How Can I Efficiently Stream Large Files in PHP to Avoid Memory Exhaustion?

Streaming Large Files with PHP

In scenarios where you want to securely offer users a one-time download of a massive file without consuming excessive memory, the question arises: how can you stream the file efficiently?

The conventional approach of using file_get_contents() to retrieve the entire file content simultaneously proves impractical due to potential memory limitations. To address this issue, consider employing a streaming method that delivers data in manageable chunks.

One solution, as suggested in an online source, is to use the readfile_chunked() function. This function allows you to specify a chunk size and iteratively read and output the file content, avoiding memory overload.

The provided code sample demonstrates the implementation of this approach:

// Define the chunk size in bytes
define('CHUNK_SIZE', 1024*1024);

// Function to read a file and display its content chunk by chunk
function readfile_chunked($filename, $retbytes = TRUE) {
    $buffer = '';
    $cnt = 0;
    $handle = fopen($filename, 'rb');

    if ($handle === false) {
        return false;
    }

    while (!feof($handle)) {
        $buffer = fread($handle, CHUNK_SIZE);
        echo $buffer;
        ob_flush();
        flush();

        if ($retbytes) {
            $cnt += strlen($buffer);
        }
    }

    $status = fclose($handle);

    if ($retbytes & $status) {
        return $cnt; // Return the number of bytes delivered.
    }

    return $status;
}

// Restrict access to logged-in users
if ($logged_in) {
    $filename = 'path/to/your/file';
    $mimetype = 'mime/type';
    header('Content-Type: '.$mimetype );
    readfile_chunked($filename);
} else {
    echo 'Access denied.';
}

This approach streams the file in manageable chunks, avoiding memory constraints and delivering the file to users efficiently.

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