.\" $OpenBSD: compress.3,v 1.10 2007/05/31 19:19:39 jmc Exp $ .\" .\" Copyright (C) 1995-2005 Jean-loup Gailly and Mark Adler .\" .\" This software is provided 'as-is', without any express or implied .\" warranty. In no event will the authors be held liable for any damages .\" arising from the use of this software. .\" .\" Permission is granted to anyone to use this software for any purpose, .\" including commercial applications, and to alter it and redistribute it .\" freely, subject to the following restrictions: .\" .\" The origin of this software must not be misrepresented; you must not .\" claim that you wrote the original software. If you use this software .\" in a product, an acknowledgment in the product documentation would be .\" appreciated but is not required. .\" Altered source versions must be plainly marked as such, and must not be .\" misrepresented as being the original software. .\" This notice may not be removed or altered from any source distribution. .\" .\" Converted to mdoc format for the OpenBSD project .\" by Jason McIntyre <jmc@openbsd.org> .\" .\" This page corresponds to zlib version 1.2.3 .\" .Dd $Mdocdate: May 31 2007 $ .Dt COMPRESS 3 .Os .Sh NAME .Nm compress .Nd zlib general purpose compression library .Sh SYNOPSIS .Fd "#include <zlib.h>" .Pp Basic functions .Pp .Ft const char * .Fn zlibVersion "void" .Ft int .Fn deflateInit "z_streamp strm" "int level" .Ft int .Fn deflate "z_streamp strm" "int flush" .Ft int .Fn deflateEnd "z_streamp strm" .Ft int .Fn inflateInit "z_streamp strm" .Ft int .Fn inflate "z_streamp strm" "int flush" .Ft int .Fn inflateEnd "z_streamp strm" .Pp Advanced functions .Pp .Ft int .Fn deflateInit2 "z_streamp strm" "int level" "int method" "int windowBits" "int memLevel" "int strategy" .Ft int .Fn deflateSetDictionary "z_streamp strm" "const Bytef *dictionary" "uInt dictLength" .Ft int .Fn deflateCopy "z_streamp dest" "z_streamp source" .Ft int .Fn deflateReset "z_streamp strm" .Ft int .Fn deflateParams "z_streamp strm" "int level" "int strategy" .Ft int .Fn deflateTune "z_streamp strm" "int good_length" "int max_lazy" "int nice_length" "int max_chain" .Ft uLong .Fn deflateBound "z_streamp strm" "uLong sourceLen" .Ft int .Fn deflatePrime "z_streamp strm" "int bits" "int value" .Ft int .Fn deflateSetHeader "z_streamp strm" "gz_headerp head" .Ft int .Fn inflateInit2 "z_streamp strm" "int windowBits" .Ft int .Fn inflateSetDictionary "z_streamp strm" "const Bytef *dictionary" "uInt dictLength" .Ft int .Fn inflateSync "z_streamp strm" .Ft int .Fn inflateCopy "z_streamp dst" "z_streamp source" .Ft int .Fn inflateReset "z_streamp strm" .Ft int .Fn inflatePrime "z_streamp strm" "int bits" "int value" .Ft int .Fn inflateGetHeader "z_streamp strm" "gz_headerp head" .Ft int .Fn inflateBackInit "z_stream *strm" "int windowBits" "unsigned char FAR *window" .Ft int .Fn inflateBack "z_stream *strm" "in_func in" "void FAR *in_desc" "out_func out" "void FAR *out_desc" .Ft int .Fn inflateBackEnd "z_stream *strm" .Ft uLong .Fn zlibCompileFlags "void" .Pp Utility functions .Pp .Fd typedef voidp gzFile; .Pp .Ft int .Fn compress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" .Ft int .Fn compress2 "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" "int level" .Ft uLong .Fn compressBound "uLong sourceLen" .Ft int .Fn uncompress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" .Ft gzFile .Fn gzopen "const char *path" "const char *mode" .Ft gzFile .Fn gzdopen "int fd" "const char *mode" .Ft int .Fn gzsetparams "gzFile file" "int level" "int strategy" .Ft int .Fn gzread "gzFile file" "voidp buf" "unsigned len" .Ft int .Fn gzwrite "gzFile file" "voidpc buf" "unsigned len" .Ft int .Fn gzprintf "gzFile file" "const char *format" "..." .Ft int .Fn gzputs "gzFile file" "const char *s" .Ft char * .Fn gzgets "gzFile file" "char *buf" "int len" .Ft int .Fn gzputc "gzFile file" "int c" .Ft int .Fn gzgetc "gzFile file" .Ft int .Fn gzungetc "int c" "gzFile file" .Ft int .Fn gzflush "gzFile file" "int flush" .Ft z_off_t .Fn gzseek "gzFile file" "z_off_t offset" "int whence" .Ft int .Fn gzrewind "gzFile file" .Ft z_off_t .Fn gztell "gzFile file" .Ft int .Fn gzeof "gzFile file" .Ft int .Fn gzdirect "gzFile file" .Ft int .Fn gzclose "gzFile file" .Ft const char * .Fn gzerror "gzFile file" "int *errnum" .Ft void .Fn gzclearerr "gzFile file" .Pp Checksum functions .Pp .Ft uLong .Fn adler32 "uLong adler" "const Bytef *buf" "uInt len" .Ft uLong .Fn adler32_combine "uLong adler1" "uLong adler2" "z_off_t len2" .Ft uLong .Fn crc32 "uLong crc" "const Bytef *buf" "uInt len" .Ft uLong .Fn crc32_combine "uLong crc1" "uLong crc2" "z_off_t len2" .Sh DESCRIPTION This manual page describes the .Nm zlib general purpose compression library, version 1.2.3. .Pp The .Nm 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 .Pq deflation but other algorithms will be added later and will have the same stream interface. .Pp Compression can be done in a single step if the buffers are large enough .Pq for example if an input file is mmap'ed , or can be done by repeated calls of the compression function. In the latter case, the application must provide more input and/or consume the output .Pq providing more output space before each call. .Pp The compressed data format used by default by the in-memory functions is the .Nm zlib format, which is a zlib wrapper documented in RFC 1950, wrapped around a deflate stream, which is itself documented in RFC 1951. .Pp The library also supports reading and writing files in .Xr gzip 1 .Pq .gz format with an interface similar to that of .Xr stdio 3 using the functions that start with .Qq 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 streams in memory as well. .Pp 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. .Pp The library does not install any signal handler. The decoder checks the consistency of the compressed data, so the library should never crash even in case of corrupted input. .Pp The functions within the library are divided into the following sections: .Pp .Bl -dash -offset indent -compact .It Basic functions .It Advanced functions .It Utility functions .It Checksum functions .El .Sh BASIC FUNCTIONS .Bl -tag -width Ds .It Xo .Fa const char * .Fn zlibVersion "void" ; .Xc .Pp The application can compare .Fn zlibVersion and .Dv ZLIB_VERSION for consistency. If the first character differs, the library code actually used is not compatible with the .Aq Pa zlib.h header file used by the application. This check is automatically made by .Fn deflateInit and .Fn inflateInit . .It Xo .Fa int .Fn deflateInit "z_streamp strm" "int level" ; .Xc .Pp The .Fn deflateInit function initializes the internal stream state for compression. The fields .Fa zalloc , .Fa zfree , and .Fa opaque must be initialized before by the caller. If .Fa zalloc and .Fa zfree are set to .Dv Z_NULL , .Fn deflateInit updates them to use default allocation functions. .Pp The compression level must be .Dv Z_DEFAULT_COMPRESSION , or between 0 and 9: 1 gives best speed, 9 gives best compression, 0 gives no compression at all (the input data is simply copied a block at a time). .Pp .Dv Z_DEFAULT_COMPRESSION requests a default compromise between speed and compression .Pq currently equivalent to level 6 . .Pp .Fn deflateInit returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_STREAM_ERROR if level is not a valid compression level, .Dv Z_VERSION_ERROR if the .Nm zlib library version .Pq zlib_version is incompatible with the version assumed by the caller .Pq ZLIB_VERSION . .Fa msg is set to null if there is no error message. .Fn deflateInit does not perform any compression: this will be done by .Fn deflate . .It Xo .Fa int .Fn deflate "z_streamp strm" "int flush" ; .Xc .Pp .Fn deflate compresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency .Pq reading input without producing any output except when forced to flush. .Pp The detailed semantics are as follows. .Fn deflate performs one or both of the following actions: .Pp Compress more input starting at .Fa next_in and update .Fa next_in and .Fa avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), .Fa next_in and .Fa avail_in are updated and processing will resume at this point for the next call to .Fn deflate . .Pp Provide more output starting at .Fa next_out and update .Fa next_out and .Fa avail_out accordingly. This action is forced if the parameter .Fa flush is non-zero. Forcing .Fa flush frequently degrades the compression ratio, so this parameter should be set only when necessary .Pq in interactive applications . Some output may be provided even if .Fa flush is not set. .Pp Before the call to .Fn deflate , the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating .Fa avail_in or .Fa avail_out accordingly; .Fa avail_out should never be zero before the call. The application can consume the compressed output when it wants, for example when the output buffer is full .Pq avail_out == 0 , or after each call to .Fn deflate . If .Fn deflate returns .Dv Z_OK and with zero .Fa avail_out , it must be called again after making room in the output buffer because there might be more output pending. .Pp Normally the parameter .Fa flush is set to .Dv Z_NO_FLUSH , which allows .Fn deflate to decide how much data to accumulate before producing output, in order to maximise compression. .Pp If the parameter .Fa flush is set to .Dv Z_SYNC_FLUSH , all pending output is flushed to the output buffer and the output is aligned on a byte boundary, so that the decompressor can get all input data available so far. (In particular, .Fa avail_in is zero after the call if enough output space has been provided before the call.) Flushing may degrade compression for some compression algorithms and so it should be used only when necessary. .Pp If .Fa flush is set to .Dv Z_FULL_FLUSH , all output is flushed as with .Dv Z_SYNC_FLUSH , and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Using .Dv Z_FULL_FLUSH too often can seriously degrade compression. .Pp If .Fn deflate returns with avail_out == 0, this function must be called again with the same value of the flush parameter and more output space (updated .Fa avail_out ) , until the flush is complete .Pf ( Fn deflate returns with non-zero .Fa avail_out ) . In the case of a .Dv Z_FULL_FLUSH or a .Dv Z_SYNC_FLUSH , make sure that .Fa avail_out is greater than six to avoid repeated flush markers due to avail_out == 0 on return. .Pp If the parameter .Fa flush is set to .Dv Z_FINISH , pending input is processed, pending output is flushed and .Fn deflate returns with .Dv Z_STREAM_END if there was enough output space; if .Fn deflate returns with .Dv Z_OK , this function must be called again with .Dv Z_FINISH and more output space (updated .Fa avail_out but no more input data, until it returns with .Dv Z_STREAM_END or an error. After .Fn deflate has returned .Dv Z_STREAM_END , the only possible operations on the stream are .Fn deflateReset or .Fn deflateEnd . .Pp .Dv Z_FINISH can be used immediately after .Fn deflateInit if all the compression is to be done in a single step. In this case, .Fa avail_out must be at least the value returned by .Fn deflateBound .Pq see below . If .Fn deflate does not return .Dv Z_STREAM_END , then it must be called again as described above. .Pp .Fn deflate sets strm-\*(Gtadler to the Adler-32 checksum of all input read so far (that is, .Fa total_in bytes). .Pp .Fn deflate may update strm-\*(Gtdata_type if it can make a good guess about the input data type .Pq 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. .Pp .Fn deflate returns .Dv Z_OK if some progress has been made .Pq more input processed or more output produced , .Dv Z_STREAM_END if all input has been consumed and all output has been produced (only when .Fa flush is set to .Dv Z_FINISH ) , .Dv Z_STREAM_ERROR if the stream state was inconsistent (for example, if .Fa next_in or .Fa next_out was .Dv NULL ) , .Dv Z_BUF_ERROR if no progress is possible (for example, .Fa avail_in or .Fa avail_out was zero). Note that .Dv Z_BUF_ERROR is not fatal, and .Fn deflate can be called again with more input and more output space to continue processing. .It Xo .Fa int .Fn deflateEnd "z_streamp strm" ; .Xc .Pp All dynamically allocated data structures for this stream are freed. This function discards any unprocessed input and does not flush any pending output. .Pp .Fn deflateEnd returns .Dv Z_OK if successful, .Dv Z_STREAM_ERROR if the stream state was inconsistent, .Dv Z_DATA_ERROR if the stream was freed prematurely .Pq some input or output was discarded . In the error case, .Fa msg may be set but then points to a static string .Pq which must not be deallocated . .It Xo .Fa int .Fn inflateInit "z_streamp strm" ; .Xc The .Fn inflateInit function initializes the internal stream state for decompression. The fields .Fa next_in , .Fa avail_in , .Fa zalloc , .Fa zfree , and .Fa opaque must be initialized before by the caller. If .Fa next_in is not .Dv Z_NULL and .Fa avail_in is large enough .Pq the exact value depends on the compression method , .Fn inflateInit determines the compression method from the .Nm zlib header and allocates all data structures accordingly; otherwise the allocation will be deferred to the first call to .Fn inflate . If .Fa zalloc and .Fa zfree are set to .Dv Z_NULL , .Fn inflateInit updates them to use default allocation functions. .Pp .Fn inflateInit returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_VERSION_ERROR if the .Nm zlib library version is incompatible with the version assumed by the caller. .Fa msg is set to null if there is no error message. .Fn inflateInit does not perform any decompression apart from reading the .Nm zlib header if present: this will be done by .Fn inflate . (So .Fa next_in and .Fa avail_in may be modified, but .Fa next_out and .Fa avail_out are unchanged.) .It Xo .Fa int .Fn inflate "z_streamp strm" "int flush" ; .Xc .Fn inflate decompresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. It may introduce some output latency .Pq reading input without producing any output except when forced to flush. .Pp The detailed semantics are as follows. .Fn inflate performs one or both of the following actions: .Pp Decompress more input starting at .Fa next_in and update .Fa next_in and .Fa avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), .Fa next_in is updated and processing will resume at this point for the next call to .Fn inflate . .Pp Provide more output starting at .Fa next_out and update .Fa next_out and .Fa avail_out accordingly. .Fn inflate provides as much output as possible, until there is no more input data or no more space in the output buffer .Pq see below about the flush parameter . .Pp Before the call to .Fn inflate , the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating the next_* and avail_* values accordingly. The application can consume the uncompressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call to .Fn inflate . If .Fn inflate returns .Dv Z_OK and with zero .Fa avail_out , it must be called again after making room in the output buffer because there might be more output pending. .Pp The .Fa flush parameter of .Fn inflate can be .Dv Z_NO_FLUSH , Z_SYNC_FLUSH , Z_FINISH , or .Dv Z_BLOCK . .Dv Z_SYNC_FLUSH requests that .Fn inflate flush as much output as possible to the output buffer. .Dv Z_BLOCK requests that .Fn inflate stop if and when it gets to the next deflate block boundary. When decoding the zlib or gzip format, this will cause .Fn inflate to return immediately after the header and before the first block. When doing a raw inflate, .Fn 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. .Pp The .Dv Z_BLOCK option assists in appending to or combining deflate streams. Also to assist in this, on return .Fn inflate will set strm-\*(Gtdata_type to the number of unused bits in the last byte taken from strm-\*(Gtnext_in, plus 64 if .Fn inflate is currently decoding the last block in the deflate stream, plus 128 if .Fn 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-\*(Gtnext_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. .Pp .Fn inflate should normally be called until it returns .Dv Z_STREAM_END or an error. However if all decompression is to be performed in a single step .Pq a single call to inflate , the parameter .Fa flush should be set to .Dv Z_FINISH . In this case all pending input is processed and all pending output is flushed; .Fa avail_out must be large enough to hold all the uncompressed data. (The size of the uncompressed data may have been saved by the compressor for this purpose.) The next operation on this stream must be .Fn inflateEnd to deallocate the decompression state. The use of .Dv Z_FINISH is never required, but can be used to inform .Fn inflate that a faster approach may be used for the single .Fn inflate call. .Pp In this implementation, .Fn 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 .Fa flush parameter in this implementation is on the return value of .Fn inflate , as noted below, or when it returns early because .Dv Z_BLOCK is used. .Pp If a preset dictionary is needed after this call (see .Fn inflateSetDictionary below), .Fn inflate sets strm-\*(Gtadler to the Adler-32 checksum of the dictionary chosen by the compressor and returns Z_NEED_DICT; otherwise it sets strm-\*(Gtadler to the Adler-32 checksum of all output produced so far (that is, .Fa total_out bytes) and returns .Dv Z_OK , Z_STREAM_END or an error code as described below. At the end of the stream, .Fn inflate checks that its computed Adler-32 checksum is equal to that saved by the compressor and returns .Dv Z_STREAM_END only if the checksum is correct. .Pp .Fn inflate 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 .Fn inflateInit2 below, or .Fn inflateBack and perform their own processing of the gzip header and trailer. .Pp .Fn inflate returns .Dv Z_OK if some progress has been made .Pq more input processed or more output produced , .Dv Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, .Dv Z_NEED_DICT if a preset dictionary is needed at this point, .Dv Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the .Nm zlib format or incorrect check value), .Dv Z_STREAM_ERROR if the stream structure was inconsistent (for example, if .Fa next_in or .Fa next_out was .Dv NULL ) , .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_BUF_ERROR if no progress is possible or if there was not enough room in the output buffer when .Dv Z_FINISH is used. Note that .Dv Z_BUF_ERROR is not fatal, and .Fn inflate can be called again with more input and more output space to continue compressing. If .Dv Z_DATA_ERROR is returned, the application may then call .Fn inflateSync to look for a good compression block if a partial recovery of the data is desired. .It Xo .Fa int .Fn inflateEnd "z_streamp strm" ; .Xc All dynamically allocated data structures for this stream are freed. This function discards any unprocessed input and does not flush any pending output. .Pp .Fn inflateEnd returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the stream state was inconsistent. In the error case, .Fa msg may be set but then points to a static string .Pq which must not be deallocated . .El .Sh ADVANCED FUNCTIONS The following functions are needed only in some special applications. .Bl -tag -width Ds .It Xo .Fa int .Fn deflateInit2 "z_streamp strm" "int level" "int method" "int windowBits" "int memLevel" "int strategy" ; .Xc .Pp This is another version of .Fn deflateInit with more compression options. The fields .Fa next_in , .Fa zalloc , .Fa zfree , and .Fa opaque must be initialized before by the caller. .Pp The .Fa method parameter is the compression method. It must be .Dv Z_DEFLATED in this version of the library. .Pp The .Fa windowBits parameter is the base two logarithm of the window size .Pq the size of the history buffer . It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage. The default value is 15 if .Fn deflateInit is used instead. .Pp .Fa windowBits can also be -8..-15 for raw deflate. In this case, -windowBits determines the window size. .Fn deflate will then generate raw deflate data with no zlib header or trailer, and will not compute an Adler-32 check value. .Pp .Fa windowBits can also be greater than 15 for optional gzip encoding. Add 16 to .Fa 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 .Pq set to zero , no header crc, and the operating system will be set to 255 .Pq unknown . If a gzip stream is being written, strm-\*(Gtadler is a crc32 instead of an adler32. .Pp The .Fa memLevel parameter specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed. The default value is 8. See .Aq Pa zconf.h for total memory usage as a function of .Fa windowBits and .Fa memLevel . .Pp The .Fa strategy parameter is used to tune the compression algorithm. Use the value .Dv Z_DEFAULT_STRATEGY for normal data; .Dv Z_FILTERED for data produced by a filter .Pq or predictor ; .Dv Z_HUFFMAN_ONLY to force Huffman encoding only .Pq no string match , or .Dv Z_RLE to limit match distances to one .Pq 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 .Dv Z_FILTERED is to force more Huffman coding and less string matching; it is somewhat intermediate between .Dv Z_DEFAULT and .Dv Z_HUFFMAN_ONLY . .Dv Z_RLE is designed to be almost as fast as .Dv Z_HUFFMAN_ONLY , but gives better compression for PNG image data. The .Fa strategy parameter only affects the compression ratio but not the correctness of the compressed output, even if it is not set appropriately. .Dv Z_FIXED prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications. .Pp .Fn deflateInit2 returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_STREAM_ERROR if a parameter is invalid .Pq such as an invalid method . .Fa msg is set to null if there is no error message. .Fn deflateInit2 does not perform any compression: this will be done by .Fn deflate . .It Xo .Fa int .Fn deflateSetDictionary "z_streamp strm" "const Bytef *dictionary" "uInt dictLength" ; .Xc .Pp Initializes the compression dictionary from the given byte sequence without producing any compressed output. This function must be called immediately after .Fn deflateInit , .Fn deflateInit2 , or .Fn deflateReset , before any call to .Fn deflate . The compressor and decompressor must use exactly the same dictionary (see .Fn inflateSetDictionary ) . .Pp The dictionary should consist of strings .Pq byte sequences that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary. .Pp Depending on the size of the compression data structures selected by .Fn deflateInit or .Fn deflateInit2 , a part of the dictionary may in effect be discarded, for example if the dictionary is larger than the window size in .Fn deflate or .Fn deflate2 . Thus the strings most likely to be useful should be put at the end of the dictionary, not at the front. In addition, the current implementation of .Fn deflate will use at most the window size minus 262 bytes of the provided dictionary. .Pp Upon return of this function, strm-\*(Gtadler 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-\*(Gtadler is not set. .Pp .Fn deflateSetDictionary returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if a parameter is invalid .Pq such as NULL dictionary or the stream state is inconsistent (for example if .Fn deflate has already been called for this stream or if the compression method is bsort). .Fn deflateSetDictionary does not perform any compression: this will be done by .Fn deflate . .It Xo .Fa int .Fn deflateCopy "z_streamp dest" "z_streamp source" ; .Xc .Pp The .Fn deflateCopy function sets the destination stream as a complete copy of the source stream. .Pp This function can be useful when several compression strategies will be tried, for example when there are several ways of pre-processing the input data with a filter. The streams that will be discarded should then be freed by calling .Fn deflateEnd . Note that .Fn deflateCopy duplicates the internal compression state which can be quite large, so this strategy is slow and can consume lots of memory. .Pp .Fn deflateCopy returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_STREAM_ERROR if the source stream state was inconsistent (such as .Fa zalloc being NULL). .Fa msg is left unchanged in both source and destination. .It Xo .Fa int .Fn deflateReset "z_streamp strm" ; .Xc .Pp This function is equivalent to .Fn deflateEnd followed by .Fn deflateInit , but does not free and reallocate all the internal compression state. The stream will keep the same compression level and any other attributes that may have been set by .Fn deflateInit2 . .Pp .Fn deflateReset returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent (such as .Fa zalloc or .Fa state being NULL). .It Xo .Fa int .Fn deflateParams "z_streamp strm" "int level" "int strategy" ; .Xc .Pp The .Fn deflateParams function dynamically updates the compression level and compression strategy. The interpretation of level and strategy is as in .Fn deflateInit2 . This can be used to switch between compression and straight copy of the input data, or to switch to a different kind of input data requiring a different strategy. If the compression level is changed, the input available so far is compressed with the old level .Pq and may be flushed ; the new level will take effect only at the next call to .Fn deflate . .Pp Before the call to .Fn deflateParams , the stream state must be set as for a call to .Fn deflate , since the currently available input may have to be compressed and flushed. In particular, strm-\*(Gtavail_out must be non-zero. .Pp .Fn deflateParams returns .Dv Z_OK if successful, .Dv Z_STREAM_ERROR if the source stream state was inconsistent or if a parameter was invalid, or .Dv Z_BUF_ERROR if strm-\*(Gtavail_out was zero. .It Xo .Fa int .Fn deflateTune "z_streamp strm" "int good_length" "int max_lazy" "int nice_length" "int max_chain" .Xc .Pp Fine tune .Fn deflate Ns '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 .Pa deflate.c source code for the meaning of the .Fa max_lazy , good_length , nice_length , and .Fa max_chain parameters. .Pp .Fn deflateTune can be called after .Fn deflateInit or .Fn deflateInit2 , and returns .Dv Z_OK on success, or .Dv Z_STREAM_ERROR for an invalid deflate stream. .It Xo .Fa uLong .Fn deflateBound "z_streamp strm" "uLong sourceLen" .Xc .Pp .Fn deflateBound returns an upper bound on the compressed size after deflation of .Fa sourceLen bytes. It must be called after .Fn deflateInit or .Fn deflateInit2 . This would be used to allocate an output buffer for deflation in a single pass, and so would be called before .Fn deflate . .It Xo .Fa int .Fn deflatePrime "z_streamp strm" "int bits" "int value" .Xc .Pp .Fn deflatePrime inserts .Fa 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 .Fn deflate call after a .Fn deflateInit2 or .Fn deflateReset . .Fa bits must be less than or equal to 16, and that many of the least significant bits of .Fa value will be inserted in the output. .Pp .Fn deflatePrime returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent. .It Xo .Fa int .Fn deflateSetHeader "z_streamp strm" "gz_headerp head" .Xc .Pp .Fn deflateSetHeader provides gzip header information for when a gzip stream is requested by .Fn deflateInit2 . .Fn deflateSetHeader may be called after .Fn deflateInit2 or .Fn deflateReset and before the first call of .Fn 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 .Dv Z_NULL , .Fa name and .Fa comment are terminated with a zero byte, and that if .Fa extra is not .Dv Z_NULL , that .Fa 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 .Xr gzip 1 do not support header CRCs, and will report that it is a .Dq multi-part gzip file and give up. .Pp If .Fn 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 .Fn deflateReset . .Pp .Fn deflateSetHeader returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent. .It Xo .Fa int .Fn inflateInit2 "z_streamp strm" "int windowBits" ; .Xc .Pp This is another version of .Fn inflateInit with an extra parameter. The fields .Fa next_in , .Fa avail_in , .Fa zalloc , .Fa zfree , and .Fa opaque must be initialized before by the caller. .Pp The .Fa windowBits parameter is the base two logarithm of the maximum window size .Pq the size of the history buffer . It should be in the range 8..15 for this version of the library. The default value is 15 if .Fn inflateInit is used instead. .Fa windowBits must be greater than or equal to the .Fa windowBits value provided to .Fn deflateInit2 while compressing, or it must be equal to 15 if .Fn deflateInit2 was not used. If a compressed stream with a larger window size is given as input, .Fn inflate will return with the error code .Dv Z_DATA_ERROR instead of trying to allocate a larger window. .Pp .Fa windowBits can also be -8..-15 for raw inflate. In this case, -windowBits determines the window size. .Fn 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 .Fn deflateInit2 applies to the magnitude of .Fa windowBits . .Pp .Fa 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 .Dv Z_DATA_ERROR ) . If a gzip stream is being decoded, strm-\*(Gtadler is a crc32 instead of an adler32. .Pp .Fn inflateInit2 returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_STREAM_ERROR if a parameter is invalid (such as a null strm). .Fa msg is set to null if there is no error message. .Fn inflateInit2 does not perform any decompression apart from reading the .Nm zlib header if present: this will be done by .Fn inflate . (So .Fa next_in and .Fa avail_in may be modified, but .Fa next_out and .Fa avail_out are unchanged.) .It Xo .Fa int .Fn inflateSetDictionary "z_streamp strm" "const Bytef *dictionary" "uInt dictLength" ; .Xc .Pp Initializes the decompression dictionary from the given uncompressed byte sequence. This function must be called immediately after a call to .Fn inflate if that call returned .Dv Z_NEED_DICT . The dictionary chosen by the compressor can be determined from the Adler-32 value returned by that call to .Fn inflate . The compressor and decompressor must use exactly the same dictionary (see .Fn deflateSetDictionary ) . For raw inflate, this function can be called immediately after .Fn inflateInit2 or .Fn inflateReset and before any call to .Fn inflate to set the dictionary. The application must ensure that the dictionary that was used for compression is provided. .Pp .Fn inflateSetDictionary returns .Dv Z_OK if successful, .Dv Z_STREAM_ERROR if a parameter is invalid .Pq such as NULL dictionary or the stream state is inconsistent, .Dv Z_DATA_ERROR if the given dictionary doesn't match the expected one .Pq incorrect Adler-32 value . .Fn inflateSetDictionary does not perform any decompression: this will be done by subsequent calls of .Fn inflate . .It Xo .Fa int .Fn inflateSync "z_streamp strm" ; .Xc .Pp Skips invalid compressed data until a full flush point (see above the description of .Fn deflate with .Dv Z_FULL_FLUSH ) can be found, or until all available input is skipped. No output is provided. .Pp .Fn inflateSync returns .Dv Z_OK if a full flush point has been found, .Dv Z_BUF_ERROR if no more input was provided, .Dv Z_DATA_ERROR if no flush point has been found, or .Dv Z_STREAM_ERROR if the stream structure was inconsistent. In the success case, the application may save the current value of .Fa total_in which indicates where valid compressed data was found. In the error case, the application may repeatedly call .Fn inflateSync , providing more input each time, until success or end of the input data. .It Xo .Fa int .Fn inflateCopy "z_streamp dest" "z_streamp source" .Xc .Pp Sets the destination stream as a complete copy of the source stream. .Pp 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. .Pp .Fn inflateCopy returns .Dv Z_OK if success, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_STREAM_ERROR if the source stream state was inconsistent (such as .Fa zalloc being NULL). .Fa msg is left unchanged in both .Fa source and .Fa dest . .It Xo .Fa int .Fn inflateReset "z_streamp strm" ; .Xc .Pp This function is equivalent to .Fn inflateEnd followed by .Fn inflateInit , but does not free and reallocate all the internal decompression state. The stream will keep attributes that may have been set by .Fn inflateInit2 . .Pp .Fn inflateReset returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent (such as .Fa zalloc or .Fa state being NULL). .It Xo .Fa int .Fn inflatePrime "z_stream strm" "int bits" "int value" .Xc .Pp 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 .Fa next_in . This function should only be used with raw inflate, and should be used before the first .Fn inflate call after .Fn inflateInit2 or .Fn inflateReset . .Fa 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. .Pp .Fn inflatePrime returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent. .It Xo .Fa int .Fn inflateGetHeader "z_streamp strm" "gz_headerp head" .Xc .Pp .Fn inflateGetHeader requests that gzip header information be stored in the provided gz_header structure. .Fn inflateGetHeader may be called after .Fn inflateInit2 or .Fn inflateReset , and before the first call of .Fn inflate . As .Fn inflate processes the gzip stream, head-\*(Gtdone is zero until the header is completed, at which time head-\*(Gtdone is set to one. If a zlib stream is being decoded, then head-\*(Gtdone is set to \-1 to indicate that there will be no gzip header information forthcoming. Note that .Dv Z_BLOCK can be used to force .Fn inflate to return immediately after header processing is complete and before any actual data is decompressed. .Pp 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 .Dv Z_NULL , then .Fa extra_max contains the maximum number of bytes to write to .Fa extra . Once done is true, .Fa extra_len contains the actual extra field length, and .Fa extra contains the extra field, or that field truncated if .Fa extra_max is less than .Fa extra_len . If name is not .Dv Z_NULL , then up to .Fa name_max characters are written there, terminated with a zero unless the length is greater than .Fa name_max . If comment is not .Dv Z_NULL , then up to .Fa comm_max characters are written there, terminated with a zero unless the length is greater than .Fa comm_max . When any of extra, name, or comment are not .Dv Z_NULL and the respective field is not present in the header, then that field is set to .Dv Z_NULL to signal its absence. This allows the use of .Fn 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. .Pp If .Fn inflateGetHeader is not used, then the header information is simply discarded. The header is always checked for validity, including the header CRC if present. .Fn inflateReset will reset the process to discard the header information. The application would need to call .Fn inflateGetHeader again to retrieve the header from the next gzip stream. .Pp .Fn inflateGetHeader returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the source stream state was inconsistent. .It Xo .Fa int .Fn inflateBackInit "z_stream *strm" "int windowBits" "unsigned char FAR *window" .Xc .Pp Initialize the internal stream state for decompression using .Fn inflateBack calls. The fields .Fa zalloc , zfree and .Fa opaque in .Fa strm must be initialized before the call. If .Fa zalloc and .Fa zfree are .Dv Z_NULL , then the default library-derived memory allocation routines are used. .Fa windowBits is the base two logarithm of the window size, in the range 8..15. .Fa window is a caller supplied buffer of that size. Except for special applications where it is assured that .Fn deflate was used with small window sizes, .Fa windowBits must be 15 and a 32K byte window must be supplied to be able to decompress general deflate streams. .Pp See .Fn inflateBack for the usage of these routines. .Pp .Fn inflateBackInit will return .Dv Z_OK on success, .Dv Z_STREAM_ERROR if any of the parameters are invalid, .Dv Z_MEM_ERROR if the internal state could not be allocated, or .Dv Z_VERSION_ERROR if the version of the library does not match the version of the header file. .It Xo .Fa int .Fn inflateBack "z_stream *strm" "in_func in" "void FAR *in_desc" "out_func out" "void FAR *out_desc" .Xc .Pp .Fn inflateBack does a raw inflate with a single call using a call-back interface for input and output. This is more efficient than .Fn 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 .Fn inflateBack returns. .Pp .Fn inflateBackInit must be called first to allocate the internal state and to initialize the state with the user-provided window buffer. .Fn inflateBack may then be used multiple times to inflate a complete, raw deflate stream with each call. .Fn inflateBackEnd is then called to free the allocated state. .Pp 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 .Fn inflate , which expects either a zlib or gzip header and trailer around the deflate stream. .Pp .Fn inflateBack uses two subroutines supplied by the caller that are then called by .Fn inflateBack for input and output. .Fn 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. .Fn inflateBack will call in(in_desc, &buf) which should return the number of bytes of provided input, and a pointer to that input in .Fa buf . If there is no input available, .Fn in must return zero \(em buf is ignored in that case \(em and .Fn inflateBack will return a buffer error. .Fn inflateBack will call out(out_desc, buf, len) to write the uncompressed data buf[0..len-1]. .Fn out should return zero on success, or non-zero on failure. If .Fn out returns non-zero, .Fn inflateBack will return with an error. Neither .Fn in nor .Fn out are permitted to change the contents of the window provided to .Fn inflateBackInit , which is also the buffer that .Fn out uses to write from. The length written by .Fn out will be at most the window size. Any non-zero amount of input may be provided by .Fn in . .Pp For convenience, .Fn inflateBack can be provided input on the first call by setting strm-\*(Gtnext_in and strm-\*(Gtavail_in. If that input is exhausted, then .Fn in will be called. Therefore strm-\*(Gtnext_in must be initialized before calling .Fn inflateBack . If strm-\*(Gtnext_in is .Dv Z_NULL , then .Fn in will be called immediately for input. If strm-\*(Gtnext_in is not .Dv Z_NULL , then strm-\*(Gtavail_in must also be initialized, and then if strm-\*(Gtavail_in is not zero, input will initially be taken from strm-\*(Gtnext_in[0 .. strm-\*(Gtavail_in \- 1]. .Pp The .Fa in_desc and .Fa out_desc parameters of .Fn inflateBack are passed as the first parameter of .Fn in and .Fn out respectively when they are called. These descriptors can be optionally used to pass any information that the caller-supplied .Fn in and .Fn out functions need to do their job. .Pp On return, .Fn inflateBack will set strm-\*(Gtnext_in and strm-\*(Gtavail_in to pass back any unused input that was provided by the last .Fn in call. The return values of .Fn inflateBack can be .Dv Z_STREAM_END on success, .Dv Z_BUF_ERROR if .Fn in or .Fn out returned an error, .Dv Z_DATA_ERROR if there was a format error in the deflate stream (in which case strm-\*(Gtmsg is set to indicate the nature of the error), or .Dv Z_STREAM_ERROR if the stream was not properly initialized. In the case of .Dv Z_BUF_ERROR , an input or output error can be distinguished using strm-\*(Gtnext_in which will be .Dv Z_NULL only if .Fn in returned an error. If strm-\*(Gtnext is not .Dv Z_NULL , then the .Dv Z_BUF_ERROR was due to .Fn out returning non-zero. (in() will always be called before out(), so strm-\*(Gtnext_in is assured to be defined if out() returns non-zero.) Note that .Fn inflateBack cannot return .Dv Z_OK . .It Xo .Fa int .Fn inflateBackEnd "z_stream *strm" .Xc .Pp All memory allocated by .Fn inflateBackInit is freed. .Pp .Fn inflateBackEnd returns .Dv Z_OK on success, or .Dv Z_STREAM_ERROR if the stream state was inconsistent. .It Xo .Fa uLong .Fn zlibCompileFlags "void" .Xc .Pp This function returns flags indicating compile-time options. .Pp Type sizes, two bits each: .Pp .Bl -tag -width Ds -offset indent -compact .It 00 16 bits .It 01 32 bits .It 10 64 bits .It 11 other: .Pp .Bl -tag -width Ds -offset indent -compact .It 1.0 size of uInt .It 3.2 size of uLong .It 5.4 size of voidpf .Pq pointer .It 7.6 size of z_off_t .El .El .Pp Compiler, assembler, and debug options: .Pp .Bl -tag -width Ds -offset indent -compact .It 8 DEBUG .It 9 ASMV or ASMINF \(em use ASM code .It 10 ZLIB_WINAPI \(em exported functions use the WINAPI calling convention .It 11 0 .Pq reserved .El .Pp One-time table building .Pq smaller code, but not thread-safe if true : .Pp .Bl -tag -width Ds -offset indent -compact .It 12 BUILDFIXED -- build static block decoding tables when needed .It 13 DYNAMIC_CRC_TABLE -- build CRC calculation tables when needed .It 14,15 0 .Pq reserved .El .Pp Library content (indicates missing functionality): .Pp .Bl -tag -width Ds -offset indent -compact .It 16 NO_GZCOMPRESS \(em gz* functions cannot compress .Pq to avoid linking deflate code when not needed .It 17 NO_GZIP \(em deflate can't write gzip streams, and inflate can't detect and decode gzip streams .Pq to avoid linking CRC code .It 18-19 0 .Pq reserved .El .Pp Operation variations (changes in library functionality): .Pp .Bl -tag -width Ds -offset indent -compact .It 20 PKZIP_BUG_WORKAROUND \(em slightly more permissive inflate .It 21 FASTEST \(em deflate algorithm with only one, lowest compression level .It 22,23 0 .Pq reserved .El .Pp The sprintf variant used by gzprintf .Pq zero is best : .Pp .Bl -tag -width Ds -offset indent -compact .It 24 0 = vs*, 1 = s* \(em 1 means limited to 20 arguments after the format .It 25 0 = *nprintf, 1 = *printf \(em 1 means .Fn gzprintf not secure! .It 26 0 = returns value, 1 = void \(em 1 means inferred string length returned .El .Pp Remainder: .Pp .Bl -tag -width Ds -offset indent -compact .It 27-31 0 .Pq reserved .El .El .Sh UTILITY FUNCTIONS The following utility functions are implemented on top of the basic stream-oriented functions. To simplify the interface, some default options are assumed (compression level and memory usage, standard memory allocation functions). The source code of these utility functions can easily be modified if you need special options. .Bl -tag -width Ds .It Xo .Fa int .Fn compress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" ; .Xc .Pp The .Fn compress function compresses the source buffer into the destination buffer. .Fa sourceLen is the byte length of the source buffer. Upon entry, .Fa destLen is the total size of the destination buffer, which must be at least the value returned by .Fn compressBound sourcelen . Upon exit, .Fa destLen is the actual size of the compressed buffer. This function can be used to compress a whole file at once if the input file is mmap'ed. .Pp .Fn compress returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, or .Dv Z_BUF_ERROR if there was not enough room in the output buffer. .It Xo .Fa int .Fn compress2 "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" "int level" ; .Xc .Pp The .Fn compress2 function compresses the source buffer into the destination buffer. The .Fa level parameter has the same meaning as in .Fn deflateInit . .Fa sourceLen is the byte length of the source buffer. Upon entry, .Fa destLen is the total size of the destination buffer, which must be at least the value returned by .Fn compressBound sourceLen . Upon exit, .Fa destLen is the actual size of the compressed buffer. .Pp .Fn compress2 returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_BUF_ERROR if there was not enough room in the output buffer, or .Dv Z_STREAM_ERROR if the level parameter is invalid. .It Xo .Fa int .Fn compressBound "uLong sourceLen" .Xc .Pp .Fn compressBound returns an upper bound on the compressed size after .Fn compress or .Fn compress2 on .Fa sourceLen bytes. It would be used before a .Fn compress or .Fn compress2 call to allocate the destination buffer. .It Xo .Fa int .Fn uncompress "Bytef *dest" "uLongf *destLen" "const Bytef *source" "uLong sourceLen" ; .Xc .Pp The .Fn uncompress function decompresses the source buffer into the destination buffer. .Fa sourceLen is the byte length of the source buffer. Upon entry, .Fa destLen is the total size of the destination buffer, which must be large enough to hold the entire uncompressed data. (The size of the uncompressed data must have been saved previously by the compressor and transmitted to the decompressor by some mechanism outside the scope of this compression library.) Upon exit, .Fa destLen is the actual size of the compressed buffer. This function can be used to decompress a whole file at once if the input file is mmap'ed. .Pp .Fn uncompress returns .Dv Z_OK if successful, .Dv Z_MEM_ERROR if there was not enough memory, .Dv Z_BUF_ERROR if there was not enough room in the output buffer, or .Dv Z_DATA_ERROR if the input data was corrupted or incomplete. .It Xo .Fa gzFile .Fn gzopen "const char *path" "const char *mode" ; .Xc .Pp The .Fn gzopen function opens a gzip .Pq .gz file for reading or writing. The mode parameter is as in .Xr fopen 3 .Po .Qq rb or .Qq wb .Pc but can also include a compression level .Pq "wb9" or a strategy: .Sq f for filtered data, as in .Qq wb6f ; .Sq h for Huffman only compression, as in .Qq wb1h , or .Sq R for run-length encoding as in .Qq wb1R . (See the description of .Fn deflateInit2 for more information about the strategy parameter.) .Pp .Fn gzopen can be used to read a file which is not in gzip format; in this case .Fn gzread will directly read from the file without decompression. .Pp .Fn gzopen returns .Dv NULL if the file could not be opened or if there was insufficient memory to allocate the (de)compression state; errno can be checked to distinguish the two cases (if errno is zero, the .Nm zlib error is .Dv Z_MEM_ERROR ) . .It Xo .Fa gzFile .Fn gzdopen "int fd" "const char *mode" ; .Xc .Pp The .Fn gzdopen function associates a gzFile with the file descriptor .Fa fd . File descriptors are obtained from calls like .Xr open 2 , .Xr dup 2 , .Xr creat 3 , .Xr pipe 2 , or .Xr fileno 3 (if the file has been previously opened with .Xr fopen 3 ) . The .Fa mode parameter is as in .Fn gzopen . .Pp The next call to .Fn gzclose on the returned gzFile will also close the file descriptor fd, just like fclose(fdopen(fd), mode) closes the file descriptor fd. If you want to keep fd open, use gzdopen(dup(fd), mode). .Pp .Fn gzdopen returns .Dv NULL if there was insufficient memory to allocate the (de)compression state. .It Xo .Fa int .Fn gzsetparams "gzFile file" "int level" "int strategy" ; .Xc .Pp The .Fn gzsetparams function dynamically updates the compression level or strategy. See the description of .Fn deflateInit2 for the meaning of these parameters. .Pp .Fn gzsetparams returns .Dv Z_OK if successful, or .Dv Z_STREAM_ERROR if the file was not opened for writing. .It Xo .Fa int .Fn gzread "gzFile file" "voidp buf" "unsigned len" ; .Xc .Pp The .Fn gzread function reads the given number of uncompressed bytes from the compressed file. If the input file was not in gzip format, .Fn gzread copies the given number of bytes into the buffer. .Pp .Fn gzread returns the number of uncompressed bytes actually read (0 for end of file, \-1 for error). .It Xo .Fa int .Fn gzwrite "gzFile file" "voidpc buf" "unsigned len" ; .Xc .Pp The .Fn gzwrite function writes the given number of uncompressed bytes into the compressed file. .Fn gzwrite returns the number of uncompressed bytes actually written .Pq 0 in case of error . .It Xo .Fa int .Fn gzprintf "gzFile file" "const char *format" "..." ; .Xc .Pp The .Fn gzprintf function converts, formats, and writes the args to the compressed file under control of the format string, as in .Xr fprintf 3 . .Fn gzprintf returns the number of uncompressed bytes actually written .Pq 0 in case of error . 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 .Fn gzprintf will return an error .Pq 0 with nothing written. In this case, there may also be a buffer overflow with unpredictable consequences, which is possible only if .Nm zlib was compiled with the insecure functions .Fn sprintf or .Fn vsprintf because the secure .Fn snprintf or .Fn vsnprintf functions were not available. .It Xo .Fa int .Fn gzputs "gzFile file" "const char *s" ; .Xc .Pp The .Fn gzputs function writes the given null-terminated string to the compressed file, excluding the terminating null character. .Pp .Fn gzputs returns the number of characters written, or \-1 in case of error. .It Xo .Fa char * .Fn gzgets "gzFile file" "char *buf" "int len" ; .Xc .Pp The .Fn gzgets function reads bytes from the compressed file until len\-1 characters are read, or a newline character is read and transferred to .Fa buf , or an end-of-file condition is encountered. The string is then terminated with a null character. .Pp .Fn gzgets returns .Fa buf , or .Dv Z_NULL in case of error. .It Xo .Fa int .Fn gzputc "gzFile file" "int c" ; .Xc .Pp The .Fn gzputc function writes .Fa c , converted to an unsigned char, into the compressed file. .Fn gzputc returns the value that was written, or \-1 in case of error. .It Xo .Fa int .Fn gzgetc "gzFile file" ; .Xc .Pp The .Fn gzgetc function reads one byte from the compressed file. .Fn gzgetc returns this byte or \-1 in case of end of file or error. .It Xo .Fa int .Fn gzungetc "int c" "gzFile file" .Xc .Pp Push one character back onto the stream to be read again later. Only one character of push-back is allowed. .Fn gzungetc returns the character pushed, or \-1 on failure. .Fn gzungetc will fail if a character has been pushed but not read yet, or if .Fa c is \-1. The pushed character will be discarded if the stream is repositioned with .Fn gzseek or .Fn gzrewind . .It Xo .Fa int .Fn gzflush "gzFile file" "int flush" ; .Xc .Pp The .Fn gzflush function flushes all pending output into the compressed file. The parameter .Fa flush is as in the .Fn deflate function. The return value is the .Nm zlib error number (see function .Fn gzerror below). .Fn gzflush returns .Dv Z_OK if the flush parameter is .Dv Z_FINISH and all output could be flushed. .Pp .Fn gzflush should be called only when strictly necessary because it can degrade compression. .It Xo .Fa z_off_t .Fn gzseek "gzFile file" "z_off_t offset" "int whence" ; .Xc .Pp Sets the starting position for the next .Fn gzread or .Fn gzwrite on the given compressed file. The offset represents a number of bytes in the uncompressed data stream. The whence parameter is defined as in .Xr lseek 2 ; the value .Dv SEEK_END is not supported. .Pp If the file is opened for reading, this function is emulated but can be extremely slow. If the file is opened for writing, only forward seeks are supported; .Fn gzseek then compresses a sequence of zeroes up to the new starting position. .Pp .Fn gzseek returns the resulting offset location as measured in bytes from the beginning of the uncompressed stream, or \-1 in case of error, in particular if the file is opened for writing and the new starting position would be before the current position. .It Xo .Fa int .Fn gzrewind "gzFile file" ; .Xc .Pp The .Fn gzrewind function rewinds the given .Fa file . This function is supported only for reading. .Pp gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET). .It Xo .Fa z_off_t .Fn gztell "gzFile file" ; .Xc .Pp The .Fn gztell function returns the starting position for the next .Fn gzread or .Fn gzwrite on the given compressed file. This position represents a number of bytes in the uncompressed data stream. .Pp gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR). .It Xo .Fa int .Fn gzeof "gzFile file" ; .Xc .Pp The .Fn gzeof function returns 1 when .Dv EOF has previously been detected reading the given input stream, otherwise zero. .It Xo .Fa int .Fn gzdirect "gzFile file" ; .Xc .Pp The .Fn gzdirect function returns 1 if the file is being read directly without compression; otherwise it returns 0. .It Xo .Fa int .Fn gzclose "gzFile file" ; .Xc .Pp The .Fn gzclose function flushes all pending output if necessary, closes the compressed file and deallocates all the (de)compression state. The return value is the .Nm zlib error number (see function .Fn gzerror below). .It Xo .Fa const char * .Fn gzerror "gzFile file" "int *errnum" ; .Xc .Pp The .Fn gzerror function returns the error message for the last error which occurred on the given compressed .Fa file . .Fa errnum is set to the .Nm zlib error number. If an error occurred in the file system and not in the compression library, .Fa errnum is set to .Dv Z_ERRNO and the application may consult errno to get the exact error code. .It Xo .Fa void .Fn gzclearerr "gzFile file" .Xc Clears the error and end-of-file flags for .Fa file . This is analogous to the .Fn clearerr function in stdio. This is useful for continuing to read a gzip file that is being written concurrently. .El .Sh CHECKSUM FUNCTIONS These functions are not related to compression but are exported anyway because they might be useful in applications using the compression library. .Bl -tag -width Ds .It Xo .Fa uLong .Fn adler32 "uLong adler" "const Bytef *buf" "uInt len" ; .Xc The .Fn adler32 function updates a running Adler-32 checksum with the bytes buf[0..len-1] and returns the updated checksum. If .Fa buf is .Dv NULL , this function returns the required initial value for the checksum. .Pp An Adler-32 checksum is almost as reliable as a CRC32 but can be computed much faster. Usage example: .Bd -unfilled -offset indent uLong adler = adler32(0L, Z_NULL, 0); while (read_buffer(buffer, length) != EOF) { adler = adler32(adler, buffer, length); } if (adler != original_adler) error(); .Ed .It Xo .Fa uLong .Fn adler32_combine "uLong adler1" "uLong adler2" "z_off_t len2" .Xc .Pp The .Fn 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. .Fn adler32_combine returns the Adler-32 checksum of seq1 and seq2 concatenated, requiring only adler1, adler2, and len2. .It Xo .Fa uLong .Fn crc32 "uLong crc" "const Bytef *buf" "uInt len" ; .Xc .Pp The .Fn crc32 function updates a running CRC-32 with the bytes buf[0..len-1] and returns the updated CRC-32. If .Fa buf is .Dv NULL , this function returns the required initial value for the CRC. Pre- and post-conditioning .Pq one's complement is performed within this function so it shouldn't be done by the application. Usage example: .Bd -unfilled -offset indent uLong crc = crc32(0L, Z_NULL, 0); while (read_buffer(buffer, length) != EOF) { crc = crc32(crc, buffer, length); } if (crc != original_crc) error(); .Ed .It Xo .Fa uLong .Fn crc32_combine "uLong crc1" "uLong crc2" "z_off_t len2" .Xc .Pp The .Fn 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. .Fn crc32_combine returns the CRC-32 check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and len2. .El .Sh STRUCTURES .Bd -unfilled 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; .Ed .Bd -unfilled /* 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; .Ed .Pp The application must update .Fa next_in and .Fa avail_in when .Fa avail_in has dropped to zero. It must update .Fa next_out and .Fa avail_out when .Fa avail_out has dropped to zero. The application must initialize .Fa zalloc , .Fa zfree , and .Fa opaque before calling the init function. All other fields are set by the compression library and must not be updated by the application. .Pp The .Fa opaque value provided by the application will be passed as the first parameter for calls to .Fn zalloc and .Fn zfree . This can be useful for custom memory management. The compression library attaches no meaning to the .Fa opaque value. .Pp .Fa zalloc must return .Dv Z_NULL if there is not enough memory for the object. If .Nm zlib is used in a multi-threaded application, .Fa zalloc and .Fa zfree must be thread safe. .Pp On 16-bit systems, the functions .Fa zalloc and .Fa zfree must be able to allocate exactly 65536 bytes, but will not be required to allocate more than this if the symbol MAXSEG_64K is defined (see .Aq Pa zconf.h ) . .Pp WARNING: On MSDOS, pointers returned by .Fa zalloc for objects of exactly 65536 bytes *must* have their offset normalized to zero. The default allocation function provided by this library ensures this (see .Pa zutil.c ) . To reduce memory requirements and avoid any allocation of 64K objects, at the expense of compression ratio, compile the library with -DMAX_WBITS=14 (see .Aq Pa zconf.h ) . .Pp The fields .Fa total_in and .Fa total_out can be used for statistics or progress reports. After compression, .Fa total_in holds the total size of the uncompressed data and may be saved for use in the decompressor (particularly if the decompressor wants to decompress everything in a single step). .Sh CONSTANTS .Bd -unfilled #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 \*(Lt 1.0.2 */ .Ed .Sh VARIOUS HACKS deflateInit and inflateInit are macros to allow checking the .Nm zlib version and the compiler's view of .Fa z_stream . .Bl -tag -width Ds .It Xo .Fa int .Fn deflateInit_ "z_stream strm" "int level" "const char *version" "int stream_size" ; .Xc .It Xo .Fa int .Fn inflateInit_ "z_stream strm" "const char *version" "int stream_size" ; .Xc .It Xo .Fa int .Fo deflateInit2_ .Fa "z_stream strm" .Fa "int level" .Fa "int method" .Fa "int windowBits" .Fa "int memLevel" .Fa "int strategy" .Fa "const char *version" .Fa "int stream_size" .Fc .Xc .It Xo .Fa int .Fn inflateInit2_ "z_stream strm" "int windowBits" "const char *version" "int stream_size" ; .Xc .It Xo .Fa int .Fn inflateBackInit_ "z_stream *strm" "int windowBits" "unsigned char FAR *window" "const char *version" "int stream_size" .Xc .It Xo .Fa const char * .Fn zError "int err" ; .Xc .It Xo .Fa int .Fn inflateSyncPoint "z_streamp z" ; .Xc .It Xo .Fa const uLongf * .Fn "get_crc_table" "void" ; .Xc .El .Sh SEE ALSO .Xr compress 1 , .Xr gzip 1 .Pp .Bl -tag -width 12n -compact .It RFC 1950 ZLIB Compressed Data Format Specification. .It RFC 1951 DEFLATE Compressed Data Format Specification. .It RFC 1952 GZIP File Format Specification. .El .Pp .Pa http://www.gzip.org/zlib/ .Sh HISTORY This manual page is based on an HTML version of .Aq Pa zlib.h converted by .An piaip Aq piaip@csie.ntu.edu.tw and was converted to mdoc format by the .Ox project. .Sh AUTHORS .An Jean-loup Gailly Aq jloup@gzip.org .An Mark Adler Aq madler@alumni.caltech.edu