webrtc: correctly report incoming packet address on muxed connection #2586
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This was referenced Oct 10, 2023
marten-seemann
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Oct 12, 2023
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The address in ReadFrom should be the address of the received packet and not the address of the first packet received from the peer. If the interface used to send the first packet disallows incoming packets, this will lead to a connection not being established.
The simplest way to test this is to use tailscale. Packets originated from tailscale address can be sent to localhost addresses, packets from localhost can't be sent to tailscale listeners. So if the first packet from the dialer is from the tailscale interface, the connection will never be established because muxedConnection.ReadFrom will always return the address of the packet as the tailscale address and we will ignore all reachable localhost packets.
My theory is that this is what is causing flakiness like the one observed here: https://github.com/libp2p/go-libp2p/actions/runs/6312484104/job/17138640142?pr=2584
The difference being the interface is a docker interface on the machine.
The change is inline with the pion provided udp_mux implementation: https://github.com/pion/ice/blob/master/udp_muxed_conn.go#L140. They maintain a list of addresses on the connection, we keep this list on the udpmux.
Also fixes: #2536