@libp2p/gossipsub/src/gossipsub.ts

A typescript implementation of gossipsub

import { TypedEventEmitter, serviceCapabilities, serviceDependencies } from '@libp2p/interface'
import { peerIdFromMultihash, peerIdFromString } from '@libp2p/peer-id'
import { encode } from 'it-length-prefixed'
import { pipe } from 'it-pipe'
import { pushable } from 'it-pushable'
import * as Digest from 'multiformats/hashes/digest'
import * as constants from './constants.js'
import {
  ACCEPT_FROM_WHITELIST_DURATION_MS,
  ACCEPT_FROM_WHITELIST_MAX_MESSAGES,
  ACCEPT_FROM_WHITELIST_THRESHOLD_SCORE,
  BACKOFF_SLACK
} from './constants.js'
import { StrictNoSign, StrictSign, TopicValidatorResult } from './index.ts'
import { defaultDecodeRpcLimits } from './message/decodeRpc.js'
import { RPC } from './message/rpc.js'
import { MessageCache } from './message-cache.js'
import {
  ChurnReason,
  getMetrics,
  IHaveIgnoreReason,
  InclusionReason,

  ScorePenalty

} from './metrics.js'
import {
  PeerScore,

  createPeerScoreParams,
  createPeerScoreThresholds

} from './score/index.js'
import { computeAllPeersScoreWeights } from './score/scoreMetrics.js'
import { InboundStream, OutboundStream } from './stream.js'
import { IWantTracer } from './tracer.js'
import {

  ValidateError,

  MessageStatus,
  RejectReason,

  rejectReasonFromAcceptance

} from './types.js'
import { buildRawMessage, validateToRawMessage } from './utils/buildRawMessage.js'
import { createGossipRpc, ensureControl } from './utils/create-gossip-rpc.js'
import { shuffle, messageIdToString } from './utils/index.js'
import { msgIdFnStrictNoSign, msgIdFnStrictSign } from './utils/msgIdFn.js'
import { multiaddrToIPStr } from './utils/multiaddr.js'
import { getPublishConfigFromPeerId } from './utils/publishConfig.js'
import { removeFirstNItemsFromSet, removeItemsFromSet } from './utils/set.js'
import { SimpleTimeCache } from './utils/time-cache.js'
import type { GossipSubComponents, GossipSubEvents, GossipsubMessage, GossipsubOpts, MeshPeer, Message, PublishResult, SubscriptionChangeData, TopicValidatorFn } from './index.ts'
import type { DecodeRPCLimits } from './message/decodeRpc.js'
import type { MessageCacheRecord } from './message-cache.js'
import type { Metrics, ToSendGroupCount } from './metrics.js'
import type { PeerScoreParams, PeerScoreThresholds, PeerScoreStatsDump } from './score/index.js'
import type { MsgIdFn, PublishConfig, TopicStr, MsgIdStr, PeerIdStr, RejectReasonObj, FastMsgIdFn, DataTransform, MsgIdToStrFn, MessageId, PublishOpts } from './types.js'
import type {
  Connection, Stream, PeerId, Peer,
  Logger,
  Topology,
  TypedEventTarget,
  MessageStreamDirection
} from '@libp2p/interface'
import type { Multiaddr } from '@multiformats/multiaddr'
import type { Uint8ArrayList } from 'uint8arraylist'

enum GossipStatusCode {
  started,
  stopped
}

type GossipStatus =
  | {
    code: GossipStatusCode.started
    registrarTopologyIds: string[]
    heartbeatTimeout: ReturnType<typeof setTimeout>
    hearbeatStartMs: number
  }
  | {
    code: GossipStatusCode.stopped
  }

interface GossipOptions extends GossipsubOpts {
  scoreParams: PeerScoreParams
  scoreThresholds: PeerScoreThresholds
}

interface AcceptFromWhitelistEntry {
  /** number of messages accepted since recomputing the peer's score */
  messagesAccepted: number
  /** have to recompute score after this time */
  acceptUntil: number
}

type ReceivedMessageResult =
  | { code: MessageStatus.duplicate, msgIdStr: MsgIdStr }
  | ({ code: MessageStatus.invalid, msgIdStr?: MsgIdStr } & RejectReasonObj)
  | { code: MessageStatus.valid, messageId: MessageId, msg: Message }

export class GossipSub extends TypedEventEmitter<GossipSubEvents> implements TypedEventTarget<GossipSubEvents> {
  /**
   * The signature policy to follow by default
   */
  public readonly globalSignaturePolicy: typeof StrictSign | typeof StrictNoSign
  public protocols: string[] = [constants.GossipsubIDv12, constants.GossipsubIDv11, constants.GossipsubIDv10]

  private publishConfig: PublishConfig | undefined

  private readonly dataTransform: DataTransform | undefined

  // State

  public readonly peers = new Map<PeerIdStr, PeerId>()
  public readonly streamsInbound = new Map<PeerIdStr, InboundStream>()
  public readonly streamsOutbound = new Map<PeerIdStr, OutboundStream>()

  /** Ensures outbound streams are created sequentially */
  private outboundInflightQueue = pushable<{ peerId: PeerId, connection: Connection }>({ objectMode: true })

  /** Direct peers */
  public readonly direct = new Set<PeerIdStr>()

  /** Floodsub peers */
  private readonly floodsubPeers = new Set<PeerIdStr>()

  /** Cache of seen messages */
  private readonly seenCache: SimpleTimeCache<void>

  /**
   * Map of peer id and AcceptRequestWhileListEntry
   */
  private readonly acceptFromWhitelist = new Map<PeerIdStr, AcceptFromWhitelistEntry>()

  /**
   * Map of topics to which peers are subscribed to
   */
  private readonly topics = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * List of our subscriptions
   */
  private readonly subscriptions = new Set<TopicStr>()

  /**
   * Map of topic meshes
   * topic => peer id set
   */
  public readonly mesh = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * Map of topics to set of peers. These mesh peers are the ones to which we are publishing without a topic membership
   * topic => peer id set
   */
  public readonly fanout = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * Map of last publish time for fanout topics
   * topic => last publish time
   */
  private readonly fanoutLastpub = new Map<TopicStr, number>()

  /**
   * Map of pending messages to gossip
   * peer id => control messages
   */
  public readonly gossip = new Map<PeerIdStr, RPC.ControlIHave[]>()

  /**
   * Map of control messages
   * peer id => control message
   */
  public readonly control = new Map<PeerIdStr, RPC.ControlMessage>()

  /**
   * Number of IHAVEs received from peer in the last heartbeat
   */
  private readonly peerhave = new Map<PeerIdStr, number>()

  /** Number of messages we have asked from peer in the last heartbeat */
  private readonly iasked = new Map<PeerIdStr, number>()

  /** Prune backoff map */
  private readonly backoff = new Map<TopicStr, Map<PeerIdStr, number>>()

  /**
   * Connection direction cache, marks peers with outbound connections
   * peer id => direction
   */
  private readonly outbound = new Map<PeerIdStr, boolean>()
  private readonly msgIdFn: MsgIdFn

  /**
   * A fast message id function used for internal message de-duplication
   */
  private readonly fastMsgIdFn: FastMsgIdFn | undefined

  private readonly msgIdToStrFn: MsgIdToStrFn

  /** Maps fast message-id to canonical message-id */
  private readonly fastMsgIdCache: SimpleTimeCache<MsgIdStr> | undefined

  /**
   * Short term cache for published message ids. This is used for penalizing peers sending
   * our own messages back if the messages are anonymous or use a random author.
   */
  private readonly publishedMessageIds: SimpleTimeCache<void>

  /**
   * A message cache that contains the messages for last few heartbeat ticks
   */
  private readonly mcache: MessageCache

  /** Peer score tracking */
  public readonly score: PeerScore

  /**
   * Custom validator function per topic.
   * Must return or resolve quickly (< 100ms) to prevent causing penalties for late messages.
   * If you need to apply validation that may require longer times use `asyncValidation` option and callback the
   * validation result through `Gossipsub.reportValidationResult`
   */
  public readonly topicValidators = new Map<TopicStr, TopicValidatorFn>()

  /**
   * Make this protected so child class may want to redirect to its own log.
   */
  protected readonly log: Logger

  /**
   * Number of heartbeats since the beginning of time
   * This allows us to amortize some resource cleanup -- eg: backoff cleanup
   */
  private heartbeatTicks = 0

  /**
   * Tracks IHAVE/IWANT promises broken by peers
   */
  readonly gossipTracer: IWantTracer

  /**
   * Tracks IDONTWANT messages received by peers in the current heartbeat
   */
  private readonly idontwantCounts = new Map<PeerIdStr, number>()

  /**
   * Tracks IDONTWANT messages received by peers and the heartbeat they were received in
   *
   * idontwants are stored for `mcacheLength` heartbeats before being pruned,
   * so this map is bounded by peerCount * idontwantMaxMessages * mcacheLength
   */
  private readonly idontwants = new Map<PeerIdStr, Map<MsgIdStr, number>>()

  private readonly components: GossipSubComponents

  private directPeerInitial: ReturnType<typeof setTimeout> | null = null

  public static multicodec: string = constants.GossipsubIDv12

  // Options
  readonly opts: Required<GossipOptions>
  private readonly decodeRpcLimits: DecodeRPCLimits

  private readonly metrics: Metrics | null
  private status: GossipStatus = { code: GossipStatusCode.stopped }
  private readonly maxInboundStreams?: number
  private readonly maxOutboundStreams?: number
  private readonly runOnLimitedConnection?: boolean
  private readonly allowedTopics: Set<TopicStr> | null

  private heartbeatTimer: {
    _intervalId: ReturnType<typeof setInterval> | undefined
    runPeriodically(fn: () => void, period: number): void
    cancel(): void
  } | null = null

  constructor (components: GossipSubComponents, options: Partial<GossipsubOpts> = {}) {
    super()

    const opts = {
      fallbackToFloodsub: true,
      floodPublish: true,
      batchPublish: false,
      tagMeshPeers: true,
      doPX: false,
      directPeers: [],
      D: constants.GossipsubD,
      Dlo: constants.GossipsubDlo,
      Dhi: constants.GossipsubDhi,
      Dscore: constants.GossipsubDscore,
      Dout: constants.GossipsubDout,
      Dlazy: constants.GossipsubDlazy,
      heartbeatInterval: constants.GossipsubHeartbeatInterval,
      fanoutTTL: constants.GossipsubFanoutTTL,
      mcacheLength: constants.GossipsubHistoryLength,
      mcacheGossip: constants.GossipsubHistoryGossip,
      seenTTL: constants.GossipsubSeenTTL,
      gossipsubIWantFollowupMs: constants.GossipsubIWantFollowupTime,
      prunePeers: constants.GossipsubPrunePeers,
      pruneBackoff: constants.GossipsubPruneBackoff,
      unsubcribeBackoff: constants.GossipsubUnsubscribeBackoff,
      graftFloodThreshold: constants.GossipsubGraftFloodThreshold,
      opportunisticGraftPeers: constants.GossipsubOpportunisticGraftPeers,
      opportunisticGraftTicks: constants.GossipsubOpportunisticGraftTicks,
      directConnectTicks: constants.GossipsubDirectConnectTicks,
      gossipFactor: constants.GossipsubGossipFactor,
      idontwantMinDataSize: constants.GossipsubIdontwantMinDataSize,
      idontwantMaxMessages: constants.GossipsubIdontwantMaxMessages,
      ...options,
      scoreParams: createPeerScoreParams(options.scoreParams),
      scoreThresholds: createPeerScoreThresholds(options.scoreThresholds)
    }

    this.components = components
    this.decodeRpcLimits = opts.decodeRpcLimits ?? defaultDecodeRpcLimits

    this.globalSignaturePolicy = opts.globalSignaturePolicy ?? StrictSign

    // Also wants to get notified of peers connected using floodsub
    if (opts.fallbackToFloodsub) {
      this.protocols.push(constants.FloodsubID)
    }

    // From pubsub
    this.log = components.logger.forComponent(opts.debugName ?? 'libp2p:gossipsub')

    // Gossipsub

    this.opts = opts as Required<GossipOptions>
    this.direct = new Set(opts.directPeers.map((p) => p.id.toString()))
    this.seenCache = new SimpleTimeCache<void>({ validityMs: opts.seenTTL })
    this.publishedMessageIds = new SimpleTimeCache<void>({ validityMs: opts.seenTTL })

    if (options.msgIdFn != null) {
      // Use custom function
      this.msgIdFn = options.msgIdFn
    } else {
      switch (this.globalSignaturePolicy) {
        case StrictSign:
          this.msgIdFn = msgIdFnStrictSign
          break
        case StrictNoSign:
          this.msgIdFn = msgIdFnStrictNoSign
          break
        default:
          throw new Error(`Invalid globalSignaturePolicy: ${this.globalSignaturePolicy}`)
      }
    }

    if (options.fastMsgIdFn != null) {
      this.fastMsgIdFn = options.fastMsgIdFn
      this.fastMsgIdCache = new SimpleTimeCache<MsgIdStr>({ validityMs: opts.seenTTL })
    }

    // By default, gossipsub only provide a browser friendly function to convert Uint8Array message id to string.
    this.msgIdToStrFn = options.msgIdToStrFn ?? messageIdToString

    this.mcache = options.messageCache ?? new MessageCache(opts.mcacheGossip, opts.mcacheLength, this.msgIdToStrFn)

    if (options.dataTransform != null) {
      this.dataTransform = options.dataTransform
    }

    if (options.metricsRegister != null) {
      if (options.metricsTopicStrToLabel == null) {
        throw Error('Must set metricsTopicStrToLabel with metrics')
      }

      // in theory, each topic has its own meshMessageDeliveriesWindow param
      // however in lodestar, we configure it mostly the same so just pick the max of positive ones
      // (some topics have meshMessageDeliveriesWindow as 0)
      const maxMeshMessageDeliveriesWindowMs = Math.max(
        ...Object.values(opts.scoreParams.topics).map((topicParam) => topicParam.meshMessageDeliveriesWindow),
        constants.DEFAULT_METRIC_MESH_MESSAGE_DELIVERIES_WINDOWS
      )

      const metrics = getMetrics(options.metricsRegister, options.metricsTopicStrToLabel, {
        gossipPromiseExpireSec: this.opts.gossipsubIWantFollowupMs / 1000,
        behaviourPenaltyThreshold: opts.scoreParams.behaviourPenaltyThreshold,
        maxMeshMessageDeliveriesWindowSec: maxMeshMessageDeliveriesWindowMs / 1000
      })

      metrics.mcacheSize.addCollect(() => { this.onScrapeMetrics(metrics) })
      for (const protocol of this.protocols) {
        metrics.protocolsEnabled.set({ protocol }, 1)
      }

      this.metrics = metrics
    } else {
      this.metrics = null
    }

    this.gossipTracer = new IWantTracer(this.opts.gossipsubIWantFollowupMs, this.msgIdToStrFn, this.metrics)

    /**
     * libp2p
     */
    this.score = new PeerScore(this.opts.scoreParams, this.metrics, this.components.logger, {
      scoreCacheValidityMs: opts.heartbeatInterval
    })

    this.maxInboundStreams = options.maxInboundStreams
    this.maxOutboundStreams = options.maxOutboundStreams
    this.runOnLimitedConnection = options.runOnLimitedConnection

    this.allowedTopics = (opts.allowedTopics != null) ? new Set(opts.allowedTopics) : null
  }

  readonly [Symbol.toStringTag] = '@chainsafe/libp2p-gossipsub'

  readonly [serviceCapabilities]: string[] = [
    '@libp2p/pubsub'
  ]

  readonly [serviceDependencies]: string[] = [
    '@libp2p/identify'
  ]

  getPeers (): PeerId[] {
    return [...this.peers.values()]
  }

  isStarted (): boolean {
    return this.status.code === GossipStatusCode.started
  }

  // LIFECYCLE METHODS

  /**
   * Mounts the gossipsub protocol onto the libp2p node and sends our
   * our subscriptions to every peer connected
   */
  async start (): Promise<void> {
    // From pubsub
    if (this.isStarted()) {
      return
    }

    this.log('starting')

    this.publishConfig = getPublishConfigFromPeerId(this.globalSignaturePolicy, this.components.peerId, this.components.privateKey)

    // Create the outbound inflight queue
    // This ensures that outbound stream creation happens sequentially
    this.outboundInflightQueue = pushable({ objectMode: true })
    pipe(this.outboundInflightQueue, async (source) => {
      for await (const { peerId, connection } of source) {
        await this.createOutboundStream(peerId, connection)
      }
    }).catch((e) => { this.log.error('outbound inflight queue error', e) })

    // set direct peer addresses in the address book
    await Promise.all(
      this.opts.directPeers.map(async (p) => {
        await this.components.peerStore.merge(p.id, {
          multiaddrs: p.addrs
        })
      })
    )

    const registrar = this.components.registrar
    // Incoming streams
    // Called after a peer dials us
    await Promise.all(
      this.protocols.map(async (protocol) =>
        registrar.handle(protocol, this.onIncomingStream.bind(this), {
          maxInboundStreams: this.maxInboundStreams,
          maxOutboundStreams: this.maxOutboundStreams,
          runOnLimitedConnection: this.runOnLimitedConnection
        })
      )
    )

    // # How does Gossipsub interact with libp2p? Rough guide from Mar 2022
    //
    // ## Setup:
    // Gossipsub requests libp2p to callback, TBD
    //
    // `this.libp2p.handle()` registers a handler for `/meshsub/1.1.0` and other Gossipsub protocols
    // The handler callback is registered in libp2p Upgrader.protocols map.
    //
    // Upgrader receives an inbound connection from some transport and (`Upgrader.upgradeInbound`):
    // - Adds encryption (NOISE in our case)
    // - Multiplex stream
    // - Create a muxer and register that for each new stream call Upgrader.protocols handler
    //
    // ## Topology
    // - new instance of Topology (unlinked to libp2p) with handlers
    // - registar.register(topology)

    // register protocol with topology
    // Topology callbacks called on connection manager changes
    const topology: Topology = {
      onConnect: this.onPeerConnected.bind(this),
      onDisconnect: this.onPeerDisconnected.bind(this),
      notifyOnLimitedConnection: this.runOnLimitedConnection
    }
    const registrarTopologyIds = await Promise.all(
      this.protocols.map(async (protocol) => registrar.register(protocol, topology))
    )

    // Schedule to start heartbeat after `GossipsubHeartbeatInitialDelay`
    const heartbeatTimeout = setTimeout(this.runHeartbeat, constants.GossipsubHeartbeatInitialDelay)
    // Then, run heartbeat every `heartbeatInterval` offset by `GossipsubHeartbeatInitialDelay`

    this.status = {
      code: GossipStatusCode.started,
      registrarTopologyIds,
      heartbeatTimeout,
      hearbeatStartMs: Date.now() + constants.GossipsubHeartbeatInitialDelay
    }

    this.score.start()
    // connect to direct peers
    this.directPeerInitial = setTimeout(() => {
      Promise.resolve()
        .then(async () => {
          await Promise.all(Array.from(this.direct).map(async (id) => this.connect(id)))
        })
        .catch((err) => {
          this.log(err)
        })
    }, constants.GossipsubDirectConnectInitialDelay)

    if (this.opts.tagMeshPeers) {
      this.addEventListener('gossipsub:graft', this.tagMeshPeer)
      this.addEventListener('gossipsub:prune', this.untagMeshPeer)
    }

    this.log('started')
  }

  /**
   * Unmounts the gossipsub protocol and shuts down every connection
   */
  async stop (): Promise<void> {
    this.log('stopping')
    // From pubsub

    if (this.status.code !== GossipStatusCode.started) {
      return
    }

    const { registrarTopologyIds } = this.status
    this.status = { code: GossipStatusCode.stopped }

    if (this.opts.tagMeshPeers) {
      this.removeEventListener('gossipsub:graft', this.tagMeshPeer)
      this.removeEventListener('gossipsub:prune', this.untagMeshPeer)
    }

    // unregister protocol and handlers
    const registrar = this.components.registrar
    await Promise.all(this.protocols.map(async (protocol) => registrar.unhandle(protocol)))
    registrarTopologyIds.forEach((id) => { registrar.unregister(id) })

    this.outboundInflightQueue.end()

    const closePromises = []
    for (const outboundStream of this.streamsOutbound.values()) {
      closePromises.push(outboundStream.close())
    }
    this.streamsOutbound.clear()

    for (const inboundStream of this.streamsInbound.values()) {
      closePromises.push(inboundStream.close())
    }
    this.streamsInbound.clear()

    await Promise.all(closePromises)

    this.peers.clear()
    this.subscriptions.clear()

    // Gossipsub

    if (this.heartbeatTimer != null) {
      this.heartbeatTimer.cancel()
      this.heartbeatTimer = null
    }

    this.score.stop()

    this.mesh.clear()
    this.fanout.clear()
    this.fanoutLastpub.clear()
    this.gossip.clear()
    this.control.clear()
    this.peerhave.clear()
    this.iasked.clear()
    this.backoff.clear()
    this.outbound.clear()
    this.gossipTracer.clear()
    this.seenCache.clear()
    if (this.fastMsgIdCache != null) { this.fastMsgIdCache.clear() }
    if (this.directPeerInitial != null) { clearTimeout(this.directPeerInitial) }
    this.idontwantCounts.clear()
    this.idontwants.clear()

    this.log('stopped')
  }

  /** FOR DEBUG ONLY - Dump peer stats for all peers. Data is cloned, safe to mutate */
  dumpPeerScoreStats (): PeerScoreStatsDump {
    return this.score.dumpPeerScoreStats()
  }

  /**
   * On an inbound stream opened
   */
  private onIncomingStream (stream: Stream, connection: Connection): void {
    if (!this.isStarted()) {
      return
    }

    const peerId = connection.remotePeer
    // add peer to router
    this.addPeer(peerId, connection.direction, connection.remoteAddr)
    // create inbound stream
    this.createInboundStream(peerId, stream)
    // attempt to create outbound stream
    this.outboundInflightQueue.push({ peerId, connection })
  }

  /**
   * Registrar notifies an established connection with pubsub protocol
   */
  private onPeerConnected (peerId: PeerId, connection: Connection): void {
    this.metrics?.newConnectionCount.inc({ status: connection.status })
    // libp2p may emit a closed connection and never issue peer:disconnect event
    // see https://github.com/ChainSafe/js-libp2p-gossipsub/issues/398
    if (!this.isStarted() || connection.status !== 'open') {
      return
    }

    this.addPeer(peerId, connection.direction, connection.remoteAddr)
    this.outboundInflightQueue.push({ peerId, connection })
  }

  /**
   * Registrar notifies a closing connection with pubsub protocol
   */
  private onPeerDisconnected (peerId: PeerId): void {
    this.log('connection ended %p', peerId)
    this.removePeer(peerId)
  }

  private async createOutboundStream (peerId: PeerId, connection: Connection): Promise<void> {
    if (!this.isStarted()) {
      return
    }

    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // TODO make this behavior more robust
    // This behavior is different than for inbound streams
    // If an outbound stream already exists, don't create a new stream
    if (this.streamsOutbound.has(id)) {
      return
    }

    try {
      const stream = new OutboundStream(
        await connection.newStream(this.protocols, {
          runOnLimitedConnection: this.runOnLimitedConnection
        }),
        (e) => { this.log.error('outbound pipe error', e) },
        { maxBufferSize: this.opts.maxOutboundBufferSize }
      )

      this.log('create outbound stream %p', peerId)

      this.streamsOutbound.set(id, stream)

      const protocol = stream.protocol
      if (protocol === constants.FloodsubID) {
        this.floodsubPeers.add(id)
      }
      this.metrics?.peersPerProtocol.inc({ protocol }, 1)

      // Immediately send own subscriptions via the newly attached stream
      if (this.subscriptions.size > 0) {
        this.log('send subscriptions to', id)
        this.sendSubscriptions(id, Array.from(this.subscriptions), true)
      }
    } catch (e) {
      this.log.error('createOutboundStream error', e)
    }
  }

  private createInboundStream (peerId: PeerId, stream: Stream): void {
    if (!this.isStarted()) {
      return
    }

    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // TODO make this behavior more robust
    // This behavior is different than for outbound streams
    // If a peer initiates a new inbound connection
    // we assume that one is the new canonical inbound stream
    const priorInboundStream = this.streamsInbound.get(id)
    if (priorInboundStream !== undefined) {
      this.log('replacing existing inbound steam %s', id)
      priorInboundStream.close().catch((err) => { this.log.error(err) })
    }

    this.log('create inbound stream %s', id)

    const inboundStream = new InboundStream(stream, { maxDataLength: this.opts.maxInboundDataLength })
    this.streamsInbound.set(id, inboundStream)

    this.pipePeerReadStream(peerId, inboundStream.source).catch((err) => { this.log(err) })
  }

  /**
   * Add a peer to the router
   */
  private addPeer (peerId: PeerId, direction: MessageStreamDirection, addr: Multiaddr): void {
    const id = peerId.toString()

    if (!this.peers.has(id)) {
      this.peers.set(id, peerId)

      // Add to peer scoring
      this.score.addPeer(id)
      const currentIP = multiaddrToIPStr(addr)
      if (currentIP !== null) {
        this.score.addIP(id, currentIP)
      } else {
        this.log('Added peer has no IP in current address %s %s', id, addr.toString())
      }

      // track the connection direction. Don't allow to unset outbound
      if (!this.outbound.has(id)) {
        this.outbound.set(id, direction === 'outbound')
      }
    }
  }

  /**
   * Removes a peer from the router
   */
  private removePeer (peerId: PeerId): void {
    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // delete peer
    this.log('delete peer %p', peerId)
    this.peers.delete(id)

    const outboundStream = this.streamsOutbound.get(id)
    const inboundStream = this.streamsInbound.get(id)

    if (outboundStream != null) {
      this.metrics?.peersPerProtocol.inc({ protocol: outboundStream.protocol }, -1)
    }

    // close streams
    outboundStream?.close().catch((err) => { this.log.error(err) })
    inboundStream?.close().catch((err) => { this.log.error(err) })

    // remove streams
    this.streamsOutbound.delete(id)
    this.streamsInbound.delete(id)

    // remove peer from topics map
    for (const peers of this.topics.values()) {
      peers.delete(id)
    }

    // Remove this peer from the mesh
    for (const [topicStr, peers] of this.mesh) {
      if (peers.delete(id)) {
        this.metrics?.onRemoveFromMesh(topicStr, ChurnReason.Dc, 1)
      }
    }

    // Remove this peer from the fanout
    for (const peers of this.fanout.values()) {
      peers.delete(id)
    }

    // Remove from floodsubPeers
    this.floodsubPeers.delete(id)
    // Remove from gossip mapping
    this.gossip.delete(id)
    // Remove from control mapping
    this.control.delete(id)
    // Remove from backoff mapping
    this.outbound.delete(id)
    // Remove from idontwant tracking
    this.idontwantCounts.delete(id)
    this.idontwants.delete(id)

    // Remove from peer scoring
    this.score.removePeer(id)

    this.acceptFromWhitelist.delete(id)
  }

  // API METHODS

  get started (): boolean {
    return this.status.code === GossipStatusCode.started
  }

  /**
   * Get a the peer-ids in a topic mesh
   */
  getMeshPeers (topic: TopicStr): PeerIdStr[] {
    const peersInTopic = this.mesh.get(topic)
    return (peersInTopic != null) ? Array.from(peersInTopic) : []
  }

  /**
   * Get a list of the peer-ids that are subscribed to one topic.
   */
  getSubscribers (topic: TopicStr): PeerId[] {
    const peersInTopic = this.topics.get(topic)
    return ((peersInTopic != null) ? Array.from(peersInTopic) : []).map((str) => this.peers.get(str) ?? peerIdFromString(str))
  }

  /**
   * Get the list of topics which the peer is subscribed to.
   */
  getTopics (): TopicStr[] {
    return Array.from(this.subscriptions)
  }

  // TODO: Reviewing Pubsub API

  // MESSAGE METHODS

  /**
   * Responsible for processing each RPC message received by other peers.
   */
  private async pipePeerReadStream (peerId: PeerId, stream: AsyncIterable<Uint8ArrayList>): Promise<void> {
    try {
      await pipe(stream, async (source) => {
        for await (const data of source) {
          try {
            // TODO: Check max gossip message size, before decodeRpc()
            const rpcBytes = data.subarray()
            // Note: This function may throw, it must be wrapped in a try {} catch {} to prevent closing the stream.
            // TODO: What should we do if the entire RPC is invalid?
            const rpc = RPC.decode(rpcBytes, {
              limits: {
                subscriptions: this.decodeRpcLimits.maxSubscriptions,
                messages: this.decodeRpcLimits.maxMessages,
                control$: {
                  ihave: this.decodeRpcLimits.maxIhaveMessageIDs,
                  iwant: this.decodeRpcLimits.maxIwantMessageIDs,
                  graft: this.decodeRpcLimits.maxControlMessages,
                  prune: this.decodeRpcLimits.maxControlMessages,
                  prune$: {
                    peers: this.decodeRpcLimits.maxPeerInfos
                  },
                  idontwant: this.decodeRpcLimits.maxControlMessages,
                  idontwant$: {
                    messageIDs: this.decodeRpcLimits.maxIdontwantMessageIDs
                  }
                }
              }
            })

            this.metrics?.onRpcRecv(rpc, rpcBytes.length)

            // Since processRpc may be overridden entirely in unsafe ways,
            // the simplest/safest option here is to wrap in a function and capture all errors
            // to prevent a top-level unhandled exception
            // This processing of rpc messages should happen without awaiting full validation/execution of prior messages
            if (this.opts.awaitRpcHandler) {
              try {
                await this.handleReceivedRpc(peerId, rpc)
              } catch (err) {
                this.metrics?.onRpcRecvError()
                this.log(err)
              }
            } else {
              this.handleReceivedRpc(peerId, rpc).catch((err) => {
                this.metrics?.onRpcRecvError()
                this.log(err)
              })
            }
          } catch (e) {
            this.metrics?.onRpcDataError()
            this.log(e as Error)
          }
        }
      })
    } catch (err) {
      this.metrics?.onPeerReadStreamError()
      this.handlePeerReadStreamError(err as Error, peerId)
    }
  }

  /**
   * Handle error when read stream pipe throws, less of the functional use but more
   * to for testing purposes to spy on the error handling
   */
  private handlePeerReadStreamError (err: Error, peerId: PeerId): void {
    this.log.error(err)
    this.onPeerDisconnected(peerId)
  }

  /**
   * Handles an rpc request from a peer
   */
  public async handleReceivedRpc (from: PeerId, rpc: RPC): Promise<void> {
    // Check if peer is graylisted in which case we ignore the event
    if (!this.acceptFrom(from.toString())) {
      this.log('received message from unacceptable peer %p', from)
      this.metrics?.rpcRecvNotAccepted.inc()
      return
    }

    const subscriptions = (rpc.subscriptions != null) ? rpc.subscriptions.length : 0
    const messages = (rpc.messages != null) ? rpc.messages.length : 0
    let ihave = 0
    let iwant = 0
    let graft = 0
    let prune = 0
    if (rpc.control != null) {
      if (rpc.control.ihave != null) { ihave = rpc.control.ihave.length }
      if (rpc.control.iwant != null) { iwant = rpc.control.iwant.length }
      if (rpc.control.graft != null) { graft = rpc.control.graft.length }
      if (rpc.control.prune != null) { prune = rpc.control.prune.length }
    }
    this.log(
      `rpc.from ${from.toString()} subscriptions ${subscriptions} messages ${messages} ihave ${ihave} iwant ${iwant} graft ${graft} prune ${prune}`
    )

    // Handle received subscriptions
    if ((rpc.subscriptions != null) && rpc.subscriptions.length > 0) {
      // update peer subscriptions

      const subscriptions: Array<{ topic: TopicStr, subscribe: boolean }> = []

      rpc.subscriptions.forEach((subOpt) => {
        const topic = subOpt.topic
        const subscribe = subOpt.subscribe === true

        if (topic != null) {
          if ((this.allowedTopics != null) && !this.allowedTopics.has(topic)) {
            // Not allowed: subscription data-structures are not bounded by topic count
            // TODO: Should apply behaviour penalties?
            return
          }

          this.handleReceivedSubscription(from, topic, subscribe)

          subscriptions.push({ topic, subscribe })
        }
      })

      this.safeDispatchEvent<SubscriptionChangeData>('subscription-change', {
        detail: { peerId: from, subscriptions }
      })
    }

    // Handle messages
    // TODO: (up to limit)
    for (const message of rpc.messages) {
      if ((this.allowedTopics != null) && !this.allowedTopics.has(message.topic)) {
        // Not allowed: message cache data-structures are not bounded by topic count
        // TODO: Should apply behaviour penalties?
        continue
      }

      const handleReceivedMessagePromise = this.handleReceivedMessage(from, message)
        // Should never throw, but handle just in case
        .catch((err) => {
          this.metrics?.onMsgRecvError(message.topic)
          this.log(err)
        })

      if (this.opts.awaitRpcMessageHandler) {
        await handleReceivedMessagePromise
      }
    }

    // Handle control messages
    if (rpc.control != null) {
      await this.handleControlMessage(from.toString(), rpc.control)
    }
  }

  /**
   * Handles a subscription change from a peer
   */
  private handleReceivedSubscription (from: PeerId, topic: TopicStr, subscribe: boolean): void {
    this.log('subscription update from %p topic %s', from, topic)

    let topicSet = this.topics.get(topic)
    if (topicSet == null) {
      topicSet = new Set()
      this.topics.set(topic, topicSet)
    }

    if (subscribe) {
      // subscribe peer to new topic
      topicSet.add(from.toString())
    } else {
      // unsubscribe from existing topic
      topicSet.delete(from.toString())
    }

    // TODO: rust-libp2p has A LOT more logic here
  }

  /**
   * Handles a newly received message from an RPC.
   * May forward to all peers in the mesh.
   */
  private async handleReceivedMessage (from: PeerId, rpcMsg: RPC.Message): Promise<void> {
    this.metrics?.onMsgRecvPreValidation(rpcMsg.topic)

    const validationResult = await this.validateReceivedMessage(from, rpcMsg)

    this.metrics?.onPrevalidationResult(rpcMsg.topic, validationResult.code)

    const validationCode = validationResult.code
    switch (validationCode) {
      case MessageStatus.duplicate:
        // Report the duplicate
        this.score.duplicateMessage(from.toString(), validationResult.msgIdStr, rpcMsg.topic)
        // due to the collision of fastMsgIdFn, 2 different messages may end up the same fastMsgId
        // so we need to also mark the duplicate message as delivered or the promise is not resolved
        // and peer gets penalized. See https://github.com/ChainSafe/js-libp2p-gossipsub/pull/385
        this.gossipTracer.deliverMessage(validationResult.msgIdStr, true)
        this.mcache.observeDuplicate(validationResult.msgIdStr, from.toString())
        return

      case MessageStatus.invalid:
        // invalid messages received
        // metrics.register_invalid_message(&raw_message.topic)
        // Tell peer_score about reject
        // Reject the original source, and any duplicates we've seen from other peers.
        if (validationResult.msgIdStr != null) {
          const msgIdStr = validationResult.msgIdStr
          this.score.rejectMessage(from.toString(), msgIdStr, rpcMsg.topic, validationResult.reason)
          this.gossipTracer.rejectMessage(msgIdStr, validationResult.reason)
        } else {
          this.score.rejectInvalidMessage(from.toString(), rpcMsg.topic)
        }

        this.metrics?.onMsgRecvInvalid(rpcMsg.topic, validationResult)
        return

      case MessageStatus.valid:
        // Tells score that message arrived (but is maybe not fully validated yet).
        // Consider the message as delivered for gossip promises.
        this.score.validateMessage(validationResult.messageId.msgIdStr)
        this.gossipTracer.deliverMessage(validationResult.messageId.msgIdStr)

        // Add the message to our memcache
        // if no validation is required, mark the message as validated
        this.mcache.put(validationResult.messageId, rpcMsg, !this.opts.asyncValidation)

        // Dispatch the message to the user if we are subscribed to the topic
        if (this.subscriptions.has(rpcMsg.topic)) {
          const isFromSelf = this.components.peerId.equals(from)

          if (!isFromSelf || this.opts.emitSelf) {
            super.dispatchEvent(
              new CustomEvent<GossipsubMessage>('gossipsub:message', {
                detail: {
                  propagationSource: from,
                  msgId: validationResult.messageId.msgIdStr,
                  msg: validationResult.msg
                }
              })
            )
            // TODO: Add option to switch between emit per topic or all messages in one
            super.dispatchEvent(new CustomEvent<Message>('message', { detail: validationResult.msg }))
          }
        }

        // Forward the message to mesh peers, if no validation is required
        // If asyncValidation is ON, expect the app layer to call reportMessageValidationResult(), then forward
        if (!this.opts.asyncValidation) {
          // TODO: in rust-libp2p
          // .forward_msg(&msg_id, raw_message, Some(propagation_source))
          this.forwardMessage(validationResult.messageId.msgIdStr, rpcMsg, from.toString())
        }
        break
      default:
        throw new Error(`Invalid validation result: ${validationCode}`)
    }
  }

  /**
   * Handles a newly received message from an RPC.
   * May forward to all peers in the mesh.
   */
  private async validateReceivedMessage (
    propagationSource: PeerId,
    rpcMsg: RPC.Message
  ): Promise<ReceivedMessageResult> {
    // Fast message ID stuff
    const fastMsgIdStr = this.fastMsgIdFn?.(rpcMsg)
    const msgIdCached = fastMsgIdStr !== undefined ? this.fastMsgIdCache?.get(fastMsgIdStr) : undefined

    if (msgIdCached != null) {
      // This message has been seen previously. Ignore it
      return { code: MessageStatus.duplicate, msgIdStr: msgIdCached }
    }

    // Perform basic validation on message and convert to RawGossipsubMessage for fastMsgIdFn()
    const validationResult = await validateToRawMessage(this.globalSignaturePolicy, rpcMsg)

    if (!validationResult.valid) {
      return { code: MessageStatus.invalid, reason: RejectReason.Error, error: validationResult.error }
    }

    const msg = validationResult.message

    // Try and perform the data transform to the message. If it fails, consider it invalid.
    try {
      if (this.dataTransform != null) {
        msg.data = this.dataTransform.inboundTransform(rpcMsg.topic, msg.data)
      }
    } catch (e) {
      this.log('Invalid message, transform failed', e)
      return { code: MessageStatus.invalid, reason: RejectReason.Error, error: ValidateError.TransformFailed }
    }

    // TODO: Check if message is from a blacklisted source or propagation origin
    // - Reject any message from a blacklisted peer
    // - Also reject any message that originated from a blacklisted peer
    // - reject messages claiming to be from ourselves but not locally published

    // Calculate the message id on the transformed data.
    const msgId = await this.msgIdFn(msg)
    const msgIdStr = this.msgIdToStrFn(msgId)
    const messageId = { msgId, msgIdStr }

    // Add the message to the duplicate caches
    if (fastMsgIdStr !== undefined && (this.fastMsgIdCache != null)) {
      const collision = this.fastMsgIdCache.put(fastMsgIdStr, msgIdStr)
      if (collision) {
        this.metrics?.fastMsgIdCacheCollision.inc()
      }
    }

    if (this.seenCache.has(msgIdStr)) {
      return { code: MessageStatus.duplicate, msgIdStr }
    } else {
      this.seenCache.put(msgIdStr)
    }

    // possibly send IDONTWANTs to mesh peers
    if ((rpcMsg.data?.length ?? 0) >= this.opts.idontwantMinDataSize) {
      this.sendIDontWants(msgId, rpcMsg.topic, propagationSource.toString())
    }

    // (Optional) Provide custom validation here with dynamic validators per topic
    // NOTE: This custom topicValidator() must resolve fast (< 100ms) to allow scores
    // to not penalize peers for long validation times.
    const topicValidator = this.topicValidators.get(rpcMsg.topic)
    if (topicValidator != null) {
      let acceptance: TopicValidatorResult
      // Use try {} catch {} in case topicValidator() is synchronous
      try {
        acceptance = await topicValidator(propagationSource, msg)
      } catch (e) {
        const errCode = (e as { code: string }).code
        if (errCode === constants.ERR_TOPIC_VALIDATOR_IGNORE) { acceptance = TopicValidatorResult.Ignore }
        if (errCode === constants.ERR_TOPIC_VALIDATOR_REJECT) { acceptance = TopicValidatorResult.Reject } else { acceptance = TopicValidatorResult.Ignore }
      }

      if (acceptance !== TopicValidatorResult.Accept) {
        return { code: MessageStatus.invalid, reason: rejectReasonFromAcceptance(acceptance), msgIdStr }
      }
    }

    return { code: MessageStatus.valid, messageId, msg }
  }

  /**
   * Return score of a peer.
   */
  getScore (peerId: PeerIdStr): number {
    return this.score.score(peerId)
  }

  /**
   * Send an rpc object to a peer with subscriptions
   */
  private sendSubscriptions (toPeer: PeerIdStr, topics: string[], subscribe: boolean): void {
    this.sendRpc(toPeer, {
      subscriptions: topics.map((topic) => ({ topic, subscribe })),
      messages: []
    })
  }

  /**
   * Handles an rpc control message from a peer
   */
  private async handleControlMessage (id: PeerIdStr, controlMsg: RPC.ControlMessage): Promise<void> {
    if (controlMsg === undefined) {
      return
    }

    const iwant = (controlMsg.ihave?.length > 0) ? this.handleIHave(id, controlMsg.ihave) : []
    const ihave = (controlMsg.iwant?.length > 0) ? this.handleIWant(id, controlMsg.iwant) : []
    const prune = (controlMsg.graft?.length > 0) ? await this.handleGraft(id, controlMsg.graft) : []
    ;(controlMsg.prune?.length > 0) && (await this.handlePrune(id, controlMsg.prune))
    ;(controlMsg.idontwant?.length > 0) && this.handleIdontwant(id, controlMsg.idontwant)

    if ((iwant.length === 0) && (ihave.length === 0) && (prune.length === 0)) {
      return
    }

    const sent = this.sendRpc(id, createGossipRpc(ihave, { iwant, prune }))
    const iwantMessageIds = iwant[0]?.messageIDs
    if (iwantMessageIds != null) {
      if (sent) {
        this.gossipTracer.addPromise(id, iwantMessageIds)
      } else {
        this.metrics?.iwantPromiseUntracked.inc(1)
      }
    }
  }

  /**
   * Whether to accept a message from a peer
   */
  public acceptFrom (id: PeerIdStr): boolean {
    if (this.direct.has(id)) {
      return true
    }

    const now = Date.now()
    const entry = this.acceptFromWhitelist.get(id)

    if ((entry != null) && entry.messagesAccepted < ACCEPT_FROM_WHITELIST_MAX_MESSAGES && entry.acceptUntil >= now) {
      entry.messagesAccepted += 1
      return true
    }

    const score = this.score.score(id)
    if (score >= ACCEPT_FROM_WHITELIST_THRESHOLD_SCORE) {
      // peer is unlikely to be able to drop its score to `graylistThreshold`
      // after 128 messages or 1s
      this.acceptFromWhitelist.set(id, {
        messagesAccepted: 0,
        acceptUntil: now + ACCEPT_FROM_WHITELIST_DURATION_MS
      })
    } else {
      this.acceptFromWhitelist.delete(id)
    }

    return score >= this.opts.scoreThresholds.graylistThreshold
  }

  /**
   * Handles IHAVE messages
   */
  private handleIHave (id: PeerIdStr, ihave: RPC.ControlIHave[]): RPC.ControlIWant[] {
    if (ihave.length === 0) {
      return []
    }

    // we ignore IHAVE gossip from any peer whose score is below the gossips threshold
    const score = this.score.score(id)
    if (score < this.opts.scoreThresholds.gossipThreshold) {
      this.log('IHAVE: ignoring peer %s with score below threshold [ score = %d ]', id, score)
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.LowScore })
      return []
    }

    // IHAVE flood protection
    const peerhave = (this.peerhave.get(id) ?? 0) + 1
    this.peerhave.set(id, peerhave)
    if (peerhave > constants.GossipsubMaxIHaveMessages) {
      this.log(
        'IHAVE: peer %s has advertised too many times (%d) within this heartbeat interval; ignoring',
        id,
        peerhave
      )
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.MaxIhave })
      return []
    }

    const iasked = this.iasked.get(id) ?? 0
    if (iasked >= constants.GossipsubMaxIHaveLength) {
      this.log('IHAVE: peer %s has already advertised too many messages (%d); ignoring', id, iasked)
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.MaxIasked })
      return []
    }

    // string msgId => msgId
    const iwant = new Map<MsgIdStr, Uint8Array>()

    ihave.forEach(({ topicID, messageIDs }) => {
      if (topicID == null || (messageIDs == null) || !this.mesh.has(topicID)) {
        return
      }

      let idonthave = 0

      messageIDs.forEach((msgId) => {
        const msgIdStr = this.msgIdToStrFn(msgId)
        if (!this.seenCache.has(msgIdStr)) {
          iwant.set(msgIdStr, msgId)
          idonthave++
        }
      })

      this.metrics?.onIhaveRcv(topicID, messageIDs.length, idonthave)
    })

    if (iwant.size === 0) {
      return []
    }

    let iask = iwant.size
    if (iask + iasked > constants.GossipsubMaxIHaveLength) {
      iask = constants.GossipsubMaxIHaveLength - iasked
    }

    this.log('IHAVE: Asking for %d out of %d messages from %s', iask, iwant.size, id)

    let iwantList = Array.from(iwant.values())
    // ask in random order
    shuffle(iwantList)

    // truncate to the messages we are actually asking for and update the iasked counter
    iwantList = iwantList.slice(0, iask)
    this.iasked.set(id, iasked + iask)

    // do not add gossipTracer promise here until a successful sendRpc()

    return [
      {
        messageIDs: iwantList
      }
    ]
  }

  /**
   * Handles IWANT messages
   * Returns messages to send back to peer
   */
  private handleIWant (id: PeerIdStr, iwant: RPC.ControlIWant[]): RPC.Message[] {
    if (iwant.length === 0) {
      return []
    }

    // we don't respond to IWANT requests from any per whose score is below the gossip threshold
    const score = this.score.score(id)
    if (score < this.opts.scoreThresholds.gossipThreshold) {
      this.log('IWANT: ignoring peer %s with score below threshold [score = %d]', id, score)
      return []
    }

    const ihave = new Map<MsgIdStr, RPC.Message>()
    const iwantByTopic = new Map<TopicStr, number>()
    let iwantDonthave = 0

    iwant.forEach(({ messageIDs }) => {
      messageIDs?.forEach((msgId) => {
        const msgIdStr = this.msgIdToStrFn(msgId)
        const entry = this.mcache.getWithIWantCount(msgIdStr, id)
        if (entry == null) {
          iwantDonthave++
          return
        }

        iwantByTopic.set(entry.msg.topic, 1 + (iwantByTopic.get(entry.msg.topic) ?? 0))

        if (entry.count > constants.GossipsubGossipRetransmission) {
          this.log('IWANT: Peer %s has asked for message %s too many times: ignoring request', id, msgId)
          return
        }

        ihave.set(msgIdStr, entry.msg)
      })
    })

    this.metrics?.onIwantRcv(iwantByTopic, iwantDonthave)

    if (ihave.size === 0) {
      this.log('IWANT: Could not provide any wanted messages to %s', id)
      return []
    }

    this.log('IWANT: Sending %d messages to %s', ihave.size, id)

    return Array.from(ihave.values())
  }

  /**
   * Handles Graft messages
   */
  private async handleGraft (id: PeerIdStr, graft: RPC.ControlGraft[]): Promise<RPC.ControlPrune[]> {
    const prune: TopicStr[] = []
    const score = this.score.score(id)
    const now = Date.now()
    let doPX = this.opts.doPX

    graft.forEach(({ topicID }) => {
      if (topicID == null) {
        return
      }

      const peersInMesh = this.mesh.get(topicID)
      if (peersInMesh == null) {
        // don't do PX when there is an unknown topic to avoid leaking our peers
        doPX = false
        // spam hardening: ignore GRAFTs for unknown topics
        return
      }

      // check if peer is already in the mesh; if so do nothing
      if (peersInMesh.has(id)) {
        return
      }

      const backoffExpiry = this.backoff.get(topicID)?.get(id)

      // This if/else chain contains the various cases of valid (and semi-valid) GRAFTs
      // Most of these cases result in a PRUNE immediately being sent in response

      // we don't GRAFT to/from direct peers; complain loudly if this happens
      if (this.direct.has(id)) {
        this.log('GRAFT: ignoring request from direct peer %s', id)
        // this is possibly a bug from a non-reciprical configuration; send a PRUNE
        prune.push(topicID)
        // but don't px
        doPX = false

        // make sure we are not backing off that peer
      } else if (typeof backoffExpiry === 'number' && now < backoffExpiry) {
        this.log('GRAFT: ignoring backed off peer %s', id)
        // add behavioral penalty
        this.score.addPenalty(id, 1, ScorePenalty.GraftBackoff)
        // no PX
        doPX = false
        // check the flood cutoff -- is the GRAFT coming too fast?
        const floodCutoff = backoffExpiry + this.opts.graftFloodThreshold - this.opts.pruneBackoff
        if (now < floodCutoff) {
          // extra penalty
          this.score.addPenalty(id, 1, ScorePenalty.GraftBackoff)
        }
        // refresh the backoff
        this.addBackoff(id, topicID)
        prune.push(topicID)

        // check the score
      } else if (score < 0) {
        // we don't GRAFT peers with negative score
        this.log('GRAFT: ignoring peer %s with negative score: score=%d, topic=%s', id, score, topicID)