Enhance hole punching

[optman]

We can try to establish direct connection before transfer (while hole-punching is going on background). I also enable libp2p "p2p-holepunching" log when -debug flag set, so we can see why hole punching fail (in my case it will mostly timeout with the default dial timeout value).

[dennis-tra]

With the new decentralized hole punching, there is a connection reversal mechanism. I could imagine that this step here is not really necessary. I'll give it a try!

[optman]

@dennis-tra The reversal connection is auto start after the relay connection established, it may take several round trip time(maybe 10~60 seconds, depend on where the relay node is) . NewStream will settle on already available connection, it wouldn't wait the direct-connection, who know when it will be. So when transfer start immediately, it will always use the only (relay) connection.

[dennis-tra]

So you want to make sure we actually use a direct connection for the new stream that gets created a couple of lines later, right?

[optman]

yes, try to create direct connection is one way to check hole-punch is completed, I don't think there is other better way.

[dennis-tra]

There's the option to pass a tracer into the EnableHolePunch libp2p option. I thought of listening for the StartHolePunchEvt and EndHolePunchEvtevents:

https://github.com/libp2p/go-libp2p/blob/f0db9cc407a2982faa5a04563ad5fc48326932ce/p2p/protocol/holepunch/tracer.go#L90

[optman]

Good idea, I didn't thought tracer can be used in these ways, but it should work. :)