceinflate
() to return immediately after header processing is complete and before any actual data is decompressed.The text, time, xflags, and os fields are filled in with the gzip header contents. hcrc is set to true if there is a header CRC. (The header CRC was valid if done is set to one.) If extra is not
Z_NULL
, then extra_max contains the maximum number of bytes to write to extra. Once done is true, extra_len contains the actual extra field length, and extra contains the extra field, or that field truncated if extra_max is less than extra_len. If name is notZ_NULL
, then up to name_max characters are written there, terminated with a zero unless the length is greater than name_max. If comment is notZ_NULL
, then up to comm_max characters are written there, terminated with a zero unless the length is greater than comm_max. When any of extra, name, or comment are notZ_NULL
and the respective field is not present in the header, then that field is set toZ_NULL
to signal its absence. This allows the use ofdeflateSetHeader
() with the returned structure to duplicate the header. However if those fields are set to allocated memory, then the application will need to save those pointers elsewhere so that they can be eventually freed.If
inflateGetHeader
() is not used, then the header information is simply discarded. The header is always checked for validity, including the header CRC if present.inflateReset
() will reset the process to discard the header information. The application would need to callinflateGetHeader
() again to retrieve the header from the next gzip stream.inflateGetHeader
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the source stream state was inconsistent. - int
inflateBackInit
(z_stream *strm, int windowBits, unsigned char FAR *window) -
Initialize the internal stream state for decompression using
inflateBack
() calls. The fields zalloc, zfree and opaque in strm must be initialized before the call. If zalloc and zfree areZ_NULL
, then the default library-derived memory allocation routines are used. windowBits is the base two logarithm of the window size, in the range 8..15. window is a caller supplied buffer of that size. Except for special applications where it is assured thatdeflate
() was used with small window sizes, windowBits must be 15 and a 32K byte window must be supplied to be able to decompress general deflate streams.See
inflateBack
() for the usage of these routines.inflateBackInit
() will returnZ_OK
on success,Z_STREAM_ERROR
if any of the parameters are invalid,Z_MEM_ERROR
if the internal state could not be allocated, orZ_VERSION_ERROR
if the version of the library does not match the version of the header file. - int
inflateBack
(z_stream *strm, in_func in, void FAR *in_desc, out_func out, void FAR *out_desc) -
inflateBack
() does a raw inflate with a single call using a call-back interface for input and output. This is more efficient thaninflate
() for file I/O applications in that it avoids copying between the output and the sliding window by simply making the window itself the output buffer. This function trusts the application to not change the output buffer passed by the output function, at least untilinflateBack
() returns.inflateBackInit
() must be called first to allocate the internal state and to initialize the state with the user-provided window buffer.inflateBack
() may then be used multiple times to inflate a complete, raw deflate stream with each call.inflateBackEnd
() is then called to free the allocated state.A raw deflate stream is one with no zlib or gzip header or trailer. This routine would normally be used in a utility that reads zip or gzip files and writes out uncompressed files. The utility would decode the header and process the trailer on its own, hence this routine expects only the raw deflate stream to decompress. This is different from the normal behavior of
inflate
(), which expects either a zlib or gzip header and trailer around the deflate stream.inflateBack
() uses two subroutines supplied by the caller that are then called byinflateBack
() for input and output.inflateBack
() calls those routines until it reads a complete deflate stream and writes out all of the uncompressed data, or until it encounters an error. The function's parameters and return types are defined above in the in_func and out_func typedefs.inflateBack
() will call in(in_desc, &buf) which should return the number of bytes of provided input, and a pointer to that input in buf. If there is no input available,in
() must return zero — buf is ignored in that case — andinflateBack
() will return a buffer error.inflateBack
() will call out(out_desc, buf, len) to write the uncompressed data buf[0..len-1].out
() should return zero on success, or non-zero on failure. Ifout
() returns non-zero,inflateBack
() will return with an error. Neitherin
() norout
() are permitted to change the contents of the window provided toinflateBackInit
(), which is also the buffer thatout
() uses to write from. The length written byout
() will be at most the window size. Any non-zero amount of input may be provided byin
().For convenience,
inflateBack
() can be provided input on the first call by setting strm->next_in and strm->avail_in. If that input is exhausted, thenin
() will be called. Therefore strm->next_in must be initialized before callinginflateBack
(). If strm->next_in isZ_NULL
, thenin
() will be called immediately for input. If strm->next_in is notZ_NULL
, then strm->avail_in must also be initialized, and then if strm->avail_in is not zero, input will initially be taken from strm->next_in[0 .. strm->avail_in - 1].The in_desc and out_desc parameters of
inflateBack
() are passed as the first parameter ofin
() andout
() respectively when they are called. These descriptors can be optionally used to pass any information that the caller-suppliedin
() andout
() functions need to do their job.On return,
inflateBack
() will set strm->next_in and strm->avail_in to pass back any unused input that was provided by the lastin
() call. The return values ofinflateBack
() can beZ_STREAM_END
on success,Z_BUF_ERROR
ifin
() orout
() returned an error,Z_DATA_ERROR
if there was a format error in the deflate stream (in which case strm->msg is set to indicate the nature of the error), orZ_STREAM_ERROR
if the stream was not properly initialized. In the case ofZ_BUF_ERROR
, an input or output error can be distinguished using strm->next_in which will beZ_NULL
only ifin
() returned an error. If strm->next is notZ_NULL
, then theZ_BUF_ERROR
was due toout
() returning non-zero. (in() will always be called before out(), so strm->next_in is assured to be defined if out() returns non-zero.) Note thatinflateBack
() cannot returnZ_OK
. - int
inflateBackEnd
(z_stream *strm) -
All memory allocated by
inflateBackInit
() is freed.inflateBackEnd
() returnsZ_OK
on success, orZ_STREAM_ERROR
if the stream state was inconsistent. - uLong
zlibCompileFlags
(void) -
This function returns flags indicating compile-time options.
Type sizes, two bits each:
- 00
- 16 bits
- 01
- 32 bits
- 10
- 64 bits
- 11
- other:
- 1.0
- size of uInt
- 3.2
- size of uLong
- 5.4
- size of voidpf (pointer)
- 7.6
- size of z_off_t
Compiler, assembler, and debug options:
- 8
- DEBUG
- 9
- ASMV or ASMINF — use ASM code
- 10
- ZLIB_WINAPI — exported functions use the WINAPI calling convention
- 11
- 0 (reserved)
One-time table building (smaller code, but not thread-safe if true):
- 12
- BUILDFIXED -- build static block decoding tables when needed
- 13
- DYNAMIC_CRC_TABLE -- build CRC calculation tables when needed
- 14,15
- 0 (reserved)
Library content (indicates missing functionality):
- 16
- NO_GZCOMPRESS — gz* functions cannot compress (to avoid linking deflate code when not needed)
- 17
- NO_GZIP — deflate can't write gzip streams, and inflate can't detect and decode gzip streams (to avoid linking CRC code)
- 18-19
- 0 (reserved)
Operation variations (changes in library functionality):
- 20
- PKZIP_BUG_WORKAROUND — slightly more permissive inflate
- 21
- FASTEST — deflate algorithm with only one, lowest compression level
- 22,23
- 0 (reserved)
The sprintf variant used by gzprintf (zero is best):
- 24
- 0 = vs*, 1 = s* — 1 means limited to 20 arguments after the format
- 25
- 0 = *nprintf, 1 = *printf — 1 means
gzprintf
() not secure! - 26
- 0 = returns value, 1 = void — 1 means inferred string length returned
Remainder:
- 27-31
- 0 (reserved)
UTILITY FUNCTIONS
The following utility functions are implemented on top of the basic stream-oriented functions. To simplify the interface, some default options are assumed (compression level and memory usage, standard memory allocation functions). The source code of these utility functions can easily be modified if you need special options.
- int
compress
(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen); -
The
compress
() function compresses the source buffer into the destination buffer. sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned bycompressBound
(sourcelen). Upon exit, destLen is the actual size of the compressed buffer. This function can be used to compress a whole file at once if the input file is mmap'ed.compress
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory, orZ_BUF_ERROR
if there was not enough room in the output buffer. - int
compress2
(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level); -
The
compress2
() function compresses the source buffer into the destination buffer. The level parameter has the same meaning as indeflateInit
(). sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned bycompressBound
(sourceLen). Upon exit, destLen is the actual size of the compressed buffer.compress2
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_BUF_ERROR
if there was not enough room in the output buffer, orZ_STREAM_ERROR
if the level parameter is invalid. - int
compressBound
(uLong sourceLen) -
compressBound
() returns an upper bound on the compressed size aftercompress
() orcompress2
() on sourceLen bytes. It would be used before acompress
() orcompress2
() call to allocate the destination buffer. - int
uncompress
(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen); -
The
uncompress
() function decompresses the source buffer into the destination buffer. sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. (The size of the uncompressed data must have been saved previously by the compressor and transmitted to the decompressor by some mechanism outside the scope of this compression library.) Upon exit, destLen is the actual size of the compressed buffer. This function can be used to decompress a whole file at once if the input file is mmap'ed.uncompress
() returnsZ_OK
if successful,Z_MEM_ERROR
if there was not enough memory,Z_BUF_ERROR
if there was not enough room in the output buffer, orZ_DATA_ERROR
if the input data was corrupted or incomplete. - gzFile
gzopen
(const char *path, const char *mode); -
The
gzopen
() function opens a gzip (.gz) file for reading or writing. The mode parameter is as in fopen(3) ("rb" or "wb") but can also include a compression level (wb9) or a strategy: ‘f’ for filtered data, as in "wb6f"; ‘h’ for Huffman only compression, as in "wb1h", or ‘R’ for run-length encoding as in "wb1R". (See the description ofdeflateInit2
() for more information about the strategy parameter.)gzopen
() can be used to read a file which is not in gzip format; in this casegzread
() will directly read from the file without decompression.gzopen
() returnsNULL
if the file could not be opened or if there was insufficient memory to allocate the (de)compression state; errno can be checked to distinguish the two cases (if errno is zero, thezlib
error isZ_MEM_ERROR
). - gzFile
gzdopen
(int fd, const char *mode); -
The
gzdopen
() function associates a gzFile with the file descriptor fd. File descriptors are obtained from calls like open(2), dup(2), creat(3), pipe(2), or fileno(3) (if the file has been previously opened with fopen(3)). The mode parameter is as ingzopen
().The next call to
gzclose
() on the returned gzFile will also close the file descriptor fd, just like fclose(fdopen(fd), mode) closes the file descriptor fd. If you want to keep fd open, use gzdopen(dup(fd), mode).gzdopen
() returnsNULL
if there was insufficient memory to allocate the (de)compression state. - int
gzsetparams
(gzFile file, int level, int strategy); -
The
gzsetparams
() function dynamically updates the compression level or strategy. See the description ofdeflateInit2
() for the meaning of these parameters.gzsetparams
() returnsZ_OK
if successful, orZ_STREAM_ERROR
if the file was not opened for writing. - int
gzread
(gzFile file, voidp buf, unsigned len); -
The
gzread
() function reads the given number of uncompressed bytes from the compressed file. If the input file was not in gzip format,gzread
() copies the given number of bytes into the buffer.gzread
() returns the number of uncompressed bytes actually read (0 for end of file, -1 for error). - int
gzwrite
(gzFile file, voidpc buf, unsigned len); -
The
gzwrite
() function writes the given number of uncompressed bytes into the compressed file.gzwrite
() returns the number of uncompressed bytes actually written (0 in case of error). - int
gzprintf
(gzFile file, const char *format, ...); -
The
gzprintf
() function converts, formats, and writes the args to the compressed file under control of the format string, as in fprintf(3).gzprintf
() returns the number of uncompressed bytes actually written (0 in case of error). The number of uncompressed bytes written is limited to 4095. The caller should make sure that this limit is not exceeded. If it is exceeded, thengzprintf
() will return an error (0) with nothing written. In this case, there may also be a buffer overflow with unpredictable consequences, which is possible only ifzlib
was compiled with the insecure functionssprintf
() orvsprintf
() because the securesnprintf
() orvsnprintf
() functions were not available. - int
gzputs
(gzFile file, const char *s); -
The
gzputs
() function writes the given null-terminated string to the compressed file, excluding the terminating null character.gzputs
() returns the number of characters written, or -1 in case of error. - char *
gzgets
(gzFile file, char *buf, int len); -
The
gzgets
() function reads bytes from the compressed file until len-1 characters are read, or a newline character is read and transferred to buf, or an end-of-file condition is encountered. The string is then terminated with a null character.gzgets
() returns buf, orZ_NULL
in case of error. - int
gzputc
(gzFile file, int c); -
The
gzputc
() function writes c, converted to an unsigned char, into the compressed file.gzputc
() returns the value that was written, or -1 in case of error. - int
gzgetc
(gzFile file); -
The
gzgetc
() function reads one byte from the compressed file.gzgetc
() returns this byte or -1 in case of end of file or error. - int
gzungetc
(int c, gzFile file) -
Push one character back onto the stream to be read again later. Only one character of push-back is allowed.
gzungetc
() returns the character pushed, or -1 on failure.gzungetc
() will fail if a character has been pushed but not read yet, or if c is -1. The pushed character will be discarded if the stream is repositioned withgzseek
() orgzrewind
(). - int
gzflush
(gzFile file, int flush); -
The
gzflush
() function flushes all pending output into the compressed file. The parameter flush is as in thedeflate
() function. The return value is thezlib
error number (see functiongzerror
() below).gzflush
() returnsZ_OK
if the flush parameter isZ_FINISH
and all output could be flushed.gzflush
() should be called only when strictly necessary because it can degrade compression. - z_off_t
gzseek
(gzFile file, z_off_t offset, int whence); -
Sets the starting position for the next
gzread
() orgzwrite
() on the given compressed file. The offset represents a number of bytes in the uncompressed data stream. The whence parameter is defined as in lseek(2); the valueSEEK_END
is not supported.If the file is opened for reading, this function is emulated but can be extremely slow. If the file is opened for writing, only forward seeks are supported;
gzseek
() then compresses a sequence of zeroes up to the new starting position.gzseek
() returns the resulting offset location as measured in bytes from the beginning of the uncompressed stream, or -1 in case of error, in particular if the file is opened for writing and the new starting position would be before the current position. - int
gzrewind
(gzFile file); -
The
gzrewind
() function rewinds the given file. This function is supported only for reading.gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET).
- z_off_t
gztell
(gzFile file); -
The
gztell
() function returns the starting position for the nextgzread
() orgzwrite
() on the given compressed file. This position represents a number of bytes in the uncompressed data stream.gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).
- int
gzeof
(gzFile file); -
The
gzeof
() function returns 1 whenEOF
has previously been detected reading the given input stream, otherwise zero. - int
gzdirect
(gzFile file); -
The
gzdirect
() function returns 1 if the file is being read directly without compression; otherwise it returns 0. - int
gzclose
(gzFile file); -
The
gzclose
() function flushes all pending output if necessary, closes the compressed file and deallocates all the (de)compression state. The return value is thezlib
error number (see functiongzerror
() below). - const char *
gzerror
(gzFile file, int *errnum); -
The
gzerror
() function returns the error message for the last error which occurred on the given compressed file. errnum is set to thezlib
error number. If an error occurred in the file system and not in the compression library, errnum is set toZ_ERRNO
and the application may consult errno to get the exact error code. - void
gzclearerr
(gzFile file) - Clears the error and end-of-file flags for file.
This is analogous to the
clearerr
() function in stdio. This is useful for continuing to read a gzip file that is being written concurrently.
CHECKSUM FUNCTIONS
These functions are not related to compression but are exported anyway because they might be useful in applications using the compression library.
- uLong
adler32
(uLong adler, const Bytef *buf, uInt len); - The
adler32
() function updates a running Adler-32 checksum with the bytes buf[0..len-1] and returns the updated checksum. If buf isNULL
, this function returns the required initial value for the checksum.An Adler-32 checksum is almost as reliable as a CRC32 but can be computed much faster. Usage example:
uLong adler = adler32(0L, Z_NULL, 0); while (read_buffer(buffer, length) != EOF) { adler = adler32(adler, buffer, length); } if (adler != original_adler) error();
- uLong
adler32_combine
(uLong adler1, uLong adler2, z_off_t len2) -
The
adler32_combine
() function combines two Adler-32 checksums into one. For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, Adler-32 checksums are calculated for each, adler1 and adler2.adler32_combine
() returns the Adler-32 checksum of seq1 and seq2 concatenated, requiring only adler1, adler2, and len2. - uLong
crc32
(uLong crc, const Bytef *buf, uInt len); -
The
crc32
() function updates a running CRC-32 with the bytes buf[0..len-1] and returns the updated CRC-32. If buf isNULL
, this function returns the required initial value for the CRC. Pre- and post-conditioning (one's complement) is performed within this function so it shouldn't be done by the application. Usage example:uLong crc = crc32(0L, Z_NULL, 0); while (read_buffer(buffer, length) != EOF) { crc = crc32(crc, buffer, length); } if (crc != original_crc) error();
- uLong
crc32_combine
(uLong crc1, uLong crc2, z_off_t len2) -
The
crc32_combine
() function combines two CRC-32 check values into one. For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, CRC-32 check values are calculated for each, crc1 and crc2.crc32_combine
() returns the CRC-32 check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and len2.
STRUCTURES
struct internal_state; typedef struct z_stream_s { Bytef *next_in; /* next input byte */ uInt avail_in; /* number of bytes available at next_in */ off_t total_in; /* total nb of input bytes read so far */ Bytef *next_out; /* next output byte should be put there */ uInt avail_out; /* remaining free space at next_out */ off_t total_out; /* total nb of bytes output so far */ char *msg; /* last error message, NULL if no error */ struct internal_state FAR *state; /* not visible by applications */ alloc_func zalloc; /* used to allocate the internal state */ free_func zfree; /* used to free the internal state */ voidpf opaque; /* private data object passed to zalloc and zfree*/ int data_type; /* best guess about the data type: binary or text*/ uLong adler; /* adler32 value of the uncompressed data */ uLong reserved; /* reserved for future use */ } z_stream; typedef z_stream FAR * z_streamp;
/* gzip header information passed to and from zlib routines. See RFC 1952 for more details on the meanings of these fields. */ typedef struct gz_header_s { int text; /* true if compressed data believed to be text */ uLong time; /* modification time */ int xflags; /*extra flags (not used when writing a gzip file)*/ int os; /* operating system */ Bytef *extra; /* pointer to extra field or Z_NULL if none */ uInt extra_len; /* extra field length (valid if extra != Z_NULL) */ uInt extra_max; /* space at extra (only when reading header) */ Bytef *name; /* pointer to zero-terminated file name or Z_NULL*/ uInt name_max; /* space at name (only when reading header) */ Bytef *comment; /* pointer to zero-terminated comment or Z_NULL */ uInt comm_max; /* space at comment (only when reading header) */ int hcrc; /* true if there was or will be a header crc */ int done; /* true when done reading gzip header (not used when writing a gzip file) */ } gz_header; typedef gz_header FAR *gz_headerp;
The application must update next_in and avail_in when avail_in has dropped to zero. It must update next_out and avail_out when avail_out has dropped to zero. The application must initialize zalloc, zfree, and opaque before calling the init function. All other fields are set by the compression library and must not be updated by the application.
The opaque value provided by the
application will be passed as the first parameter for calls to
zalloc
() and
zfree
().
This can be useful for custom memory management. The compression library
attaches no meaning to the opaque value.
zalloc must return
Z_NULL
if there is not enough memory for the object.
If zlib
is used in a multi-threaded application,
zalloc and zfree must be thread
safe.
On 16-bit systems, the functions zalloc and zfree must be able to allocate exactly 65536 bytes, but will not be required to allocate more than this if the symbol MAXSEG_64K is defined (see ⟨zconf.h⟩).
WARNING: On MSDOS, pointers returned by zalloc for objects of exactly 65536 bytes *must* have their offset normalized to zero. The default allocation function provided by this library ensures this (see zutil.c). To reduce memory requirements and avoid any allocation of 64K objects, at the expense of compression ratio, compile the library with -DMAX_WBITS=14 (see ⟨zconf.h⟩).
The fields total_in and total_out can be used for statistics or progress reports. After compression, total_in holds the total size of the uncompressed data and may be saved for use in the decompressor (particularly if the decompressor wants to decompress everything in a single step).
CONSTANTS
#define Z_NO_FLUSH 0 #define Z_PARTIAL_FLUSH 1 /* will be removed, use Z_SYNC_FLUSH instead */ #define Z_SYNC_FLUSH 2 #define Z_FULL_FLUSH 3 #define Z_FINISH 4 #define Z_BLOCK 5 /* Allowed flush values; see deflate() and inflate() below for details */ #define Z_OK 0 #define Z_STREAM_END 1 #define Z_NEED_DICT 2 #define Z_ERRNO (-1) #define Z_STREAM_ERROR (-2) #define Z_DATA_ERROR (-3) #define Z_MEM_ERROR (-4) #define Z_BUF_ERROR (-5) #define Z_VERSION_ERROR (-6) /* Return codes for the compression/decompression functions. * Negative values are errors, * positive values are used for special but normal events. */ #define Z_NO_COMPRESSION 0 #define Z_BEST_SPEED 1 #define Z_BEST_COMPRESSION 9 #define Z_DEFAULT_COMPRESSION (-1) /* compression levels */ #define Z_FILTERED 1 #define Z_HUFFMAN_ONLY 2 #define Z_RLE 3 #define Z_FIXED 4 #define Z_DEFAULT_STRATEGY 0 /* compression strategy; see deflateInit2() below for details */ #define Z_BINARY 0 #define Z_TEXT 1 #define Z_ASCII Z_TEXT /* for compatibility with 1.2.2 and earlier */ #define Z_UNKNOWN 2 /* Possible values of the data_type field (though see inflate()) */ #define Z_DEFLATED 8 /* The deflate compression method * (the only one supported in this version) */ #define Z_NULL 0 /* for initializing zalloc, zfree, opaque */ #define zlib_version zlibVersion() /* for compatibility with versions < 1.0.2 */
VARIOUS HACKS
deflateInit and inflateInit are macros to allow checking the
zlib
version and the compiler's view of
z_stream.
- int
deflateInit_
(z_stream strm, int level, const char *version, int stream_size); - int
inflateInit_
(z_stream strm, const char *version, int stream_size); - int
deflateInit2_
(z_stream strm, int level, int method, int windowBits, int memLevel, int strategy, const char *version, int stream_size); - int
inflateInit2_
(z_stream strm, int windowBits, const char *version, int stream_size); - int
inflateBackInit_
(z_stream *strm, int windowBits, unsigned char FAR *window, const char *version, int stream_size) - const char *
zError
(int err); - int
inflateSyncPoint
(z_streamp z); - const uLongf *
get_crc_table
(void);
SEE ALSO
STANDARDS
P. Deutsch and J-L. Gailly, ZLIB Compressed Data Format Specification version 3.3, RFC 1950, May 1996.
P. Deutsch, DEFLATE Compressed Data Format Specification version 1.3, RFC 1951, May 1996.
P. Deutsch, GZIP file format specification version 4.3, RFC 1952, May 1996.
HISTORY
This manual page is based on an HTML version of ⟨zlib.h⟩ converted by piaip ⟨piaip@csie.ntu.edu.tw⟩ and was converted to mdoc format by the OpenBSD project.
AUTHORS
Jean-loup Gailly
⟨jloup@gzip.org⟩
Mark Adler
⟨madler@alumni.caltech.edu⟩