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>
February 8, 2021 | OpenBSD-current |