gzuncompress()

(PHP 4 >= 4.0.1, PHP 5, PHP 7)

Uncompress a compressed string

说明

gzuncompress(string $data[,int $length= 0]): string

This function uncompress a compressed string.

参数

$data: The data compressed by gzcompress().
$length: The maximum length of data to decode.

返回值

The original uncompressed data or FALSE on error.

The function will return an error if the uncompressed data is more than 32768 times the length of the compressed input$dataor more than the optional parameter$length.

范例

gzuncompress() example

<?php
$compressed   = gzcompress('Compress me', 9);
$uncompressed = gzuncompress($compressed);
echo $uncompressed;
?>

参见

gzcompress()Compress a string
gzinflate()Inflate a deflated string
gzdeflate()Deflate a string
gzencode()Create a gzip compressed string

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);
  }
?>

To decode / uncompress the received HTTP POST data in PHP code, request data coming from Java / Android application via HTTP POST GZIP / DEFLATE compressed format
1) Data sent from Java Android app to PHP using DeflaterOutputStream java class and received in PHP as shown below
echo gzinflate( substr($HTTP_RAW_POST_DATA,2,-4) ) . PHP_EOL . PHP_EOL;
2) Data sent from Java Android app to PHP using GZIPOutputStream java class and received in PHP code as shown below
echo gzinflate( substr($HTTP_RAW_POST_DATA,10,-8) ) . PHP_EOL . PHP_EOL;
From Java Android side (API level 10+), data being sent in DEFLATE compressed format
    String body = "Lorem ipsum shizzle ma nizle";
    URL url = new URL("http://www.url.com/postthisdata.php");
    URLConnection conn = url.openConnection();
    conn.setDoOutput(true);
    conn.setRequestProperty("Content-encoding", "deflate");
    conn.setRequestProperty("Content-type", "application/octet-stream");
    DeflaterOutputStream dos = new DeflaterOutputStream(
        conn.getOutputStream());
    dos.write(body.getBytes());
    dos.flush();
    dos.close();
    BufferedReader in = new BufferedReader(new InputStreamReader(
        conn.getInputStream()));
    String decodedString = "";
    while ((decodedString = in.readLine()) != null) {
      Log.e("dump",decodedString);
    }
    in.close();
On PHP side (v 5.3.1), code for decompressing this DEFLATE data will be
  echo substr($HTTP_RAW_POST_DATA,2,-4);
From Java Android side (API level 10+), data being sent in GZIP compressed format
    String body1 = "Lorem ipsum shizzle ma nizle";
    URL url1 = new URL("http://www.url.com/postthisdata.php");
    URLConnection conn1 = url1.openConnection();
    conn1.setDoOutput(true);
    conn1.setRequestProperty("Content-encoding", "gzip");
    conn1.setRequestProperty("Content-type", "application/octet-stream");
    GZIPOutputStream dos1 = new GZIPOutputStream(conn1.getOutputStream());
    dos1.write(body1.getBytes());
    dos1.flush();
    dos1.close();
    BufferedReader in1 = new BufferedReader(new InputStreamReader(
        conn1.getInputStream()));
    String decodedString1 = "";
    while ((decodedString1 = in1.readLine()) != null) {
      Log.e("dump",decodedString1);
    }
    in1.close();
On PHP side (v 5.3.1), code for decompressing this GZIP data will be
  echo substr($HTTP_RAW_POST_DATA,10,-8);
Useful PHP code for printing out compressed data using all available formats.
$data = "Lorem ipsum shizzle ma nizle";
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
  echo chunk_split(strtoupper(bin2hex(gzcompress($data,$i))),2," ") . PHP_EOL . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
  echo chunk_split(strtoupper(bin2hex(gzdeflate($data,$i))),2," ") . PHP_EOL . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
  echo chunk_split(strtoupper(bin2hex(gzencode($data,$i,FORCE_GZIP))),2," ") . PHP_EOL . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
  echo chunk_split(strtoupper(bin2hex(gzencode($data,$i,FORCE_DEFLATE))),2," ") . PHP_EOL . PHP_EOL;
echo "\n\n\n";
Hope this helps. Please ThumbsUp if this saved you a lot of effort and time.

Hi, I got an alternative for those zipped strings that gzuncompress() cannot extract.
It is a bit better than previous options as it do not create any temporary files, but it has to encode the string in base64, meaning it won't be as fast as a native equivalent (which is probably going to be gzdecode())
<?php
if (!function_exists('gzdecode')) {
  function gzdecode($string) { // no support for 2nd argument
    return file_get_contents('compress.zlib://data:who/cares;base64,'. base64_encode($string));
  }
}
?>

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.

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<br>';
}
echo $content;
?>

One way to uncompress zlib-compressed data that is in a file without first reading in the file and then gzuncompressing it (maybe you have memory problems doing it that way) is to compile the zpipe.c program from zlib ( http://www.zlib.net/zpipe.c )...
on linux, etc:
# gcc -lz -o zpipe zpipe.c
# cp zpipe /usr/local/bin 
Then do this
<?php
$uncompressed = shell_exec("cat $compressed_file | zpipe -d");
?>

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