Unpack large files with gzip in PHP - php

Question

I'm using a simple unzip function (as seen below) for my files so I don't have to unzip files manually before they are processed further.
function uncompress($srcName, $dstName) {
$string = implode("", gzfile($srcName));
$fp = fopen($dstName, "w");
fwrite($fp, $string, strlen($string));
fclose($fp);
}
The problem is that if the gzip file is large (e.g. 50mb) the unzipping takes a large amount of ram to process.
The question: can I parse a gzipped file in chunks and still get the correct result? Or is there a better other way to handle the issue of extracting large gzip files (even if it takes a few seconds more)?

Answer 1

gzfile() is a convenience method that calls gzopen, gzread, and gzclose.
So, yes, you can manually do the gzopen and gzread the file in chunks.
This will uncompress the file in 4kB chunks:
function uncompress($srcName, $dstName) {
$sfp = gzopen($srcName, "rb");
$fp = fopen($dstName, "w");
while (!gzeof($sfp)) {
$string = gzread($sfp, 4096);
fwrite($fp, $string, strlen($string));
}
gzclose($sfp);
fclose($fp);
}

Answer 2

try with
function uncompress($srcName, $dstName) {
$fp = fopen($dstName, "w");
fwrite($fp, implode("", gzfile($srcName)));
fclose($fp);
}
$length parameter is optional.

Answer 3

If you are on a Linux host, have the required privilegies to run commands, and the gzip command is installed, you could try calling it with something like shell_exec
SOmething a bit like this, I guess, would do :
shell_exec('gzip -d your_file.gz');
This way, the file wouldn't be unzip by PHP.
As a sidenote :
Take care where the command is run from (ot use a swith to tell "decompress to that directory")
You might want to take a look at escapeshellarg too ;-)

Answer 4

As maliayas mentioned, it may lead to a bug. I experienced an unexpected fall out of the while loop, but the gz file has been decompressed successfully. The whole code looks like this and works better for me:
function gzDecompressFile($srcName, $dstName) {
$error = false;
if( $file = gzopen($srcName, 'rb') ) { // open gz file
$out_file = fopen($dstName, 'wb'); // open destination file
while (($string = gzread($file, 4096)) != '') { // read 4kb at a time
if( !fwrite($out_file, $string) ) { // check if writing was successful
$error = true;
}
}
// close files
fclose($out_file);
gzclose($file);
} else {
$error = true;
}
if ($error)
return false;
else
return true;
}