Greeting crash

[ThatsNotMyCode]

If I use NetMQ (https://github.com/zeromq/netmq) to connect to a socket hosted by zmq4, the zmq4 host crashes with "zmq4: invalid greeting received" (

zmq4/protocol.go

Line 115 in 78ce94b

return errGreeting

).

It seems that NetMQ does follow the negotiation protocol correctly (https://rfc.zeromq.org/spec:23/ZMTP/#version-negotiation), but zmq4 does not...

• zmq4 should handle the greeting as specified in the ZMTP protocol
• zmq4 should not give panic errors

Unfortunately I lack Go skills to fix this bug.

[sbinet]

do you have the panic traceback?
(before investing time in implementing "version negotiation", I'd prefer to be sure this is actually the issue at hand :P)

[ThatsNotMyCode]

Hi sbinet,

I only have this stacktrace. And I can provide a minimal example project that causes the crash.
Example code: https://filebin.net/okurjnjpohukq2oo
Compiled for Linux: https://filebin.net/hldy9oyn0ips4aan (connects to tcp://localhost:5556)

[sbinet]

I have updated zmq4 to display the version announced by the greeting.
could you update the issue with the version you received?
that would help in devising the amount of work to fix this.

thanks.

[IoTMOD]

Hi @sbinet,
regarding this issue there is another point.
For example with a nmap localhost -p <zmq-port> we'll get a panic too. Couldn't we replace the panic(err) with a continue?
This way we'll ignore if a connection couldn't be opened, but we wouldn't break active connections due to the panic:

zmq4/socket.go

Lines 194 to 198 in 018f24d

	zconn, err := Open(conn, sck.sec, sck.typ, sck.id, true, sck.scheduleRmConn)
	if err != nil {
	panic(err)
	// return xerrors.Errorf("zmq4: could not open a ZMTP connection: %w", err)
	}

I'll open a PR, if wanted

[sbinet]

looks like the panic is an old "debug catch all" of mine.
continue-ing seems fine. (perhaps we should at some point bubble up that error w/o breaking the accept-loop. but that probably can be addressed in another PR)