2. ZLIB#

group ZLIB_API

The ‘zlib’ compression library provides in-memory compression and decompression functions, including integrity checks of the uncompressed data. This version of the library supports only one compression method (deflation) but other algorithms will be added later and will have the same stream interface.

Compression can be done in a single step if the buffers are large enough, or can be done by repeated calls of the compression function. In the latter case, the application must provide more input and/or consume the output (providing more output space) before each call.

The compressed data format used by default by the in-memory functions is the zlib format, which is a zlib wrapper documented in RFC 1950, wrapped around a deflate stream, which is itself documented in RFC 1951.

The library also supports reading and writing files in gzip (.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.

This library can optionally read and write gzip and raw deflate streams in memory as well.

The zlib format was designed to be compact and fast for use in memory and on communications channels. The gzip format was designed for single- file compression on file systems, has a larger header than zlib to maintain directory information, and uses a different, slower check method than zlib.

The library does not install any signal handler. The decoder checks the consistency of the compressed data, so the library should never crash even in the case of corrupted input.

The application must update next_in and avail_in when avail_in has dropped to zero. It must update next_out and avail_out when avail_out has dropped to zero. The application must initialize zalloc, zfree and opaque before calling the init function. All other fields are set by the compression library and must not be updated by the application.

The opaque value provided by the application will be passed as the first parameter for calls of zalloc and zfree. This can be useful for custom memory management. The compression library attaches no meaning to the opaque value.

zalloc must return Z_NULL if there is not enough memory for the object. If zlib is used in a multi-threaded application, zalloc and zfree must be thread safe. In that case, zlib is thread-safe. When zalloc and zfree are Z_NULL on entry to the initialization function, they are set to internal routines that use the standard library functions malloc() and free().

On 16-bit systems, the functions zalloc and zfree must be able to allocate exactly 65536 bytes, but will not be required to allocate more than this if the symbol MAXSEG_64K is defined (see zconf.h).

The fields total_in and total_out can be used for statistics or progress reports. After compression, total_in holds the total size of the uncompressed data and may be saved for use by the decompressor (particularly if the decompressor wants to decompress everything in a single step).

Warning

On MSDOS, pointers returned by zalloc for objects of exactly 65536 bytes must have their offset normalized to zero. The default allocation function provided by this library ensures this (see zutil.c). To reduce memory requirements and avoid any allocation of 64K objects, at the expense of compression ratio, compile the library with -DMAX_WBITS=14 (see zconf.h).

Advanced functions

unsigned(* in_func )(void FAR *, z_const unsigned char FAR *FAR *): This is used for reading input from in_desc.

int(* out_func )(void FAR *, unsigned char FAR *, unsigned): It is used for writing to output.

int deflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt dictLength)#

Initializes the compression dictionary from the given byte sequence without producing any compressed output.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
dictionary	in	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.
dictionary	in	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.
dictLength	in	Length of dictionary.

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).

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 Adler-32 value of the dictionary; the decompressor may later use this value to determine which dictionary has been used by the compressor. (The Adler-32 value applies to the whole dictionary even if only a subset of the dictionary is actually used by the compressor.) If a raw deflate was requested, then the Adler-32 value is not computed and strm->adler is not set.

Note

deflateSetDictionary does not perform any compression: this will be done by deflate().

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If a parameter is invalid (e.g. dictionary being Z_NULL) or the stream state is inconsistent (example if deflate has already been called for this stream or if not at a block boundary for raw deflate).

int deflateGetDictionary(z_streamp strm, Bytef *dictionary, uInt *dictLength)#

Returns the sliding dictionary being maintained by deflate.

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 deflateGetDictionary() 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
dictionary	out	Returns the sliding dictionary being maintained by deflate (stored in the buffer pointed by dictionary).
dictLength	in	It is set to the number of bytes in the dictionary, and that many bytes are copied to dictionary.

deflateGetDictionary() may return a length less than the window size, even when more than the window size in input has been provided. It may return up to 258 bytes less in that case, due to how zlib’s implementation of deflate manages the sliding window and lookahead for matches, where matches can be up to 258 bytes long. If the application needs the last window-size bytes of input, then that would need to be saved by the application outside of zlib.

Returns:

Result	Description
Z_OK	deflateGetDictionary returns Z_OK on success.
Z_STREAM_ERROR	If the stream state is inconsistent.

int deflateCopy(z_streamp dest, z_streamp source)#

Sets the destination stream as a complete copy of the source stream.

Parameters	Direction	Description
dest	in,out	This is a pointer to which we want to copy *source data, it works as a handle for compression, refer z_stream_s for more info.
source	in,out	This points to data from where we want to copy data, it works as a handle for compression, refer z_stream_s for more info.

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.

Returns:

Result	Description
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(z_streamp strm)#

This function is equivalent to deflateEnd followed by deflateInit, but does not free and reallocate the internal compression state.

The stream will leave the compression level and any other attributes that may have been set unchanged. total_in, total_out, adler, and msg are initialized.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the source stream state was inconsistent.(such as zalloc or state being Z_NULL).

int deflateParams(z_streamp strm, int level, int strategy)#

Dynamically update the compression level and compression strategy.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
level	out	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).
strategy	in,out	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 approach (which is a function of the level) or the strategy is changed, and if any input has been consumed in a previous deflate() call, then the input available so far is compressed with the old level and strategy using deflate(strm, Z_BLOCK).
		There are three approaches for the compression levels 0, 1..3, and 4..9 respectively. The new level and strategy will take effect at the next call of deflate().

If a deflate(strm, Z_BLOCK) is performed by deflateParams(), and it does not have enough output space to complete, then the parameter change will not take effect. In this case, deflateParams() can be called again with the same parameters and more output space to try again.

In order to assure a change in the parameters on the first try, the deflate stream should be flushed using deflate() with Z_BLOCK or other flush request until strm.avail_out is not zero, before calling deflateParams(). Then no more input data should be provided before the deflateParams() call. If this is done, the old level and strategy will be applied to the data compressed before deflateParams(), and the new level and strategy will be applied to the the data compressed after deflateParams().

Note

In the case of a Z_BUF_ERROR, the parameters are not changed. A return value of Z_BUF_ERROR is not fatal, in which case deflateParams() can be retried with more output space.

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the stream state is inconsistent or if a parameter was invalid.
Z_BUF_ERROR	If there was not enough output space to complete the compression of the available input data before a change in the strategy or approach.

int deflateTune(z_streamp strm, int good_length, int max_lazy, int nice_length, int max_chain)#

Fine tune deflate’s internal compression parameters using this function.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
good_length	in	reduce lazy search above this match length.
max_lazy	in	do not perform lazy search above this match length.
nice_length	in	quit search above this match length
max_chain	out	max number of sub-strings with which the given string has to be compared, given that initial hash is same.

Warning

This function 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.

Returns:

deflateTune() can be called after deflateInit() or deflateInit2(), and it returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	For an invalid deflate stream.

uLong deflateBound(z_streamp strm, uLong sourceLen)#

This function returns an upper bound on the compressed size after deflation of sourceLen bytes.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
sourceLen	out	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().

Note

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.

Returns:

Result	Description
Success	Returns an upper bound on the compressed size after deflation of sourceLen bytes.

int deflatePending(z_streamp strm, unsigned *pending, int *bits)#

This function returns the number of bytes and bits of output that have been generated, but not yet provided in the available output.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
pending	out	returns the number of bytes of output that have been generated, but not yet provided in the available output.
bits	out	returns the number of 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.

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the source stream state was inconsistent.

int deflatePrime(z_streamp strm, int bits, int value)#

This function 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
bits	in	It contains the number of least significant bits from the value we have to consider for insertion.
value	out	It contains the data which we want to insert into output stream.

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.

Returns:

Result	Description
Z_OK	If success.
Z_BUF_ERROR	If there was not enough room in the internal buffer to insert the bits.
Z_STREAM_ERROR	If the source stream state was inconsistent.

int deflateSetHeader(z_streamp strm, gz_headerp head)#

This function provides gzip header information for when a gzip stream is requested by deflateInit2().

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
head	in,out	gzip header information passed to and from zlib routines. refer gz_header_s

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 the current operating system, with no extra, name, or comment fields. The gzip header is returned to the default state by deflateReset().

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the source stream state was inconsistent.

int inflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt dictLength)#

Initializes the decompression dictionary from the given uncompressed byte sequence.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
dictionary	out	- The dictionary chosen by the compressor can be determined from the Adler-32 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.
dictLength	in	Length of dictionary.

Note

This function must be called immediately after a call of inflate, if that call returned Z_NEED_DICT.
The application must insure that the dictionary that was used for compression is provided.

Returns:

Result	Description
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 Adler-32 value). inflateSetDictionary does not perform any decompression: this will be done by subsequent calls of inflate().

int inflateGetDictionary(z_streamp strm, Bytef *dictionary, uInt *dictLength)#

Returns the sliding dictionary being maintained by inflate.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
dictLength	in	set to the number of bytes in the dictionary, and that many bytes are copied to dictionary.
dictionary	out	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.

Returns:

Returns the sliding dictionary being maintained by inflate.

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the stream state is inconsistent.

int inflateSync(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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

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.

Note

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.
No output is provided.

Returns:

Result	Description
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
Z_STREAM_ERROR	If the stream structure was inconsistent.

int inflateCopy(z_streamp dest, z_streamp source)#

Sets the destination stream as a complete copy of the source stream.

Parameters	Direction	Description
dest	in,out	This is a pointer to which we want to copy *source data, it works as a handle for compression, refer z_stream_s for more info.
source	in,out	This points to data from where we want to copy data, it works as a handle for compression, refer z_stream_s for more info.

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.

Returns:

Result	Description
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(z_streamp strm)#

This function is equivalent to inflateEnd followed by inflateInit, but does not free and reallocate the internal decompression state.

The stream will keep attributes that may have been set by inflateInit2.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If the source stream state was inconsistent (such as zalloc or state being Z_NULL).

int inflateReset2(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. If the window size is changed, then the memory allocated for the window is freed, and the window will be reallocated by inflate() if needed.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
windowBits	in	The windowBits parameter is interpreted the same as it is for inflateInit2().

Returns:

Result	Description
Z_OK	If success
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(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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
bits	in	It contains the number of least significant bits from the value we have to consider for insertion.
value	in	It contains the data which we want to insert into input stream

The provided bits will be used before any bytes are used from next_in.

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.

Attention: 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.

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If the source stream state was inconsistent

long inflateMark(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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

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.

Returns:

Result	Description
Success	The value noted above
-65536	If the provided source stream state was inconsistent.

int inflateGetHeader(z_streamp strm, gz_headerp head)#

This function requests that gzip header information be stored in the provided gz_header structure.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
head	in,out	gzip header information passed to and from zlib routines. refer gz_header_s

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.

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If the source stream state was inconsistent

int inflateBack (z_streamp strm, in_func in, void FAR *in_desc, out_func out, void FAR *out_desc)

It 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
in_func	in	This is a function which is used for reading input from in_desc.
in_desc	in	Input descriptor
out_func	out	This is a function which is used for writing to output.
out_desc	out	Output descriptor.

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 default behavior of inflate(), which expects a zlib 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.

Note

inflateBack() cannot return Z_OK.

Returns:

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.

Result	Description
Z_STREAM_END	The return values of inflateBack() can be on success.
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).
Z_STREAM_ERROR	If the stream was not properly initialized.
Z_BUF_ERROR	If in() or out() returned an error. 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).

int inflateBackEnd(z_streamp strm)#

All memory allocated by inflateBackInit() is freed using this function.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If the stream state was inconsistent.

uLong zlibCompileFlags(void)#

It returns 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: ZLIB_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 (not supported in AOCL ZLIB)
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)

Returns:

Result	Description
Success	Return flags indicating compile-time options.

deflateInit2(strm, level, method, windowBits, memLevel, 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
level	in	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).
method	in	The method parameter is the compression method. It must be Z_DEFLATED in this version of the library.
windowBits	in	It 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.
		For the current implementation of deflate(), a windowBits value of 8 (a window size of 256 bytes) is not supported. As a result, a request for 8 will result in 9 (a 512-byte window). In that case, providing 8 to inflateInit2() will result in an error when the zlib header with 9 is checked against the initialization of inflate(). The remedy is to not use 8 with deflateInit2() with this initialization, or at least in that case use 9 with inflateInit2().
		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 a 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 the appropriate value, if the operating system was determined at compile time. If a gzip stream is being written, strm->adler is a CRC-32 instead of an Adler-32.
		For raw deflate or gzip encoding, a request for a 256-byte window is rejected as invalid, since only the zlib header provides a means of transmitting the window size to the decompressor.
memLevel	in	It 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.
strategy	in	It 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).
		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.

Note

deflateInit2 does not perform any compression: this will be done by deflate().

Returns:

Result	Description
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)
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.

inflateInit2(strm, 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
windowBits	in	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 Adler-32 or a CRC-32 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 CRC-32 instead of an Adler-32. Unlike the gunzip utility and gzread() (see below), inflate() will not automatically decode concatenated gzip streams. inflate() will return Z_STREAM_END at the end of the gzip stream. The state would need to be reset to continue decoding a subsequent gzip stream.

Note

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.

Returns:

Result	Description
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
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.

inflateBackInit(strm, windowBits, window)#

It initializes the internal stream state for decompression using inflateBack() calls.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

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.

Returns:

Result	Description
Z_OK	if success.
Z_STREAM_ERROR	if any of the parameters are invalid
Z_MEM_ERROR	if the internal state could not be allocated
Z_VERSION_ERROR	if the version of the library does not match the version of the header file.

gzip file access functions

typedef struct gzFile_s *gzFile#: semi-opaque gzip file descriptor

gzFile gzdopen(int fd, const char *mode)#

This function 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).

Parameters	Direction	Description
fd	in,out	file descriptor
mode	in,out	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.

Returns:

Result	Description
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(gzFile file, unsigned size)#

Use this function to 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. Three times that size in buffer space is allocated. 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().

Parameters	Direction	Description
file	in,out	Semi-opaque gzip file descriptor.
size	in	This is size we want to set to the internal buffer of file.

Returns:

Result	Description
0	on success
-1	on failure, such as being called too late.

int gzsetparams(gzFile file, int level, int strategy)#

It updates the compression level and strategy dynamically.

See the description of deflateInit2() for the meaning of these parameters. Previously provided data is flushed before the parameter change.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.
level	out	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).
strategy	in,out	see deflateInit2()

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If the file was not opened for writing.
Z_ERRNO	If there is an error writing the flushed data.
Z_MEM_ERROR	If there is a memory allocation error.

int gzread(gzFile file, voidp buf, unsigned len)#

It reads the given number of uncompressed bytes from the compressed file.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.
buf	in	It is a buffer where uncompressed bytes are written into.
len	in,out	This represent the number of bytes we wish to read from 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

If the input file is not in gzip format, gzread copies the given number of bytes into the buffer directly from the file.
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.

Returns:

Result	Description
Success	Returns the number of uncompressed bytes actually read, less than len for end of file.
-1	If len is too large to fit in an int, then nothing is read, -1 is returned , and the error state is set to Z_STREAM_ERROR.

z_size_t gzfread(voidp buf, z_size_t size, z_size_t nitems, gzFile file)#

It reads and decompresses up to nitems items of size size from file to buf using.

This duplicates the interface of stdio’s fread(), with size_t request and return types. If the library defines size_t, then z_size_t is identical to size_t. If not, then z_size_t is an unsigned integer type that can contain a pointer.

Parameters	Direction	Description
buf	in	This is a buffer into which the data read is written to.
size	in	This is the size of each item.
nitems	in	This is the number of items of size `size`.
file	in,out	Semi-opaque gzip file descriptor.

In the event that the end of file is reached and only a partial item is available at the end, i.e. the remaining uncompressed data length is not a multiple of size, then the final partial item is nevetheless read into buf and the end-of-file flag is set. The length of the partial item read is not provided, but could be inferred from the result of gztell(). This behavior is the same as the behavior of fread() implementations in common libraries, but it prevents the direct use of gzfread() to read a concurrently written file, reseting and retrying on end-of-file, when size is not 1.

Note

If the input file is not in gzip format, gzread copies the given number of bytes into the buffer directly from the file.
gzerror() must be consulted if zero is returned in order to determine if there was an error.

Returns:

Result	Description
Success	It returns the number of full items read of size size.
Zero	If the end of the file was reached and a full item could not be read, or if there was an error. If the multiplication of size and nitems overflows, i.e. the product does not fit in a z_size_t, then nothing is read, zero is returned, and the error state is set to Z_STREAM_ERROR.

int gzwrite(gzFile file, voidpc buf, unsigned len)#

It writes the given number of uncompressed bytes into the compressed file.

Parameters	Direction	Description
file	in,out	Semi-opaque gzip file descriptor.
buf	in	This is a buffer into which the data read is written to.
len	in	The number of bytes that are there in buf to write into file.

Returns:

Result	Description
Success	The number of uncompressed bytes written.
Zero	0 in case of error.

z_size_t gzfwrite(voidpc buf, z_size_t size, z_size_t nitems, gzFile file)#

It writes nitems items of size size from buf to file, duplicating the interface of stdio’s fwrite(), with size_t request and return types.

If the library defines size_t, then z_size_t is identical to size_t. If not, then z_size_t is an unsigned integer type that can contain a pointer.

Returns:

Result	Description
Success	It returns the number of full items written of size `size`.
Zero	If there was an error. If the multiplication of size and nitems overflows,i.e. the product does not fit in a z_size_t, then nothing is written, zero is returned, and the error state is set to Z_STREAM_ERROR.

int gzprintf(gzFile file, const char *format, ...)#

It converts, formats, and writes the arguments to the compressed file under control of the format string, as in fprintf.

Returns:

Result	Description
Success	The number of uncompressed bytes actually written
Negative `int`	Negative zlib error code 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.
0	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(gzFile file, const char *s)#

It writes the given null-terminated string to the compressed file, excluding the terminating null character.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.
s	in,out	writes this null-termintated string to compressed file.

Returns:

Result	Description
Success	It returns the number of characters written.
-1	It returns in case of error.

char *gzgets(gzFile file, char *buf, int len)#

It 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.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.
buf	in	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.
len	in,out	The length of the data that should be read from file.

Returns:

Result	Description
Success	It returns a buffer which is a null-terminated string.
NULL	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(gzFile file, int c)#

It writes c, converted to an unsigned char, into the compressed file.

Parameters	Direction	Description
file	in,out	Semi-opaque gzip file descriptor.
c	in	It acts as a byte for writing into compressed file.

Returns:

Result	Description
Success	The value that was written.
-1	It returns in case of error.

int gzgetc(gzFile file)#

It reads one byte from the compressed file.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Note

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.

Returns:

Result	Description
Success	Returns this byte.
-1	It returns in case of end of file or error.

int gzungetc(int c, gzFile file)#

Push one character back onto the stream to be read as the first character on the next read using this function.

At least one character of push-back is allowed. 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().

Parameters	Direction	Description
c	in,out	It contains the character we want to push.
file	in,out	semi-opaque gzip file descriptor.

Returns:

Result	Description
Success	The character pushed.
-1	It returns on failure.

int gzflush(gzFile file, int flush)#

It flushes all pending output into the compressed file.

Parameters	Direction	Description
file	in,out	Semi-opaque gzip file descriptor.
flush	out	The parameter flush is as in the deflate() function.
flush	out	If the flush parameter is Z_FINISH, the remaining data is written and the gzip stream is completed in the output.

gzflush is only permitted when writing. If gzwrite() is called again, a new gzip stream will be started in the output. gzread() is able to read such concatenated gzip streams.

Note

gzflush should be called only when strictly necessary because it will degrade compression if called too often.

Returns:

Result	Description
error number	The return value is the zlib error number (see function gzerror below).

int gzrewind(gzFile file)#

It rewinds the given file. This function is supported only for reading.

gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET)

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Returns:

Result	Description
-1	on error
0	on success

int gzeof(gzFile file)#

This function returns true if the end-of-file indicator has been set while reading, otherwise it returns false (0).

If the end-of-file indicator has been set while reading, 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.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Note

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.

Returns:

Result	Description
true (1)	If the end-of-file indicator has been set while reading.
false (0)	If the end-of-file indicator is not set while reading.

int gzdirect(gzFile file)#

This function 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

Result	Description
true (1)	If transparent writing was requested (“wT” for the gzopen() mode)
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.

Returns:

When reading

Result	Description
true (1)	If file is being copied directly while reading.
false (0)	If file is a gzip stream being decompressed.

int gzclose(gzFile file)#

Flushes all pending output if necessary, closes the compressed file and deallocates the (de)compression state.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Note

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.

Returns:

Result	Description
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.
Z_OK	On success.

int gzclose_r(gzFile file)#

Same as gzclose(), but gzclose_r() is only for use when reading.

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.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Returns:

Result	Description
Z_STREAM_ERROR	If file is not valid.
Z_OK	If everything goes fine.
Z_ERRNO	If file is unable to close properly.

int gzclose_w(gzFile file)#

Same as gzclose(), gzclose_w() is only for use when writing or appending.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

Returns:

Result	Description
Z_STREAM_ERROR	If input is NULL .
Z_OK	If everything goes fine.
Z_ERRNO	If file is unable to close properly.

const char *gzerror(gzFile file, int *errnum)#

It returns the error message for the last error which occurred on the given compressed file.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.
errnum	in	It 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.

Note

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.

Warning

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.

Returns:

Result	Description
error message	Returns the error message for the last error which occurred on the given compressed file.

void gzclearerr(gzFile file)#

It 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.

Parameters	Direction	Description
file	in,out	semi-opaque gzip file descriptor.

int gzgetc_(gzFile file)#

It returns the semi-opaque gzip file.

It is provided for backward compatibility.

gzFile gzopen(const char*, const char*)#

Opens a gzip (.gz) file for reading or writing.

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.

Parameters	Direction	Description
path	in,out	The path to gzip file you want to open.
mode	in	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.

Returns:

Result	Description
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	It can be checked to determine if the reason gzopen failed was that the file could not be opened.

z_off_t gzseek(gzFile, z_off_t, int)#

Sets the starting position for the next gzread or gzwrite on the given compressed file.

Parameters	Direction	Description
offset	out	The offset represents a number of bytes in the uncompressed data stream.
whence	in	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.

Returns:

Result	Description
Success	Returns the resulting offset location as measured in bytes from the beginning of the uncompressed stream
-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.

z_off_t gztell(gzFile)#

It 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)

Returns:

Returns the starting position for the next gzread or gzwrite on the given compressed file.

Returns:

Result	Description
Success	Returns the starting position for the next gzread or gzwrite on the given compressed file.

z_off_t gzoffset(gzFile)#

It 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.

Returns:

Result	Description
Success	Returs the current offset in the file being read or written.
-1	On error, gzoffset() returns -1.

int gzvprintf(gzFile file, const char *format, va_list va)#

It converts, formats, and writes the arguments to the compressed file under control of the format string, as in fprintf.

Returns:

Result	Description
Success	The number of uncompressed bytes actually written, or a negative zlib error code 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.
Fails	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().

Basic Functions

const char *zlibVersion(void)#

This function provide the ZLIB version.

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.

Returns:

Result	Description
Success	Returns ZLIB version in const char * format

int deflate(z_streamp strm, int flush)#

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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
flush	out	Flush can be of
		- Z_NO_FLUSH
		- Z_PARTIAL_FLUSH
		- Z_SYNC_FLUSH
		- Z_FULL_FLUSH
		- Z_FINISH
		- Z_BLOCK

The following section describes their usage.

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().
Generate 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. Some output may be provided even if flush is zero.

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. See deflatePending(), which can be used if desired to determine whether or not there is more output in that case.

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 codes 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 when the flush marker begins, in order to avoid repeated flush markers upon calling deflate() again when avail_out == 0.

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 or Z_BUF_ERROR, 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 in the first deflate call after deflateInit if all the compression is to be done in a single step. In order to complete in one call, 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 Adler-32 checksum of all input read so far (that is, total_in bytes). If a gzip stream is being generated, then strm->adler will be the CRC-32 checksum of the input read so far. (See deflateInit2 below.)

deflate() may update strm->data_type if it can make a good guess about the input data type (Z_BINARY or Z_TEXT). If in doubt, the data is considered binary. This field is only for information purposes and does not affect the compression algorithm in any manner.

Note

that Z_BUF_ERROR is not fatal, and deflate() can be called again with more input and more output space to continue compressing.

Returns:

Result	Description
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 or the state was inadvertently written over by the application)
Z_BUF_ERROR	If no progress is possible (for example if avail_in or avail_out was zero)

int deflateEnd(z_streamp strm)#

All dynamically allocated data structures for this stream strm are freed.

This function discards any unprocessed input and does not flush any pending output.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

Note

In the error case, msg may be set but then points to a static string (which must not be deallocated).

Returns:

Result	Description
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).

int inflate(z_streamp strm, int flush)#

This function 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
flush	out	Flush can be of
		- Z_NO_FLUSH
		- Z_PARTIAL_FLUSH
		- Z_SYNC_FLUSH
		- Z_FULL_FLUSH
		- Z_FINISH
		- Z_BLOCK

The following section describes their usage.

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), then next_in and avail_in are updated accordingly, and processing will resume at this point for the next call of inflate().
Generate 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. If the caller of inflate() does not provide both available input and available output space, it is possible that there will be no progress made. 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. To assist in this, on return inflate() always sets 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 Adler-32 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 unless inflateGetHeader() is used. When processing gzip-wrapped deflate data, strm->adler32 is set to the CRC-32 of the output produced so far. The CRC-32 is checked against the gzip trailer, as is the uncompressed length, modulo 2^32.

Note

Z_BUF_ERROR is not fatal, and inflate() can be called again with more input and more output space to continue decompressing.

Note

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 to be attempted.

Returns:

Result	Description
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, in which case strm->msg points to a string with a more specific error)
Z_STREAM_ERROR	If the stream state was inconsistent (for example if next_in or next_out was Z_NULL or the state was inadvertently written over by the application)
Z_MEM_ERROR	If there was not enough memory
Z_BUF_ERROR	If no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used.

int inflateEnd(z_streamp strm)#

All dynamically allocated data structures for this stream are freed.

This function discards any unprocessed input and does not flush any pending output.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.

Returns:

Result	Description
Z_OK	If success
Z_STREAM_ERROR	If the stream state was inconsistent

deflateInit(strm, level)#

It 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
level	out	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).

Note

deflateInit does not perform any compression: this will be done by deflate().

Returns:

Result	Description
Z_OK	If success
Z_MEM_ERROR	If there was not enough memory.
Z_STREAM_ERROR	If level is not a valid compression level.
Z_VERSION_ERROR	If the zlib library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION). msg is set to null if there is no error message.

inflateInit(strm)#

It initializes the internal stream state for decompression.

The fields next_in, avail_in, zalloc, zfree and opaque must be initialized before by the caller. In the current version of inflate, the provided input is not read or consumed. The allocation of a sliding window will be deferred to the first call of inflate (if the decompression does not complete on the first call). If zalloc and zfree are set to Z_NULL, inflateInit updates them to use default allocation functions.

Parameters	Direction	Description
strm	in,out	It works as a handle for decompression, refer z_stream_s for more info.

Note

inflateInit does not perform any decompression. Actual decompression will be done by inflate(). So next_in, and avail_in, 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.

Returns:

Result	Description
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
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.

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(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen)#

This function compresses the source buffer into the destination buffer.

sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned by compressBound(sourceLen). Upon exit, destLen is the actual size of the compressed data. compress() is equivalent to compress2() with a level parameter of Z_DEFAULT_COMPRESSION.

Parameters	Direction	Description
dest	in,out	The compressed data is stored in this buffer.
destLen	in	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 data.
source	out	It is the buffer where the data we want to compress resides.
sourceLen	in	Length of source buffer to be compressed.

Returns:

Result	Description
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(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level)#

This function compresses the source buffer into the destination buffer.

The level parameter has the same meaning as in deflateInit. sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned by compressBound(sourceLen). Upon exit, destLen is the actual size of the compressed data.

Parameters	Direction	Description
dest	in,out	The compressed data is stored in this buffer.
destLen	in	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 data.
source	out	It is the buffer where the data we want to compress resides.
sourceLen	in	Length of source buffer to be compressed.
level	out	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).

Returns:

Result	Description
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(uLong sourceLen)#

It 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.

Parameters	Direction	Description
sourceLen	in	Length of source buffer to be compressed.

Returns:

Result	Description
Success	Returns an upper bound on the compressed size after compress() or compress2() on sourceLen bytes.

int uncompress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen)#

This function decompresses the source buffer into the destination buffer.

sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. (The size of the uncompressed data must have been saved previously by the compressor and transmitted to the decompressor by some mechanism outside the scope of this compression library.) Upon exit, destLen is the actual size of the uncompressed data.

Parameters	Direction	Description
dest	in,out	The compressed data is stored in this buffer.
destLen	in	Upon entry, destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. Upon exit, destLen is the actual size of the compressed data.
source	out	This buffer contains the compressed data which will be decompressed into dest buffer.
sourceLen	in	It is the byte length of the source buffer.

Returns:

Result	Description
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_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.

int uncompress2(Bytef *dest, uLongf *destLen, const Bytef *source, uLong *sourceLen)#

This function decompresses the source buffer into the destination buffer.

Same as uncompress(), except that sourceLen is a pointer, where the length of the source is *sourceLen. On return, *sourceLen is the number of source bytes consumed.

Parameters	Direction	Description
dest	in,out	The decompressed data is stored in this buffer.
destLen	in	Upon entry, destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. Upon exit, destLen is the actual size of the compressed data.
source	out	This buffer contains the compressed data which will be decompressed into dest buffer.
sourceLen	in	Upon entry sourceLen is the byte length of the source buffer.On return sourceLen is the number of source bytes consumed.

Returns:

Result	Description
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_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.

Checksum functions

uLong adler32(uLong adler, const Bytef *buf, uInt len)#

It updates a running Adler-32 checksum with the bytes buf[0..len-1] and return the updated checksum.

Parameters	Direction	Description
adler	in,out	initial adler check sum which will be modified according to buf and returned.
buf	in	it contains data on which this function is called
len	in	length of buf in bytes.

An Adler-32 checksum is almost as reliable as a CRC-32 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();

Note

If buf is Z_NULL, this function returns the required initial value for the checksum.

Returns:

Result	Description
Success	Returns the Updated checksum.
Success	If buf is Z_NULL, this function returns the required initial value for the checksum.

uint32_t adler32_x86(uint32_t adler, const Bytef *buf, z_size_t len)#: AOCL-Compression optimized adler32 checksum for zlib.

uLong adler32_z(uLong adler, const Bytef *buf, z_size_t len)#

Same as adler32(), but with a size_t length.

Parameters	Direction	Description
adler	in,out	initial adler check sum which will be modified according to buf and returned.
buf	in	it contains data on which this function is called.
len	in	length of buf in bytes.

Returns:

Result	Description
Success	Returns the Updated checksum.
Success	If buf is Z_NULL, this function returns the required initial value for the checksum.

uLong crc32(uLong crc, const Bytef *buf, uInt len)#

It updates 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.

Parameters	Direction	Description
crc	in,out	Existing checksum value
buf	in	It contains data on which this function is called.
len	in	Length of buf in bytes.

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();

Returns:

Result	Description
Success	Returns the Updated CRC-32.
Success	If buf is Z_NULL, this function returns the required initial value for the crc.

uLong crc32_z(uLong crc, const Bytef *buf, z_size_t len)#

Same as crc32(), but with a size_t length.

Parameters	Direction	Description
adler	in,out	existing checksum value which will be modified according to buf and returned.
buf	in	it contains data on which this function is called.If buf is Z_NULL, this function returns the required initial value for the crc.
len	in	length of buf in bytes.

Returns:

Result	Description
Success	Returns the Updated CRC-32.
Success	If buf is Z_NULL, this function returns the required initial value for the crc.

uLong crc32_combine_op(uLong crc1, uLong crc2, uLong op)#

Give the same result as crc32_combine(), using op in place of len2. op is generated from len2 by crc32_combine_gen().

This will be faster than crc32_combine() if the generated op is used more than once.

Returns:

Result	Description
Success	Give the same result as crc32_combine(), using op in place of len2. op is generated from len2 by crc32_combine_gen()

uLong adler32_combine(uLong, uLong, z_off_t)#

This function combines 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.

Note

The z_off_t type (like off_t) is a signed integer. If len2 is negative, the result has no meaning or utility.

Returns:

Result	Description
Success	The Adler-32 checksum of seq1 and seq2 concatenated, requiring only adler1, adler2, and len2.

uLong crc32_combine(uLong, uLong, z_off_t)#

This function combines two CRC-32 check values into one.

For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, CRC-32 check values were calculated for each, crc1 and crc2.

Returns:

Result	Description
Success	The CRC-32 check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and len2.

uLong crc32_combine_gen(z_off_t)#

Return the operator corresponding to length len2, to be used with crc32_combine_op().

Returns:

Result	Description
Success	The operator corresponding to length len2, to be used with crc32_combine_op().

const z_crc_t FAR * get_crc_table (void): This function can be used by asm versions of crc32().

Additional Functions

int deflateInit_(z_streamp strm, int level, const char *version, int stream_size)#

It 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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
level	out	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).
version	in,out	It is used to set version assumed by the caller (ZLIB_VERSION).
stream_size	in	It is used to check the sizeof(z_stream) if not equal return Z_VERSION_ERROR.

Note

deflateInit does not perform any compression: this will be done by deflate().

Returns:

Result	Description
Z_OK	If success.
Z_MEM_ERROR	If the internal state could not be allocated
Z_STREAM_ERROR	If level is not a valid compression level.
Z_VERSION_ERROR	If the zlib library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION). msg is set to null if there is no error message.

int inflateInit_(z_streamp strm, const char *version, int stream_size)#

It initializes the internal stream state for decompression.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
version	in,out	It is used to set version assumed by the caller (ZLIB_VERSION).
stream_size	in	It is used to check the sizeof(z_stream) if not equal return Z_VERSION_ERROR.

Note

Returns:

Result	Description
Z_OK	If success.
Z_MEM_ERROR	If the internal state could not be allocated
Z_STREAM_ERROR	If level is not a valid compression level.
Z_VERSION_ERROR	If the zlib library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION). msg is set to null if there is no error message.

int deflateInit2_(z_streamp strm, int level, int method, int windowBits, int memLevel, int strategy, const char *version, int stream_size)#

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.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
level	out	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).
method	in	The method parameter is the compression method. It must be Z_DEFLATED in this version of the library.
windowBits	in	It 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.
		For the current implementation of deflate(), a windowBits value of 8 (a window size of 256 bytes) is not supported. As a result, a request for 8 will result in 9 (a 512-byte window). In that case, providing 8 to inflateInit2() will result in an error when the zlib header with 9 is checked against the initialization of inflate(). The remedy is to not use 8 with deflateInit2() with this initialization, or at least in that case use 9 with inflateInit2().
		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 a 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 the appropriate value, if the operating system was determined at compile time. If a gzip stream is being written, strm->adler is a CRC-32 instead of an Adler-32.
		For raw deflate or gzip encoding, a request for a 256-byte window is rejected as invalid, since only the zlib header provides a means of transmitting the window size to the decompressor.
memLevel	in,out	It 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.
strategy	in.out	It 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).
		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.
version	in,out	It is used to set version assumed by the caller (ZLIB_VERSION).
stream_size	in	It is used to check the sizeof(z_stream) if not equal return Z_VERSION_ERROR.

Note

deflateInit2 does not perform any compression: this will be done by deflate().

Returns:

Result	Description
Z_OK	If success.
Z_MEM_ERROR	If the internal state could not be allocated
Z_STREAM_ERROR	If any parameter is invalid (such as an invalid method)
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.

int inflateInit2_(z_streamp strm, int windowBits, const char *version, int stream_size)#

This is another version of inflateInit with an extra parameter.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
windowBits	in	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 Adler-32 or a CRC-32 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.
version	in	It is used to set version assumed by the caller (ZLIB_VERSION).
stream_size	in	It is used to check the sizeof(z_stream) if not equal return Z_VERSION_ERROR.

Note

Returns:

Result	Description
Z_OK	If success.
Z_MEM_ERROR	If the internal state could not be allocated
Z_STREAM_ERROR	If any parameter is invalid (such as an invalid method)
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.

int inflateBackInit_ (z_streamp strm, int windowBits, unsigned char FAR *window, const char *version, int stream_size)

It initializes the internal stream state for decompression using inflateBack() calls.

The fields next_in, avail_in, zalloc, zfree and opaque must be initialized before by the caller.

Parameters	Direction	Description
strm	in,out	It works as a handle for compression, refer z_stream_s for more info.
windowBits	in	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 Adler-32 or a CRC-32 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.
window	in	window is a user-supplied.
version	in,out	It is used to set version assumed by the caller (ZLIB_VERSION).
stream_size	in	It is used to check the sizeof(z_stream) if not equal return Z_VERSION_ERROR.

See inflateBack() for the usage of these routines.

Returns:

Result	Description
Z_OK	If success.
Z_STREAM_ERROR	If any of the parameters are invalid
Z_MEM_ERROR	If the internal state could not be allocated
Z_VERSION_ERROR	If the version of the library does not match the version of the header file.

const char *zError(int)#: exported to allow conversion of error code to string for compress() and uncompress()

int inflateSyncPoint(z_streamp)#

This function is used by one PPP implementation to provide an additional safety check.

Returns true if inflate is currently at the end of a block generated by Z_SYNC_FLUSH or Z_FULL_FLUSH. PPP uses Z_SYNC_FLUSH but removes the length bytes of the resulting empty stored block. When decompressing, PPP checks that at the end of input packet, inflate is waiting for these length bytes.

int inflateUndermine(z_streamp, int)#: This fuction is used to check the distance INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR.

int inflateValidate(z_streamp, int)#: It is used to check the wrap state and validate it.

unsigned long inflateCodesUsed(z_streamp)#: This function is used to set the space for code table.

int inflateResetKeep(z_streamp)#: This function is used to reset the stream state to maintain inflate() calls.

int deflateResetKeep(z_streamp)#: This function is used to reset the stream state and return Z_Ok.

Allowed flush values

see deflate() and inflate() below for details.

Z_NO_FLUSH#

Z_PARTIAL_FLUSH#

Z_SYNC_FLUSH#

Z_FULL_FLUSH#

Z_FINISH#

Z_BLOCK#

Z_TREES#

Return codes for compression/decompression functions

Negative values are errors, positive values are used for special but normal events.

Z_OK#

Z_STREAM_END#

Z_NEED_DICT#

Z_ERRNO#

Z_STREAM_ERROR#

Z_DATA_ERROR#

Z_MEM_ERROR#

Z_BUF_ERROR#

Z_VERSION_ERROR#

Compression levels

Z_NO_COMPRESSION#

Z_BEST_SPEED#

Z_BEST_COMPRESSION#

Z_DEFAULT_COMPRESSION#

Compression strategy

see deflateInit2() below for details

Z_FILTERED#

Z_HUFFMAN_ONLY#

Z_RLE#

Z_FIXED#

Z_DEFAULT_STRATEGY#

Possible values of the data_type field for deflate()

Z_BINARY#

Z_TEXT#

Z_ASCII#: for compatibility with 1.2.2 and earlier

Z_UNKNOWN#

Defines

gzgetc(g)#

Z_DEFLATED#: The deflate compression method (the only one supported in this version)

Z_NULL#: for initializing zalloc, zfree, opaque

zlib_version#: for compatibility with versions < 1.0.2

Typedefs

typedef voidpf (*alloc_func)(voidpf opaque, uInt items, uInt size)#: Function pointer for memory allocation function.

typedef void (*free_func)(voidpf opaque, voidpf address)#: Function pointer for memory deallocation function.

typedef struct gz_header_s gz_header#: gzip header information passed to and from zlib routines. See RFC 1952 for more details on the meanings of these fields.

gz_header FAR * gz_headerp: This stores the gzip header information provided in the gz_header structure.

typedef struct z_stream_s z_stream#: It works as a handle for compression and decompression.

z_stream FAR * z_streamp: the internal stream state for decompression/compression.

struct gz_header_s#

#include <zlib.h>

gzip header information passed to and from zlib routines. See RFC 1952 for more details on the meanings of these fields.

Public Members

uInt comm_max#: space at comment (only when reading header)

Bytef *comment#: pointer to zero-terminated comment or Z_NULL

int done#: true when done reading gzip header (not used when writing a gzip file)

Bytef *extra#: pointer to extra field or Z_NULL if none

uInt extra_len#: extra field length (valid if extra != Z_NULL)

uInt extra_max#: space at extra (only when reading header)

int hcrc#: true if there was or will be a header crc

Bytef *name#: pointer to zero-terminated file name or Z_NULL

uInt name_max#: space at name (only when reading header)

int os#: operating system

int text#: true if compressed data believed to be text

uLong time#: modification time

int xflags#: extra flags (not used when writing a gzip file)

struct gzFile_s#

#include <zlib.h>

gzgetc() macro and its supporting function and exposed data structure.

Note that the real internal state is much larger than the exposed structure. This abbreviated structure exposes just enough for the gzgetc() macro. The user should not mess with these exposed elements, since their names or behavior could change in the future, perhaps even capriciously. They can only be used by the gzgetc() macro. You have been warned.

Public Members

unsigned have#: number of bytes available at next

unsigned char *next#: next output data to deliver or write

z_off64_t pos#: current position in uncompressed data

struct z_stream_s#

#include <zlib.h>

It works as a handle for compression and decompression.

Public Members

uLong adler#: Adler-32 or CRC-32 value of the uncompressed data

uInt avail_in#: number of bytes available at next_in

uInt avail_out#: remaining free space at next_out

int data_type#: best guess about the data type: binary or text for deflate, or the decoding state for inflate

z_const char * msg: last error message, NULL if no error

z_const Bytef * next_in: next input byte

Bytef *next_out#: next output byte will go here

voidpf opaque#: private data object passed to zalloc and zfree

uLong reserved#: reserved for future use

struct internal_state FAR * state: not visible by applications

uLong total_in#: total number of input bytes read so far

uLong total_out#: total number of bytes output so far

alloc_func zalloc#: used to allocate the internal state

free_func zfree#: used to free the internal state