Add RPC method for extended information on connected peers

[EdgeDLT]

Is your feature request related to a problem? Please describe.

I want to be able to quickly query my node for the network state (see last height of peers and their user agents). I've called it getPeerHeights because that's the main thing I want to check but maybe getConnectedPeerInfo or getNetworkState etc is better.

Describe the solution you'd like

Example usage:

{
  "jsonrpc": "2.0",
  "method": "getpeerheights",
  "params": [],
  "id": 1
}

Example response:

{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "peerHeights": [
      {
        "address": "34.16.114.243:20333",
        "userAgent": "/Neo:3.7.4+7f227a3026fadeb9723280e6f961b6f29b0f8a7a/",
        "height": 4104904
      },
      {
        "address": "159.203.28.78:21333",
        "userAgent": "/NEO-GO:0.106.1/",
        "height": 4104904
      }
    ]
  }
}

Describe alternatives you've considered

RPC extension seemed sensible enough.

Additional context

I have already implemented this method to meet my current needs. If consensus is that its useful, I am happy to send a PR for review.

[AnnaShaleva]

I think this extension is quite a useful one since getpeers doesn’t give us anything except addresses. Vote up from my side for PR.

[roman-khimov]

How do you get this data? To me it requires P2P ping to every neighbor and thus this RPC can't be safely exposed to everyone.

Refs. neo-project/neo#1844.

[EdgeDLT]

@roman-khimov I use LastBlockIndex() and Version().UserAgent on Peer. Admittedly I don't know how often this is updated, but I was thinking it would be sufficient to detect stuck-but-live nodes.

[ixje]

This sounds like a more useful alternative to the getpeers RPC method. Perhaps including useragent and height for connected nodes is a worthy update to that method instead (then neo-cli users can also benefit from it)

[roman-khimov]

I had this thought as well, but current getpeers is symmetric for all types of nodes. Maybe it's not a problem though.

Semantically this height is more like lastknownheight I should also add.

[ixje]

I agree if we only add the fields to connected it sacrifices the symmetry. We could use something like useragent: "unknown" and height: -1 for unconnected/bad. I just feel that the current getpeers output is so limited that likely nobody is consuming it. But you might have some stats on that from your nodes.

Semantically this height is more like lastknownheight I should also add.

Sure, depending on how its implemented it's a "best effort". Even what's returned in the VERSION payload during the P2P handshake can be outdated by the time you're connected. I don't think it has to be 100% accurate to be useful though.