Match Fetch and WHATWG Streams Spec

[ariutta]

We've discussed matching the WHATWG streams spec: async read method returns a Promise, which is fulfilled by an ArrayBuffer. I'm understanding that to mean we want to build an abstraction over the various fetch and xhr implementations so that they all give a reader with an async read method to the parsers. Here's what it would look like for various implementations:

• Chrome: use native reader from fetch
• FF: set responseType to moz-chunked-arraybuffer, get ArrayBuffer(s) from xhr.response progress event(s), accumulate if needed, resolve reader.read Promise
• IE10+: set responseType to ms-stream, call readAsArrayBuffer on xhr.response to get an eventemitter, get ArrayBuffer(s) from eventemitter progress event(s), accumulate if needed, resolve reader.read Promise
• IE9: set responseType to text, slice xhr.responseText on progress event(s) to get chunk(s), convert to ArrayBuffer(s) using text-encoding-utf-8, accumulate if needed, resolve reader.read Promise
• Safari: until it supports fetch, basically do the same thing as for IE9, except use native Uint8Array when converting to ArrayBuffer like this.

Are we on the same page with this?

[ariutta]

Here's a demo of this (ms-stream not yet implemented): #15 (comment)

[ariutta]

We want to dedup code for XHR, but I'm not sure how to best do this, because the patch for ms-stream needs to handle the readAsArrayBuffer method, which returns an eventemitter, meaning we have two eventemitters: the XHR response and the result from readAsArrayBuffer. So we might not be able to just create a single abstraction by applying browser-specific "patches" to a generic XHR request.

Also, do we want to use try/catch (something roughly like this) for feature detection or use browser detection as we are at present or use a combination of both?

[jonnyreeves]

Changing the milestone to 0.6; looking to land 0.5 with binary data support (and fix for chrome) in the mean time as real-life keeps getting in the way :(

[jonnyreeves]

Implemented in https://github.com/jonnyreeves/fetch-readablestream