GOAWAY with StreamID == 0

[lnicco]

The current text says about the StreamID in the GOAWAY frame definition:

This identifier ... MAY be zero if no requests were processed.

With the latest transport changes, stream 0 is now a valid bidirectional stream, so GOAWAY(0) actually means that stream 0 is accepted/could be opened.
This opens up a case where an endpoint cannot know for sure whether the remote endpoint has accepted stream 0 or not.

If you agree this is an issue, I see two options to fix this:
one is to add a flag to the GOAWAY frame that identify this particular case;
another one is to sacrifice one stream and slightly change the GOAWAY semantics to say that StreamID is the id of the last client-initiated stream plus one, i.e. the endpoint agree that any stream with ID >= StreamID was not accepted.

[martinthomson]

Good catch. I prefer the "this stream and all higher ones were not processed, guaranteed" interpretation. Flags are awful.