Unpack large files with gzip in 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

try with

function uncompress($srcName, $dstName) {
    $fp = fopen($dstName, "w");
    fwrite($fp, implode("", gzfile($srcName)));
    fclose($fp);
}

$length parameter is optional.

Answer 2

Hi,

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 3

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 ($string = gzread($sfp, 4096)) {
        fwrite($fp, $string, strlen($string));
    }
    gzclose($sfp);
    fclose($fp);
}