ping-client example is not working properly.

[echupriyanov]

There is an issue with ping-client. It never receives ping to itself.
Enabling trace log reveals following error:

TRACE 2018-08-28T15:49:55Z: libp2p_mplex: Received message: Open { substream_id: 0 }
DEBUG 2018-08-28T15:49:55Z: libp2p_core::upgrade::apply: Error while negotiated protocol upgrade: Custom { kind: Other, error: MultistreamSelectError(IoError(Custom { kind: Other, error: StringError("invalid substream id opened") })) }

Looking further into mplex code shows, that error happens here:

            // Handle substreams opening/closing.
            match elem {
                codec::Elem::Open { substream_id } => {
                    if (substream_id % 2) == (inner.next_outbound_stream_id % 2) {
                        inner.error = Err(IoError::new(IoErrorKind::Other, "invalid substream id opened"));
                        for task in inner.to_notify.drain() {
                            task.1.notify();
                        }
                        return Err(IoError::new(IoErrorKind::Other, "invalid substream id opened"));
                    }

Since in this example we are in dialing mode, mplex attempts to open substream with id 0, advancing inner.next_outbound_stream_id to 2. And when it tries to accept inbound Open request for the substream with id 0 on the same endpoint, we hit "invalid substream id opened" condition.

Not sure at this moment how this problem can be resolved properly.

[tomaka]

Coincidentally @twittner and me just discussed this IRL.

It appears that the JS implementation, which the Rust implementation is based upon, was actually not conforming to what it should be.

Dialers and listeners are both allowed to open the same substream, and they are differentiated by flags.

[twittner]

cf. libp2p/mplex#3 and libp2p/go-mplex#26

[twittner]

@echupriyanov: With #436 being merged, would you mind testing this again?

[echupriyanov]

@twittner Thanks! Example is now working perfectly!