Define "to read a request" more specifically

[yutakahirano]

https://fetch.spec.whatwg.org/#read-a-request

See web-platform-tests/wpt#4362 (comment) for the background.

[yutakahirano]

@annevk I would like to make a separate change from #425. Right now I'm not sure the capability of the network layer in the fetch spec. What kind of object does it consume / generate?

[annevk]

It's rather opaque. Bytes go in and bytes come out. But with Request and Response objects JavaScript developers now have some control over what happens there in a way. So we need to filter when reading from them (or when creating them, but it seems like that was not the way streams ended up being designed).

[annevk]

The high-level goal is that we only allow Uint8Array objects in streams associated with either Request or Response objects, right? That seems important to test for and implement, even if we haven't quite figured out how to require that in the specification.

[yutakahirano]

My understanding is you can create a Request object from arbitrary ReadableStream, but you need to pass a ReadableStream each of whose chunks is a Uint8Array object if you want to make a fetch() call.

[yutakahirano]

For receiving a response body, it is specified in https://fetch.spec.whatwg.org/#http-network-fetch.

Whenever one or more bytes are transmitted from response’s message body, ...

For transferring a response from a service worker, it's specified in https://w3c.github.io/ServiceWorker/#dom-fetchevent-respondwith.

If response’s body is non-null, run these substeps:

[annevk]

My understanding is you can create a Request object from arbitrary ReadableStream

So the only case for this is you also write the reader to consume the request yourself, right? Because any browser-supplied reader for a request, be it fetch() or req.json() or some such, will error.