Download Large Files with PHP

Posted on: March 2, 2015 by Dimitar Ivanov

Introduction

Often a simple task as file downloading may lead to an out of memory. To accomplish successfully file download exists few approaches. Let's see the options:

Send headers

When starting a file download you need to send the proper headers to the browser.

<?php
function sendHeaders($file, $type, $name=NULL)
{
    if (empty($name))
    {
        $name = basename($file);
    }
    header('Pragma: public');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Cache-Control: private', false);
    header('Content-Transfer-Encoding: binary');
    header('Content-Disposition: attachment; filename="'.$name.'";');
    header('Content-Type: ' . $type);
    header('Content-Length: ' . filesize($file));
}
?>

Simple download

Using the file_get_contents() may be it's not the best choise, but should works perfectly for small files. The main disadvantage is that when you store the file contents into a variable, the memory for it is reserved.

<?php
$file = '/path/to/files/photo.jpg';
if (is_file($file))
{
    sendHeaders($file, 'image/jpeg', 'My picture.jpg');
    $string = @file_get_contents($file);
    if ($string !== FALSE) {
        echo $string;
    }
    exit;
}
?>

More advanced download

Using the readfile() will not present any memory issues, even when sending large files, on its own. If you encounter an out of memory error ensure that output buffering is off with ob_get_level().

<?php
$file = '/path/to/files/photo.jpg';
if (is_file($file))
{
    sendHeaders($file, 'image/jpeg', 'My picture.jpg');
    ob_clean();
    flush();
    @readfile($file);
    exit;
}
?>

Chunked download

This is the old fashioned, but still the most right way to download large files with PHP.

<?php
$file = '/path/to/files/photo.jpg';
if (is_file($file))
{
    sendHeaders($file, 'image/jpeg', 'My picture.jpg');
    $chunkSize = 1024 * 1024;
    $handle = fopen($file, 'rb');
    while (!feof($handle))
    {
        $buffer = fread($handle, $chunkSize);
        echo $buffer;
        ob_flush();
        flush();
    }
    fclose($handle);
    exit;
}
?>

Conclusion

Basically all the presented three methods can be used to force downloading a file, but when it comes to large files the chunked download is the most right way.