gzdecode

(PHP 5 >= 5.4.0)

gzdecodeDecodes a gzip compressed string

Description

string gzdecode ( string $data [, int $length ] )

This function returns a decoded version of the input data.

Parameters

data

The data to decode, encoded by gzencode().

length

The maximum length of data to decode.

Return Values

The decoded string, or FALSE if an error occurred.

See Also

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User Contributed Notes 8 notes

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7
tomas at slax dot org
3 years ago
I don't have any deep knowledge in compression algorithms and formats, so I have no idea if this works the same on all platforms. But by several experiments on my Linux box I found how to get gzdecoded data without temporary files. Here it is:

<?php
function gzdecode($data)
{
   return
gzinflate(substr($data,10,-8));
}
?>

That's it. Simply strip header and footer bytes and you get raw deflated data for inflation.
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7
anonymous at dekho-ji dot com
1 year ago
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.
up
2
webmaster at askapache dot com
6 years ago
I have used this simple function to gzdecode gzipped files downloaded from the web.

<?php

function gzdecode($data){
 
$g=tempnam('/tmp','ff');
  @
file_put_contents($g,$data);
 
ob_start();
 
readgzfile($g);
 
$d=ob_get_clean();
  return
$d;
}

?>
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1
katzlbtjunk at hotmail dot com
6 years ago
3 more bugs found and fixed:
1. failed to work when the gz contained a filename - FIXED
2. failed to work on 64-bit architecture (checksum) - FIXED
3. failed to work when the gz contained a comment - cannot verify.
Returns some errors (not all!) and filename.
<?php function gzdecode($data,&$filename='',&$error='',$maxlength=null)
{
   
$len = strlen($data);
    if (
$len < 18 || strcmp(substr($data,0,2),"\x1f\x8b")) {
       
$error = "Not in GZIP format.";
        return
null// Not GZIP format (See RFC 1952)
   
}
   
$method = ord(substr($data,2,1));  // Compression method
   
$flags  = ord(substr($data,3,1));  // Flags
   
if ($flags & 31 != $flags) {
       
$error = "Reserved bits not allowed.";
        return
null;
    }
   
// NOTE: $mtime may be negative (PHP integer limitations)
   
$mtime = unpack("V", substr($data,4,4));
   
$mtime = $mtime[1];
   
$xfl   = substr($data,8,1);
   
$os    = substr($data,8,1);
   
$headerlen = 10;
   
$extralen  = 0;
   
$extra     = "";
    if (
$flags & 4) {
       
// 2-byte length prefixed EXTRA data in header
       
if ($len - $headerlen - 2 < 8) {
            return
false// invalid
       
}
       
$extralen = unpack("v",substr($data,8,2));
       
$extralen = $extralen[1];
        if (
$len - $headerlen - 2 - $extralen < 8) {
            return
false// invalid
       
}
       
$extra = substr($data,10,$extralen);
       
$headerlen += 2 + $extralen;
    }
   
$filenamelen = 0;
   
$filename = "";
    if (
$flags & 8) {
       
// C-style string
       
if ($len - $headerlen - 1 < 8) {
            return
false; // invalid
       
}
       
$filenamelen = strpos(substr($data,$headerlen),chr(0));
        if (
$filenamelen === false || $len - $headerlen - $filenamelen - 1 < 8) {
            return
false; // invalid
       
}
       
$filename = substr($data,$headerlen,$filenamelen);
       
$headerlen += $filenamelen + 1;
    }
   
$commentlen = 0;
   
$comment = "";
    if (
$flags & 16) {
       
// C-style string COMMENT data in header
       
if ($len - $headerlen - 1 < 8) {
            return
false;    // invalid
       
}
       
$commentlen = strpos(substr($data,$headerlen),chr(0));
        if (
$commentlen === false || $len - $headerlen - $commentlen - 1 < 8) {
            return
false;    // Invalid header format
       
}
       
$comment = substr($data,$headerlen,$commentlen);
       
$headerlen += $commentlen + 1;
    }
   
$headercrc = "";
    if (
$flags & 2) {
       
// 2-bytes (lowest order) of CRC32 on header present
       
if ($len - $headerlen - 2 < 8) {
            return
false;    // invalid
       
}
       
$calccrc = crc32(substr($data,0,$headerlen)) & 0xffff;
       
$headercrc = unpack("v", substr($data,$headerlen,2));
       
$headercrc = $headercrc[1];
        if (
$headercrc != $calccrc) {
           
$error = "Header checksum failed.";
            return
false;    // Bad header CRC
       
}
       
$headerlen += 2;
    }
   
// GZIP FOOTER
   
$datacrc = unpack("V",substr($data,-8,4));
   
$datacrc = sprintf('%u',$datacrc[1] & 0xFFFFFFFF);
   
$isize = unpack("V",substr($data,-4));
   
$isize = $isize[1];
   
// decompression:
   
$bodylen = $len-$headerlen-8;
    if (
$bodylen < 1) {
       
// IMPLEMENTATION BUG!
       
return null;
    }
   
$body = substr($data,$headerlen,$bodylen);
   
$data = "";
    if (
$bodylen > 0) {
        switch (
$method) {
        case
8:
           
// Currently the only supported compression method:
           
$data = gzinflate($body,$maxlength);
            break;
        default:
           
$error = "Unknown compression method.";
            return
false;
        }
    } 
// zero-byte body content is allowed
    // Verifiy CRC32
   
$crc   = sprintf("%u",crc32($data));
   
$crcOK = $crc == $datacrc;
   
$lenOK = $isize == strlen($data);
    if (!
$lenOK || !$crcOK) {
       
$error = ( $lenOK ? '' : 'Length check FAILED. ') . ( $crcOK ? '' : 'Checksum FAILED.');
        return
false;
    }
    return
$data;
}
?>
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2
Anonymous
5 months ago
if (!function_exists('gzdecode')) {
    function gzdecode($data)
    {
        return gzinflate(substr($data,10,-8));
    }
}
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2
katzlbtjunk at hotmail dot com
6 years ago
Aaron G. 07-Aug-2004 03:29 posted the function gzdecode()
to gzencode comments. I FIXED the BUG: if($flags & 1) to the correct if($flags & 2)

Unfortunately the function gzencode() does NOT append a CRC so I did not notice until I tried to upload a file compressed with gzip itself.

<?php

function gzdecode($data) {
 
$len = strlen($data);
  if (
$len < 18 || strcmp(substr($data,0,2),"\x1f\x8b")) {
    return
null// Not GZIP format (See RFC 1952)
 
}
 
$method = ord(substr($data,2,1));  // Compression method
 
$flags  = ord(substr($data,3,1));  // Flags
 
if ($flags & 31 != $flags) {
   
// Reserved bits are set -- NOT ALLOWED by RFC 1952
   
return null;
  }
 
// NOTE: $mtime may be negative (PHP integer limitations)
 
$mtime = unpack("V", substr($data,4,4));
 
$mtime = $mtime[1];
 
$xfl   = substr($data,8,1);
 
$os    = substr($data,8,1);
 
$headerlen = 10;
 
$extralen  = 0;
 
$extra     = "";
  if (
$flags & 4) {
   
// 2-byte length prefixed EXTRA data in header
   
if ($len - $headerlen - 2 < 8) {
      return
false;    // Invalid format
   
}
   
$extralen = unpack("v",substr($data,8,2));
   
$extralen = $extralen[1];
    if (
$len - $headerlen - 2 - $extralen < 8) {
      return
false;    // Invalid format
   
}
   
$extra = substr($data,10,$extralen);
   
$headerlen += 2 + $extralen;
  }

 
$filenamelen = 0;
 
$filename = "";
  if (
$flags & 8) {
   
// C-style string file NAME data in header
   
if ($len - $headerlen - 1 < 8) {
      return
false;    // Invalid format
   
}
   
$filenamelen = strpos(substr($data,8+$extralen),chr(0));
    if (
$filenamelen === false || $len - $headerlen - $filenamelen - 1 < 8) {
      return
false;    // Invalid format
   
}
   
$filename = substr($data,$headerlen,$filenamelen);
   
$headerlen += $filenamelen + 1;
  }

 
$commentlen = 0;
 
$comment = "";
  if (
$flags & 16) {
   
// C-style string COMMENT data in header
   
if ($len - $headerlen - 1 < 8) {
      return
false;    // Invalid format
   
}
   
$commentlen = strpos(substr($data,8+$extralen+$filenamelen),chr(0));
    if (
$commentlen === false || $len - $headerlen - $commentlen - 1 < 8) {
      return
false;    // Invalid header format
   
}
   
$comment = substr($data,$headerlen,$commentlen);
   
$headerlen += $commentlen + 1;
  }

 
$headercrc = "";
  if (
$flags & 2) {
   
// 2-bytes (lowest order) of CRC32 on header present
   
if ($len - $headerlen - 2 < 8) {
      return
false;    // Invalid format
   
}
   
$calccrc = crc32(substr($data,0,$headerlen)) & 0xffff;
   
$headercrc = unpack("v", substr($data,$headerlen,2));
   
$headercrc = $headercrc[1];
    if (
$headercrc != $calccrc) {
      return
false;    // Bad header CRC
   
}
   
$headerlen += 2;
  }

 
// GZIP FOOTER - These be negative due to PHP's limitations
 
$datacrc = unpack("V",substr($data,-8,4));
 
$datacrc = $datacrc[1];
 
$isize = unpack("V",substr($data,-4));
 
$isize = $isize[1];

 
// Perform the decompression:
 
$bodylen = $len-$headerlen-8;
  if (
$bodylen < 1) {
   
// This should never happen - IMPLEMENTATION BUG!
   
return null;
  }
 
$body = substr($data,$headerlen,$bodylen);
 
$data = "";
  if (
$bodylen > 0) {
    switch (
$method) {
      case
8:
       
// Currently the only supported compression method:
       
$data = gzinflate($body);
        break;
      default:
       
// Unknown compression method
       
return false;
    }
  } else {
   
// I'm not sure if zero-byte body content is allowed.
    // Allow it for now...  Do nothing...
 
}

 
// Verifiy decompressed size and CRC32:
  // NOTE: This may fail with large data sizes depending on how
  //       PHP's integer limitations affect strlen() since $isize
  //       may be negative for large sizes.
 
if ($isize != strlen($data) || crc32($data) != $datacrc) {
   
// Bad format!  Length or CRC doesn't match!
   
return false;
  }
  return
$data;
}

?>
up
-5
6869hlopcik at inbox dot lv
3 years ago
Windows compitable with auto delete temp file.

<?php
function softcoded_gzdecode($data){
   
$g=tempnam('./','gz');
   
file_put_contents($g,$data);
   
ob_start();
   
readgzfile($g);
   
$d=ob_get_clean();
   
unlink($g);
    return
$d;
}
?>
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-5
TheSeoDude
7 years ago
This function is not found in any of the PHP distribution I use and used so had to figure out a replacement in order to extract and process my server's raw logs automagically.

Check it here http://www.tellinya.com/art2/83/gzdecode . Just a function to extract gzencoded data and hope it helps any1.
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