gzencode()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

创建gzip压缩字符串

说明

gzencode (string $data[,int $level= -1 [,int $encoding_mode= FORCE_GZIP ]] ) : string

This function returns a compressed version of the input$datacompatible with the output of the gzip program.

For more information on the GZIP file format, see the document: » GZIP file format specification version 4.3 (RFC 1952).

参数

$data

The data to encode.

$level

压缩程度。如果不压缩到9，则可以指定为0。用于最大压缩。如果未给定，则默认压缩级别将。是zlib库的默认压缩级别。

$encoding_mode

The encoding mode. Can be FORCE_GZIP (the default) or FORCE_DEFLATE.

Prior to PHP 5.4.0, using FORCE_DEFLATE results in a standard zlib deflated string (inclusive zlib headers) after a gzip file header but without the trailing crc32 checksum.

In PHP 5.4.0 and later, FORCE_DEFLATE generates RFC 1950 compliant output, consisting of a zlib header, the deflated data, and an Adler checksum.

返回值

The encoded string, or FALSE if an error occurred.

更新日志

版本	说明
5.4.0	`FORCE_DEFLATE` now generates RFC 1950 compliant output.

范例

The resulting data contains the appropriate headers and data structure to make a standard .gz file, e.g.:

Creating a gzip file

<?php
$data = implode("", file("bigfile.txt"));
$gzdata = gzencode($data, 9);
$fp = fopen("bigfile.txt.gz", "w");
fwrite($fp, $gzdata);
fclose($fp);
?>

参见

gzdecode()Decodes a gzip compressed string
gzdeflate()Deflate a string
gzinflate()Inflate a deflated string
gzuncompress()Uncompress a compressed string
gzcompress()Compress a string
» ZLIB Compressed Data Format Specification (RFC 1950)

Had some trouble finding the correct way to send a Content-Length header with HTTP compression.
The pitch is to use gzencode (not gzdeflaten not gzcompress).
<?php
// disable ZLIB ouput compression
ini_set('zlib.output_compression','Off');
// compress data
$gzipoutput = gzencode($output,6);
// various headers, those with # are mandatory
header('Content-Type: application/x-download');
header('Content-Encoding: gzip'); #
header('Content-Length: '.strlen($gzipoutput)); #
header('Content-Disposition: attachment; filename="myfile.name"');
header('Cache-Control: no-cache, no-store, max-age=0, must-revalidate');
header('Pragma: no-cache');
// output data
echo $gzipoutput;
?>

NOTE:
doing like this and so on
<?php
 file_put_contents('output.gz', gzencode( file_get_contents('input.file'),9));
?>
(complete file reading)
may cause memory overflow (Fatal error: Allowed memory size of ..), so it's better to read by parts/bytes.

this is a benchmark test of gzencode (.txt file)
----------------------------------------------
original file size = 3.29 MB (3,459,978 bytes)
compress lvl 1 = 1.09 MB (1,144,006 bytes)
compress lvl 2 = 1.06 MB (1,119,518 bytes)
compress lvl 3 = 1.03 MB (1,085,567 bytes)
compress lvl 4 = 953 KB (976,538 bytes)
compress lvl 5 = 909 KB (931,486 bytes)
compress lvl 6 = 910 KB (932,516 bytes)
compress lvl 7 = 910 KB (932,608 bytes)
compress lvl 8 = 910 KB (932,646 bytes)
compress lvl 9 = 910 KB (932,652 bytes)
----------------------------------------------

here is my clean up of supaplex %at% pcbkits %d0t% c0m
submission above.
function alt_gzdecode($gzdatadecode) {
 // seed with microseconds since last "whole" second.
 mt_srand((float)microtime()*1000000);
 $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";
 if(file_exists($eh)){
 $gzf=fopen($eh,"w");
 fwrite($gzf,$gzdatadecode);
 fclose($gzf);
 $gzf = gzopen ($eh, "r");
 $gzdatadecode=gzpassthru($gzf);
 unlink($eh);
 return $gzdatadecode;
 }else{
 return 'File '.$eh.' was not found.';
 }
}

The 10 byte string in gzencode is the standard gzip header. The first two bytes (1f 8b) define the return as a gzip file, the third byte (08) means that the body is compressed using the "deflate" algorithm. The rest is padding (00)'s.
Technically, I believe one should check if the third byte is hex 08 and if so strip off the first ten bytes and last four bytes and run inflate on it. The last four bytes are file size and checksum bits.
In practice, you can get away with just stripping the first 10 bytes and running inflate on it.
Hope this helps,
terry

Aaron G. 07-Aug-2004 03:29 posted the excellent function gzdecode() (SEE BELOW)
BUGFIX: Change: if($flags & 1) to ... if($flags & 2)
Unfortunately the function gzencode() does NOT append a CRC! So the previous version worked with output of gzencode but not with output of the gzip program itself.

I was almost discouraged when I didn't find a gzdecode() function! However, fear not, for I'll contribute my work... :)
function alt_gzdecode($str) {
 // seed with microseconds since last "whole" second.
 mt_srand((float)microtime()*1000000);
 $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";
 $fd=fopen($eh,"w");
 fwrite($fd,$str);
 fclose($fd);
 $fd = gzopen ($eh, "r");
 $str=gzpassthru($fd);
 unlink($eh);
 return $str;
}
It's only ugly point is that it does not check to see if the file already exists. You may also have to adjust reference names like $str and $fd if they stomp on your code. (Sorry, but this is all you get atm! ;} ) If your conserned about a race condition, cry for a internal gzdecode() function that actualy functions...
I spent about 3 hours straight debugging this problem. I know the input data was valid, becuase I validated it with MD5() to compare to the md5's I had made of the input data before hand. I'm not sure whats up with gzuncompress or gzinflate, but this works in its place . . .
Enjoy!

Well, I was looking for a gzdecode too and didn't consider the temporary file example above to be very elegant. 
However, as is noted in the very first comment: gzencode() only adds a 10 byte header. 
I don't quite know what this header is supposed to be used for, but gzinflate() certainly doesn't like it, so I stripped it off:
function my_gzdecode($string) {
 $string = substr($string, 10);
 return gzinflate($string);
 }
That's useful to read HTTP-Connections that were compressed by mod_gzip.
-- 
Henryk Pltz
Gre aus Berlin

Correct is:
<?php
 file_put_contents('output.gz', gzencode( file_get_contents('input.file'),9));
?>

function alt_gzdecode($str) {
 // seed with microseconds since last "whole" second
 mt_srand((float)microtime()*1000000);
 $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";
 $fd=fopen($eh,"w");
 fwrite($fd,$str);
 fclose($fd);
 unset($str);
 $fd = gzopen ($eh, "r");
 while (1==1) {
  $s=gzread($fd,10240);
  if ("$s" == "") {
   break;
  }
  $str=$str . $s;
 }
 unlink($eh);
 return $str;
}