emscripten-core
[fetch] Support streaming fetch requests.
Add a new FETCH_BACKEND setting that can either be 'xhr' or 'fetch' to use the corresponding DOM API. To keep the emscripten Fetch.js code the same I've implemented a polyfill of XMLHttpRequest using Fetch. To support streaming I wired up the fetch code to use the old onprogress code that old versions of Firefox supported.
Most of the current API is supported with some notable exceptions:
- synchronous requests
- overriding the mime type
I also changed a few of the tests to support both sync and async so I could test them with the fetch backend.
Just adding a comment here to say I'd appreciate this change.
I had just hacked up Fetch.js to also do this, and then found this PR while searching for issues (and this looks much better than my hack and slash).
RE: overrideMimeType, it's effectively supported in that it doesn't matter - you don't need the XHR to reinterpret whatever mime type the server specified, you treat it as a big binary buffer regardless thanks to the readable stream.
I've been meaning to come back to this. I was thinking of changing it so that the DOM fetch is only used when streaming is requested. That way I don't have to try and replicate all the old XHR behavior when streaming isn't enabled.
I've changed how it works from original PR, now when FETCH_STREAMING is enabled we'll only use the DOM fetch API when a streaming data is requested. This way we can worry less about fully polyfilling XHR and hopefully have less breakage.