COMPRESS(3) OpenBSD Programmer's Manual COMPRESS(3)
NAME
compress - zlib general purpose compression library
SYNOPSIS
#include <zlib.h>
Basic functions
const char *
zlibVersion(void);
int
deflateInit(z_streamp strm, int level);
int
deflate(z_streamp strm, int flush);
int
deflateEnd(z_streamp strm);
int
inflateInit(z_streamp strm);
int
inflate(z_streamp strm, int flush);
int
inflateEnd(z_streamp strm);
Advanced functions
int
deflateInit2(z_streamp strm, int level, int method, int windowBits,
int memLevel, int strategy);
int
deflateSetDictionary(z_streamp strm, const Bytef *dictionary,
uInt dictLength);
int
deflateCopy(z_streamp dest, z_streamp source);
int
deflateReset(z_streamp strm);
int
deflateParams(z_streamp strm, int level, int strategy);
uLong
deflateBound(z_streamp strm, uLong sourceLen);
int
deflatePrime(z_streamp strm, int bits, int value);
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
inflateBackInit(z_stream FAR *strm, int windowBits,
unsigned char FAR *window);
int
inflateBack(z_stream FAR *strm, in_func in, void FAR *in_desc,
out_func out, void FAR *out_desc);
int
inflateBackEnd(z_stream FAR *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
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
crc32(uLong crc, const Bytef *buf, uInt len);
DESCRIPTION
This manual page describes the zlib general purpose compression library,
version 1.1.4.
The zlib compression library provides in-memory compression and decom-
pression 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 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) for-
mat 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.
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.
This library does not provide any functions to write gzip files in memo-
ry. However such functions could be easily written using zlib's
deflate() function, the documentation in the gzip RFC, and the examples
in gzio.c.
The library does not install any signal handler. The decoder checks the
consistency of the compressed data, so the library should never crash
even in case of corrupted input.
The functions within the library are divided into the following sections:
- Basic functions
- Advanced functions
- Utility functions
- Checksum functions
BASIC FUNCTIONS
const char * zlibVersion(void);
The application can compare zlibVersion() 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().
int deflateInit(z_streamp strm, int level);
The deflateInit() function initializes the internal stream state
for compression. The fields zalloc, zfree, and opaque must be
initialized before by the caller. If zalloc and zfree are set 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().
int deflate(z_streamp strm, int flush);
deflate() compresses as much data as possible, and stops when the
input buffer becomes empty or the output buffer becomes full. It
may introduce some output latency (reading input without
producing any output) except when forced to flush.
The detailed semantics are as follows. deflate() performs one or
both of the following actions:
Compress more input starting at next_in and update next_in and
avail_in accordingly. If not all input can be processed (because
there is not enough room in the output buffer), next_in and
avail_in are updated and processing will resume at this point for
the next call to deflate().
Provide more output starting at next_out and update next_out and
avail_out accordingly. This action is forced if the parameter
flush is non-zero. Forcing flush frequently degrades the com-
pression ratio, so this parameter should be set only when neces-
sary (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 out-
put buffer because there might be more output pending.
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 decom-
pression 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 the 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 pro-
cessed, pending output is flushed and deflate() returns with
Z_STREAM_END if there was enough output space; if deflate() re-
turns 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 data_type if it can make a good guess about
the input data type (Z_ASCII or Z_BINARY). If in doubt, the data
is considered binary. This field is only for information purpos-
es 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 in-
consistent (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.
int deflateEnd(z_streamp strm);
All dynamically allocated data structures for this stream are
freed. This function discards any unprocessed input and does not
flush any pending output.
deflateEnd() 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).
int inflateInit(z_streamp strm);
The inflateInit() function initializes the internal stream state
for decompression. The fields next_in, avail_in, zalloc, zfree,
and opaque must be initialized before by the caller. If next_in
is 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 ver-
sion 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 un-
changed.)
int inflate(z_streamp strm, int flush);
inflate() decompresses as much data as possible, and stops when
the input buffer becomes empty or the output buffer becomes full.
It may introduce some output latency (reading input without
producing any output) except when forced to flush.
The detailed semantics are as follows. inflate() performs one or
both of the following actions:
Decompress more input starting at next_in and update next_in and
avail_in accordingly. If not all input can be processed (because
there is not enough room in the output buffer), next_in is updat-
ed 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 pos-
sible, 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 af-
ter 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 re-
quests that inflate() stop if and when it gets to the next de-
flate 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 de-
coding 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 indi-
cated until all of the uncompressed data from that block has been
written to strm->next_out. The number of unused bits may in gen-
eral 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 ap-
proach on the first call. So the only effect of the flush param-
eter 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 cor-
rect.
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 (in-
put 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 possi-
ble 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 com-
pression block if a partial recovery of the data is desired.
int inflateEnd(z_streamp strm);
All dynamically allocated data structures for this stream are
freed. This function discards any unprocessed input and does not
flush any pending output.
inflateEnd() 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).
ADVANCED FUNCTIONS
The following functions are needed only in some special applications.
int deflateInit2(z_streamp strm, int level, int method, int windowBits,
int memLevel, int strategy);
This is another version of deflateInit() with more compression
options. The fields next_in, zalloc, zfree, and opaque must be
initialized before by the caller.
The method parameter is the compression method. It must be
Z_DEFLATED in this version of the library.
The windowBits parameter is the base two logarithm of the window
size (the size of the history buffer). It should be in the range
8..15 for this version of the library. Larger values of this pa-
rameter result in better compression at the expense of memory us-
age. 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 gen-
erate 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 encod-
ing. 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 com-
ment, no modification time (set to zero), no header crc, and the
operating system will be set to 255 (unknown).
The memLevel parameter specifies how much memory should be allo-
cated for the internal compression state. memLevel=1 uses mini-
mum 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 im-
age data. The strategy parameter only affects the compression
ratio but not the correctness of the compressed output, even if
it is not set appropriately.
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().
int deflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt
dictLength);
Initializes the compression dictionary from the given byte se-
quence 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.
Upon return of this function, strm->adler is set to the Adler-32
value of the dictionary; the decompressor may later use this val-
ue 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 com-
pression method is bsort). deflateSetDictionary() does not per-
form any compression: this will be done by deflate().
int deflateCopy(z_streamp dest, z_streamp source);
The deflateCopy() function sets the destination stream as a com-
plete 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 con-
sume 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 un-
changed in both source and destination.
int 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).
int deflateParams(z_streamp strm, int level, int strategy);
The deflateParams() function dynamically updates the compression
level and compression strategy. The interpretation of level and
strategy is as in deflateInit2(). This can be used to switch be-
tween 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 avail-
able 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 in-
valid, or Z_BUF_ERROR if strm->avail_out was zero.
uLong deflateBound(z_streamp strm, uLong sourceLen)
deflateBound() returns an upper bound on the compressed size af-
ter 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().
int deflatePrime(z_streamp strm, int bits, int value)
deflatePrime() inserts bits in the deflate output stream. The
intent is that this function is used to start off the deflate
output with the bits leftover from a previous deflate stream when
appending to it. As such, this function can only be used for raw
deflate, and must be used before the 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.
int inflateInit2(z_streamp strm, int windowBits);
This is another version of inflateInit() with an extra parameter.
The fields next_in, avail_in, zalloc, zfree, and opaque must be
initialized before by the caller.
The windowBits parameter is the base two logarithm of the maximum
window size (the size of the history buffer). It should be in
the range 8..15 for this version of the library. The default
value is 15 if inflateInit() is used instead. windowBits must be
greater than or equal to the windowBits value provided to
deflateInit2() while compressing, or it must be equal to 15 if
deflateInit2() was not used. If a compressed stream with a larg-
er 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 pro-
cess 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 decod-
ing. 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).
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 negative memLevel). 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.)
int inflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt
dictLength);
Initializes the decompression dictionary from the given uncom-
pressed byte sequence. This function must be called immediately
after a call to inflate() if this call returned Z_NEED_DICT. The
dictionary chosen by the compressor can be determined from the
Adler-32 value returned by this call to inflate(). The compres-
sor and decompressor must use exactly the same dictionary (see
deflateSetDictionary()).
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().
int 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 applica-
tion may repeatedly call inflateSync(), providing more input each
time, until success or end of the input data.
int inflateCopy(z_streamp dest, z_streamp source)
Sets the destination stream as a complete copy of the source
stream.
This function can be useful when randomly accessing a large
stream. The first pass through the stream can periodically
record the inflate state, allowing restarting inflate at those
points when randomly accessing the stream.
inflateCopy() 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.
int 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).
int inflateBackInit(z_stream FAR *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 rou-
tines are used. windowBits is the base two logarithm of the win-
dow size, in the range 8..15. window is a caller supplied buffer
of that size. Except for special applications where it is as-
sured 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.
int inflateBack(z_stream FAR *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 be-
tween the output and the sliding window by simply making the win-
dow itself the output buffer. This function trusts the applica-
tion to not change the output buffer passed by the output func-
tion, 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 trail-
er. 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 de-
flate 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 de-
flate stream and writes out all of the uncompressed data, or un-
til 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 win-
dow 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, in-
put 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 ini-
tialized. In the case of Z_BUF_ERROR, an input or output error
can be distinguished using strm->next_in which will be Z_NULL on-
ly 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() can-
not return Z_OK.
int inflateBackEnd(z_stream FAR *strm)
All memory allocated by inflateBackInit() is freed.
inflateBackEnd() returns Z_OK on success, or Z_STREAM_ERROR if
the stream state was inconsistent.
uLong zlibCompileFlags(void)
This function returns flags indicating compile-time options.
Type sizes, two bits each:
00 16 bits
01 32 bits
10 64 bits
11 other:
1.0 size of uInt
3.2 size of uLong
5.4 size of voidpf (pointer)
7.6 size of z_off_t
Compiler, assembler, and debug options:
8 DEBUG
9 ASMV or ASMINF -- use ASM code
10 ZLIB_WINAPI -- exported functions use the WINAPI
calling convention
11 0 (reserved)
One-time table building (smaller code, but not thread-safe if
true):
12 BUILDFIXED -- build static block decoding tables
when needed
13 DYNAMIC_CRC_TABLE -- build CRC calculation tables
when needed
14,15 0 (reserved)
Library content (indicates missing functionality):
16 NO_GZCOMPRESS -- gz* functions cannot compress (to
avoid linking deflate code when not needed)
17 NO_GZIP -- deflate can't write gzip streams, and
inflate can't detect and decode gzip streams (to
avoid linking CRC code)
18-19 0 (reserved)
Operation variations (changes in library functionality):
20 PKZIP_BUG_WORKAROUND -- slightly more permissive
inflate
21 FASTEST -- deflate algorithm with only one, lowest
compression level
22,23 0 (reserved)
The sprintf variant used by gzprintf (zero is best):
24 0 = vs*, 1 = s* -- 1 means limited to 20 arguments
after the format
25 0 = *nprintf, 1 = *printf -- 1 means gzprintf() not
secure!
26 0 = returns value, 1 = void -- 1 means inferred
string length returned
Remainder:
27-31 0 (reserved)
UTILITY FUNCTIONS
The following utility functions are implemented on top of the basic
stream-oriented functions. To simplify the interface, some default op-
tions are assumed (compression level and memory usage, standard memory
allocation functions). The source code of these utility functions can
easily be modified if you need special options.
int compress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
sourceLen);
The compress() function compresses the source buffer into the
destination buffer. sourceLen is the byte length of the source
buffer. Upon entry, destLen is the total size of the destination
buffer, which must be at least the value returned 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.
int compress2(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
sourceLen, int level);
The compress2() function compresses the source buffer into the
destination buffer. The level parameter has the same meaning as
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.
int compressBound(uLong sourceLen)
compressBound() returns an upper bound on the compressed size af-
ter compress() or compress2() on sourceLen bytes. It would be
used before a compress() or compress2() call to allocate the des-
tination buffer.
int uncompress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
sourceLen);
The uncompress() function decompresses the source buffer into the
destination buffer. sourceLen is the byte length of the source
buffer. Upon entry, destLen is the total size of the destination
buffer, which must be large enough to hold the entire uncom-
pressed data. (The size of the uncompressed data must have been
saved previously by the compressor and transmitted to the decom-
pressor by some mechanism outside the scope of this compression
library.) Upon exit, destLen is the actual size of the com-
pressed 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 corrupt-
ed or incomplete.
gzFile gzopen(const char *path, const char *mode);
The gzopen() function opens a gzip (.gz) file for reading or
writing. The mode parameter is as in fopen(3) ("rb" or "wb") but
can also include a compression level (wb9) or a strategy: `f' for
filtered data, as in "wb6f"; `h' for Huffman only compression, as
in "wb1h", or `R' for run-length encoding as in "wb1R". (See the
description 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).
gzFile gzdopen(int fd, const char *mode);
The gzdopen() function associates a gzFile with the file descrip-
tor 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 gz-
dopen(dup(fd), mode).
gzdopen() returns NULL if there was insufficient memory to allo-
cate the (de)compression state.
int gzsetparams(gzFile file, int level, int strategy);
The gzsetparams() function dynamically updates the compression
level or strategy. See the description 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.
int gzread(gzFile file, voidp buf, unsigned len);
The gzread() function reads the given number of uncompressed
bytes from the compressed file. If the input file was not in
gzip format, gzread() copies the given number of bytes into the
buffer.
gzread() returns the number of uncompressed bytes actually read
(0 for end of file, -1 for error).
int gzwrite(gzFile file, voidpc buf, unsigned len);
The gzwrite() function writes the given number of uncompressed
bytes into the compressed file. gzwrite() returns the number of
uncompressed bytes actually written (0 in case of error).
int gzprintf(gzFile file, const char *format, ...);
The gzprintf() function converts, formats, and writes the args to
the compressed file under control of the format string, as in
fprintf(3). gzprintf() returns the number of uncompressed bytes
actually written (0 in case of error). The number of uncom-
pressed 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.
int gzputs(gzFile file, const char *s);
The gzputs() function writes the given null-terminated string to
the compressed file, excluding the terminating null character.
gzputs() returns the number of characters written, or -1 in case
of error.
char * gzgets(gzFile file, char *buf, int len);
The gzgets() function reads bytes from the compressed file until
len-1 characters are read, or a newline character is read and
transferred to buf, or an end-of-file condition is encountered.
The string is then terminated with a null character.
gzgets() returns buf, or Z_NULL in case of error.
int gzputc(gzFile file, int c);
The gzputc() function writes c, converted to an unsigned char,
into the compressed file. gzputc() returns the value that was
written, or -1 in case of error.
int gzgetc(gzFile file);
The gzgetc() function reads one byte from the compressed file.
gzgetc() returns this byte or -1 in case of end of file or error.
int gzungetc(int c, gzFile file)
Push one character back onto the stream to be read again later.
Only one character of push-back is allowed. gzungetc() returns
the character pushed, or -1 on failure. gzungetc() will fail if
a character has been pushed but not read yet, or if c is -1. The
pushed character will be discarded if the stream is repositioned
with gzseek() or gzrewind().
int gzflush(gzFile file, int flush);
The gzflush() function flushes all pending output into the com-
pressed file. The parameter flush is as in the deflate() func-
tion. 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.
z_off_t 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 posi-
tion.
int gzrewind(gzFile file);
The gzrewind() function rewinds the given file. This function is
supported only for reading.
gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET).
z_off_t gztell(gzFile file);
The gztell() function returns the starting position for the next
gzread() or gzwrite() on the given compressed file. This posi-
tion represents a number of bytes in the uncompressed data
stream.
gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).
int gzeof(gzFile file);
The gzeof() function returns 1 when EOF has previously been de-
tected reading the given input stream, otherwise zero.
int gzclose(gzFile file);
The gzclose() function flushes all pending output if necessary,
closes the compressed file and deallocates all the (de)compres-
sion state. The return value is the zlib error number (see func-
tion gzerror() below).
const char * gzerror(gzFile file, int *errnum);
The gzerror() function returns the error message for the last er-
ror which occurred on the given compressed file. errnum is set
to the zlib error number. If an error occurred in the file sys-
tem and not in the compression library, errnum is set to Z_ERRNO
and the application may consult errno to get the exact error
code.
void gzclearerr(gzFile file)
Clears the error and end-of-file flags for file. This is analo-
gous to the clearerr() function in stdio. This is useful for
continuing to read a gzip file that is being written concurrent-
ly.
CHECKSUM FUNCTIONS
These functions are not related to compression but are exported anyway
because they might be useful in applications using the compression li-
brary.
uLong adler32(uLong adler, const Bytef *buf, uInt len);
The adler32() function updates a running Adler-32 checksum with
the bytes buf[0..len-1] and returns the updated checksum. If buf
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();
uLong crc32(uLong crc, const Bytef *buf, uInt len);
The crc32() function updates a running CRC with the bytes
buf[0..len-1] and returns the updated CRC. 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 exam-
ple:
uLong crc = crc32(0L, Z_NULL, 0);
while (read_buffer(buffer, length) != EOF) {
crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();
STRUCTURES
struct internal_state;
typedef struct z_stream_s {
Bytef *next_in; /* next input byte */
uInt avail_in; /* number of bytes available at next_in */
off_t total_in; /* total nb of input bytes read so far */
Bytef *next_out; /* next output byte should be put there */
uInt avail_out; /* remaining free space at next_out */
off_t total_out; /* total nb of bytes output so far */
char *msg; /* last error message, NULL if no error */
struct internal_state FAR *state; /* not visible by applications */
alloc_func zalloc; /* used to allocate the internal state */
free_func zfree; /* used to free the internal state */
voidpf opaque; /* private data object passed to zalloc and zfree*/
int data_type; /*best guess about the data type: ascii or binary*/
uLong adler; /* adler32 value of the uncompressed data */
uLong reserved; /* reserved for future use */
} z_stream;
typedef z_stream FAR * z_streamp;
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 cus-
tom 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 allo-
cate 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 al-
location 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 uncom-
pressed data and may be saved for use in the decompressor (particularly
if the decompressor wants to decompress everything in a single step).
CONSTANTS
#define Z_NO_FLUSH 0
#define Z_PARTIAL_FLUSH 1 /* will be removed, use Z_SYNC_FLUSH instead */
#define Z_SYNC_FLUSH 2
#define Z_FULL_FLUSH 3
#define Z_FINISH 4
#define Z_BLOCK 5
/* Allowed flush values; see deflate() and inflate() below for details */
#define Z_OK 0
#define Z_STREAM_END 1
#define Z_NEED_DICT 2
#define Z_ERRNO (-1)
#define Z_STREAM_ERROR (-2)
#define Z_DATA_ERROR (-3)
#define Z_MEM_ERROR (-4)
#define Z_BUF_ERROR (-5)
#define Z_VERSION_ERROR (-6)
/* Return codes for the compression/decompression functions.
* Negative values are errors,
* positive values are used for special but normal events.
*/
#define Z_NO_COMPRESSION 0
#define Z_BEST_SPEED 1
#define Z_BEST_COMPRESSION 9
#define Z_DEFAULT_COMPRESSION (-1)
/* compression levels */
#define Z_FILTERED 1
#define Z_HUFFMAN_ONLY 2
#define Z_RLE 3
#define Z_DEFAULT_STRATEGY 0
/* compression strategy; see deflateInit2() below for details */
#define Z_BINARY 0
#define Z_ASCII 1
#define Z_UNKNOWN 2
/* Possible values of the data_type field (though see inflate()) */
#define Z_DEFLATED 8
/* The deflate compression method
* (the only one supported in this version)
*/
#define Z_NULL 0 /* for initializing zalloc, zfree, opaque */
#define zlib_version zlibVersion()
/* for compatibility with versions < 1.0.2 */
VARIOUS HACKS
deflateInit and inflateInit are macros to allow checking the zlib version
and the compiler's view of z_stream.
int deflateInit_(z_stream strm, int level, const char *version, int
stream_size);
int inflateInit_(z_stream strm, const char *version, int stream_size);
int deflateInit2_(z_stream strm, int level, int method, int windowBits,
int memLevel, int strategy, const char *version, int stream_size)
int inflateInit2_(z_stream strm, int windowBits, const char *version, int
stream_size);
int inflateBackInit_(z_stream FAR *strm, int windowBits, unsigned char
FAR *window, const char *version, int stream_size)
const char * zError(int err);
int inflateSyncPoint(z_streamp z);
const uLongf * get_crc_table(void);
SEE ALSO
compress(1)
RFC 1950 ZLIB Compressed Data Format Specification.
RFC 1951 DEFLATE Compressed Data Format Specification.
RFC 1952 GZIP File Format Specification.
http://www.gzip.org/zlib/
HISTORY
This manual page is based on an HTML version of <zlib.h> converted by
piaip <piaip@csie.ntu.edu.tw> and was converted to mdoc format by the
OpenBSD project.
AUTHORS
Jean-loup Gailly <jloup@gzip.org>
Mark Adler <madler@alumni.caltech.edu>
OpenBSD 3.6 September 17, 2003 21