NAME

SYNOPSIS

DESCRIPTION

• Basic functions
• Advanced functions
• Utility functions
• Checksum functions

BASIC FUNCTIONS

 

 

const char * zlibVersion(void);

The application can compare zlibVersion() and ZLIB_VERSION for consistency. If the first character differs, the library code actually used is not compatible with the <zlib.h> header file used by the application. This check is automatically made by deflateInit() and inflateInit().

 

 

int deflateInit(z_streamp strm, int level);

The deflateInit() function initializes the internal stream state for compression. The fields zalloc, zfree, and opaque must be initialized before by the caller. If zalloc and zfree are set to Z_NULL, deflateInit() updates them to use default allocation functions.

The compression level must be Z_DEFAULT_COMPRESSION, or between 0 and 9: 1 gives best speed, 9 gives best compression, 0 gives no compression at all (the input data is simply copied a block at a time).

Z_DEFAULT_COMPRESSION requests a default compromise between speed and compression (currently equivalent to level 6).

deflateInit() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if level is not a valid compression level, Z_VERSION_ERROR if the zlib library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION). msg is set to null if there is no error message. deflateInit() does not perform any compression: this will be done by deflate().

 

 

int deflate(z_streamp strm, int flush);

deflate() compresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency (reading input without producing any output) except when forced to flush.

The detailed semantics are as follows. deflate() performs one or both of the following actions:

Compress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in and avail_in are updated and processing will resume at this point for the next call to deflate().

Provide more output starting at next_out and update next_out and avail_out accordingly. This action is forced if the parameter flush is non-zero. Forcing flush frequently degrades the compression ratio, so this parameter should be set only when necessary (in interactive applications). Some output may be provided even if flush is not set.

Before the call to deflate(), the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating avail_in or avail_out accordingly; avail_out should never be zero before the call. The application can consume the compressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call to deflate(). If deflate() returns Z_OK and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.

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 maximise 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.

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 a Z_SYNC_FLUSH, make sure that avail_out is greater than six to avoid repeated flush markers due to avail_out == 0 on return.

If the parameter flush is set to Z_FINISH, pending input is processed, pending output is flushed and deflate() returns with Z_STREAM_END if there was enough output space; if deflate() returns with Z_OK, this function must be called again with Z_FINISH and more output space (updated avail_out but no more input data, until it returns with Z_STREAM_END or an error. After deflate() has returned Z_STREAM_END, the only possible operations on the stream are deflateReset() or deflateEnd().

Z_FINISH can be used immediately after deflateInit() if all the compression is to be done in a single step. In this case, avail_out must be at least the value returned by deflateBound() (see below). If deflate() does not return Z_STREAM_END, then it must be called again as described above.

deflate() sets strm->adler to the Adler-32 checksum of all input read so far (that is, total_in bytes).

deflate() may update 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.

deflate() returns Z_OK if some progress has been made (more input processed or more output produced), Z_STREAM_END if all input has been consumed and all output has been produced (only when flush is set to Z_FINISH), Z_STREAM_ERROR if the stream state was inconsistent (for example, if next_in or next_out was NULL), Z_BUF_ERROR if no progress is possible (for example, avail_in or avail_out was zero). Note that Z_BUF_ERROR is not fatal, and deflate() can be called again with more input and more output space to continue processing.

 

 

int deflateEnd(z_streamp strm);

All dynamically allocated data structures for this stream are freed. This function discards any unprocessed input and does not flush any pending output.

deflateEnd() returns Z_OK if successful, Z_STREAM_ERROR if the stream state was inconsistent, Z_DATA_ERROR if the stream was freed prematurely (some input or output was discarded). In the error case, msg may be set but then points to a static string (which must not be deallocated).

 

 

int inflateInit(z_streamp strm);

The inflateInit() function initializes the internal stream state for decompression. The fields next_in, avail_in, zalloc, zfree, and opaque must be initialized before by the caller. If next_in is not Z_NULL and avail_in is large enough (the exact value depends on the compression method), inflateInit() determines the compression method from the zlib header and allocates all data structures accordingly; otherwise the allocation will be deferred to the first call to inflate(). If zalloc and zfree are set to Z_NULL, inflateInit() updates them to use default allocation functions.

inflateInit() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_VERSION_ERROR if the zlib library version is incompatible with the version assumed by the caller. msg is set to null if there is no error message. inflateInit() does not perform any decompression apart from reading the zlib header if present: this will be done by inflate(). (So next_in and avail_in may be modified, but next_out and avail_out are unchanged.)

 

 

int inflate(z_streamp strm, int flush);

inflate() decompresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency (reading input without producing any output) except when forced to flush.

The detailed semantics are as follows. inflate() performs one or both of the following actions:

Decompress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in is updated and processing will resume at this point for the next call to inflate().

Provide more output starting at next_out and update next_out and avail_out accordingly. inflate() provides as much output as possible, until there is no more input data or no more space in the output buffer (see below about the flush parameter).

Before the call to inflate(), the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating the next_* and avail_* values accordingly. The application can consume the uncompressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call to inflate(). If inflate() returns Z_OK and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.

The flush parameter of inflate() can be Z_NO_FLUSH, Z_SYNC_FLUSH, Z_FINISH, or Z_BLOCK. Z_SYNC_FLUSH requests that inflate() flush as much output as possible to the output buffer. Z_BLOCK requests that inflate() stop if and when it gets to the next deflate block boundary. When decoding the zlib or gzip format, this will cause inflate() to return immediately after the header and before the first block. When doing a raw inflate, inflate() will go ahead and process the first block, and will return when it gets to the end of that block, or when it runs out of data.

The Z_BLOCK option assists in appending to or combining deflate streams. Also to assist in this, on return inflate() will set strm->data_type to the number of unused bits in the last byte taken from strm->next_in, plus 64 if inflate() is currently decoding the last block in the deflate stream, plus 128 if inflate() returned immediately after decoding an end-of-block code or decoding the complete header up to just before the first byte of the deflate stream. The end-of-block will not be indicated until all of the uncompressed data from that block has been written to strm->next_out. The number of unused bits may in general be greater than seven, except when bit 7 of data_type is set, in which case the number of unused bits will be less than eight.

inflate() should normally be called until it returns Z_STREAM_END or an error. However if all decompression is to be performed in a single step (a single call to inflate), the parameter flush should be set to Z_FINISH. In this case all pending input is processed and all pending output is flushed; avail_out must be large enough to hold all the uncompressed data. (The size of the uncompressed data may have been saved by the compressor for this purpose.) The next operation on this stream must be inflateEnd() to deallocate the decompression state. The use of Z_FINISH is never required, but can be used to inform inflate() that a faster approach may be used for the single inflate() call.

In this implementation, inflate() always flushes as much output as possible to the output buffer, and always uses the faster approach on the first call. So the only effect of the flush parameter in this implementation is on the return value of inflate(), as noted below, or when it returns early because Z_BLOCK is used.

If a preset dictionary is needed after this call (see inflateSetDictionary() below), inflate() sets 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() will decompress and check either zlib-wrapped or gzip-wrapped deflate data. The header type is detected automatically. Any information contained in the gzip header is not retained, so applications that need that information should instead use raw inflate; see inflateInit2() below, or inflateBack() and perform their own processing of the gzip header and trailer.

inflate() returns Z_OK if some progress has been made (more input processed or more output produced), Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, Z_NEED_DICT if a preset dictionary is needed at this point, Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value), Z_STREAM_ERROR if the stream structure was inconsistent (for example, if next_in or next_out was NULL), Z_MEM_ERROR if there was not enough memory, Z_BUF_ERROR if no progress is possible or if there was not enough room in the output buffer when Z_FINISH is used. Note that Z_BUF_ERROR is not fatal, and inflate() can be called again with more input and more output space to continue compressing. If Z_DATA_ERROR is returned, the application may then call inflateSync() to look for a good compression block if a partial recovery of the data is desired.

 

 

int inflateEnd(z_streamp strm);

All dynamically allocated data structures for this stream are freed. This function discards any unprocessed input and does not flush any pending output.

inflateEnd() returns Z_OK if successful, or Z_STREAM_ERROR if the stream state was inconsistent. In the error case, msg may be set but then points to a static string (which must not be deallocated).

ADVANCED FUNCTIONS

 

 

int deflateInit2(z_streamp strm, int level, int method, int windowBits, int memLevel, int strategy);

This is another version of deflateInit() with more compression options. The fields next_in, zalloc, zfree, and opaque must be initialized before by the caller.

The method parameter is the compression method. It must be Z_DEFLATED in this version of the library.

The windowBits parameter is the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage. The default value is 15 if deflateInit() is used instead.

windowBits can also be -8..-15 for raw deflate. In this case, -windowBits determines the window size. deflate() will then generate raw deflate data with no zlib header or trailer, and will not compute an Adler-32 check value.

windowBits can also be greater than 15 for optional gzip encoding. Add 16 to windowBits to write a simple gzip header and trailer around the compressed data instead of a zlib wrapper. The gzip header will have no file name, no extra data, no comment, no modification time (set to zero), no header crc, and the operating system will be set to 255 (unknown). If a gzip stream is being written, strm->adler is a crc32 instead of an adler32.

The memLevel parameter specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed. The default value is 8. See <zconf.h> for total memory usage as a function of windowBits and memLevel.

The strategy parameter is used to tune the compression algorithm. Use the value Z_DEFAULT_STRATEGY for normal data; Z_FILTERED for data produced by a filter (or predictor); Z_HUFFMAN_ONLY to force Huffman encoding only (no string match), or Z_RLE to limit match distances to one (run-length encoding). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of Z_FILTERED is to force more Huffman coding and less string matching; it is somewhat intermediate between Z_DEFAULT and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as fast as Z_HUFFMAN_ONLY, but gives better compression for PNG image data. The strategy parameter only affects the compression ratio but not the correctness of the compressed output, even if it is not set appropriately. Z_FIXED prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.

deflateInit2() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if a parameter is invalid (such as an invalid method). msg is set to null if there is no error message. deflateInit2() does not perform any compression: this will be done by deflate().

 

 

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

Initializes the compression dictionary from the given byte sequence without producing any compressed output. This function must be called immediately after deflateInit(), deflateInit2(), or deflateReset(), before any call to deflate(). The compressor and decompressor must use exactly the same dictionary (see inflateSetDictionary()).

The dictionary should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary.

Depending on the size of the compression data structures selected by deflateInit() or deflateInit2(), a part of the dictionary may in effect be discarded, for example if the dictionary is larger than the window size in deflate() or deflate2(). Thus the strings most likely to be useful should be put at the end of the dictionary, not at the front. 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.

deflateSetDictionary() returns Z_OK if successful, or Z_STREAM_ERROR if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent (for example if deflate() has already been called for this stream or if the compression method is bsort). deflateSetDictionary() does not perform any compression: this will be done by deflate().

 

 

int deflateCopy(z_streamp dest, z_streamp source);

The deflateCopy() function sets the destination stream as a complete copy of the source stream.

This function can be useful when several compression strategies will be tried, for example when there are several ways of pre-processing the input data with a filter. The streams that will be discarded should then be freed by calling deflateEnd(). Note that deflateCopy() duplicates the internal compression state which can be quite large, so this strategy is slow and can consume lots of memory.

deflateCopy() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if the source stream state was inconsistent (such as zalloc being NULL). msg is left unchanged in both source and destination.

 

 

int deflateReset(z_streamp strm);

This function is equivalent to deflateEnd() followed by deflateInit(), but does not free and reallocate all the internal compression state. The stream will keep the same compression level and any other attributes that may have been set by deflateInit2().

deflateReset() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent (such as zalloc or state being NULL).

 

 

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

The deflateParams() function dynamically updates the compression level and compression strategy. The interpretation of level and strategy is as in deflateInit2(). This can be used to switch between compression and straight copy of the input data, or to switch to a different kind of input data requiring a different strategy. If the compression level is changed, the input available so far is compressed with the old level (and may be flushed); the new level will take effect only at the next call to deflate().

Before the call to deflateParams(), the stream state must be set as for a call to deflate(), since the currently available input may have to be compressed and flushed. In particular, strm->avail_out must be non-zero.

deflateParams() returns Z_OK if successful, Z_STREAM_ERROR if the source stream state was inconsistent or if a parameter was invalid, or Z_BUF_ERROR if strm->avail_out was zero.

 

 

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

Fine tune deflate()'s internal compression parameters. This should only be used by someone who understands the algorithm used by zlib's deflate for searching for the best matching string, and even then only by the most fanatic optimizer trying to squeeze out the last compressed bit for their specific input data. Read the deflate.c source code for the meaning of the max_lazy, good_length, nice_length, and max_chain parameters.

deflateTune() can be called after deflateInit() or deflateInit2(), and returns Z_OK on success, or Z_STREAM_ERROR for an invalid deflate stream.

 

 

uLong deflateBound(z_streamp strm, uLong sourceLen)

deflateBound() returns an upper bound on the compressed size after deflation of sourceLen bytes. It must be called after deflateInit() or deflateInit2(). This would be used to allocate an output buffer for deflation in a single pass, and so would be called before deflate().

 

 

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

deflatePrime() inserts bits in the deflate output stream. The intent is that this function is used to start off the deflate output with the bits leftover from a previous deflate stream when appending to it. As such, this function can only be used for raw deflate, and must be used before the first deflate() call after a deflateInit2() or deflateReset(). bits must be less than or equal to 16, and that many of the least significant bits of value will be inserted in the output.

deflatePrime() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent.

 

 

int deflateSetHeader(z_streamp strm, gz_headerp head)

deflateSetHeader() provides gzip header information for when a gzip stream is requested by deflateInit2(). deflateSetHeader() may be called after deflateInit2() or deflateReset() and before the first call of deflate(). The text, time, os, extra field, name, and comment information in the provided gz_header structure are written to the gzip header (xflag is ignored - the extra flags are set according to the compression level). The caller must assure that, if not Z_NULL, name and comment are terminated with a zero byte, and that if extra is not Z_NULL, that extra_len bytes are available there. If hcrc is true, a gzip header CRC is included. Note that the current versions of the command-line version of gzip(1) do not support header CRCs, and will report that it is a “multi-part gzip file” and give up.

If deflateSetHeader() is not used, the default gzip header has text false, the time set to zero, and os set to 255, with no extra, name, or comment fields. The gzip header is returned to the default state by deflateReset().

deflateSetHeader() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent.

 

 

int inflateInit2(z_streamp strm, int windowBits);

This is another version of inflateInit() with an extra parameter. The fields next_in, avail_in, zalloc, zfree, and opaque must be initialized before by the caller.

The windowBits parameter is the base two logarithm of the maximum window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. The default value is 15 if inflateInit() is used instead. windowBits must be greater than or equal to the windowBits value provided to deflateInit2() while compressing, or it must be equal to 15 if deflateInit2() was not used. If a compressed stream with a larger window size is given as input, inflate() will return with the error code Z_DATA_ERROR instead of trying to allocate a larger window.

windowBits can also be -8..-15 for raw inflate. In this case, -windowBits determines the window size. inflate() will then process raw deflate data, not looking for a zlib or gzip header, not generating a check value, and not looking for any check values for comparison at the end of the stream. This is for use with other formats that use the deflate compressed data format such as zip. Those formats provide their own check values. If a custom format is developed using the raw deflate format for compressed data, it is recommended that a check value such as an Adler-32 or a crc32 be applied to the uncompressed data as is done in the zlib, gzip, and zip formats. For most applications, the zlib format should be used as is. Note that comments above on the use in deflateInit2() applies to the magnitude of windowBits.

windowBits can also be greater than 15 for optional gzip decoding. Add 32 to windowBits to enable zlib and gzip decoding with automatic header detection, or add 16 to decode only the gzip format (the zlib format will return a Z_DATA_ERROR). If a gzip stream is being decoded, strm->adler is a crc32 instead of an adler32.

inflateInit2() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if a parameter is invalid (such as a null strm). msg is set to null if there is no error message. inflateInit2() does not perform any decompression apart from reading the zlib header if present: this will be done by inflate(). (So next_in and avail_in may be modified, but next_out and avail_out are unchanged.)

 

 

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

Initializes the decompression dictionary from the given uncompressed byte sequence. This function must be called immediately after a call to inflate() if that call returned Z_NEED_DICT. The dictionary chosen by the compressor can be determined from the Adler-32 value returned by that call to inflate(). The compressor and decompressor must use exactly the same dictionary (see deflateSetDictionary()). For raw inflate, this function can be called immediately after inflateInit2() or inflateReset() and before any call to inflate() to set the dictionary. The application must ensure that the dictionary that was used for compression is provided.

inflateSetDictionary() returns Z_OK if successful, Z_STREAM_ERROR if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent, Z_DATA_ERROR if the given dictionary doesn't match the expected one (incorrect Adler-32 value). inflateSetDictionary() does not perform any decompression: this will be done by subsequent calls of inflate().

 

 

int inflateSync(z_streamp strm);

Skips invalid compressed data until a full flush point (see above the description of deflate() with Z_FULL_FLUSH) can be found, or until all available input is skipped. No output is provided.

inflateSync() returns Z_OK if a full flush point has been found, Z_BUF_ERROR if no more input was provided, Z_DATA_ERROR if no flush point has been found, or Z_STREAM_ERROR if the stream structure was inconsistent. In the success case, the application may save the current value of total_in which indicates where valid compressed data was found. In the error case, the application may repeatedly call inflateSync(), providing more input each time, until success or end of the input data.

 

 

int inflateCopy(z_streamp dest, z_streamp source)

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

This function can be useful when randomly accessing a large stream. The first pass through the stream can periodically record the inflate state, allowing restarting inflate at those points when randomly accessing the stream.

inflateCopy() returns Z_OK if success, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if the source stream state was inconsistent (such as zalloc being NULL). msg is left unchanged in both source and dest.

 

 

int inflateReset(z_streamp strm);

This function is equivalent to inflateEnd() followed by inflateInit(), but does not free and reallocate all the internal decompression state. The stream will keep attributes that may have been set by inflateInit2().

inflateReset() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent (such as zalloc or state being NULL).

 

 

int inflatePrime(z_stream strm, int bits, int value)

This function inserts bits in the inflate input stream. The intent is that this function is used to start inflating at a bit position in the middle of a byte. The provided bits will be used before any bytes are used from next_in. This function should only be used with raw inflate, and should be used before the first inflate() call after inflateInit2() or inflateReset(). bits must be less than or equal to 16, and that many of the least significant bits of value will be inserted in the input.

inflatePrime() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent.

 

 

int inflateGetHeader(z_streamp strm, gz_headerp head)

inflateGetHeader() requests that gzip header information be stored in the provided gz_header structure. inflateGetHeader() may be called after inflateInit2() or inflateReset(), and before the first call of inflate(). As inflate() processes the gzip stream, head->done is zero until the header is completed, at which time head->done is set to one. If a zlib stream is being decoded, then head->done is set to -1 to indicate that there will be no gzip header information forthcoming. Note that Z_BLOCK can be used to force inflate() to return immediately after header processing is complete and before any actual data is decompressed.

The text, time, xflags, and os fields are filled in with the gzip header contents. hcrc is set to true if there is a header CRC. (The header CRC was valid if done is set to one.) If extra is not Z_NULL, then extra_max contains the maximum number of bytes to write to extra. Once done is true, extra_len contains the actual extra field length, and extra contains the extra field, or that field truncated if extra_max is less than extra_len. If name is not Z_NULL, then up to name_max characters are written there, terminated with a zero unless the length is greater than name_max. If comment is not Z_NULL, then up to comm_max characters are written there, terminated with a zero unless the length is greater than comm_max. When any of extra, name, or comment are not Z_NULL and the respective field is not present in the header, then that field is set to Z_NULL to signal its absence. This allows the use of deflateSetHeader() with the returned structure to duplicate the header. However if those fields are set to allocated memory, then the application will need to save those pointers elsewhere so that they can be eventually freed.

If inflateGetHeader() is not used, then the header information is simply discarded. The header is always checked for validity, including the header CRC if present. inflateReset() will reset the process to discard the header information. The application would need to call inflateGetHeader() again to retrieve the header from the next gzip stream.

inflateGetHeader() returns Z_OK if successful, or Z_STREAM_ERROR if the source stream state was inconsistent.

 

 

int inflateBackInit(z_stream *strm, int windowBits, unsigned char FAR *window)

Initialize the internal stream state for decompression using inflateBack() calls. The fields zalloc, zfree and opaque in strm must be initialized before the call. If zalloc and zfree are Z_NULL, then the default library-derived memory allocation routines are used. windowBits is the base two logarithm of the window size, in the range 8..15. window is a caller supplied buffer of that size. Except for special applications where it is assured that deflate() was used with small window sizes, windowBits must be 15 and a 32K byte window must be supplied to be able to decompress general deflate streams.

See inflateBack() for the usage of these routines.

inflateBackInit() will return Z_OK on success, Z_STREAM_ERROR if any of the parameters are invalid, Z_MEM_ERROR if the internal state could not be allocated, or Z_VERSION_ERROR if the version of the library does not match the version of the header file.

 

 

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

inflateBack() does a raw inflate with a single call using a call-back interface for input and output. This is more efficient than inflate() for file I/O applications in that it avoids copying between the output and the sliding window by simply making the window itself the output buffer. This function trusts the application to not change the output buffer passed by the output function, at least until inflateBack() returns.

inflateBackInit() must be called first to allocate the internal state and to initialize the state with the user-provided window buffer. inflateBack() may then be used multiple times to inflate a complete, raw deflate stream with each call. inflateBackEnd() is then called to free the allocated state.

A raw deflate stream is one with no zlib or gzip header or trailer. This routine would normally be used in a utility that reads zip or gzip files and writes out uncompressed files. The utility would decode the header and process the trailer on its own, hence this routine expects only the raw deflate stream to decompress. This is different from the normal behavior of inflate(), which expects either a zlib or gzip header and trailer around the deflate stream.

inflateBack() uses two subroutines supplied by the caller that are then called by inflateBack() for input and output. inflateBack() calls those routines until it reads a complete deflate stream and writes out all of the uncompressed data, or until it encounters an error. The function's parameters and return types are defined above in the in_func and out_func typedefs. inflateBack() will call in(in_desc, &buf) which should return the number of bytes of provided input, and a pointer to that input in buf. If there is no input available, in() must return zero — buf is ignored in that case — and inflateBack() will return a buffer error. inflateBack() will call out(out_desc, buf, len) to write the uncompressed data buf[0..len-1]. out() should return zero on success, or non-zero on failure. If out() returns 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() are passed as the first parameter of in() and out() respectively when they are called. These descriptors can be optionally used to pass any information that the caller-supplied in() and out() functions need to do their job.

On return, inflateBack() will set strm->next_in and strm->avail_in to pass back any unused input that was provided by the last in() call. The return values of inflateBack() can be Z_STREAM_END on success, Z_BUF_ERROR if in() or out() returned an error, Z_DATA_ERROR if there was a format error in the deflate stream (in which case strm->msg is set to indicate the nature of the error), or Z_STREAM_ERROR if the stream was not properly initialized. In the case of Z_BUF_ERROR, an input or output error can be distinguished using strm->next_in which will be Z_NULL only if in() returned an error. If strm->next is not Z_NULL, then the Z_BUF_ERROR was due to out() returning non-zero. (in() will always be called before out(), so strm->next_in is assured to be defined if out() returns non-zero.) Note that inflateBack() cannot return Z_OK.

 

 

int inflateBackEnd(z_stream *strm)

All memory allocated by inflateBackInit() is freed.

inflateBackEnd() returns Z_OK on success, or Z_STREAM_ERROR if the stream state was inconsistent.

 

 

uLong zlibCompileFlags(void)

This function returns flags indicating compile-time options.

Type sizes, two bits each:

00

16 bits

01

32 bits

10

64 bits

11

other:

1.0

size of uInt

3.2

size of uLong

5.4

size of voidpf (pointer)

7.6

size of z_off_t

Compiler, assembler, and debug options:

8

DEBUG

9

ASMV or ASMINF — use ASM code

10

ZLIB_WINAPI — exported functions use the WINAPI calling convention

11

0 (reserved)

One-time table building (smaller code, but not thread-safe if true):

12

BUILDFIXED — build static block decoding tables when needed

13

DYNAMIC_CRC_TABLE — build CRC calculation tables when needed

14,15

0 (reserved)

Library content (indicates missing functionality):

16

NO_GZCOMPRESS — gz* functions cannot compress (to avoid linking deflate code when not needed)

17

NO_GZIP — deflate can't write gzip streams, and inflate can't detect and decode gzip streams (to avoid linking CRC code)

18-19

0 (reserved)

Operation variations (changes in library functionality):

20

PKZIP_BUG_WORKAROUND — slightly more permissive inflate

21

FASTEST — deflate algorithm with only one, lowest compression level

22,23

0 (reserved)

The sprintf variant used by gzprintf (zero is best):

24

0 = vs*, 1 = s* — 1 means limited to 20 arguments after the format

25

0 = *nprintf, 1 = *printf — 1 means gzprintf() not secure!

26

0 = returns value, 1 = void — 1 means inferred string length returned

Remainder:

27-31

0 (reserved)

UTILITY FUNCTIONS

 

 

int compress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);

The compress() function compresses the source buffer into the destination buffer. sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned by compressBound(sourcelen). Upon exit, destLen is the actual size of the compressed buffer. This function can be used to compress a whole file at once if the input file is mmap'ed.

compress() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, or Z_BUF_ERROR if there was not enough room in the output buffer.

 

 

int compress2(Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level);

The compress2() function compresses the source buffer into the destination buffer. The level parameter has the same meaning as in deflateInit(). sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be at least the value returned by compressBound(sourceLen). Upon exit, destLen is the actual size of the compressed buffer.

compress2() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_BUF_ERROR if there was not enough room in the output buffer, or Z_STREAM_ERROR if the level parameter is invalid.

 

 

int compressBound(uLong sourceLen)

compressBound() returns an upper bound on the compressed size after compress() or compress2() on sourceLen bytes. It would be used before a compress() or compress2() call to allocate the destination buffer.

 

 

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

The uncompress() function decompresses the source buffer into the destination buffer. sourceLen is the byte length of the source buffer. Upon entry, destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. (The size of the uncompressed data must have been saved previously by the compressor and transmitted to the decompressor by some mechanism outside the scope of this compression library.) Upon exit, destLen is the actual size of the compressed buffer. This function can be used to decompress a whole file at once if the input file is mmap'ed.

uncompress() returns Z_OK if successful, Z_MEM_ERROR if there was not enough memory, Z_BUF_ERROR if there was not enough room in the output buffer, or Z_DATA_ERROR if the input data was corrupted or incomplete.

 

 

gzFile gzopen(const char *path, const char *mode);

The gzopen() function opens a gzip (.gz) file for reading or writing. The mode parameter is as in fopen(3) (“rb” or “wb”) but can also include a compression level (wb9) or a strategy: ‘f’ for filtered data, as in “wb6f”; ‘h’ for Huffman only compression, as in “wb1h”, or ‘R’ for run-length encoding as in “wb1R”. (See the description of deflateInit2() for more information about the strategy parameter.)

gzopen() can be used to read a file which is not in gzip format; in this case gzread() will directly read from the file without decompression.

gzopen() returns NULL if the file could not be opened or if there was insufficient memory to allocate the (de)compression state; errno can be checked to distinguish the two cases (if errno is zero, the zlib error is Z_MEM_ERROR).

 

 

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

The gzdopen() function associates a gzFile with the file descriptor fd. File descriptors are obtained from calls like open(2), dup(2), creat(3), pipe(2), or fileno(3) (if the file has been previously opened with fopen(3)). The mode parameter is as in gzopen().

The next call to gzclose() on the returned gzFile will also close the file descriptor fd, just like fclose(fdopen(fd), mode) closes the file descriptor fd. If you want to keep fd open, use gzdopen(dup(fd), mode).

gzdopen() returns NULL if there was insufficient memory to allocate the (de)compression state.

 

 

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

The gzsetparams() function dynamically updates the compression level or strategy. See the description of deflateInit2() for the meaning of these parameters.

gzsetparams() returns Z_OK if successful, or Z_STREAM_ERROR if the file was not opened for writing.

 

 

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

The gzread() function reads the given number of uncompressed bytes from the compressed file. If the input file was not in gzip format, gzread() copies the given number of bytes into the buffer.

gzread() returns the number of uncompressed bytes actually read (0 for end of file, -1 for error).

 

 

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

The gzwrite() function writes the given number of uncompressed bytes into the compressed file. gzwrite() returns the number of uncompressed bytes actually written (0 in case of error).

 

 

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

The gzprintf() function converts, formats, and writes the args to the compressed file under control of the format string, as in fprintf(3). gzprintf() returns the number of uncompressed bytes actually written (0 in case of error). The number of uncompressed bytes written is limited to 4095. The caller should make sure that this limit is not exceeded. If it is exceeded, then gzprintf() will return an error (0) with nothing written. In this case, there may also be a buffer overflow with unpredictable consequences, which is possible only if zlib was compiled with the insecure functions sprintf() or vsprintf() because the secure snprintf() or vsnprintf() functions were not available.

 

 

int gzputs(gzFile file, const char *s);

The gzputs() function writes the given null-terminated string to the compressed file, excluding the terminating null character.

gzputs() returns the number of characters written, or -1 in case of error.

 

 

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

The gzgets() function reads bytes from the compressed file until len-1 characters are read, or a newline character is read and transferred to buf, or an end-of-file condition is encountered. The string is then terminated with a null character.

gzgets() returns buf, or Z_NULL in case of error.

 

 

int gzputc(gzFile file, int c);

The gzputc() function writes c, converted to an unsigned char, into the compressed file. gzputc() returns the value that was written, or -1 in case of error.

 

 

int gzgetc(gzFile file);

The gzgetc() function reads one byte from the compressed file. gzgetc() returns this byte or -1 in case of end of file or error.

 

 

int gzungetc(int c, gzFile file)

Push one character back onto the stream to be read again later. Only one character of push-back is allowed. gzungetc() returns the character pushed, or -1 on failure. gzungetc() will fail if a character has been pushed but not read yet, or if c is -1. The pushed character will be discarded if the stream is repositioned with gzseek() or gzrewind().

 

 

int gzflush(gzFile file, int flush);

The gzflush() function flushes all pending output into the compressed file. The parameter flush is as in the deflate() function. The return value is the zlib error number (see function gzerror() below). gzflush() returns Z_OK if the flush parameter is Z_FINISH and all output could be flushed.

gzflush() should be called only when strictly necessary because it can degrade compression.

 

 

z_off_t gzseek(gzFile file, z_off_t offset, int whence);

Sets the starting position for the next gzread() or gzwrite() on the given compressed file. The offset represents a number of bytes in the uncompressed data stream. The whence parameter is defined as in lseek(2); the value SEEK_END is not supported.

If the file is opened for reading, this function is emulated but can be extremely slow. If the file is opened for writing, only forward seeks are supported; gzseek() then compresses a sequence of zeroes up to the new starting position.

gzseek() returns the resulting offset location as measured in bytes from the beginning of the uncompressed stream, or -1 in case of error, in particular if the file is opened for writing and the new starting position would be before the current position.

 

 

int gzrewind(gzFile file);

The gzrewind() function rewinds the given file. This function is supported only for reading.

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

 

 

z_off_t gztell(gzFile file);

The gztell() function returns the starting position for the next gzread() or gzwrite() on the given compressed file. This position represents a number of bytes in the uncompressed data stream.

gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).

 

 

int gzeof(gzFile file);

The gzeof() function returns 1 when EOF has previously been detected reading the given input stream, otherwise zero.

 

 

int gzdirect(gzFile file);

The gzdirect() function returns 1 if the file is being read directly without compression; otherwise it returns 0.

 

 

int gzclose(gzFile file);

The gzclose() function flushes all pending output if necessary, closes the compressed file and deallocates all the (de)compression state. The return value is the zlib error number (see function gzerror() below).

 

 

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

The gzerror() function returns the error message for the last error which occurred on the given compressed file. errnum is set to the 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.

 

 

void gzclearerr(gzFile file)

Clears the error and end-of-file flags for file. This is analogous to the clearerr() function in stdio. This is useful for continuing to read a gzip file that is being written concurrently.

CHECKSUM FUNCTIONS

 

 

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

The adler32() function updates a running Adler-32 checksum with the bytes buf[0..len-1] and returns the updated checksum. If buf is NULL, this function returns the required initial value for the checksum.

An Adler-32 checksum is almost as reliable as a CRC32 but can be computed much faster. Usage example:

uLong adler = adler32(0L, Z_NULL, 0); 
 
while (read_buffer(buffer, length) != EOF) { 
adler = adler32(adler, buffer, length); 
} 
if (adler != original_adler) error();
    

 

 

uLong adler32_combine(uLong adler1, uLong adler2, z_off_t len2)

The adler32_combine() function combines two Adler-32 checksums into one. For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, Adler-32 checksums are calculated for each, adler1 and adler2. adler32_combine() returns the Adler-32 checksum of seq1 and seq2 concatenated, requiring only adler1, adler2, and len2.

 

 

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

The crc32() function updates a running CRC-32 with the bytes buf[0..len-1] and returns the updated CRC-32. If buf is NULL, this function returns the required initial value for the CRC. Pre- and post-conditioning (one's complement) is performed within this function so it shouldn't be done by the application. Usage example:

uLong crc = crc32(0L, Z_NULL, 0); 
 
while (read_buffer(buffer, length) != EOF) { 
crc = crc32(crc, buffer, length); 
} 
if (crc != original_crc) error();
    

 

 

uLong crc32_combine(uLong crc1, uLong crc2, z_off_t len2)

The crc32_combine() 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 are calculated for each, crc1 and crc2. crc32_combine() returns the CRC-32 check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and len2.

STRUCTURES

struct internal_state; 
 
typedef struct z_stream_s { 
    Bytef    *next_in;  /* next input byte */ 
    uInt     avail_in;  /* number of bytes available at next_in */ 
    off_t    total_in;  /* total nb of input bytes read so far */ 
 
    Bytef    *next_out; /* next output byte should be put there */ 
    uInt     avail_out; /* remaining free space at next_out */ 
    off_t    total_out; /* total nb of bytes output so far */ 
 
    char     *msg;      /* last error message, NULL if no error */ 
    struct internal_state FAR *state; /* not visible by applications */ 
 
    alloc_func zalloc;  /* used to allocate the internal state */ 
    free_func  zfree;   /* used to free the internal state */ 
    voidpf     opaque;  /* private data object passed to zalloc and zfree*/ 
 
    int     data_type;  /* best guess about the data type: binary or text*/ 
    uLong   adler;      /* adler32 value of the uncompressed data */ 
    uLong   reserved;   /* reserved for future use */ 
} z_stream; 
 
typedef z_stream FAR * z_streamp;

/* 
     gzip header information passed to and from zlib routines. 
  See RFC 1952 for more details on the meanings of these fields. 
*/ 
typedef struct gz_header_s { 
    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)*/ 
    int     os;         /* operating system */ 
    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) */ 
    Bytef   *name;      /* pointer to zero-terminated file name or Z_NULL*/ 
    uInt    name_max;   /* space at name (only when reading header) */ 
    Bytef   *comment;   /* pointer to zero-terminated comment or Z_NULL */ 
    uInt    comm_max;   /* space at comment (only when reading header) */ 
    int     hcrc;       /* true if there was or will be a header crc */ 
    int     done;       /* true when done reading gzip header (not used 
                           when writing a gzip file) */ 
} gz_header; 
 
typedef gz_header FAR *gz_headerp;

CONSTANTS

#define Z_NO_FLUSH      0 
#define Z_PARTIAL_FLUSH 1 /* will be removed, use Z_SYNC_FLUSH instead */ 
#define Z_SYNC_FLUSH    2 
#define Z_FULL_FLUSH    3 
#define Z_FINISH        4 
#define Z_BLOCK		5 
/* Allowed flush values; see deflate() and inflate() below for details */ 
 
#define Z_OK            0 
#define Z_STREAM_END    1 
#define Z_NEED_DICT     2 
#define Z_ERRNO        (-1) 
#define Z_STREAM_ERROR (-2) 
#define Z_DATA_ERROR   (-3) 
#define Z_MEM_ERROR    (-4) 
#define Z_BUF_ERROR    (-5) 
#define Z_VERSION_ERROR (-6) 
/* Return codes for the compression/decompression functions. 
 * Negative values are errors, 
 * positive values are used for special but normal events. 
 */ 
 
#define Z_NO_COMPRESSION         0 
#define Z_BEST_SPEED             1 
#define Z_BEST_COMPRESSION       9 
#define Z_DEFAULT_COMPRESSION  (-1) 
/* compression levels */ 
 
#define Z_FILTERED            1 
#define Z_HUFFMAN_ONLY        2 
#define Z_RLE                 3 
#define Z_FIXED               4 
#define Z_DEFAULT_STRATEGY    0 
/* compression strategy; see deflateInit2() below for details */ 
 
#define Z_BINARY   0 
#define Z_TEXT     1 
#define Z_ASCII    Z_TEXT /* for compatibility with 1.2.2 and earlier */ 
#define Z_UNKNOWN  2 
/* Possible values of the data_type field (though see inflate()) */ 
 
#define Z_DEFLATED   8 
/* The deflate compression method 
 * (the only one supported in this version) 
*/ 
 
#define Z_NULL  0  /* for initializing zalloc, zfree, opaque */ 
 
#define zlib_version zlibVersion() 
/* for compatibility with versions < 1.0.2 */

VARIOUS HACKS

 

 

int deflateInit_(z_stream strm, int level, const char *version, int stream_size);

 

int inflateInit_(z_stream strm, const char *version, int stream_size);

 

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

 

int inflateInit2_(z_stream strm, int windowBits, const char *version, int stream_size);

 

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

 

const char * zError(int err);

 

int inflateSyncPoint(z_streamp z);

 

const uLongf * get_crc_table(void);

 

SEE ALSO

STANDARDS

HISTORY

AUTHORS