NAT traversal: Implement support for simultaneous open in mulstistream

[vyzo]

Tracking issue for the implementation of libp2p/specs#196

PRs:

• Implement simultaneous open extension multiformats/go-multistream#42
• Add SecureMuxer interface to facilitate simultaneous open go-libp2p-core#53
• Implement support for simultaneous open go-conn-security-multistream#14
• Implement support for simultaneous open go-libp2p-transport-upgrader#25
• Hole Punching Protocol #711

[marten-seemann]

Continuing the discussion started in libp2p/go-libp2p-tls#38 (comment) here.

@vyzo, it seems like our suggested interface changes for solving simultaneous open in ms-1.0 are very similar, but slightly different: I was suggesting to change the SecureTransport.SecureOutbound function, whereas in libp2p/go-conn-security-multistream#14 you're changing the SecureMuxer.SecureOutbound function.

If I understand things correctly, changing SecureMuxer.SecureOutbound only works if you negotiate the roles before actually starting the cryptographic handshake. So it's a perfectly fine thing to do for multistream-1.0, but unfortunately will not work with multiselect-2.0, since we there discover during the handshake that a simultaneous open occurred.

[vyzo]

Yeah, that was required for multiselect/1.1 because we negotiate the role.
We'll have to figure out something slightly different for ms/2.0.

[marten-seemann]

It would be nice if we only had to change one of the interfaces to make it work for both ms-1.1 and ms-2.0 though. Arguably, dealing with simultaneous open belongs more into the transport than in the muxer, so I was wondering if libp2p/specs#196 could also be implemented that way.

[aarshkshah1992]

This is now being tracked as part of #1039.