PHP - SSH2 SFTP Downloads With Progress

Question

I feel this deserves a question as StackOverflow doesn't seem to have enough on the subject.

I want to SFTP, using PHP with a Progress Bar

I love progress bars. However, this time I want to do something a little different. I want to do the following with PHP, and this one looks a lot harder than the last:

• Perform downloads via SFTP (over SSH?)
• Give the user a visible indication of download progress
• Enable the pausing and continuing of downloads

Think FileZilla, but in-browser, built with PHP. I don't want to hack Apache or add any Apache mods.

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Options for the actual download

There are plenty of questions here, here, here and here for the basic SFTP download.

These document PHP's SSH2 extension (which I am using at the moment - you install this via pecl) and the alternative PHPSecLib, which I'm not using, but may look into later.
My interface allows swapping in/out easily - coding to the interface rather than the implementation etc...

That's great, but they just perform the actual download and that's it.

The download progress

PHP has a really interesting callback called stream_notification_callback, which you can read more about here.

This looks great, and was a promising step until someone looked into the source code of PHP and found that, unfortunately, SSH2 / SFTP doesn't allow integration with this.
Thanks to hek2mgl for putting in the effort to research this.

The idea with stream_notification_callback was to pass a notification of the current download size every time data is retrieved; therefore giving the data required to calculate a percentage using the currently downloaded amount and the total file size. But that doesn't go with SSH2 and SFTP...

And what about the pausing / continuing?

In my opinion, this would be the hardest to accomplish. Downloading data to a temporary file would be possible... Here's what I managed to dig up: http://ee.php.net/manual/en/function.fread.php#84115 - But integrating that sort of code with the progress bar seems crazy.

Finally

There's also cURL, however I didn't see the pausing / resuming of downloads as possible with this over SFTP. Correct me if I'm wrong.

So, how would I go about integration of the aforementioned requirements in-browser using PHP? Forget the client-side stuff, just getting the data to the browser is enough, so recommendations to perform this would be great.

Answer 1

Here is a sample I took from this site:

    // Write from our remote stream to our local stream
    $read = 0;
    $fileSize = filesize("ssh2.sftp://$sftp/$fileName");
    while ($read < $fileSize && ($buffer = fread($remoteStream, $fileSize - $read))) {
        // Increase our bytes read
        $read += strlen($buffer);

        // Write to our local file
        if (fwrite($localStream, $buffer) === FALSE) {
            throw new Exception("Unable to write to local file: /localdir/$fileName");
        }
    }

Since you have the size of the file and you read from it with fread it is trivial to determine your progress.

Pausing can be done by checking a value from lets say APC that you set if user clicks on the Pause button (do this in an iframe so you do not stop the main script).