zlib.inc -- interface of the 'zlib' general purpose compression library
version 1.2.8, April 28th, 2013
Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
basic functions
const char * zlibVersion OF((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 OF((z_streamp strm, int level));
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 success, Z_MEM_ERROR if there was not enough
memory, Z_STREAM_ERROR if level is not a valid compression level, or
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 OF((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 of 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 of 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 of deflate(). If deflate returns Z_OK and with
zero avail_out, it must be called again after making room in the output
buffer because there might be more output pending.
Normally the parameter flush is set to Z_NO_FLUSH, which allows deflate to
decide how much data to accumulate before producing output, in order to
maximize compression.
If the parameter flush is set to Z_SYNC_FLUSH, all pending output is
flushed to the output buffer and the output is aligned on a byte boundary, so
that the decompressor can get all input data available so far. (In
particular avail_in is zero after the call if enough output space has been
provided before the call.) Flushing may degrade compression for some
compression algorithms and so it should be used only when necessary. This
completes the current deflate block and follows it with an empty stored block
that is three bits plus filler bits to the next byte, followed by four bytes
(00 00 ff ff).
If flush is set to Z_PARTIAL_FLUSH, all pending output is flushed to the
output buffer, but the output is not aligned to a byte boundary. All of the
input data so far will be available to the decompressor, as for Z_SYNC_FLUSH.
This completes the current deflate block and follows it with an empty fixed
codes block that is 10 bits long. This assures that enough bytes are output
in order for the decompressor to finish the block before the empty fixed code
block.
If flush is set to Z_BLOCK, a deflate block is completed and emitted, as
for Z_SYNC_FLUSH, but the output is not aligned on a byte boundary, and up to
seven bits of the current block are held to be written as the next byte after
the next deflate block is completed. In this case, the decompressor may not
be provided enough bits at this point in order to complete decompression of
the data provided so far to the compressor. It may need to wait for the next
block to be emitted. This is for advanced applications that need to control
the emission of deflate blocks.
If flush is set to Z_FULL_FLUSH, all output is flushed as with
Z_SYNC_FLUSH, and the compression state is reset so that decompression can
restart from this point if previous compressed data has been damaged or if
random access is desired. Using Z_FULL_FLUSH too often can seriously degrade
compression.
If deflate returns with avail_out == 0, this function must be called again
with the same value of the flush parameter and more output space (updated
avail_out), until the flush is complete (deflate returns with non-zero
avail_out). In the case of a Z_FULL_FLUSH or 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). Then deflate is guaranteed to
return Z_STREAM_END. If not enough output space is provided, deflate will
not return Z_STREAM_END, and it must be called again as described above.
deflate() sets strm->adler to the adler32 checksum of all input read
so far (that is, total_in bytes).
deflate() may update strm->data_type if it can make a good guess about
the input data type (Z_BINARY or Z_TEXT). 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 Z_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 compressing.
int deflateEnd OF((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 success, 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 OF((z_streamp strm));
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 of
inflate. If zalloc and zfree are set to Z_NULL, inflateInit updates them to
use default allocation functions.
inflateInit returns Z_OK if success, 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, or Z_STREAM_ERROR if the parameters are
invalid, such as a null pointer to the structure. msg is set to null if
there is no error message. inflateInit does not perform any decompression
apart from possibly reading the zlib header if present: actual decompression
will be done by inflate(). (So next_in and avail_in may be modified, but
next_out and avail_out are unused and unchanged.) The current implementation
of inflateInit() does not process any header information -- that is deferred
until inflate() is called.
int inflate OF((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 of 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 of 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 of
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,
Z_BLOCK, or Z_TREES. 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. data_type is set as noted here every time inflate() returns for all
flush options, and so can be used to determine the amount of currently
consumed input in bits.
The Z_TREES option behaves as Z_BLOCK does, but it also returns when the
end of each deflate block header is reached, before any actual data in that
block is decoded. This allows the caller to determine the length of the
deflate block header for later use in random access within a deflate block.
256 is added to the value of strm->data_type when inflate() returns
immediately after reaching the end of the deflate block header.
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 of 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 of the uncompressed data for the
operation to complete. (The size of the uncompressed data may have been
saved by the compressor for this purpose.) The use of Z_FINISH is not
required to perform an inflation in one step. However it may be used to
inform inflate that a faster approach can be used for the single inflate()
call. Z_FINISH also informs inflate to not maintain a sliding window if the
stream completes, which reduces inflate's memory footprint. If the stream
does not complete, either because not all of the stream is provided or not
enough output space is provided, then a sliding window will be allocated and
inflate() can be called again to continue the operation as if Z_NO_FLUSH had
been used.
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 effects of the flush parameter in this implementation are
on the return value of inflate() as noted below, when inflate() returns early
when Z_BLOCK or Z_TREES is used, and when inflate() avoids the allocation of
memory for a sliding window when Z_FINISH 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 adler32
checksum is equal to that saved by the compressor and returns Z_STREAM_END
only if the checksum is correct.
inflate() can decompress and check either zlib-wrapped or gzip-wrapped
deflate data. The header type is detected automatically, if requested when
initializing with inflateInit2(). 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. When processing
gzip-wrapped deflate data, strm->adler32 is set to the CRC-32 of the output
producted so far. The CRC-32 is checked against the gzip 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
next_in or next_out was Z_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 decompressing. 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 OF((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 success, 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 OF((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 adler32 check value.
windowBits can also be greater than 15 for optional gzip encoding. Add
16 to windowBits to write a simple gzip header and trailer around the
compressed data instead of a zlib wrapper. The gzip header will have no
file name, no extra data, no comment, no modification time (set to zero), no
header crc, and the operating system will be set to 255 (unknown). If a
gzip stream is being written, strm->adler is a crc32 instead of an adler32.
The memLevel parameter specifies how much memory should be allocated
for the internal compression state. memLevel=1 uses minimum memory but is
slow and reduces compression ratio; memLevel=9 uses maximum memory for
optimal speed. The default value is 8. See zconf.h for total memory usage
as a function of windowBits and memLevel.
The strategy parameter is used to tune the compression algorithm. Use the
value Z_DEFAULT_STRATEGY for normal data, Z_FILTERED for data produced by a
filter (or predictor), Z_HUFFMAN_ONLY to force Huffman encoding only (no
string match), or Z_RLE to limit match distances to one (run-length
encoding). Filtered data consists mostly of small values with a somewhat
random distribution. In this case, the compression algorithm is tuned to
compress them better. The effect of Z_FILTERED is to force more Huffman
coding and less string matching; it is somewhat intermediate between
Z_DEFAULT_STRATEGY and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as
fast as Z_HUFFMAN_ONLY, but give better compression for PNG image data. The
strategy parameter only affects the compression ratio but not the
correctness of the compressed output even if it is not set appropriately.
Z_FIXED prevents the use of dynamic Huffman codes, allowing for a simpler
decoder for special applications.
deflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
memory, Z_STREAM_ERROR if any parameter is invalid (such as an invalid
method), or 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. deflateInit2 does not perform any
compression: this will be done by deflate().
int deflateSetDictionary OF((z_streamp strm,
const Bytef *dictionary,
uInt dictLength));
Initializes the compression dictionary from the given byte sequence
without producing any compressed output. When using the zlib format, this
function must be called immediately after deflateInit, deflateInit2 or
deflateReset, and before any call of deflate. When doing raw deflate, this
function must be called either before any call of deflate, or immediately
after the completion of a deflate block, i.e. after all input has been
consumed and all output has been delivered when using any of the flush
options Z_BLOCK, Z_PARTIAL_FLUSH, Z_SYNC_FLUSH, or Z_FULL_FLUSH. 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
provided in deflateInit or deflateInit2. Thus the strings most likely to be
useful should be put at the end of the dictionary, not at the front. In
addition, the current implementation of deflate will use at most the window
size minus 262 bytes of the provided dictionary.
Upon return of this function, strm->adler is set to the adler32 value
of the dictionary; the decompressor may later use this value to determine
which dictionary has been used by the compressor. (The adler32 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
adler32 value is not computed and strm->adler is not set.
deflateSetDictionary returns Z_OK if success, or Z_STREAM_ERROR if a
parameter is invalid (e.g. dictionary being Z_NULL) or the stream state is
inconsistent (for example if deflate has already been called for this stream
or if not at a block boundary for raw deflate). deflateSetDictionary does
not perform any compression: this will be done by deflate().
int deflateCopy OF((z_streamp dest,
z_streamp source));
Sets the destination stream as a complete copy of the source stream.
This function can be useful when several compression strategies will be
tried, for example when there are several ways of pre-processing the input
data with a filter. The streams that will be discarded should then be freed
by calling deflateEnd. Note that deflateCopy duplicates the internal
compression state which can be quite large, so this strategy is slow and can
consume lots of memory.
deflateCopy returns Z_OK if success, Z_MEM_ERROR if there was not
enough memory, Z_STREAM_ERROR if the source stream state was inconsistent
(such as zalloc being Z_NULL). msg is left unchanged in both source and
destination.
int deflateReset OF((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 success, or Z_STREAM_ERROR if the source
stream state was inconsistent (such as zalloc or state being Z_NULL).
int deflateParams OF((z_streamp strm,
int level,
int strategy));
Dynamically update 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 of deflate().
Before the call of deflateParams, the stream state must be set as for
a call of 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 success, Z_STREAM_ERROR if the source
stream state was inconsistent or if a parameter was invalid, Z_BUF_ERROR if
strm->avail_out was zero.
int deflateTune OF((z_streamp strm,
int good_length,
int max_lazy,
int nice_length,
int max_chain));
Fine tune deflate's internal compression parameters. This should only be
used by someone who understands the algorithm used by zlib's deflate for
searching for the best matching string, and even then only by the most
fanatic optimizer trying to squeeze out the last compressed bit for their
specific input data. Read the deflate.c source code for the meaning of the
max_lazy, good_length, nice_length, and max_chain parameters.
deflateTune() can be called after deflateInit() or deflateInit2(), and
returns Z_OK on success, or Z_STREAM_ERROR for an invalid deflate stream.
uLong deflateBound OF((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(), and after deflateSetHeader(), if used. This would be used
to allocate an output buffer for deflation in a single pass, and so would be
called before deflate(). If that first deflate() call is provided the
sourceLen input bytes, an output buffer allocated to the size returned by
deflateBound(), and the flush value Z_FINISH, then deflate() is guaranteed
to return Z_STREAM_END. Note that it is possible for the compressed size to
be larger than the value returned by deflateBound() if flush options other
than Z_FINISH or Z_NO_FLUSH are used.
int deflatePending OF((z_streamp strm,
unsigned *pending,
int *bits));
deflatePending() returns the number of bytes and bits of output that have
been generated, but not yet provided in the available output. The bytes not
provided would be due to the available output space having being consumed.
The number of bits of output not provided are between 0 and 7, where they
await more bits to join them in order to fill out a full byte. If pending
or bits are Z_NULL, then those values are not set.
deflatePending returns Z_OK if success, or Z_STREAM_ERROR if the source
stream state was inconsistent.
int deflatePrime OF((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 success, Z_BUF_ERROR if there was not enough
room in the internal buffer to insert the bits, or Z_STREAM_ERROR if the
source stream state was inconsistent.
int deflateSetHeader OF((z_streamp strm,
gz_headerp head));
deflateSetHeader() provides gzip header information for when a gzip
stream is requested by deflateInit2(). deflateSetHeader() may be called
after deflateInit2() or deflateReset() and before the first call of
deflate(). The text, time, os, extra field, name, and comment information
in the provided gz_header structure are written to the gzip header (xflag is
ignored -- the extra flags are set according to the compression level). The
caller must assure that, if not Z_NULL, name and comment are terminated with
a zero byte, and that if extra is not Z_NULL, that extra_len bytes are
available there. If hcrc is true, a gzip header crc is included. Note that
the current versions of the command-line version of gzip (up through version
1.3.x) do not support header crc's, and will report that it is a "multi-part
gzip file" and give up.
If deflateSetHeader is not used, the default gzip header has text false,
the time set to zero, and os set to 255, with no extra, name, or comment
fields. The gzip header is returned to the default state by deflateReset().
deflateSetHeader returns Z_OK if success, or Z_STREAM_ERROR if the source
stream state was inconsistent.
int inflateInit2 OF((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 zero to request that inflate use the window size in
the zlib header of the compressed stream.
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 adler32 or a crc32 be applied to
the uncompressed data as is done in the zlib, gzip, and zip formats. For
most applications, the zlib format should be used as is. Note that comments
above on the use in deflateInit2() applies to the magnitude of windowBits.
windowBits can also be greater than 15 for optional gzip decoding. Add
32 to windowBits to enable zlib and gzip decoding with automatic header
detection, or add 16 to decode only the gzip format (the zlib format will
return a Z_DATA_ERROR). If a gzip stream is being decoded, strm->adler is a
crc32 instead of an adler32.
inflateInit2 returns Z_OK if success, 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, or Z_STREAM_ERROR if the parameters are
invalid, such as a null pointer to the structure. msg is set to null if
there is no error message. inflateInit2 does not perform any decompression
apart from possibly reading the zlib header if present: actual decompression
will be done by inflate(). (So next_in and avail_in may be modified, but
next_out and avail_out are unused and unchanged.) The current implementation
of inflateInit2() does not process any header information -- that is
deferred until inflate() is called.
int inflateSetDictionary OF((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 of inflate,
if that call returned Z_NEED_DICT. The dictionary chosen by the compressor
can be determined from the adler32 value returned by that call of inflate.
The compressor and decompressor must use exactly the same dictionary (see
deflateSetDictionary). For raw inflate, this function can be called at any
time to set the dictionary. If the provided dictionary is smaller than the
window and there is already data in the window, then the provided dictionary
will amend what's there. The application must insure that the dictionary
that was used for compression is provided.
inflateSetDictionary returns Z_OK if success, Z_STREAM_ERROR if a
parameter is invalid (e.g. dictionary being Z_NULL) or the stream state is
inconsistent, Z_DATA_ERROR if the given dictionary doesn't match the
expected one (incorrect adler32 value). inflateSetDictionary does not
perform any decompression: this will be done by subsequent calls of
inflate().
int inflateGetDictionary OF((z_streamp strm,
Bytef *dictionary,
uInt *dictLength));
Returns the sliding dictionary being maintained by inflate. dictLength is
set to the number of bytes in the dictionary, and that many bytes are copied
to dictionary. dictionary must have enough space, where 32768 bytes is
always enough. If inflateGetDictionary() is called with dictionary equal to
Z_NULL, then only the dictionary length is returned, and nothing is copied.
Similary, if dictLength is Z_NULL, then it is not set.
inflateGetDictionary returns Z_OK on success, or Z_STREAM_ERROR if the
stream state is inconsistent.
int inflateSync OF((z_streamp strm));
Skips invalid compressed data until a possible full flush point (see above
for the description of deflate with Z_FULL_FLUSH) can be found, or until all
available input is skipped. No output is provided.
inflateSync searches for a 00 00 FF FF pattern in the compressed data.
All full flush points have this pattern, but not all occurrences of this
pattern are full flush points.
inflateSync returns Z_OK if a possible 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 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 OF((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 Z_NULL). msg is left unchanged in both source and
destination.
int inflateReset OF((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 success, or Z_STREAM_ERROR if the source
stream state was inconsistent (such as zalloc or state being Z_NULL).
int inflateReset2 OF((z_streamp strm,
int windowBits));
This function is the same as inflateReset, but it also permits changing
the wrap and window size requests. The windowBits parameter is interpreted
the same as it is for inflateInit2.
inflateReset2 returns Z_OK if success, or Z_STREAM_ERROR if the source
stream state was inconsistent (such as zalloc or state being Z_NULL), or if
the windowBits parameter is invalid.
int inflatePrime OF((z_streamp strm,
int bits,
int value));
This function inserts bits in the inflate input stream. The intent is
that this function is used to start inflating at a bit position in the
middle of a byte. The provided bits will be used before any bytes are used
from next_in. This function should only be used with raw inflate, and
should be used before the first inflate() call after inflateInit2() or
inflateReset(). bits must be less than or equal to 16, and that many of the
least significant bits of value will be inserted in the input.
If bits is negative, then the input stream bit buffer is emptied. Then
inflatePrime() can be called again to put bits in the buffer. This is used
to clear out bits leftover after feeding inflate a block description prior
to feeding inflate codes.
inflatePrime returns Z_OK if success, or Z_STREAM_ERROR if the source
stream state was inconsistent.
long inflateMark OF((z_streamp strm));
This function returns two values, one in the lower 16 bits of the return
value, and the other in the remaining upper bits, obtained by shifting the
return value down 16 bits. If the upper value is -1 and the lower value is
zero, then inflate() is currently decoding information outside of a block.
If the upper value is -1 and the lower value is non-zero, then inflate is in
the middle of a stored block, with the lower value equaling the number of
bytes from the input remaining to copy. If the upper value is not -1, then
it is the number of bits back from the current bit position in the input of
the code (literal or length/distance pair) currently being processed. In
that case the lower value is the number of bytes already emitted for that
code.
A code is being processed if inflate is waiting for more input to complete
decoding of the code, or if it has completed decoding but is waiting for
more output space to write the literal or match data.
inflateMark() is used to mark locations in the input data for random
access, which may be at bit positions, and to note those cases where the
output of a code may span boundaries of random access blocks. The current
location in the input stream can be determined from avail_in and data_type
as noted in the description for the Z_BLOCK flush parameter for inflate.
inflateMark returns the value noted above or -1 << 16 if the provided
source stream state was inconsistent.
int inflateGetHeader OF((z_streamp strm,
gz_headerp head));
inflateGetHeader() requests that gzip header information be stored in the
provided gz_header structure. inflateGetHeader() may be called after
inflateInit2() or inflateReset(), and before the first call of inflate().
As inflate() processes the gzip stream, head->done is zero until the header
is completed, at which time head->done is set to one. If a zlib stream is
being decoded, then head->done is set to -1 to indicate that there will be
no gzip header information forthcoming. Note that Z_BLOCK or Z_TREES can be
used to force inflate() to return immediately after header processing is
complete and before any actual data is decompressed.
The text, time, xflags, and os fields are filled in with the gzip header
contents. hcrc is set to true if there is a header CRC. (The header CRC
was valid if done is set to one.) If extra is not Z_NULL, then extra_max
contains the maximum number of bytes to write to extra. Once done is true,
extra_len contains the actual extra field length, and extra contains the
extra field, or that field truncated if extra_max is less than extra_len.
If name is not Z_NULL, then up to name_max characters are written there,
terminated with a zero unless the length is greater than name_max. If
comment is not Z_NULL, then up to comm_max characters are written there,
terminated with a zero unless the length is greater than comm_max. When any
of extra, name, or comment are not Z_NULL and the respective field is not
present in the header, then that field is set to Z_NULL to signal its
absence. This allows the use of deflateSetHeader() with the returned
structure to duplicate the header. However if those fields are set to
allocated memory, then the application will need to save those pointers
elsewhere so that they can be eventually freed.
If inflateGetHeader is not used, then the header information is simply
discarded. The header is always checked for validity, including the header
CRC if present. inflateReset() will reset the process to discard the header
information. The application would need to call inflateGetHeader() again to
retrieve the header from the next gzip stream.
inflateGetHeader returns Z_OK if success, or Z_STREAM_ERROR if the source
stream state was inconsistent.
int inflateBackInit OF((z_streamp 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.
typedef unsigned (*in_func) OF((void FAR *,
z_const unsigned char FAR * FAR *));
typedef int (*out_func) OF((void FAR *, unsigned char FAR *, unsigned));
int inflateBack OF((z_streamp 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 potentially 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. inflate() can be faster on modern CPUs when used with large
buffers. inflateBack() trusts the application to not change the output
buffer passed by the output function, at least until inflateBack() returns.
inflateBackInit() must be called first to allocate the internal state
and to initialize the state with the user-provided window buffer.
inflateBack() may then be used multiple times to inflate a complete, raw
deflate stream with each call. inflateBackEnd() is then called to free the
allocated state.
A raw deflate stream is one with no zlib or gzip header or trailer.
This routine would normally be used in a utility that reads zip or gzip
files and writes out uncompressed files. The utility would decode the
header and process the trailer on its own, hence this routine expects only
the raw deflate stream to decompress. This is different from the normal
behavior of inflate(), which expects either a zlib or gzip header and
trailer around the deflate stream.
inflateBack() uses two subroutines supplied by the caller that are then
called by inflateBack() for input and output. inflateBack() calls those
routines until it reads a complete deflate stream and writes out all of the
uncompressed data, or until it encounters an error. The function's
parameters and return types are defined above in the in_func and out_func
typedefs. inflateBack() will call in(in_desc, &buf) which should return the
number of bytes of provided input, and a pointer to that input in buf. If
there is no input available, in() must return zero--buf is ignored in that
case--and inflateBack() will return a buffer error. inflateBack() will call
out(out_desc, buf, len) to write the uncompressed data buf[0..len-1]. out()
should return zero on success, or non-zero on failure. If out() returns
non-zero, inflateBack() will return with an error. Neither in() nor out()
are permitted to change the contents of the window provided to
inflateBackInit(), which is also the buffer that out() uses to write from.
The length written by out() will be at most the window size. Any non-zero
amount of input may be provided by in().
For convenience, inflateBack() can be provided input on the first call by
setting strm->next_in and strm->avail_in. If that input is exhausted, then
in() will be called. Therefore strm->next_in must be initialized before
calling inflateBack(). If strm->next_in is Z_NULL, then in() will be called
immediately for input. If strm->next_in is not Z_NULL, then strm->avail_in
must also be initialized, and then if strm->avail_in is not zero, input will
initially be taken from strm->next_in[0 .. strm->avail_in - 1].
The in_desc and out_desc parameters of inflateBack() is 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_in 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 OF((z_streamp 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 OF((void));
Return flags indicating compile-time options.
Type sizes, two bits each, 00 = 16 bits, 01 = 32, 10 = 64, 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)
#ifndef Z_SOLO
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 be modified if
you need special options.
int compress OF((Bytef *dest, uLongf *destLen,
const Bytef *source, uLong sourceLen));
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.
compress returns Z_OK if success, Z_MEM_ERROR if there was not
enough memory, Z_BUF_ERROR if there was not enough room in the output
buffer.
int compress2 OF((Bytef *dest, uLongf *destLen,
const Bytef *source, uLong sourceLen,
int level));
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 success, Z_MEM_ERROR if there was not enough
memory, Z_BUF_ERROR if there was not enough room in the output buffer,
Z_STREAM_ERROR if the level parameter is invalid.
uLong compressBound OF((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 OF((Bytef *dest, uLongf *destLen,
const Bytef *source, uLong sourceLen));
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 uncompressed buffer.
uncompress returns Z_OK if success, 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. In
the case where there is not enough room, uncompress() will fill the output
buffer with the uncompressed data up to that point.
gzip file access functions
This library supports reading and writing files in gzip (.gz) format with
an interface similar to that of stdio, 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.
typedef struct gzFile_s *gzFile; ;semi-opaque gzip file descriptor
gzFile gzopen OF((const char *path, const char *mode));
Opens a gzip (.gz) file for reading or writing. The mode parameter is as
in fopen ("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", 'R' for run-length encoding as in "wb1R", or 'F'
for fixed code compression as in "wb9F". (See the description of
deflateInit2 for more information about the strategy parameter.) 'T' will
request transparent writing or appending with no compression and not using
the gzip format.
"a" can be used instead of "w" to request that the gzip stream that will
be written be appended to the file. "+" will result in an error, since
reading and writing to the same gzip file is not supported. The addition of
"x" when writing will create the file exclusively, which fails if the file
already exists. On systems that support it, the addition of "e" when
reading or writing will set the flag to close the file on an execve() call.
These functions, as well as gzip, will read and decode a sequence of gzip
streams in a file. The append function of gzopen() can be used to create
such a file. (Also see gzflush() for another way to do this.) When
appending, gzopen does not test whether the file begins with a gzip stream,
nor does it look for the end of the gzip streams to begin appending. gzopen
will simply append a gzip stream to the existing file.
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. When
reading, this will be detected automatically by looking for the magic two-
byte gzip header.
gzopen returns NULL if the file could not be opened, if there was
insufficient memory to allocate the gzFile state, or if an invalid mode was
specified (an 'r', 'w', or 'a' was not provided, or '+' was provided).
errno can be checked to determine if the reason gzopen failed was that the
file could not be opened.
gzFile gzdopen OF((int fd, const char *mode));
gzdopen associates a gzFile with the file descriptor fd. File descriptors
are obtained from calls like open, dup, creat, pipe or fileno (if the file
has been previously opened with fopen). The mode parameter is as in gzopen.
The next call of 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 fd = dup(fd_keep); gz = gzdopen(fd,
mode);. The duplicated descriptor should be saved to avoid a leak, since
gzdopen does not close fd if it fails. If you are using fileno() to get the
file descriptor from a FILE *, then you will have to use dup() to avoid
double-close()ing the file descriptor. Both gzclose() and fclose() will
close the associated file descriptor, so they need to have different file
descriptors.
gzdopen returns NULL if there was insufficient memory to allocate the
gzFile state, if an invalid mode was specified (an 'r', 'w', or 'a' was not
provided, or '+' was provided), or if fd is -1. The file descriptor is not
used until the next gz* read, write, seek, or close operation, so gzdopen
will not detect if fd is invalid (unless fd is -1).
int gzbuffer OF((gzFile file, unsigned size));
Set the internal buffer size used by this library's functions. The
default buffer size is 8192 bytes. This function must be called after
gzopen() or gzdopen(), and before any other calls that read or write the
file. The buffer memory allocation is always deferred to the first read or
write. Two buffers are allocated, either both of the specified size when
writing, or one of the specified size and the other twice that size when
reading. A larger buffer size of, for example, 64K or 128K bytes will
noticeably increase the speed of decompression (reading).
The new buffer size also affects the maximum length for gzprintf().
gzbuffer() returns 0 on success, or -1 on failure, such as being called
too late.
int gzsetparams OF((gzFile file, int level, int strategy));
Dynamically update the compression level or strategy. See the description
of deflateInit2 for the meaning of these parameters.
gzsetparams returns Z_OK if success, or Z_STREAM_ERROR if the file was not
opened for writing.
int gzread OF((gzFile file, voidp buf, unsigned len));
Reads the given number of uncompressed bytes from the compressed file. If
the input file is not in gzip format, gzread copies the given number of
bytes into the buffer directly from the file.
After reaching the end of a gzip stream in the input, gzread will continue
to read, looking for another gzip stream. Any number of gzip streams may be
concatenated in the input file, and will all be decompressed by gzread().
If something other than a gzip stream is encountered after a gzip stream,
that remaining trailing garbage is ignored (and no error is returned).
gzread can be used to read a gzip file that is being concurrently written.
Upon reaching the end of the input, gzread will return with the available
data. If the error code returned by gzerror is Z_OK or Z_BUF_ERROR, then
gzclearerr can be used to clear the end of file indicator in order to permit
gzread to be tried again. Z_OK indicates that a gzip stream was completed
on the last gzread. Z_BUF_ERROR indicates that the input file ended in the
middle of a gzip stream. Note that gzread does not return -1 in the event
of an incomplete gzip stream. This error is deferred until gzclose(), which
will return Z_BUF_ERROR if the last gzread ended in the middle of a gzip
stream. Alternatively, gzerror can be used before gzclose to detect this
case.
gzread returns the number of uncompressed bytes actually read, less than
len for end of file, or -1 for error.
int gzwrite OF((gzFile file,
voidpc buf, unsigned len));
Writes the given number of uncompressed bytes into the compressed file.
gzwrite returns the number of uncompressed bytes written or 0 in case of
error.
int ZEXPORTVA gzprintf Z_ARG((gzFile file, const char *format, ...));
Converts, formats, and writes the arguments to the compressed file under
control of the format string, as in fprintf. gzprintf returns the number of
uncompressed bytes actually written, or 0 in case of error. The number of
uncompressed bytes written is limited to 8191, or one less than the buffer
size given to gzbuffer(). The caller should assure 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. This can be determined using
zlibCompileFlags().
int gzputs OF((gzFile file, const char *s));
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 OF((gzFile file, char *buf, int len));
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. If any characters are read or if len == 1, the
string is terminated with a null character. If no characters are read due
to an end-of-file or len < 1, then the buffer is left untouched.
gzgets returns buf which is a null-terminated string, or it returns NULL
for end-of-file or in case of error. If there was an error, the contents at
buf are indeterminate.
int gzputc OF((gzFile file, int c));
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 OF((gzFile file));
Reads one byte from the compressed file. gzgetc returns this byte or -1
in case of end of file or error. This is implemented as a macro for speed.
As such, it does not do all of the checking the other functions do. I.e.
it does not check to see if file is NULL, nor whether the structure file
points to has been clobbered or not.
int gzungetc OF((int c, gzFile file));
Push one character back onto the stream to be read as the first character
on the next read. At least one character of push-back is allowed.
gzungetc() returns the character pushed, or -1 on failure. gzungetc() will
fail if c is -1, and may fail if a character has been pushed but not read
yet. If gzungetc is used immediately after gzopen or gzdopen, at least the
output buffer size of pushed characters is allowed. (See gzbuffer above.)
The pushed character will be discarded if the stream is repositioned with
gzseek() or gzrewind().
int gzflush OF((gzFile file, int flush));
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 is only permitted when writing.
If the flush parameter is Z_FINISH, the remaining data is written and the
gzip stream is completed in the output. If gzwrite() is called again, a new
gzip stream will be started in the output. gzread() is able to read such
concatented gzip streams.
gzflush should be called only when strictly necessary because it will
degrade compression if called too often.
z_off_t gzseek OF((gzFile file,
z_off_t offset, int whence));
Sets the starting position for the next gzread or gzwrite on the given
compressed file. The offset represents a number of bytes in the
uncompressed data stream. The whence parameter is defined as in lseek(2);
the value SEEK_END is not supported.
If the file is opened for reading, this function is emulated but can be
extremely slow. If the file is opened for writing, only forward seeks are
supported; gzseek then compresses a sequence of zeroes up to the new
starting position.
gzseek returns the resulting offset location as measured in bytes from
the beginning of the uncompressed stream, or -1 in case of error, in
particular if the file is opened for writing and the new starting position
would be before the current position.
int gzrewind OF((gzFile file));
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 OF((gzFile file));
Returns the starting position for the next gzread or gzwrite on the given
compressed file. This position represents a number of bytes in the
uncompressed data stream, and is zero when starting, even if appending or
reading a gzip stream from the middle of a file using gzdopen().
gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR)
z_off_t gzoffset OF((gzFile file));
Returns the current offset in the file being read or written. This offset
includes the count of bytes that precede the gzip stream, for example when
appending or when using gzdopen() for reading. When reading, the offset
does not include as yet unused buffered input. This information can be used
for a progress indicator. On error, gzoffset() returns -1.
int gzeof OF((gzFile file));
Returns true (1) if the end-of-file indicator has been set while reading,
false (0) otherwise. Note that the end-of-file indicator is set only if the
read tried to go past the end of the input, but came up short. Therefore,
just like feof(), gzeof() may return false even if there is no more data to
read, in the event that the last read request was for the exact number of
bytes remaining in the input file. This will happen if the input file size
is an exact multiple of the buffer size.
If gzeof() returns true, then the read functions will return no more data,
unless the end-of-file indicator is reset by gzclearerr() and the input file
has grown since the previous end of file was detected.
int gzdirect OF((gzFile file));
Returns true (1) if file is being copied directly while reading, or false
(0) if file is a gzip stream being decompressed.
If the input file is empty, gzdirect() will return true, since the input
does not contain a gzip stream.
If gzdirect() is used immediately after gzopen() or gzdopen() it will
cause buffers to be allocated to allow reading the file to determine if it
is a gzip file. Therefore if gzbuffer() is used, it should be called before
gzdirect().
When writing, gzdirect() returns true (1) if transparent writing was
requested ("wT" for the gzopen() mode), or false (0) otherwise. (Note:
gzdirect() is not needed when writing. Transparent writing must be
explicitly requested, so the application already knows the answer. When
linking statically, using gzdirect() will include all of the zlib code for
gzip file reading and decompression, which may not be desired.)
int gzclose OF((gzFile file));
Flushes all pending output if necessary, closes the compressed file and
deallocates the (de)compression state. Note that once file is closed, you
cannot call gzerror with file, since its structures have been deallocated.
gzclose must not be called more than once on the same file, just as free
must not be called more than once on the same allocation.
gzclose will return Z_STREAM_ERROR if file is not valid, Z_ERRNO on a
file operation error, Z_MEM_ERROR if out of memory, Z_BUF_ERROR if the
last read ended in the middle of a gzip stream, or Z_OK on success.
int gzclose_r OF((gzFile file));
int gzclose_w OF((gzFile file));
Same as gzclose(), but gzclose_r() is only for use when reading, and
gzclose_w() is only for use when writing or appending. The advantage to
using these instead of gzclose() is that they avoid linking in zlib
compression or decompression code that is not used when only reading or only
writing respectively. If gzclose() is used, then both compression and
decompression code will be included the application when linking to a static
zlib library.
const char * gzerror OF((gzFile file, int *errnum));
Returns the error message for the last error which occurred on the given
compressed file. errnum is set to zlib error number. If an error occurred
in the file system and not in the compression library, errnum is set to
Z_ERRNO and the application may consult errno to get the exact error code.
The application must not modify the returned string. Future calls to
this function may invalidate the previously returned string. If file is
closed, then the string previously returned by gzerror will no longer be
available.
gzerror() should be used to distinguish errors from end-of-file for those
functions above that do not distinguish those cases in their return values.
void gzclearerr OF((gzFile file));
Clears the error and end-of-file flags for file. This is analogous to the
clearerr() function in stdio. This is useful for continuing to read a gzip
file that is being written concurrently.
end if ;!Z_SOLO
checksum functions
These functions are not related to compression but are exported
anyway because they might be useful in applications using the compression
library.
uLong adler32 OF((uLong adler, const Bytef *buf, uInt len));
Update a running Adler-32 checksum with the bytes buf[0..len-1] and
return the updated checksum. If buf is Z_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 adler32_combine OF((uLong adler1, uLong adler2,
z_off_t len2));
Combine two Adler-32 checksums into one. For two sequences of bytes, seq1
and seq2 with lengths len1 and len2, Adler-32 checksums were calculated for
each, adler1 and adler2. adler32_combine() returns the Adler-32 checksum of
seq1 and seq2 concatenated, requiring only adler1, adler2, and len2. Note
that the z_off_t type (like off_t) is a signed integer. If len2 is
negative, the result has no meaning or utility.
uLong crc32 OF((uLong crc, const Bytef *buf, uInt len));
Update a running CRC-32 with the bytes buf[0..len-1] and return the
updated CRC-32. If buf is Z_NULL, this function returns the required
initial value for the crc. Pre- and post-conditioning (one's complement) is
performed within this function so it shouldn't be done by the application.
Usage example:
uLong crc = crc32(0L, Z_NULL, 0);
while (read_buffer(buffer, length) != EOF) {
crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();
uLong crc32_combine OF((uLong crc1, uLong crc2, z_off_t len2));
Combine two CRC-32 check values into one. For two sequences of bytes,
seq1 and seq2 with lengths len1 and len2, CRC-32 check values were
calculated for each, crc1 and crc2. crc32_combine() returns the CRC-32
check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and
len2.