Multiselect negotiation failure - what to do?

PKotoff · April 24, 2019, 4:21pm

Hi everybody!

Our team is implementing Libp2p in C++ language, and currently, I am working on the Multiselect protocol. So, a little question has appeared: for example, one node sends all protocols it supports (as a response to ls), and none of them is supported by the other.
What should the other node do? How to say that it is impossible to communicate and close the connection? Send na as a response to ls? Such a case is not documented here, so I am not sure.

Thanks for responses!

raul · April 24, 2019, 4:34pm

Hey @PKotoff, welcome to the forum!

We are currently a bad citizen and simply close the underlying connection.

go-libp2p doesn’t actually use the ls mechanism AFAIK, but if the connection upgrader fails to set up a secure channel as a result of no protocol intersection, we will simply close the connection:

github.com

libp2p/go-libp2p-transport-upgrader/blob/88384aaed494f45c20568ca92e4c1ae35889e8d4/upgrader.go#L87


			return nil, fmt.Errorf("failed to setup private network protector: %s", err)
		}
		conn = pconn
	} else if pnet.ForcePrivateNetwork {
		log.Error("tried to dial with no Private Network Protector but usage" +
			" of Private Networks is forced by the enviroment")
		return nil, pnet.ErrNotInPrivateNetwork
	}
	sconn, err := u.setupSecurity(ctx, conn, p)
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("failed to negotiate security protocol: %s", err)
	}
	smconn, err := u.setupMuxer(ctx, sconn, p)
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("failed to negotiate security stream multiplexer: %s", err)
	}
	return &transportConn{
		Conn:           smconn,
		ConnMultiaddrs: maconn,

In the near future, we want to introduce a wire protocol with a DISCONNECT message so we can convey the reason for closure in this case, and many others (e.g. connection manager pruning).

PKotoff · April 24, 2019, 4:50pm

Ok, I understand! Thank you again.

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Multiselect negotiation failure - what to do?

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