How to use Symfony StreamedResponse to stream large files [Example]

In Symfony, you can stream large files as part of a Response object using the StreamedResponse class. Streaming files is a memory-efficient way to deliver large files to clients without loading the entire file into memory at once. Here's how you can do it:

// ..
use Symfony\Component\HttpFoundation\StreamedResponse;

public function downloadLargeFileAction()
{
    // Replace this with the actual path to your large file
    $filePath = '/path/to/your/large/file.csv';

    $response = new StreamedResponse(function () use ($filePath) {
        // Open the file in read mode
        $fileStream = fopen($filePath, 'r');

        // Output the file content in chunks
        while (!feof($fileStream)) {
            echo fread($fileStream, 1024); // Adjust chunk size as needed
            flush();
        }

        fclose($fileStream);
    });

    // Set appropriate headers for file download
    $response->headers->set('Content-Type', 'application/octet-stream');
    $response->headers->set('Content-Disposition', 'attachment; filename="large-file.csv"');

    return $response;
}

In this example, the large .csv file is read and output in chunks of 1024 bytes. You can adjust the chunk size based on your application's requirements and the nature of the files you are streaming. This example code will work for every file extension, including .csv, .xlxs, .txt, etc.

For large JSON files, there is the StreamedJsonResponse object.

When the StreamedResponse is returned from the controller action, Symfony sends the response to the client in a streaming fashion. This means the file's content is sent to the client in chunks as it's being read instead of loading the entire file into memory and then sending it.

By using StreamedResponse, you ensure that the server doesn't need to load the entire file into memory, making it suitable for streaming large files efficiently.

What is Symfony response object?

In Symfony, the Response object is a fundamental component representing an HTTP response your application sends back to the client's browser or other requesting entities. The Response object encapsulates the various elements of an HTTP response, including the response body, headers, status code, cookies, and more.

StreamedResponse Caviats

If you have output_buffering option enabled in php.ini and ob_start() was called before flush(), you'll need to call ob_flush() before flush().

Your web server might also buffer the output. Make sure your server is configured correctly to allow buffering.

Related resources

• How to return JSON response from Symfony controller