Prepare for new http2 architecture

[edsko]

See

• A new server archtecture kazu-yamamoto/http2#127
• New server arch kazu-yamamoto/http2#130

[edsko]

The tests currently fail.

[edsko]

client \ server	old http2	new http2
old http2	✅	❌
new http2	✅	❌

So it seems something goes wrong server-side.

[edsko]

Server running old http2 up to (including) the black marked packet, server running new http2 after that (client running old http2):

The client can connect, the server even responds with HTTP 200 and the gRPC headers, but then the client is left waiting for the rest of the response.

[FinleyMcIlwaine]

The server is hanging in waitForOutbound called from outboundTrailersMaker, which is called from http2 in fillDataHeaderEnqueueNext. The change in behavior seems to be that http2 is somehow constructing the trailers before grapesy is able to mark the outbound thread as done.

[kazu-yamamoto]

waitForOutbound calls waitForNormalThreadTermination.
Which thread does waitForNormalThreadTermination` wait for?

[kazu-yamamoto]

I guess that the thread forked at https://github.com/well-typed/grapesy/blob/main/util/Network/GRPC/Util/Session/Server.hs#L72 does not terminate since respond terminates when the stream is finished in the new architecture.

The old worker just enqueues Response to the output queue and returns quickly
But the new worker collaborates with the sender after enqueuing Response and finishes when all data are sent.

[edsko]

Locally tested 1000 withoutExceptions and 10,000 withExceptions tests, all passed ✔️ @FinleyMcIlwaine did the same.

[edsko]

Have opened #190 to track #184 (comment) .