Add response header X-Uncompressed-Content-Length for JSON API

[Zwyx]

Hope you don't mind that I create a PR before discussing the subject. This is such a small change than showing it is easier than explaining it 🙂

Add response header X-Uncompressed-Content-Length for JSON API

Because the response from the API is PHP output, the usual Content-Length header is absent.

This custom header technique allows the client to know the total length of the data being received, in order to display a progress indicator.

Here's a code example with XMLHttpRequest:

xhr.addEventListener("progress", (e) => {
	if (e.lengthComputable) {
		onDownloadProgress({
			loaded: e.loaded,
			total: e.total,
		});
	} else {
		const uncompressedContentLength = xhr.getResponseHeader(
			"X-Uncompressed-Content-Length",
		);

		if (uncompressedContentLength) {
			onDownloadProgress({
				loaded: e.loaded,
				total: Number(uncompressedContentLength),
			});
		}
	}
});

Notes:

• Fetch can be used as well (only reason I use XMLHttpRequest is because fetch doesn't allow to track the progress of uploaded data (when creating a paste); whereas XMLHttpRequest does).
• e.loaded can be different between browsers; Firefox reports the length of the compressed data, Chrome reports the length of uncompressed data (see Clarify if ProgressEvent.loaded should indicate the size of compress, or uncompressed, data whatwg/xhr#388). A workaround for this is to manually set our progress indicator to 100% when the request finishes.

[elrido]

Edit: Sorry, misclicked. Let me try again.

[rugk]

That is nice, but as you indicated the frontend equivalent to this still needs to be added then, if I see that correctly?

If so, that would solve #369 / #9

[Zwyx]

This is only for the JSON API, and for downloading a paste 😉

I think we could track the upload progress easily, with XMLHttpRequest (although, as mentioned in the issues, we might want to show more steps, like encryption and compression), but this PR won't help us with that.