nimbus-eth2/beacon_chain/gossipsub_protocol.nim

import
  tables, sets, macros, base64,
  asyncdispatch2, nimcrypto/sysrand, chronicles, rlp, json_serialization,
  eth_p2p, eth_p2p/[rlpx, peer_pool],
  spec/[datatypes, crypto]

type
  TopicMsgHandler = proc(msg: string): Future[void]

  GossipSubPeer* = ref object
    sentMessages: HashSet[string]
    subscribedFor: HashSet[string]

  GossipSubNetwork* = ref object
    topicSubscribers: Table[string, TopicMsgHandler]
    handledMessages: HashSet[string]

proc initProtocolState*(network: GossipSubNetwork, _: EthereumNode) =
  network.topicSubscribers = initTable[string, TopicMsgHandler]()
  network.handledMessages = initSet[string]()

proc initProtocolState*(peer: GossipSubPeer, _: Peer) =
  peer.sentMessages = initSet[string]()
  peer.subscribedFor = initSet[string]()

p2pProtocol GossipSub(version = 1,
                      shortName = "gss",
                      peerState = GossipSubPeer,
                      networkState = GossipSubNetwork):
  # This is a very barebones emulation of the GossipSub protocol
  # available in LibP2P:

  onPeerConnected do (peer: Peer):
    info "GossipSub Peer connecetd", peer
    let gossipNet = peer.networkState
    for topic, _ in gossipNet.topicSubscribers:
      asyncCheck peer.subscribeFor(topic)

  onPeerDisconnected do (peer: Peer, reason: DisconnectionReason):
    info "GossipSub Peer disconnected", peer, reason
    writeStackTrace()

  proc subscribeFor(peer: Peer, topic: string) =
    peer.state.subscribedFor.incl topic

  proc emit(peer: Peer, topic: string, msgId: string, msg: string) =
    if msgId in peer.networkState.handledMessages:
      trace "Ignored previously handled message", msgId
      return

    peer.networkState.handledMessages.incl msgId

    for p in peer.network.peers(GossipSub):
      if msgId notin p.state.sentMessages and topic in p.state.subscribedFor:
        p.state.sentMessages.incl msgId
        asyncCheck p.emit(topic, msgId, msg)

    let handler = peer.networkState.topicSubscribers.getOrDefault(topic)
    if handler != nil:
      await handler(msg)

proc subscribeImpl(node: EthereumNode,
                   topic: string,
                   subscriber: TopicMsgHandler) =
  var gossipNet = node.protocolState(GossipSub)
  gossipNet.topicSubscribers[topic] = subscriber

  for peer in node.peers(GossipSub):
    discard peer.subscribeFor(topic)

proc broadcastImpl(node: EthereumNode, topic: string, msg: string): seq[Future[void]] {.gcsafe.} =
  var randBytes: array[10, byte];
  if randomBytes(randBytes) != 10:
    warn "Failed to generate random message id"

  let msgId = base64.encode(randBytes)
  trace "Sending GossipSub message", msgId

  for peer in node.peers(GossipSub):
    if topic in peer.state(GossipSub).subscribedFor:
      result.add peer.emit(topic, msgId, msg)

proc makeMessageHandler[MsgType](userHandler: proc(msg: MsgType): Future[void]): TopicMsgHandler =
  result = proc (msg: string): Future[void] =
    userHandler Json.decode(msg, MsgType)

macro subscribe*(node: EthereumNode, topic: string, handler: untyped): untyped =
  handler.addPragma ident"async"
  result = newCall(bindSym"subscribeImpl",
                   node, topic, newCall(bindSym"makeMessageHandler", handler))

proc broadcast*(node: EthereumNode, topic: string, msg: auto) {.async.} =
  await all(node.broadcastImpl(topic, Json.encode(msg)))