nwaku/waku/waku_relay/protocol.nim

## Waku Relay module. Thin layer on top of GossipSub.
##
## See https://github.com/vacp2p/specs/blob/master/specs/waku/v2/waku-relay.md
## for spec.
when (NimMajor, NimMinor) < (1, 4):
  {.push raises: [Defect].}
else:
  {.push raises: [].}

import
  std/strformat,
  stew/results,
  sequtils,
  chronos,
  chronicles,
  metrics,
  libp2p/multihash,
  libp2p/protocols/pubsub/pubsub,
  libp2p/protocols/pubsub/gossipsub,
  libp2p/protocols/pubsub/rpc/messages,
  libp2p/stream/connection,
  libp2p/switch
import
  ../waku_core,
  ./message_id


logScope:
  topics = "waku relay"

const
  WakuRelayCodec* = "/vac/waku/relay/2.0.0"

# see: https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.1.md#overview-of-new-parameters
const TopicParameters = TopicParams(
    topicWeight: 1,

    # p1: favours peers already in the mesh
    timeInMeshWeight: 0.01,
    timeInMeshQuantum: 1.seconds,
    timeInMeshCap: 10.0,

    # p2: rewards fast peers
    firstMessageDeliveriesWeight: 1.0,
    firstMessageDeliveriesDecay: 0.5,
    firstMessageDeliveriesCap: 10.0,

    # p3: penalizes lazy peers. safe low value
    meshMessageDeliveriesWeight: 0.0,
    meshMessageDeliveriesDecay: 0.0,
    meshMessageDeliveriesCap: 0,
    meshMessageDeliveriesThreshold: 0,
    meshMessageDeliveriesWindow: 0.milliseconds,
    meshMessageDeliveriesActivation: 0.seconds,

    # p3b: tracks history of prunes
    meshFailurePenaltyWeight: 0.0,
    meshFailurePenaltyDecay: 0.0,

    # p4: penalizes invalid messages. highly penalize
    # peers sending wrong messages
    invalidMessageDeliveriesWeight: -100.0,
    invalidMessageDeliveriesDecay: 0.5
  )

# see: https://rfc.vac.dev/spec/29/#gossipsub-v10-parameters
const GossipsubParameters = GossipSubParams(
    explicit: true,
    pruneBackoff: chronos.minutes(1),
    unsubscribeBackoff: chronos.seconds(5),
    floodPublish: true,
    gossipFactor: 0.25,

    d: 6,
    dLow: 4,
    dHigh: 8,
    dScore: 6,
    dOut: 3,
    dLazy: 6,

    heartbeatInterval: chronos.seconds(1),
    historyLength: 6,
    historyGossip: 3,
    fanoutTTL: chronos.minutes(1),
    seenTTL: chronos.minutes(2),

    # no gossip is sent to peers below this score
    gossipThreshold: -100,

    # no self-published msgs are sent to peers below this score
    publishThreshold: -1000,

    # used to trigger disconnections + ignore peer if below this score
    graylistThreshold: -10000,

    # grafts better peers if the mesh median score drops below this. unset.
    opportunisticGraftThreshold: 0,

    # how often peer scoring is updated
    decayInterval: chronos.seconds(12),

    # below this we consider the parameter to be zero
    decayToZero: 0.01,

    # remember peer score during x after it disconnects
    retainScore: chronos.minutes(10),

    # p5: application specific, unset
    appSpecificWeight: 0.0,

    # p6: penalizes peers sharing more than threshold ips
    ipColocationFactorWeight: -50.0,
    ipColocationFactorThreshold: 5.0,

    # p7: penalizes bad behaviour (weight and decay)
    behaviourPenaltyWeight: -10.0,
    behaviourPenaltyDecay: 0.986,

    # triggers disconnections of bad peers aka score <graylistThreshold
    disconnectBadPeers: true
  )

type
  WakuRelayResult*[T] = Result[T, string]
  WakuRelayHandler* = proc(pubsubTopic: PubsubTopic, message: WakuMessage): Future[void] {.gcsafe, raises: [Defect].}
  WakuValidatorHandler* = proc(pubsubTopic: PubsubTopic, message: WakuMessage): Future[ValidationResult] {.gcsafe, raises: [Defect].}
  WakuRelay* = ref object of GossipSub
    # seq of tuples: the first entry in the tuple contains the validators are called for every topic
    # the second entry contains the error messages to be returned when the validator fails
    wakuValidators: seq[tuple[handler: WakuValidatorHandler, errorMessage: string]]
    # a map of validators to error messages to return when validation fails
    validatorInserted: Table[PubsubTopic, bool]

proc initProtocolHandler(w: WakuRelay) =
  proc handler(conn: Connection, proto: string) {.async.} =
    ## main protocol handler that gets triggered on every
    ## connection for a protocol string
    ## e.g. ``/wakusub/0.0.1``, etc...
    debug "Incoming WakuRelay connection", connection=conn, protocol=proto

    try:
      await w.handleConn(conn, proto)
    except CancelledError:
      # This is top-level procedure which will work as separate task, so it
      # do not need to propogate CancelledError.
      error "Unexpected cancellation in relay handler", conn=conn, error=getCurrentExceptionMsg()
    except CatchableError:
      error "WakuRelay handler leaks an error", conn=conn, error=getCurrentExceptionMsg()

  # XXX: Handler hijack GossipSub here?
  w.handler = handler
  w.codec = WakuRelayCodec

proc new*(T: type WakuRelay,
          switch: Switch,
          maxMessageSize = int(MaxWakuMessageSize)): WakuRelayResult[T] =
  ## maxMessageSize: max num bytes that are allowed for the WakuMessage

  var w: WakuRelay
  try:
    w = WakuRelay.init(
      switch = switch,
      anonymize = true,
      verifySignature = false,
      sign = false,
      triggerSelf = true,
      msgIdProvider = defaultMessageIdProvider,
      maxMessageSize = maxMessageSize,
      parameters = GossipsubParameters
    )

    procCall GossipSub(w).initPubSub()
    w.initProtocolHandler()

  except InitializationError:
    return err("initialization error: " & getCurrentExceptionMsg())

  return ok(w)

proc addValidator*(w: WakuRelay,
                   handler: WakuValidatorHandler,
                   errorMessage: string = "") {.gcsafe.} =
  w.wakuValidators.add((handler, errorMessage))

method start*(w: WakuRelay) {.async.} =
  debug "start"
  await procCall GossipSub(w).start()

method stop*(w: WakuRelay) {.async.} =
  debug "stop"
  await procCall GossipSub(w).stop()

proc isSubscribed*(w: WakuRelay, topic: PubsubTopic): bool =
  GossipSub(w).topics.hasKey(topic)

proc subscribedTopics*(w: WakuRelay): seq[PubsubTopic] =
  return toSeq(GossipSub(w).topics.keys())

proc generateOrderedValidator(w: WakuRelay): auto {.gcsafe.} =
  # rejects messages that are not WakuMessage
  let wrappedValidator = proc(pubsubTopic: string,
                              message: messages.Message): Future[ValidationResult] {.async.} =
    # can be optimized by checking if the message is a WakuMessage without allocating memory
    # see nim-libp2p protobuf library
    let msgRes = WakuMessage.decode(message.data)
    if msgRes.isErr():
      trace "protocol generateOrderedValidator reject decode error", error=msgRes.error
      return ValidationResult.Reject
    let msg = msgRes.get()

    # now sequentially validate the message
    for (validator, _) in w.wakuValidators:
      let validatorRes = await validator(pubsubTopic, msg)
      if validatorRes != ValidationResult.Accept:
        return validatorRes
    return ValidationResult.Accept
  return wrappedValidator

proc validateMessage*(w: WakuRelay, pubsubTopic: string, msg: WakuMessage):
  Future[Result[void, string]] {.async.} =

    let messageSizeBytes = msg.encode().buffer.len

    if messageSizeBytes > w.maxMessageSize:
      let message = fmt"Message size exceeded maximum of {w.maxMessageSize} bytes"
      debug "Invalid Waku Message", error=message
      return err(message)

    for (validator, message) in w.wakuValidators:
        let validatorRes = await validator(pubsubTopic, msg)
        if validatorRes != ValidationResult.Accept:
            if message.len > 0:
              return err(message)
            else:
              return err("Validator failed")
    return ok()
  
proc subscribe*(w: WakuRelay, pubsubTopic: PubsubTopic, handler: WakuRelayHandler): TopicHandler =
  debug "subscribe", pubsubTopic=pubsubTopic

  # We need to wrap the handler since gossipsub doesnt understand WakuMessage
  let wrappedHandler =
    proc(pubsubTopic: string, data: seq[byte]): Future[void] {.gcsafe, raises: [].} =
      let decMsg = WakuMessage.decode(data)
      if decMsg.isErr():
        # fine if triggerSelf enabled, since validators are bypassed
        error "failed to decode WakuMessage, validator passed a wrong message", error = decMsg.error
        let fut = newFuture[void]()
        fut.complete()
        return fut
      else:
        return handler(pubsubTopic, decMsg.get())

  # Add the ordered validator to the topic
  # This assumes that if `w.validatorInserted.hasKey(pubSubTopic) is true`, it contains the ordered validator.
  # Otherwise this might lead to unintended behaviour.
  if not w.validatorInserted.hasKey(pubSubTopic):
    procCall GossipSub(w).addValidator(pubSubTopic, w.generateOrderedValidator())
    w.validatorInserted[pubSubTopic] = true

  # set this topic parameters for scoring
  w.topicParams[pubsubTopic] = TopicParameters

  # subscribe to the topic with our wrapped handler
  procCall GossipSub(w).subscribe(pubsubTopic, wrappedHandler)

  return wrappedHandler

proc unsubscribeAll*(w: WakuRelay, pubsubTopic: PubsubTopic) =
  ## Unsubscribe all handlers on this pubsub topic

  debug "unsubscribe all", pubsubTopic=pubsubTopic

  procCall GossipSub(w).unsubscribeAll(pubsubTopic)
  w.validatorInserted.del(pubsubTopic)

proc unsubscribe*(w: WakuRelay, pubsubTopic: PubsubTopic, handler: TopicHandler) =
  ## Unsubscribe this handler on this pubsub topic

  debug "unsubscribe", pubsubTopic=pubsubTopic

  procCall GossipSub(w).unsubscribe(pubsubTopic, handler)

proc publish*(w: WakuRelay, pubsubTopic: PubsubTopic, message: WakuMessage): Future[int] {.async.} =
  trace "publish", pubsubTopic=pubsubTopic
  let data = message.encode().buffer

  return await procCall GossipSub(w).publish(pubsubTopic, data)