zlib Basic Functions

Syntax

#include <cafe.h>
        
#include <zlib.h>

ZEXTERN const char * ZEXPORT zlibVersion OF((void));

ZEXTERN int ZEXPORT deflateInit OF((z_streamp strm, int level));

ZEXTERN int ZEXPORT deflate OF((z_streamp strm, int flush));

ZEXTERN int ZEXPORT deflateEnd OF((z_streamp strm));

ZEXTERN int ZEXPORT inflateInit OF((z_streamp strm));

ZEXTERN int ZEXPORT inflate OF((z_streamp strm, int flush));

ZEXTERN int ZEXPORT inflateEnd OF((z_streamp strm));

Parameters

strm Pointer to z_stream structure with the compression parameters.
level For deflateInit. The compression level.
flush For deflate and inflate. Flushing options for this call.

Return Value

zlibVersion

Returns a pointer to the version of the zlib runtime library.

deflateInit

Returns Z_OK if success, Z_MEM_ERROR if there was not enough memory, Z_STREAM_ERROR if level is not a valid compression level, Z_VERSION_ERROR if the zlib library version (zlib_version) is incompatible with the version assumed by the caller (ZLIB_VERSION).

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 compressing.

deflateEnd

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

inflateInit

Returns Z_OK if success, Z_MEM_ERROR if there was not enough memory, Z_VERSION_ERROR if the zlib library version is incompatible with the version assumed by the caller, or Z_STREAM_ERROR if the parameters are invalid, such as a null pointer to the structure. there is no error message.

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 decompressing. If Z_DATA_ERROR is returned, the application may then call inflateSync to look for a good compression block if a partial recovery of the data is desired.

inflateEnd

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

Description

zlibVersion

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.

deflateInit

Initializes the internal stream state for compression. The zstream 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 provides best speed, 9 provides best compression, 0 provides no compression at all (the input data is copied a block at a time). Z_DEFAULT_COMPRESSION requests a default compromise between speed and compression (currently equivalent to level 6).

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

msg is set to NULL if there is no error message.

deflate

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:

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

Normally the parameter flush is set to Z_NO_FLUSH, which allows deflate to decide how much data to accumulate before producing output to maximize compression.

If the parameter flush is set to Z_SYNC_FLUSH, all pending output is flushed to the output buffer and the output is aligned on a byte boundary, so that the decompressor can get all input data available so far. (In particular avail_in is zero after the call if enough output space has been provided before the call.) Flushing may degrade compression for some compression algorithms and so it should be used only when necessary. This completes the current deflate block and follows it with an empty stored block that is three bits plus filler bits to the next byte, followed by four bytes (00 00 ff ff).

If flush is set to Z_PARTIAL_FLUSH, all pending output is flushed to the output buffer, but the output is not aligned to a byte boundary. All of the input data so far will be available to the decompressor, as for Z_SYNC_FLUSH. This completes the current deflate block and follows it with an empty fixed codes block that is 10 bits long. This assures that enough bytes are output in order for the decompressor to finish the block before the empty fixed code block.

If flush is set to Z_BLOCK, a deflate block is completed and emitted, as for Z_SYNC_FLUSH, but the output is not aligned on a byte boundary, and up to seven bits of the current block are held to be written as the next byte after the next deflate block is completed. In this case, the decompressor may not be provided enough bits at this point to complete decompression of the data provided so far to the compressor. It may need to wait for the next block to be emitted. This is for advanced applications that need to control the emission of deflate blocks.

If flush is set to Z_FULL_FLUSH, all output is flushed as with Z_SYNC_FLUSH, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Using Z_FULL_FLUSH too often can seriously degrade compression.

If deflate returns with avail_out == 0, this function must be called again with the same value of the flush parameter and more output space (updated avail_out), until the flush is complete (deflate returns with nonzero avail_out). For a Z_FULL_FLUSH or Z_SYNC_FLUSH, make sure that avail_out is greater than six to avoid repeated flush markers due to avail_out == 0 on return.

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

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

deflate sets strm->adler to the adler32 checksum of all input read so far (that is, total_in bytes).

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

deflateEnd

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

inflateInit

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

msg is set to NULL if there is no error message. inflateInit does not perform any decompression apart from possibly reading the zlib header if present: actual decompression will be done by inflate. (So next_in and avail_in may be modified, but next_out and avail_out are unused and unchanged.) The current implementation of inflateInit does not process any header information -- that is deferred until inflate is called.

inflate

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:

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

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

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

The Z_TREES option behaves as Z_BLOCK does, but it also returns when the end of each deflate block header is reached, before any actual data in that block is decoded. This allows the caller to determine the length of the deflate block header for later use in random access within a deflate block. 256 is added to the value of strm->data_type when inflate returns immediately after reaching the end of the deflate block header.

inflate should normally be called until it returns Z_STREAM_END or an error. However, if all decompression is to be performed in a single step (a single call of inflate), the parameter flush should be set to Z_FINISH. In this case all pending input is processed and all pending output is flushed; avail_out must be large enough to hold all 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 or Z_TREES is used.

If a preset dictionary is needed after this call (see inflateSetDictionary below), inflate sets strm->adler to the adler32 checksum of the dictionary chosen by the compressor and returns Z_NEED_DICT; otherwise it sets strm->adler to the adler32 checksum of all output produced so far (that is, total_out bytes) and returns Z_OK, Z_STREAM_END or an error code as described below. At the end of the stream, inflate checks that its computed adler32 checksum is equal to that saved by the compressor and returns Z_STREAM_END only if the checksum is correct.

inflate will decompress and check either zlib-wrapped or gzip-wrapped deflate data. The header type is detected automatically, if requested when initializing with inflateInit2. Any information contained in the gzip header is not retained, so applications that need that information should instead use raw inflate, see inflateInit2 below, or inflateBack and perform their own processing of the gzip header and trailer.

inflateEnd

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

Do Not Call From

deflate

None.

deflateEnd

None.

deflateInit

None.

inflate

None.

inflateEnd

None.

inflateInit

None.

zlibVersion

None.

See Also

zlib Overview
zlib Utility Functions

Revision History

2014/12/05 Creation.


CONFIDENTIAL