Stream FTP download to output

ftp, php

Solution

Found a solution!

Create a socket pair (anonymous pipe?). Use the non-blocking `ftp_nb_fget` function to write to one end of the pipe, and `echo` the other end of the pipe.

Tested to be fast (easily 10MB/s on a 100Mbps connection) so there's not much I/O overhead.

Be sure to clear any output buffers. Frameworks commonly buffer your output.

public function echo_contents() {
    /* FTP writes to [0].  Data passed through from [1]. */
    $sockets = stream_socket_pair(STREAM_PF_UNIX, STREAM_SOCK_STREAM, STREAM_IPPROTO_IP);

    if($sockets === FALSE) {
        throw new Exception('Unable to create socket pair');
    }

    stream_set_write_buffer($sockets[0], 0);
    stream_set_timeout($sockets[1], 0);

    try {
        // $this->ftp is an FtpConnection
        $get = $this->ftp->get_non_blocking($this->path, $sockets[0]);

        while(!$get->is_finished()) {
            $contents = stream_get_contents($sockets[1]);

            if($contents !== false) {
                echo $contents;
                flush();
            }

            $get->resume();
        }

        $contents = stream_get_contents($sockets[1]);

        if($contents !== false) {
            echo $contents;
            flush();
        }
    } catch(Exception $e) {
        fclose($sockets[0]);    // wtb finally
        fclose($sockets[1]);

        throw $e;
    }

    fclose($sockets[0]);
    fclose($sockets[1]);
}

// class FtpConnection
public function get_non_blocking($path, $stream) {
    // $this->ftp is the FTP resource returned by ftp_connect
    return new FtpNonBlockingRequest($this->ftp, $path, $stream);
}

/* TODO Error handling. */
class FtpNonBlockingRequest {
    protected $ftp = NULL;
    protected $status = NULL;

    public function __construct($ftp, $path, $stream) {
        $this->ftp = $ftp;

        $this->status = ftp_nb_fget($this->ftp, $stream, $path, FTP_BINARY);
    }

    public function is_finished() {
        return $this->status !== FTP_MOREDATA;
    }

    public function resume() {
        if($this->is_finished()) {
            throw BadMethodCallException('Cannot continue download; already finished');
        }

        $this->status = ftp_nb_continue($this->ftp);
    }
}

Problem

I am trying to stream/pipe a file to the user's browser through HTTP from FTP. That is, I am trying to print the contents of a file on an FTP server. This is what I have so far: ``` public function echo_contents() { $file = fopen('php://output', 'w+'); if(!$file) { throw new Exception('Unable to open output'); } try { $this->ftp->get($this->path, $file); } catch(Exception $e) { fclose($file); // wtb finally throw $e; } fclose($file); } ``` `$this->ftp->get` looks like this: ``` public function get($path, $stream) { ftp_fget($this->ftp, $stream, $path, FTP_BINARY); // Line 200 } ``` With this approach, I am only able to send small files to the user's browser. For larger files, nothing gets printed and I get a fatal error (readable from Apache logs): PHP Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 15994881 bytes) in /xxx/ftpconnection.php on line 200 I tried replacing `php://output` with `php://stdout` without success (nothing seems to be sent to the browser). How can I efficiently download from FTP while sending that data to the browser at the same time? Note: I would not like to use `file_get_contents('ftp://user:pass@host:port/path/to/file');` or similar.

Original source