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\" Converted to mdoc format for the OpenBSD project
\" by Jason McIntyre <[email protected]>
\"
Dd May 1, 2004
Dt ZLIB 3
Os
Sh NAME
Nm zlib
Nd general purpose compression library
Sh SYNOPSIS
In zlib.h
Ss Basic functions
Ft const char *
Fn zlibVersion "void"
Ft int
Fn deflateInit "z_streamp strm" "int level"
Ft int
Fn deflate "z_streamp strm" "int flush"
Ft int
Fn deflateEnd "z_streamp strm"
Ft int
Fn inflateInit "z_streamp strm"
Ft int
Fn inflate "z_streamp strm" "int flush"
Ft int
Fn inflateEnd "z_streamp strm"
Ss Advanced functions
Ft int
Fn deflateInit2 "z_streamp strm" "int level" "int method" \
"int windowBits" "int memLevel" "int strategy"
Ft int
Fn deflateSetDictionary "z_streamp strm" "const Bytef *dictionary" \
"uInt dictLength"
Ft int
Fn deflateCopy "z_streamp dest" "z_streamp source"
Ft int
Fn deflateReset "z_streamp strm"
Ft int
Fn deflateParams "z_streamp strm" "int level" "int strategy"
Ft int
Fn inflateInit2 "z_streamp strm" "int windowBits"
Ft int
Fn inflateSetDictionary "z_streamp strm" "const Bytef *dictionary" "uInt dictLength"
Ft int
Fn inflateSync "z_streamp strm"
Ft int
Fn inflateReset "z_streamp strm"
Ss Utility functions
Fd typedef voidp gzFile ;
Pp
Ft int
Fn compress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen"
Ft int
Fn compress2 "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" "int level"
Ft int
Fn uncompress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen"
Ft gzFile
Fn gzopen "const char *path" "const char *mode"
Ft gzFile
Fn gzdopen "int fd" "const char *mode"
Ft int
Fn gzsetparams "gzFile file" "int level" "int strategy"
Ft int
Fn gzread "gzFile file" "voidp buf" "unsigned len"
Ft int
Fn gzwrite "gzFile file" "const voidp buf" "unsigned len"
Ft int
Fn gzprintf "gzFile file" "const char *format" "..."
Ft int
Fn gzputs "gzFile file" "const char *s"
Ft char *
Fn gzgets "gzFile file" "char *buf" "int len"
Ft int
Fn gzputc "gzFile file" "int c"
Ft int
Fn gzgetc "gzFile file"
Ft int
Fn gzflush "gzFile file" "int flush"
Ft z_off_t
Fn gzseek "gzFile file" "z_off_t offset" "int whence"
Ft int
Fn gzrewind "gzFile file"
Ft z_off_t
Fn gztell "gzFile file"
Ft int
Fn gzeof "gzFile file"
Ft int
Fn gzclose "gzFile file"
Ft const char *
Fn gzerror "gzFile file" "int *errnum"
Ss Checksum functions
Ft uLong
Fn adler32 "uLong adler" "const Bytef *buf" "uInt len"
Ft uLong
Fn crc32 "uLong crc" "const Bytef *buf" "uInt len"
Sh DESCRIPTION
This manual page describes the
Nm
general purpose compression library, version 1.1.4.
Pp
The
Nm
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
Pq deflation
but other algorithms will be added later and will have the same
stream interface.
Pp
Compression can be done in a single step if the buffers are large enough
Pq 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
Pq providing more output space
before each call.
Pp
The library also supports reading and writing files in
Xr gzip 1
Pq .gz
format with an interface similar to that of
Xr stdio 3 .
Pp
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.
Pp
The functions within the library are divided into the following sections:
Pp
Bl -dash -offset indent -compact
It
Basic functions
It
Advanced functions
It
Utility functions
It
Checksum functions
El
Sh BASIC FUNCTIONS
Bl -tag -width Ds
It Fa const char * Fn zlibVersion "void" ;
Pp
The application can compare
Fn zlibVersion
and
Dv ZLIB_VERSION
for consistency.
If the first character differs, the library code actually used is
not compatible with the
In zlib.h
header file used by the application.
This check is automatically made by
Fn deflateInit
and
Fn inflateInit .
It Fa int Fn deflateInit "z_streamp strm" "int level" ;
Pp
The
Fn deflateInit
function initializes the internal stream state for compression.
The fields
Fa zalloc ,
Fa zfree ,
and
Fa opaque
must be initialized before by the caller.
If
Fa zalloc
and
Fa zfree
are set to
Dv Z_NULL ,
Fn deflateInit
updates them to use default allocation functions.
Pp
The compression level must be
Dv 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).
Pp
Dv Z_DEFAULT_COMPRESSION
requests a default compromise between speed and compression
Pq currently equivalent to level 6 .
Pp
Fn deflateInit
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_STREAM_ERROR
if level is not a valid compression level,
Dv Z_VERSION_ERROR
if the
Nm
library version
Pq zlib_version
is incompatible with the version assumed by the caller
Pq ZLIB_VERSION .
Fa msg
is set to null if there is no error message.
Fn deflateInit
does not perform any compression: this will be done by
Fn deflate .
It Fa int Fn deflate "z_streamp strm" "int flush" ;
Pp
Fn 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
Pq reading input without producing any output
except when forced to flush.
Pp
The detailed semantics are as follows.
Fn deflate
performs one or both of the following actions:
Pp
Compress more input starting at
Fa next_in
and update
Fa next_in
and
Fa avail_in
accordingly.
If not all input can be processed
(because there is not enough room in the output buffer),
Fa next_in
and
Fa avail_in
are updated and processing will resume at this point for the next call to
Fn deflate .
Pp
Provide more output starting at
Fa next_out
and update
Fa next_out
and
Fa avail_out
accordingly.
This action is forced if the parameter
Fa flush
is non-zero.
Forcing
Fa flush
frequently degrades the compression ratio,
so this parameter should be set only when necessary
Pq in interactive applications .
Some output may be provided even if
Fa flush
is not set.
Pp
Before the call to
Fn 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
Fa avail_in
or
Fa avail_out
accordingly;
Fa 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
Pq avail_out == 0 ,
or after each call to
Fn deflate .
If
Fn deflate
returns
Dv Z_OK
and with zero
Fa avail_out ,
it must be called again after making room in the
output buffer because there might be more output pending.
Pp
If the parameter
Fa flush
is set to
Dv 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,
Fa 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.
Pp
If
Fa flush
is set to
Dv Z_FULL_FLUSH ,
all output is flushed as with
Dv 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
Dv Z_FULL_FLUSH
too often can seriously degrade the compression.
Pp
If
Fn 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
Fa avail_out ) ,
until the flush is complete
Pf ( Fn deflate
returns with non-zero
Fa avail_out ) .
Pp
If the parameter
Fa flush
is set to
Dv Z_FINISH ,
pending input is processed, pending output is flushed and
Fn deflate
returns with
Dv Z_STREAM_END
if there was enough output space; if
Fn deflate
returns with
Dv Z_OK ,
this function must be called again with
Dv Z_FINISH
and more output space
(updated
Fa avail_out
but no more input data, until it returns with
Dv Z_STREAM_END
or an error.
After
Fn deflate
has returned
Dv Z_STREAM_END ,
the only possible operations on the stream are
Fn deflateReset
or
Fn deflateEnd .
Pp
Dv Z_FINISH
can be used immediately after
Fn deflateInit
if all the compression is to be done in a single step.
In this case,
Fa avail_out
must be at least 0.1% larger than
Fa avail_in
plus 12 bytes.
If
Fn deflate
does not return
Dv Z_STREAM_END ,
then it must be called again as described above.
Pp
Fn deflate
sets strm->adler to the Adler-32 checksum of all input read so far
(that is,
Fa total_in
bytes).
Pp
Fn deflate
may update
Fa data_type
if it can make a good guess about the input data type
Pq 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.
Pp
Fn deflate
returns
Dv Z_OK
if some progress has been made
Pq more input processed or more output produced ,
Dv Z_STREAM_END
if all input has been consumed and all output has been produced
(only when
Fa flush
is set to
Dv Z_FINISH ) ,
Dv Z_STREAM_ERROR
if the stream state was inconsistent
(for example, if
Fa next_in
or
Fa next_out
was
Dv NULL ) ,
Dv Z_BUF_ERROR
if no progress is possible
(for example,
Fa avail_in
or
Fa avail_out
was zero).
It Fa int Fn deflateEnd "z_streamp strm" ;
Pp
All dynamically allocated data structures for this stream are freed.
This function discards any unprocessed input and does not flush any
pending output.
Pp
Fn deflateEnd
returns
Dv Z_OK
if successful,
Dv Z_STREAM_ERROR
if the stream state was inconsistent,
Dv Z_DATA_ERROR
if the stream was freed prematurely
Pq some input or output was discarded .
In the error case,
Fa msg
may be set but then points to a static string
Pq which must not be deallocated .
It Fa int Fn inflateInit "z_streamp strm" ;
The
Fn inflateInit
function initializes the internal stream state for decompression.
The fields
Fa next_in ,
Fa avail_in ,
Fa zalloc ,
Fa zfree ,
and
Fa opaque
must be initialized before by the caller.
If
Fa next_in
is not
Dv Z_NULL
and
Fa avail_in
is large enough
Pq the exact value depends on the compression method ,
Fn inflateInit
determines the compression method from the
Nm
header and allocates all data structures accordingly;
otherwise the allocation will be deferred to the first call to
Fn inflate .
If
Fa zalloc
and
Fa zfree
are set to
Dv Z_NULL ,
Fn inflateInit
updates them to use default allocation functions.
Pp
Fn inflateInit
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_VERSION_ERROR
if the
Nm
library version is incompatible with the version assumed by the caller.
Fa msg
is set to null if there is no error message.
Fn inflateInit
does not perform any decompression apart from reading the
Nm
header if present: this will be done by
Fn inflate .
(So
Fa next_in
and
Fa avail_in
may be modified,
but
Fa next_out
and
Fa avail_out
are unchanged.)
It Fa int Fn inflate "z_streamp strm" "int flush" ;
Fn 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
Pq reading input without producing any output
except when forced to flush.
Pp
The detailed semantics are as follows.
Fn inflate
performs one or both of the following actions:
Pp
Decompress more input starting at
Fa next_in
and update
Fa next_in
and
Fa avail_in
accordingly.
If not all input can be processed
(because there is not enough room in the output buffer),
Fa next_in
is updated and processing will resume at this point for the next call to
Fn inflate .
Pp
Provide more output starting at
Fa next_out
and update
Fa next_out
and
Fa avail_out
accordingly.
Fn inflate
provides as much output as possible,
until there is no more input data or no more space in the output buffer
Pq see below about the flush parameter .
Pp
Before the call to
Fn 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
Fn inflate .
If
Fn inflate
returns
Dv Z_OK
and with zero
Fa avail_out ,
it must be called again after making room
in the output buffer because there might be more output pending.
Pp
If the parameter
Fa flush
is set to
Dv Z_SYNC_FLUSH ,
Fn inflate
flushes as much output as possible to the output buffer.
The flushing behavior of
Fn inflate
is not specified for values of the flush parameter other than
Dv Z_SYNC_FLUSH
and
Dv Z_FINISH ,
but the current implementation actually flushes as much output
as possible anyway.
Pp
Fn inflate
should normally be called until it returns
Dv Z_STREAM_END
or an error.
However if all decompression is to be performed in a single step
Pq a single call to inflate ,
the parameter
Fa flush
should be set to
Dv Z_FINISH .
In this case all pending input is processed and all pending output is flushed;
Fa 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
Fn inflateEnd
to deallocate the decompression state.
The use of
Dv Z_FINISH
is never required, but can be used to inform
Fn inflate
that a faster routine may be used for the single
Fn inflate
call.
Pp
If a preset dictionary is needed at this point (see
Fn inflateSetDictionary
below),
Fn inflate
sets strm->adler to the Adler-32 checksum of the dictionary
chosen by the compressor and returns
Dv Z_NEED_DICT ;
otherwise it sets strm->adler to the Adler-32 checksum of all output produced
so far
(that is,
Fa total_out
bytes)
and returns
Dv Z_OK ,
Dv Z_STREAM_END ,
or an error code as described below.
At the end of the stream,
Fn inflate
checks that its computed Adler-32 checksum is equal to that saved by the
compressor and returns
Dv Z_STREAM_END
only if the checksum is correct.
Pp
Fn inflate
returns
Dv Z_OK
if some progress has been made
Pq more input processed or more output produced ,
Dv Z_STREAM_END
if the end of the compressed data has been reached and all uncompressed output
has been produced,
Dv Z_NEED_DICT
if a preset dictionary is needed at this point,
Dv Z_DATA_ERROR
if the input data was corrupted (input stream not conforming to the
Nm
format or incorrect Adler-32 checksum),
Dv Z_STREAM_ERROR
if the stream structure was inconsistent
(for example, if
Fa next_in
or
Fa next_out
was
Dv NULL ) ,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_BUF_ERROR
if no progress is possible or if there was not enough room in the output buffer
when
Dv Z_FINISH
is used.
In the
Dv Z_DATA_ERROR
case, the application may then call
Fn inflateSync
to look for a good compression block.
It Fa int Fn 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.
Pp
Fn inflateEnd
returns
Dv Z_OK
if successful, or
Dv Z_STREAM_ERROR
if the stream state was inconsistent.
In the error case,
Fa msg
may be set but then points to a static string
Pq which must not be deallocated .
El
Sh ADVANCED FUNCTIONS
The following functions are needed only in some special applications.
Bl -tag -width Ds
It Fa int Fn deflateInit2 "z_streamp strm" "int level" "int method" \
"int windowBits" "int memLevel" "int strategy" ;
Pp
This is another version of
Fn deflateInit
with more compression options.
The fields
Fa next_in ,
Fa zalloc ,
Fa zfree ,
and
Fa opaque
must be initialized before by the caller.
Pp
The
Fa method
parameter is the compression method.
It must be
Dv Z_DEFLATED
in this version of the library.
Pp
The
Fa windowBits
parameter is the base two logarithm of the window size
Pq 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
Fn deflateInit
is used instead.
Pp
The
Fa 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
In zconf.h
for total memory usage as a function of
Fa windowBits
and
Fa memLevel .
Pp
The
Fa strategy
parameter is used to tune the compression algorithm.
Use the value
Dv Z_DEFAULT_STRATEGY
for normal data;
Dv Z_FILTERED
for data produced by a filter
Pq or predictor ;
or
Dv Z_HUFFMAN_ONLY
to force Huffman encoding only
Pq no string match .
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
Dv Z_FILTERED
is to force more Huffman coding and less string matching;
it is somewhat intermediate between
Dv Z_DEFAULT
and
Dv Z_HUFFMAN_ONLY .
The
Fa strategy
parameter only affects the compression ratio but not the correctness of the
compressed output, even if it is not set appropriately.
Pp
Fn deflateInit2
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_STREAM_ERROR
if a parameter is invalid
Pq such as an invalid method .
Fa msg
is set to null if there is no error message.
Fn deflateInit2
does not perform any compression: this will be done by
Fn deflate .
It Fa int Fn deflateSetDictionary "z_streamp strm" \
"const Bytef *dictionary" "uInt dictLength" ;
Pp
Initializes the compression dictionary from the given byte sequence
without producing any compressed output.
This function must be called immediately after
Fn deflateInit ,
Fn deflateInit2 ,
or
Fn deflateReset ,
before any call to
Fn deflate .
The compressor and decompressor must use exactly the same dictionary
(see
Fn inflateSetDictionary ) .
Pp
The dictionary should consist of strings
Pq 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.
Pp
Depending on the size of the compression data structures selected by
Fn deflateInit
or
Fn deflateInit2 ,
a part of the dictionary may in effect be discarded,
for example if the dictionary is larger than the window size in
Fn deflate
or
Fn deflate2 .
Thus the strings most likely to be useful should be
put at the end of the dictionary, not at the front.
Pp
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.)
Pp
Fn deflateSetDictionary
returns
Dv Z_OK
if successful,
or
Dv Z_STREAM_ERROR
if a parameter is invalid
Pq such as NULL dictionary
or the stream state is inconsistent
(for example if
Fn deflate
has already been called for this stream or if the compression method is bsort).
Fn deflateSetDictionary
does not perform any compression: this will be done by
Fn deflate .
It Fa int Fn deflateCopy "z_streamp dest" "z_streamp source" ;
Pp
The
Fn deflateCopy
function sets the destination stream as a complete copy of the source stream.
Pp
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
Fn deflateEnd .
Note that
Fn deflateCopy
duplicates the internal compression state which can be quite large,
so this strategy is slow and can consume lots of memory.
Pp
Fn deflateCopy
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_STREAM_ERROR
if the source stream state was inconsistent
(such as
Fa zalloc
being NULL).
Fa msg
is left unchanged in both source and destination.
It Fa int Fn deflateReset "z_streamp strm" ;
Pp
This function is equivalent to
Fn deflateEnd
followed by
Fn 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
Fn deflateInit2 .
Pp
Fn deflateReset
returns
Dv Z_OK
if successful, or
Dv Z_STREAM_ERROR
if the source stream state was inconsistent
(such as
Fa zalloc
or
Fa state
being NULL).
It Fa int Fn deflateParams "z_streamp strm" "int level" "int strategy" ;
Pp
The
Fn deflateParams
function dynamically updates the compression level and compression strategy.
The interpretation of level and strategy is as in
Fn 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
Pq and may be flushed ;
the new level will take effect only at the next call to
Fn deflate .
Pp
Before the call to
Fn deflateParams ,
the stream state must be set as for a call to
Fn deflate ,
since the currently available input may have to be compressed and flushed.
In particular, strm->avail_out must be non-zero.
Pp
Fn deflateParams
returns
Dv Z_OK
if successful,
Dv Z_STREAM_ERROR
if the source stream state was inconsistent or if a parameter was invalid, or
Dv Z_BUF_ERROR
if strm->avail_out was zero.
It Fa int Fn inflateInit2 "z_streamp strm" "int windowBits" ;
Pp
This is another version of
Fn inflateInit
with an extra parameter.
The fields
Fa next_in ,
Fa avail_in ,
Fa zalloc ,
Fa zfree ,
and
Fa opaque
must be initialized before by the caller.
Pp
The
Fa windowBits
parameter is the base two logarithm of the maximum window size
Pq 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
Fn inflateInit
is used instead.
If a compressed stream with a larger window size is given as input,
Fn inflate
will return with the error code
Dv Z_DATA_ERROR
instead of trying to allocate a larger window.
Pp
Fn inflateInit2
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_STREAM_ERROR
if a parameter is invalid
(such as a negative
Fa memLevel ) .
Fa msg
is set to null if there is no error message.
Fn inflateInit2
does not perform any decompression apart from reading the
Nm
header if present: this will be done by
Fn inflate .
(So
Fa next_in
and
Fa avail_in
may be modified, but
Fa next_out
and
Fa avail_out
are unchanged.)
It Fa int Fn inflateSetDictionary "z_streamp strm" \
"const Bytef *dictionary" "uInt dictLength" ;
Pp
Initializes the decompression dictionary from the given uncompressed byte
sequence.
This function must be called immediately after a call to
Fn inflate
if this call returned
Dv Z_NEED_DICT .
The dictionary chosen by the compressor can be determined from the
Adler-32 value returned by this call to
Fn inflate .
The compressor and decompressor must use exactly the same dictionary
(see
Fn deflateSetDictionary ) .
Pp
Fn inflateSetDictionary
returns
Dv Z_OK
if successful,
Dv Z_STREAM_ERROR
if a parameter is invalid
Pq such as NULL dictionary
or the stream state is inconsistent,
Dv Z_DATA_ERROR
if the given dictionary doesn't match the expected one
Pq incorrect Adler-32 value .
Fn inflateSetDictionary
does not perform any decompression: this will be done by subsequent calls of
Fn inflate .
It Fa int Fn inflateSync "z_streamp strm" ;
Pp
Skips invalid compressed data until a full flush point
(see above the description of
Fn deflate
with
Dv Z_FULL_FLUSH )
can be found, or until all available input is skipped.
No output is provided.
Pp
Fn inflateSync
returns
Dv Z_OK
if a full flush point has been found,
Dv Z_BUF_ERROR
if no more input was provided,
Dv Z_DATA_ERROR
if no flush point has been found, or
Dv Z_STREAM_ERROR
if the stream structure was inconsistent.
In the success case, the application may save the current value of
Fa total_in
which indicates where valid compressed data was found.
In the error case, the application may repeatedly call
Fn inflateSync ,
providing more input each time, until success or end of the input data.
It Fa int Fn inflateReset "z_streamp strm" ;
Pp
This function is equivalent to
Fn inflateEnd
followed by
Fn inflateInit ,
but does not free and reallocate all the internal decompression state.
The stream will keep attributes that may have been set by
Fn inflateInit2 .
Pp
Fn inflateReset
returns
Dv Z_OK
if successful, or
Dv Z_STREAM_ERROR
if the source stream state was inconsistent
(such as
Fa zalloc
or
Fa state
being NULL).
El
Sh UTILITY FUNCTIONS
The following utility functions are implemented on top of the
basic stream-oriented functions.
To simplify the interface,
some default options are assumed (compression level and memory usage,
standard memory allocation functions).
The source code of these utility functions can easily be modified
if you need special options.
Bl -tag -width Ds
It Fa int Fn compress "Bytef *dest" "uLongf *destLen" \
"const Bytef *source" "uLong sourceLen" ;
Pp
The
Fn compress
function compresses the source buffer into the destination buffer.
Fa sourceLen
is the byte length of the source buffer.
Upon entry,
Fa destLen
is the total size of the destination buffer,
which must be at least 0.1% larger than
Fa sourceLen
plus 12 bytes.
Upon exit,
Fa 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.
Pp
Fn compress
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory, or
Dv Z_BUF_ERROR
if there was not enough room in the output buffer.
It Fa int Fn compress2 "Bytef *dest" "uLongf *destLen" \
"const Bytef *source" "uLong sourceLen" "int level" ;
Pp
The
Fn compress2
function compresses the source buffer into the destination buffer.
The
Fa level
parameter has the same meaning as in
Fn deflateInit .
Fa sourceLen
is the byte length of the source buffer.
Upon entry,
Fa destLen
is the total size of the destination buffer,
which must be at least 0.1% larger than
Fa sourceLen
plus 12 bytes.
Upon exit,
Fa destLen
is the actual size of the compressed buffer.
Pp
Fn compress2
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_BUF_ERROR
if there was not enough room in the output buffer, or
Dv Z_STREAM_ERROR
if the level parameter is invalid.
It Fa int Fn uncompress "Bytef *dest" "uLongf *destLen" \
"const Bytef *source" "uLong sourceLen" ;
Pp
The
Fn uncompress
function decompresses the source buffer into the destination buffer.
Fa sourceLen
is the byte length of the source buffer.
Upon entry,
Fa 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,
Fa 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.
Pp
Fn uncompress
returns
Dv Z_OK
if successful,
Dv Z_MEM_ERROR
if there was not enough memory,
Dv Z_BUF_ERROR
if there was not enough room in the output buffer, or
Dv Z_DATA_ERROR
if the input data was corrupted.
It Fa gzFile Fn gzopen "const char *path" "const char *mode" ;
Pp
The
Fn gzopen
function opens a gzip
Pq .gz
file for reading or writing.
The mode parameter is as in
Xr fopen 3
Po
Qq rb
or
Qq wb
Pc
but can also include a compression level
Pq Qq wb9
or a strategy:
Sq f
for filtered data, as in
Qq wb6f ;
Sq h
for Huffman only compression, as in
Qq wb1h .
(See the description of
Fn deflateInit2
for more information about the strategy parameter.)
Pp
Fn gzopen
can be used to read a file which is not in gzip format;
in this case
Fn gzread
will directly read from the file without decompression.
Pp
Fn gzopen
returns
Dv 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
Nm
error is
Dv Z_MEM_ERROR ) .
It Fa gzFile Fn gzdopen "int fd" "const char *mode" ;
Pp
The
Fn gzdopen
function associates a gzFile with the file descriptor
Fa fd .
File descriptors are obtained from calls like
Xr open 2 ,
Xr dup 2 ,
Xr creat 3 ,
Xr pipe 2 ,
or
Xr fileno 3
(if the file has been previously opened with
Xr fopen 3 ) .
The
Fa mode
parameter is as in
Fn gzopen .
Pp
The next call to
Fn 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).
Pp
Fn gzdopen
returns
Dv NULL
if there was insufficient memory to allocate the (de)compression state.
It Fa int Fn gzsetparams "gzFile file" "int level" "int strategy" ;
Pp
The
Fn gzsetparams
function dynamically updates the compression level or strategy.
See the description of
Fn deflateInit2
for the meaning of these parameters.
Pp
Fn gzsetparams
returns
Dv Z_OK
if successful, or
Dv Z_STREAM_ERROR
if the file was not opened for writing.
It Fa int Fn gzread "gzFile file" "voidp buf" "unsigned len" ;
Pp
The
Fn gzread
function reads the given number of uncompressed bytes from the compressed file.
If the input file was not in gzip format,
Fn gzread
copies the given number of bytes into the buffer.
Pp
Fn gzread
returns the number of uncompressed bytes actually read
(0 for end of file, \-1 for error).
It Fa int Fn gzwrite "gzFile file" "const voidp buf" "unsigned len" ;
Pp
The
Fn gzwrite
function writes the given number of uncompressed bytes into the compressed file.
Fn gzwrite
returns the number of uncompressed bytes actually written
Pq 0 in case of error .
It Fa int Fn gzprintf "gzFile file" "const char *format" "..." ;
Pp
The
Fn gzprintf
function converts, formats, and writes the args to the compressed file
under control of the format string, as in
Xr fprintf 3 .
Fn gzprintf
returns the number of uncompressed bytes actually written
Pq 0 in case of error .
It Fa int Fn gzputs "gzFile file" "const char *s" ;
Pp
The
Fn gzputs
function writes the given null-terminated string to the compressed file,
excluding the terminating null character.
Pp
Fn gzputs
returns the number of characters written, or \-1 in case of error.
It Fa char * Fn gzgets "gzFile file" "char *buf" "int len" ;
Pp
The
Fn gzgets
function reads bytes from the compressed file until len\-1 characters are read,
or a newline character is read and transferred to
Fa buf ,
or an end-of-file condition is encountered.
The string is then terminated with a null character.
Pp
Fn gzgets
returns
Fa buf ,
or
Dv Z_NULL
in case of error.
It Fa int Fn gzputc "gzFile file" "int c" ;
Pp
The
Fn gzputc
function writes
Fa c ,
converted to an unsigned char, into the compressed file.
Fn gzputc
returns the value that was written, or \-1 in case of error.
It Fa int Fn gzgetc "gzFile file" ;
Pp
The
Fn gzgetc
function reads one byte from the compressed file.
Fn gzgetc
returns this byte or \-1 in case of end of file or error.
It Fa int Fn gzflush "gzFile file" "int flush" ;
Pp
The
Fn gzflush
function flushes all pending output into the compressed file.
The parameter
Fa flush
is as in the
Fn deflate
function.
The return value is the
Nm
error number (see function
Fn gzerror
below).
Fn gzflush
returns
Dv Z_OK
if the flush parameter is
Dv Z_FINISH
and all output could be flushed.
Pp
Fn gzflush
should be called only when strictly necessary because it can
degrade compression.
It Fa z_off_t Fn gzseek "gzFile file" "z_off_t offset" "int whence" ;
Pp
Sets the starting position for the next
Fn gzread
or
Fn 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
Xr lseek 2 ;
the value
Dv SEEK_END
is not supported.
Pp
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;
Fn gzseek
then compresses a sequence of zeroes up to the new starting position.
Pp
Fn gzseek
returns the resulting offset location as measured in bytes from
the beginning of the uncompressed stream, or \-1 in case of error,
in particular if the file is opened for writing and the new starting position
would be before the current position.
It Fa int Fn gzrewind "gzFile file" ;
Pp
The
Fn gzrewind
function rewinds the given
Fa file .
This function is supported only for reading.
Pp
gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET).
It Fa z_off_t Fn gztell "gzFile file" ;
Pp
The
Fn gztell
function returns the starting position for the next
Fn gzread
or
Fn gzwrite
on the given compressed file.
This position represents a number of bytes in the uncompressed data stream.
Pp
gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).
It Fa int Fn gzeof "gzFile file" ;
Pp
The
Fn gzeof
function returns 1 when
Dv EOF
has previously been detected reading the given input stream, otherwise zero.
It Fa int Fn gzclose "gzFile file" ;
Pp
The
Fn gzclose
function flushes all pending output if necessary, closes the compressed file
and deallocates all the (de)compression state.
The return value is the
Nm
error number (see function
Fn gzerror
below).
It Fa const char * Fn gzerror "gzFile file" "int *errnum" ;
Pp
The
Fn gzerror
function returns the error message for the last error which occurred on the
given compressed
Fa file .
Fa errnum
is set to the
Nm
error number.
If an error occurred in the file system and not in the compression library,
Fa errnum
is set to
Dv Z_ERRNO
and the application may consult errno to get the exact error code.
El
Sh CHECKSUM FUNCTIONS
These functions are not related to compression but are exported
anyway because they might be useful in applications using the
compression library.
Bl -tag -width Ds
It Fa uLong Fn adler32 "uLong adler" "const Bytef *buf" "uInt len" ;
The
Fn adler32
function updates a running Adler-32 checksum with the bytes buf[0..len-1]
and returns the updated checksum.
If
Fa buf
is
Dv NULL ,
this function returns the required initial value for the checksum.
Pp
An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
much faster.
Usage example:
Bd -literal -offset indent
uLong adler = adler32(0L, Z_NULL, 0);

while (read_buffer(buffer, length) != EOF) {
adler = adler32(adler, buffer, length);
}
if (adler != original_adler) error();
Ed
It Fa uLong Fn crc32 "uLong crc" "const Bytef *buf" "uInt len" ;
The
Fn crc32
function updates a running CRC with the bytes buf[0..len-1]
and returns the updated CRC.
If
Fa buf
is
Dv NULL ,
this function returns the required initial value for the CRC.
Pre- and post-conditioning
Pq one's complement
is performed within this function so it shouldn't be done by the application.
Usage example:
Bd -literal -offset indent
uLong crc = crc32(0L, Z_NULL, 0);

while (read_buffer(buffer, length) != EOF) {
crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();
Ed
El
Sh STRUCTURES
Bd -literal
struct internal_state;

typedef struct z_stream_s {
   Bytef    *next_in;  /* next input byte */
   uInt     avail_in;  /* number of bytes available at next_in */
   uLong    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 */
   uLong    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;      /* Adler-32 value of the uncompressed data */
   uLong   reserved;   /* reserved for future use */
} z_stream;

typedef z_stream FAR * z_streamp;
Ed
Pp
The application must update
Fa next_in
and
Fa avail_in
when
Fa avail_in
has dropped to zero.
It must update
Fa next_out
and
Fa avail_out
when
Fa avail_out
has dropped to zero.
The application must initialize
Fa zalloc ,
Fa zfree ,
and
Fa opaque
before calling the init function.
All other fields are set by the compression library
and must not be updated by the application.
Pp
The
Fa opaque
value provided by the application will be passed as the first
parameter for calls to
Fn zalloc
and
Fn zfree .
This can be useful for custom memory management.
The compression library attaches no meaning to the
Fa opaque
value.
Pp
Fa zalloc
must return
Dv Z_NULL
if there is not enough memory for the object.
If
Nm
is used in a multi-threaded application,
Fa zalloc
and
Fa zfree
must be thread safe.
Pp
On 16-bit systems, the functions
Fa zalloc
and
Fa zfree
must be able to allocate exactly 65536 bytes,
but will not be required to allocate more than this if the symbol MAXSEG_64K
is defined (see
In zconf.h ) .
Pp
WARNING: On MSDOS, pointers returned by
Fa zalloc
for objects of exactly 65536 bytes *must* have their offset normalized to zero.
The default allocation function provided by this library ensures this (see
Pa 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
In zconf.h ) .
Pp
The fields
Fa total_in
and
Fa total_out
can be used for statistics or progress reports.
After compression,
Fa total_in
holds the total size of the uncompressed data and may be saved for use
in the decompressor
(particularly if the decompressor wants to decompress everything
in a single step).
Sh CONSTANTS
Bd -literal
#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
/* Allowed flush values; see deflate() 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_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 */

#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 */
Ed
Sh VARIOUS HACKS
deflateInit and inflateInit are macros to allow checking the
Nm
version and the compiler's view of
Fa z_stream .
Bl -tag -width Ds
It Fa int Fn deflateInit_ "z_stream strm" "int level" \
"const char *version" "int stream_size" ;
It Fa int Fn inflateInit_ "z_stream strm" "const char *version" \
"int stream_size" ;
It Fa int Fn deflateInit2_ "z_stream strm" "int level" "int method" \
"int windowBits" "int memLevel" "int strategy" "const char *version" \
"int stream_size" ;
It Fa int Fn inflateInit2_ "z_stream strm" "int windowBits" \
"const char *version" "int stream_size" ;
It Fa const char * Fn zError "int err" ;
It Fa int Fn inflateSyncPoint "z_streamp z" ;
It Fa const uLongf * Fn "get_crc_table" "void" ;
El
Sh SEE ALSO
Bl -tag -width 12n -compact
It RFC 1950
ZLIB Compressed Data Format Specification.
It RFC 1951
DEFLATE Compressed Data Format Specification.
It RFC 1952
GZIP File Format Specification.
El
Pp
Lk http://www.gzip.org/zlib/ "zlib"
Sh HISTORY
This manual page is based on an HTML version of
In zlib.h
converted by
An piaip Aq Mt [email protected]
and was converted to mdoc format by the
Ox
project.
Sh AUTHORS
An Jean-loup Gailly Aq Mt [email protected]
An Mark Adler Aq Mt [email protected]

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