[Masque] Non-forwarding mode in quic-proxy

[Martin Thomson <[e-mail]>]

The non-forwarded mode in quic proxy is not very well defined.  I question whether this is a necessary feature.  Or, I would suggest that serious attention be given to whether this is something that should be included in this document at all.

The sole advantage of having a proxy be aware of QUIC is that it can share the same UDP port for multiple connections.  But in order to do that, the proxy needs to choose the client connection IDs that the target will use to send packets.  The present design does not allow that.  It's backwards.

In order to share ports, the proxy needs to also participate in stateless resets.  I don't see how the present design allows that to happen.  Of particular interest is the ability of a proxy to be able to deal with clients that go away.  The client needs to be able to send a stateless reset to the proxy that will be mapped to a stateless reset that the server will recognize.  In forwarded mode, this is easier if the proxy retains state, but the present design will fail badly if the proxy loses state.  The proxy doesn't choose the connection ID that the server uses, so it can't provide a stateless reset.

That the protocol defines a way to indicate that port sharing should be disabled is a mistake, I think.  Port sharing is the point.  Disabling it is easy: use regular connect-udp without this extension at all.  In that mode, the proxy needs to allocate a port.