| COMPRESS(3) | Library Functions Manual | COMPRESS(3) |
compress,
zlibVersion, deflateInit,
deflate, deflateEnd,
inflateInit, inflate,
inflateEnd, deflateInit2,
deflateSetDictionary,
deflateCopy, deflateReset,
deflateParams, deflateTune,
deflateBound, deflatePrime,
deflateSetHeader,
inflateInit2,
inflateSetDictionary,
inflateSync, inflateCopy,
inflateReset, inflatePrime,
inflateGetHeader,
inflateBackInit,
inflateBack, inflateBackEnd,
zlibCompileFlags, compress2,
compressBound, uncompress,
gzopen, gzdopen,
gzsetparams, gzread,
gzwrite, gzprintf,
gzputs, gzgets,
gzputc, gzgetc,
gzungetc, gzflush,
gzseek, gzrewind,
gztell, gzeof,
gzdirect, gzclose,
gzerror, gzclearerr,
adler32, adler32_combine,
crc32, crc32_combine
— zlib general purpose compression
library
#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);
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:
zlibVersion(void);The application can compare
zlibVersion() and
ZLIB_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 by
deflateInit() and
inflateInit().
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
to Z_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() returns
Z_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 the
zlib 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 by deflate().
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 to deflate(). If
deflate() returns Z_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 allows
deflate() 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 with
Z_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. Using
Z_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 a
Z_FULL_FLUSH or a
Z_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 and deflate() returns with
Z_STREAM_END if there was enough output space;
if deflate() returns with
Z_OK, this function must be called again with
Z_FINISH and more output space (updated
avail_out but no more input data, until it returns
with Z_STREAM_END or an error. After
deflate() has returned
Z_STREAM_END, the only possible operations on
the stream are deflateReset() or
deflateEnd().
Z_FINISH can be used immediately after
deflateInit() if all the compression is to be
done in a single step. In this case, avail_out
must be at least the value returned by
deflateBound() (see below). If
deflate() does not return
Z_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() returns
Z_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 to
Z_FINISH),
Z_STREAM_ERROR if the stream state was
inconsistent (for example, if next_in or
next_out was NULL),
Z_BUF_ERROR if no progress is possible (for
example, avail_in or
avail_out was zero). Note that
Z_BUF_ERROR is not fatal, and
deflate() can be called again with more input
and more output space to continue processing.
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() returns
Z_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).
inflateInit(z_streamp
strm);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 not Z_NULL and
avail_in is large enough (the exact value depends on
the compression method), inflateInit() determines
the compression method from the zlib header and
allocates all data structures accordingly; otherwise the allocation will
be deferred to the first call to inflate(). If
zalloc and zfree are set to
Z_NULL, inflateInit()
updates them to use default allocation functions.
inflateInit() returns
Z_OK if successful,
Z_MEM_ERROR if there was not enough memory,
Z_VERSION_ERROR if the
zlib 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 the
zlib header if present: this will be done by
inflate(). (So next_in and
avail_in may be modified, but
next_out and avail_out are
unchanged.)
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 to
inflate(). If inflate()
returns Z_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 be
Z_NO_FLUSH,
Z_SYNC_FLUSH, Z_FINISH,
or Z_BLOCK. Z_SYNC_FLUSH
requests that inflate() flush as much output as
possible to the output buffer. Z_BLOCK requests
that inflate() stop if and when it gets to the
next deflate block boundary. When decoding the zlib or gzip format, this
will cause inflate() 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
return inflate() will set strm->data_type to
the number of unused bits in the last byte taken from strm->next_in,
plus 64 if inflate() is currently decoding the
last block in the deflate stream, plus 128 if
inflate() 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 returns Z_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 to Z_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 be inflateEnd() to deallocate the
decompression state. The use of Z_FINISH is
never required, but can be used to inform
inflate() that a faster approach may be used for
the single inflate() 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 of inflate(), as noted below,
or when it returns early because Z_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 returns Z_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 returns Z_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; see inflateInit2() below, or
inflateBack() and perform their own processing
of the gzip header and trailer.
inflate() returns
Z_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 the zlib format
or incorrect check value), Z_STREAM_ERROR if the
stream structure was inconsistent (for example, if
next_in or next_out was
NULL), 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 when Z_FINISH is used. Note that
Z_BUF_ERROR is not fatal, and
inflate() can be called again with more input
and more output space to continue compressing. If
Z_DATA_ERROR is returned, the application may
then call inflateSync() to look for a good
compression block if a partial recovery of the data is desired.
inflateEnd(z_streamp
strm);inflateEnd() returns
Z_OK if successful, or
Z_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).
The following functions are needed only in some special applications.
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), or Z_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 of Z_FILTERED is to force more
Huffman coding and less string matching; it is somewhat intermediate
between Z_DEFAULT and
Z_HUFFMAN_ONLY. Z_RLE is
designed to be almost as fast as Z_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() returns
Z_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 by
deflate().
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(), or
deflateReset(), before any call to
deflate(). The compressor and decompressor must
use exactly the same dictionary (see
inflateSetDictionary()).
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() or
deflateInit2(), a part of the dictionary may in
effect be discarded, for example if the dictionary is larger than the
window size in deflate() or
deflate2(). 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 of
deflate() 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() returns
Z_OK if successful, or
Z_STREAM_ERROR if a parameter is invalid (such
as NULL dictionary) or the stream state is inconsistent (for example if
deflate() has already been called for this
stream or if the compression method is bsort).
deflateSetDictionary() does not perform any
compression: this will be done by deflate().
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 that
deflateCopy() duplicates the internal
compression state which can be quite large, so this strategy is slow and
can consume lots of memory.
deflateCopy() returns
Z_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.
deflateReset(z_streamp
strm);This function is equivalent to
deflateEnd() followed by
deflateInit(), 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 by
deflateInit2().
deflateReset() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent (such as zalloc or
state being NULL).
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 in
deflateInit2(). 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 to deflate().
Before the call to deflateParams(),
the stream state must be set as for a call to
deflate(), since the currently available input
may have to be compressed and flushed. In particular, strm->avail_out
must be non-zero.
deflateParams() returns
Z_OK if successful,
Z_STREAM_ERROR if the source stream state was
inconsistent or if a parameter was invalid, or
Z_BUF_ERROR if strm->avail_out was zero.
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 after
deflateInit() or
deflateInit2(), and returns
Z_OK on success, or
Z_STREAM_ERROR for an invalid deflate
stream.
deflateBound(z_streamp strm,
uLong sourceLen)deflateBound() returns an upper bound
on the compressed size after deflation of
sourceLen bytes. It must be called after
deflateInit() or
deflateInit2(). This would be used to allocate
an output buffer for deflation in a single pass, and so would be called
before deflate().
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 first deflate() call after a
deflateInit2() or
deflateReset(). 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() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent.
deflateSetHeader(z_streamp
strm, gz_headerp head)deflateSetHeader() provides gzip
header information for when a gzip stream is requested by
deflateInit2().
deflateSetHeader() may be called after
deflateInit2() or
deflateReset() and before the first call of
deflate(). 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 not
Z_NULL, name and
comment are terminated with a zero byte, and that
if extra is not Z_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 by deflateReset().
deflateSetHeader() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent.
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 to
deflateInit2() while compressing, or it must be
equal to 15 if deflateInit2() was not used. If a
compressed stream with a larger window size is given as input,
inflate() will return with the error code
Z_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 in
deflateInit2() 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() returns
Z_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 the zlib
header if present: this will be done by
inflate(). (So next_in and
avail_in may be modified, but
next_out and avail_out are
unchanged.)
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 returned
Z_NEED_DICT. The dictionary chosen by the
compressor can be determined from the Adler-32 value returned by that
call to inflate(). The compressor and
decompressor must use exactly the same dictionary (see
deflateSetDictionary()). For raw inflate, this
function can be called immediately after
inflateInit2() or
inflateReset() and before any call to
inflate() to set the dictionary. The application
must ensure that the dictionary that was used for compression is
provided.
inflateSetDictionary() returns
Z_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 of
inflate().
inflateSync(z_streamp
strm);Skips invalid compressed data until a full flush point (see
above the description of deflate() with
Z_FULL_FLUSH) can be found, or until all
available input is skipped. No output is provided.
inflateSync() returns
Z_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,
or Z_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 call inflateSync(), providing more
input each time, until success or end of the input data.
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() returns
Z_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.
inflateReset(z_streamp
strm);This function is equivalent to
inflateEnd() followed by
inflateInit(), but does not free and reallocate
all the internal decompression state. The stream will keep attributes
that may have been set by inflateInit2().
inflateReset() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent (such as zalloc or
state being NULL).
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 after
inflateInit2() or
inflateReset(). 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() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent.
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 after
inflateInit2() or
inflateReset(), and before the first call of
inflate(). As inflate()
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 that
Z_BLOCK can be used to force
inflate() 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 not
Z_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 not
Z_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
not Z_NULL and the respective field is not
present in the header, then that field is set to
Z_NULL to signal its absence. This allows the
use of deflateSetHeader() 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 call
inflateGetHeader() again to retrieve the header
from the next gzip stream.
inflateGetHeader() returns
Z_OK if successful, or
Z_STREAM_ERROR if the source stream state was
inconsistent.
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 are Z_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 that deflate() 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 return
Z_OK on success,
Z_STREAM_ERROR if any of the parameters are
invalid, Z_MEM_ERROR if the internal state could
not be allocated, or Z_VERSION_ERROR if the
version of the library does not match the version of the header
file.
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 than inflate() 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 until
inflateBack() 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 by
inflateBack() 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 — and inflateBack()
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. If out()
returns non-zero, inflateBack() will return with
an error. Neither in() nor
out() are permitted to change the contents of
the window provided to inflateBackInit(), which
is also the buffer that out() uses to write
from. The length written by out() will be at
most the window size. Any non-zero amount of input may be provided by
in().
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, then
in() will be called. Therefore strm->next_in
must be initialized before calling
inflateBack(). If strm->next_in is
Z_NULL, then in() will
be called immediately for input. If strm->next_in is not
Z_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
of in() and out()
respectively when they are called. These descriptors can be optionally
used to pass any information that the caller-supplied
in() and out() 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 last in() call. The
return values of inflateBack() can be
Z_STREAM_END on success,
Z_BUF_ERROR if in() or
out() 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), or Z_STREAM_ERROR if the stream
was not properly initialized. In the case of
Z_BUF_ERROR, an input or output error can be
distinguished using strm->next_in which will be
Z_NULL only if in()
returned an error. If strm->next is not
Z_NULL, then the
Z_BUF_ERROR was due to
out() 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 that
inflateBack() cannot return
Z_OK.
inflateBackEnd(z_stream
*strm)All memory allocated by
inflateBackInit() is freed.
inflateBackEnd() returns
Z_OK on success, or
Z_STREAM_ERROR if the stream state was
inconsistent.
zlibCompileFlags(void)This function returns flags indicating compile-time options.
Type sizes, two bits each:
Compiler, assembler, and debug options:
One-time table building (smaller code, but not thread-safe if true):
Library content (indicates missing functionality):
Operation variations (changes in library functionality):
The sprintf variant used by gzprintf (zero is best):
gzprintf() not secure!Remainder:
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.
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 by
compressBound(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() returns
Z_OK if successful,
Z_MEM_ERROR if there was not enough memory, or
Z_BUF_ERROR if there was not enough room in the
output buffer.
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 in
deflateInit(). 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 by
compressBound(sourceLen).
Upon exit, destLen is the actual size of the
compressed buffer.
compress2() returns
Z_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, or Z_STREAM_ERROR if the level
parameter is invalid.
compressBound(uLong
sourceLen)compressBound() returns an upper bound
on the compressed size after compress() or
compress2() on sourceLen
bytes. It would be used before a compress() or
compress2() call to allocate the destination
buffer.
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() returns
Z_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, or Z_DATA_ERROR if the input data
was corrupted or incomplete.
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 of
deflateInit2() for more information about the
strategy parameter.)
gzopen() can be used to read a file
which is not in gzip format; in this case
gzread() will directly read from the file
without decompression.
gzopen() returns
NULL 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, the
zlib error is
Z_MEM_ERROR).
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 in
gzopen().
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() returns
NULL if there was insufficient memory to
allocate the (de)compression state.
gzsetparams(gzFile file,
int level, int strategy);The gzsetparams() function dynamically
updates the compression level or strategy. See the description of
deflateInit2() for the meaning of these
parameters.
gzsetparams() returns
Z_OK if successful, or
Z_STREAM_ERROR if the file was not opened for
writing.
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).
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).
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, then
gzprintf() 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 if
zlib was compiled with the insecure functions
sprintf() or vsprintf()
because the secure snprintf() or
vsnprintf() functions were not available.
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.
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, or Z_NULL in case of
error.
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.
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.
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
with gzseek() or
gzrewind().
gzflush(gzFile file,
int flush);The gzflush() function flushes all
pending output into the compressed file. The parameter
flush is as in the
deflate() function. The return value is the
zlib error number (see function
gzerror() below).
gzflush() returns Z_OK
if the flush parameter is Z_FINISH and all
output could be flushed.
gzflush() should be called only when
strictly necessary because it can degrade compression.
gzseek(gzFile file,
z_off_t offset, int
whence);Sets the starting position for the next
gzread() or gzwrite() 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 value
SEEK_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.
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).
gztell(gzFile file);The gztell() function returns the
starting position for the next gzread() or
gzwrite() 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).
gzeof(gzFile file);The gzeof() function returns 1 when
EOF has previously been detected reading the
given input stream, otherwise zero.
gzdirect(gzFile file);The gzdirect() function returns 1 if
the file is being read directly without compression; otherwise it
returns 0.
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 the
zlib error number (see function
gzerror() below).
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 the
zlib error number. If an error occurred in the
file system and not in the compression library,
errnum is set to Z_ERRNO
and the application may consult errno to get the exact error code.
gzclearerr(gzFile file)clearerr() function in
stdio. This is useful for continuing to read a gzip file that is being
written concurrently.These functions are not related to compression but are exported anyway because they might be useful in applications using the compression library.
adler32(uLong adler,
const Bytef *buf, uInt
len);adler32() function updates a running Adler-32
checksum with the bytes buf[0..len-1] and returns the updated checksum. If
buf is NULL, 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();
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.
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 is NULL, 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();
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.
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).
#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 */
deflateInit and inflateInit are macros to allow checking the
zlib version and the compiler's view of
z_stream.
deflateInit_(z_stream strm,
int level, const char *version,
int stream_size);inflateInit_(z_stream strm,
const char *version, int
stream_size);deflateInit2_(z_stream strm,
int level, int method,
int windowBits, int memLevel,
int strategy, const char
*version, int stream_size);inflateInit2_(z_stream strm,
int windowBits, const char
*version, int stream_size);inflateBackInit_(z_stream
*strm, int windowBits, unsigned
char FAR *window, const char *version,
int stream_size)zError(int err);inflateSyncPoint(z_streamp
z);get_crc_table(void);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.
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.
Jean-loup Gailly
<jloup@gzip.org>
Mark Adler
<madler@alumni.caltech.edu>
| March 16, 2018 | OpenBSD-current |