iroh-gossip fails to establish connection if it is established simultaneously from both sides

[link2xt]

Here if we get incoming connection and already have a connection with the same peer, old connection is dropped:

iroh/iroh-gossip/src/net.rs

Line 425 in 370075c

self.conns.insert(peer_id, conn.clone());

This is fine because connection is just a reference and it got cloned into connection_loop already.

But here we create new send_tx and evict existing one from the map:

iroh/iroh-gossip/src/net.rs

Line 428 in 370075c

self.conn_send_tx.insert(peer_id, send_tx.clone());

Previously started connection loop detects that its send_rx side got closed and breaks:

iroh/iroh-gossip/src/net.rs

Line 620 in 370075c

None => break,

Then existing connection gets dropped and only incoming connection remains.

If two peers try to establish connection to each other simultaneously, this is what happens. First, node establishes outgoing connection. Then it gets incoming connection and closes its outgoing connection because send_rx got closed. At this point "connection closed without error" is printed.

Because this happens on the other side, the other side also closes its outgoing connection. For the first peer it is incoming connection. When it detects that incoming connection got closed, it logs

iroh_gossip::net: connection closed with error connection lost

Caused by:
    closed by peer: 0

Then both sides have no connection anymore.

Not accepting incoming connection does not work either, then we have two outgoing connection and don't listen on the incoming ones. I think we should just keep incoming connection even if it is replaced (send_tx gets dropped) until it is closed by the other side, e.g. because it leaves gossip explicitly.

This is my analysis of what happens in deltachat/deltachat-core-rust#5595