swarm/: Expose time to establish connection

[mxinden]

Description

Expose the time it takes to establish an inbound or outbound connection.

Motivation

Needed for monitoring purposes, e.g. to be exposed to Prometheus via libp2p-metrics. Especially relevant now that we are adding two more transport protocols and thus might want to compare them. #2622 #2289

Open questions

• Likely best tracked in Pool, thus not requiring Transport to be aware of it.

Are you planning to do it yourself in a pull request?

Likely not.

[GlenDC]

I'm planning to pick this one up @mxinden , is that ok, or do you have something else in mind for me?

[mxinden]

Please prioritize any WebRTC and Testground related work. That said, yes, help here is very much appreciated whenever you are blocked on WebRTC and Testground. Let us know in case you need any help @GlenDC.

[GlenDC]

Understood. I am going to continue to give all my love and energy in the Protocol Labs context to Testground. Let's do it!

[John-LittleBearLabs]

I'm considering implementing this as a Histogram, but if so I'll need to come up with buckets - basically I'll need to know the resolution we're interested in.

Since we're talking about networking, I'm guessing somewhere on the order of magnitude of ms or perhaps 10s of ms?

[mxinden]

Since we're talking about networking, I'm guessing somewhere on the order of magnitude of ms or perhaps 10s of ms?

We can experiment with this over time. I suggest using exponential_buckets. Something along the lines of:

exponential_buckets(0.001 /* 1ms*/, 2, 16)

[thomaseizinger]

Thinking out loud: If we had a callback on behaviours for pending connections, this could be tracked in a behaviour with tracking the time inside Swarm.

[thomaseizinger]

The latest proposal of #3099 would allow this to be implemented as a NetworkBehaviour.

[thomaseizinger]

Done in #3134.