Locked stream should be cancellable

[ronag]

Calling cancel(reason) on a locked readable stream should not cause invalid state error. I cannot see anything that would say so in the spec and doing so causes incompatibility with the fetch spec.

Refs: nodejs/undici#1138 (comment)
Refs: https://streams.spec.whatwg.org/#readable-stream-cancel

[Svanazar]

I am not sure if it is relevant but a section on cancel(reason) seems to be mentioning this behavior:

If ! IsReadableStreamLocked(this) is true, return a promise rejected with a TypeError exception.

from https://streams.spec.whatwg.org/#rs-cancel

[jasnell]

Exactly what @Svanazar said. Throwing is the correct behavior. The rationale is that when a stream is locked, the reader takes over ownership of its lifecycle. The reader to which the stream is locked can cancel it but the stream itself cannot be directly canceled while locked.