Add API call to get general network statistics

[n1bor]

allchannels is now so slow it timesout.

This API call returns general stats on the network that is useful to know.

[codecov-io]

Codecov Report

Merging #1100 into master will increase coverage by 0.01%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master    #1100      +/-   ##
==========================================
+ Coverage   82.56%   82.57%   +0.01%     
==========================================
  Files         101      101              
  Lines        7697     7708      +11     
  Branches      302      306       +4     
==========================================
+ Hits         6355     6365      +10     
- Misses       1342     1343       +1

Impacted Files	Coverage Δ
...r-core/src/main/scala/fr/acinq/eclair/Eclair.scala	61.03% <100%> (+8.86%)	⬆️
...e/src/main/scala/fr/acinq/eclair/api/Service.scala	69.87% <66.66%> (-0.06%)	⬇️
...clair/blockchain/electrum/ElectrumClientPool.scala	75.26% <0%> (-3.23%)	⬇️
...-core/src/main/scala/fr/acinq/eclair/io/Peer.scala	74.92% <0%> (-0.31%)	⬇️
...src/main/scala/fr/acinq/eclair/router/Router.scala	85.71% <0%> (-0.24%)	⬇️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	84.18% <0%> (-0.1%)	⬇️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	73.6% <0%> (+0.37%)	⬆️
...cinq/eclair/blockchain/bitcoind/zmq/ZMQActor.scala	94.87% <0%> (+5.12%)	⬆️

[t-bast]

Instead of this hard-to-read Tuple8 why don't you directly use a GetNetworkInfoResponse here?
I think it would be cleaner.

[n1bor]

Not sure this is possible. As GetNetworkInfoResponse include results of the earlier futures too.
Could fill with dummy zeros but think that would make more confusing.
Especially if additional calls/futures were added to get more data.

[t-bast]

I would do something like (I slightly renamed the fields, you'll have to adapt):

override def getNetworkInfoResponse()(implicit timeout: Timeout): Future[GetNetworkInfoResponse] = {
    for {
      nodeCount <- allNodes().map(_.size)
      channelCount <- allChannels().map(_.size)
      channelUpdates <- allUpdates(None)
      val networkInfo = channelUpdates.foldLeft(GetNetworkInfoResponse(channelCount, nodeCount, channelUpdates.size, 0, MilliSatoshi(0), MilliSatoshi(0), 0, MilliSatoshi(0))) {
        (current, next) => current.copy(
          avgCltvExpiryDelta = current.avgCltvExpiryDelta + next.cltvExpiryDelta,
          avgFeeBaseMsat = current.avgFeeBaseMsat + next.feeBaseMsat
          // etc
        )
      }
    } yield networkInfo.copy(
      avgFeeBaseMsat = networkInfo.avgFeeBaseMsat / networkInfo.updates
      // etc
    )
  }

And I would refactor to make dividing all avg fields by the updateCount be done in a method in the case class or something like that.

[t-bast]

Thanks for your contribution, I think this is a useful addition to the API and we can enrich this response later (I'm thinking that average channel capacity would be useful to get).
I have a couple of code clean-up comments but concept ack.

[t-bast]

nit: remove fr.acinq.eclair.router

[n1bor]

Am in EclairImpSpec so do need it. Wanted to make clear was coming from another Spec.

[t-bast]

@n1bor I merged #1116 which might be useful to you: you could now simply expose that via the API. Would that be enough information for your use-case?