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.init(
  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)