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Digg gzuncompress
Uncompress a compressed string
(PHP 4 >= 4.0.1, PHP 5)
Return Values
The original uncompressed data or The function will return an error if the uncompressed data is more than 32768 times the length of the compressed input data or more than the optional parameter length. ExamplesExample 2734. gzuncompress() example<?php
See Also
Code Examples / Notes » gzuncompressgabriel
To uncompress in PHP a string that has been compressed using MySQL's COMPRESS() function, you need to discard the first four bytes of the binary data: <?php /* * Example: * * insert into mytable (myfield, ...) values (COMPRESS('foobar'), ...) * * then: */ $compressed = //...select myfield from mytable where... /* * then: */ $uncompressed = gzuncompress(substr($compressed, 4)); ?> Of course, you can use MySQL's UNCOMPRESS() function. I was just providing an alternate method. chappy
Reading an ID3v2.3+ tag it is versy useful, because these tag's frames might be compressed. Zlib compressed frame layout (ID3v2.3): Descriptior Size ------------------- Frameheader: Frame id: 4 bytes Frame size (full frame size - frameheader size): 4 bytes Frame flags: 2 bytes The 2nd byte's 7th bit must be 1 (e.g.: %1xy00000) Frame content decrompessed size: 4 bytes -------------------- Framecontent: Compressed string described in 'frame size' <?php $frame="[read from a mp3 file]"; $frame_id=substr($frame,0,4); /*....*/ $cs=substr($frame,10,4); $checksize=$cs[3]*16777216+$cs[2]*65536+$cs[1]*256+$cs[0]; $content=substr($frame,14,$contentsize); $content=gzuncompress($content); if(strlen($content)!=$checksize){ echo 'Error whil uncrompessing frame data '; } echo $content; ?> emanuele
Note that the manual states that the input parameter must be a string compressed with gzcompress(), so it is not guaranteed that it will compress ANY zlib compressed string. I realized this while decompressing some compressed string in a pdf file. The gzuncompress() function produces a data error, but the string can be successfully decompressed with other zlib decompressors. More info here: http://bugs.php.net/?id=39616 heavyccasey
Note that gzuncompress() may not decompress some compressed strings and return a Data Error. The problem could be that the outside compressed string has a CRC32 checksum at the end of the file instead of Adler-32, like PHP expects. Workaround: <?php function gzuncompress_crc32($data) { $f = tempnam('/tmp', 'gz_fix'); file_put_contents($f, "\x1f\x8b\x08\x00\x00\x00\x00\x00" . $data); return file_get_contents('compress.zlib://' . $f); } ?> |
