compress - 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);
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);
This manual page describes the zlib general purpose compression library,
version 1.1.4.
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 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.
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 memory.
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
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 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.
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 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 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 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 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.
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 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.)
int inflate(z_streamp strm, int flush);
inflate() decompresses as much data as possible, and
stops when
the input buffer becomes empty or the output buffer
becomes full.
It may introduce some output latency (reading input
without
producing any output) except when forced to flush.
The detailed semantics are as follows. inflate()
performs one or
both of the following actions:
Decompress more input starting at next_in and update
next_in and
avail_in accordingly. If not all input can be processed (because
there is not enough room in the output buffer),
next_in is updated
and processing will resume at this point for the
next call to
inflate().
Provide more output starting at next_out and update
next_out and
avail_out accordingly. inflate() provides as much
output as possible,
until there is no more input data or no more
space in the
output buffer (see below about the flush parameter).
Before the call to inflate(), the application should
ensure that
at least one of the actions is possible, by providing more input
and/or consuming more output, and updating the
next_* and avail_*
values accordingly. The application can consume the
uncompressed
output when it wants, for example when the output
buffer is full
(avail_out == 0), or after each call 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 strmadler 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 zlibwrapped or gzipwrapped
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.
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).
The following functions are needed only in some special applications.
int deflateInit2(z_streamp strm, int level, int method, int
windowBits,
int memLevel, int strategy);
This is another version of deflateInit() with more
compression
options. The fields next_in, zalloc, zfree, and
opaque must be
initialized before by the caller.
The method parameter is the compression method. It
must be
Z_DEFLATED in this version of the library.
The windowBits parameter is the base two logarithm
of the window
size (the size of the history buffer). It should be
in the range
8..15 for this version of the library. Larger values of this parameter
result in better compression at the expense
of memory usage.
The default value is 15 if deflateInit() is
used instead.
windowBits can also be -8..-15 for raw deflate. In
this case,
-windowBits determines the window size. deflate()
will then generate
raw deflate data with no zlib header or trailer, and will
not compute an Adler-32 check value.
windowBits can also be greater than 15 for optional
gzip encoding.
Add 16 to windowBits to write a simple gzip
header and
trailer around the compressed data instead of a zlib
wrapper.
The gzip header will have no file name, no extra data, no comment,
no modification time (set to zero), no header
crc, and the
operating system will be set to 255 (unknown).
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.
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 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.
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().
int deflateCopy(z_streamp dest, z_streamp source);
The deflateCopy() function sets the destination
stream as a complete
copy of the source stream.
This function can be useful when several compression
strategies
will be tried, for example when there are several
ways of preprocessing
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.
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 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.
uLong deflateBound(z_streamp strm, uLong sourceLen)
deflateBound() returns an upper bound on the compressed size after
deflation of sourceLen bytes. It must be called
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 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).
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 uncompressed
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 compressor
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 application
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 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.
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 callback
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 nonzero,
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.
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)
The following utility functions are implemented on top of
the basic
stream-oriented functions. To simplify the interface, some
default options
are assumed (compression level and memory usage, standard memory
allocation functions). The source code of these utility
functions can
easily be modified if you need special options.
int compress(Bytef *dest, uLongf *destLen, const Bytef
*source, uLong
sourceLen);
The compress() function compresses the source buffer
into the
destination buffer. sourceLen is the byte length of
the source
buffer. Upon entry, destLen is the total size of
the destination
buffer, which must be at least the value returned 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 after
compress() or compress2() on sourceLen bytes.
It would be
used before a compress() or compress2() call to allocate the destination
buffer.
int uncompress(Bytef *dest, uLongf *destLen, const Bytef
*source, uLong
sourceLen);
The uncompress() function decompresses the source
buffer into the
destination buffer. sourceLen is the byte length of
the source
buffer. Upon entry, destLen is the total size of
the destination
buffer, which must be large enough to hold the entire uncompressed
data. (The size of the uncompressed data
must have been
saved previously by the compressor and transmitted
to the decompressor
by some mechanism outside the scope of this
compression
library.) Upon exit, destLen is the actual size of
the compressed
buffer. This function can be used to decompress a whole
file at once if the input file is mmap'ed.
uncompress() 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.
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 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.
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 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.
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 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 str
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