Allow more control over Quic channel send

[hkhalili-ocado]

Currently connectionSendAndFlush() in QuicheQuicChannel is called directly from within the same class and from QuicheQuicStreamChannel (Unsafe). This does not give any control to the user in terms of flushing. Could we instead use parent().pipeline().flush()? This way the user can add a handler to the QuicChannel pipeline to modify flushing behaviour. If this is potentially acceptable I can start working on implementing this for review.

[h-khalili]

Hi @normanmaurer. Any thoughts on this? Generally it looks like this implementation is not consistent with the Netty Framework's write/flush workflow. For example, in TCP writing to a channel simply buffers the data and does not flush it. Whereas writing to a QUIC stream channel, flushes the data. If you agree that the code needs to aligned with Netty, I would be happy to put together a few design proposals before I work on this?

[normanmaurer]

@hkhalili-ocado I am happy to review a PR.

[h-khalili]

@normanmaurer That's great; please find below some thoughts.

Current behaviour

QuicStreamChannel

• write: write to quiche (quiche_conn_stream_send) + QuicChannel::connectionSendAndFlush (quiche_conn_send + Datagram channel flush)
• flush: NOOP

QuicChannel

• write: datagram written to channelOutboundBuffer
• flush: write datagram to quiche (quiche_conn_dgram_send) + QuicChannel::connectionSendAndFlush (if dgram exists)

Proposal for QuicChannel

• write: // unchanged
• flush: write datagram to quiche (quiche_conn_dgram_send) + QuicChannel::connectionSendAndFlush (if dgram data or stream data exists)

Proposal 1 for QuicStreamChannel

• write: store in channelOutboundBuffer
• flush: write to quiche (quiche_conn_stream_send)

Proposal 2 for QuicStreamChannel

• write: write to quiche (quiche_conn_stream_send)
• flush: QuicChannel::flush

Proposal 3 for QuicStreamChannel

• write: write to quiche (quiche_conn_stream_send)
• flush: throw Unimplemented exception (user would have to call flush on QuicChannel)

I'm leaning towards proposal 2. Do you have a preference for any of them or a 4th solution?