Track pending outgoing connections to peers

[sangaman]

Right now, on startup it's common to get a flood of NODES packets all at once which have a lot of overlap, which then results in multiple outgoing connection attempts to those nodes. There's no mechanism currently to check if we're attempting to connect to a given node. For this issue I suggest that we track a pendingPeers Map in Pool which maps peer's node pub keys to the unopened Peer object. When the peer connection either succeeds and the open event is fired, or fails and the close event is fired, we remove the peer from pendingPeers and add to peers if successful.

[moshababo]

So you're suggesting to ignore nodes which their pubkey is already listed on pendingPeers?

[sangaman]

Exactly.

[moshababo]

Sounds good to me. If we'll want to support parallelism (specially due to connection retries, which can take ages), we'll need to introduce address in addition or instead of pubKey.

[sangaman]

Yup. Maybe we introduce parallelism later, for now though I think this approach would be a significant improvement.

[kilrau]

Introducing pendingPeers will ensure we only try to connect to a given pubKey once all the time (not only on startup...)? @sangaman

If yes, that's what we need!

[sangaman]

Yeah, well we already have checks in place to not attempt a connection to a peer we're already connected to. This will check to make sure we're not attempting a connection a peer we're already attempting to connect to.

[kilrau]

Ok thx. As per #392 (comment) I suggest pendingPeers contains pubKey@IP:port, otherwise we can't prevent connection attempts per listeningAddress

[sangaman]

I think just nodepubkey would be enough actually, since all outgoing connections reference a peer nodepubkey, we just check if we have a pending peer for the given nodepubkey.

[kilrau]

If we do #392 the serial way yes, if we do retries in parallel we would need pubKey@IP:port

[sangaman]

Yeah that's true. But I'm pretty sure I prefer the serial approach, otherwise I think we'd see this same burst of failing connection attempts should anyone have a lot of listening addresses configured.

[robertsdotpm]

I'll take this issue

[sangaman]

That would be great, I haven't started any work on it yet. Let me know if you have any questions at all.