feat: auto relay (#723)

* feat: auto relay

* fix: leverage protoBook events to ask relay peers if they support hop

* chore: refactor disconnect

* chore: do not listen on a relayed conn

* chore: tweaks

* chore: improve _listenOnAvailableHopRelays logic

* chore: default value of 1 to maxListeners on auto-relay

src/circuit/auto-relay.js

@@ -0,0 +1,231 @@
+'use strict'
+
+const debug = require('debug')
+const log = debug('libp2p:auto-relay')
+log.error = debug('libp2p:auto-relay:error')
+
+const uint8ArrayFromString = require('uint8arrays/from-string')
+const uint8ArrayToString = require('uint8arrays/to-string')
+const multiaddr = require('multiaddr')
+const PeerId = require('peer-id')
+
+const { relay: multicodec } = require('./multicodec')
+const { canHop } = require('./circuit/hop')
+
+const circuitProtoCode = 290
+const hopMetadataKey = 'hop_relay'
+const hopMetadataValue = 'true'
+
+class AutoRelay {
+  /**
+   * Creates an instance of AutoRelay.
+   * @constructor
+   * @param {object} props
+   * @param {Libp2p} props.libp2p
+   * @param {number} [props.maxListeners = 1] maximum number of relays to listen.
+   */
+  constructor ({ libp2p, maxListeners = 1 }) {
+    this._libp2p = libp2p
+    this._peerId = libp2p.peerId
+    this._peerStore = libp2p.peerStore
+    this._connectionManager = libp2p.connectionManager
+    this._transportManager = libp2p.transportManager
+
+    this.maxListeners = maxListeners
+
+    /**
+     * @type {Set<string>}
+     */
+    this._listenRelays = new Set()
+
+    this._onProtocolChange = this._onProtocolChange.bind(this)
+    this._onPeerDisconnected = this._onPeerDisconnected.bind(this)
+
+    this._peerStore.on('change:protocols', this._onProtocolChange)
+    this._connectionManager.on('peer:disconnect', this._onPeerDisconnected)
+  }
+
+  /**
+   * Check if a peer supports the relay protocol.
+   * If the protocol is not supported, check if it was supported before and remove it as a listen relay.
+   * If the protocol is supported, check if the peer supports **HOP** and add it as a listener if
+   * inside the threshold.
+   * @param {Object} props
+   * @param {PeerId} props.peerId
+   * @param {Array<string>} props.protocols
+   * @return {Promise<void>}
+   */
+  async _onProtocolChange ({ peerId, protocols }) {
+    const id = peerId.toB58String()
+
+    // Check if it has the protocol
+    const hasProtocol = protocols.find(protocol => protocol === multicodec)
+
+    // If no protocol, check if we were keeping the peer before as a listenRelay
+    if (!hasProtocol && this._listenRelays.has(id)) {
+      this._removeListenRelay(id)
+      return
+    } else if (!hasProtocol || this._listenRelays.has(id)) {
+      return
+    }
+
+    // If protocol, check if can hop, store info in the metadataBook and listen on it
+    try {
+      const connection = this._connectionManager.get(peerId)
+
+      // Do not hop on a relayed connection
+      if (connection.remoteAddr.protoCodes().includes(circuitProtoCode)) {
+        log(`relayed connection to ${id} will not be used to hop on`)
+        return
+      }
+
+      const supportsHop = await canHop({ connection })
+
+      if (supportsHop) {
+        this._peerStore.metadataBook.set(peerId, hopMetadataKey, uint8ArrayFromString(hopMetadataValue))
+        await this._addListenRelay(connection, id)
+      }
+    } catch (err) {
+      log.error(err)
+    }
+  }
+
+  /**
+   * Peer disconnects.
+   * @param {Connection} connection connection to the peer
+   * @return {void}
+   */
+  _onPeerDisconnected (connection) {
+    const peerId = connection.remotePeer
+    const id = peerId.toB58String()
+
+    // Not listening on this relay
+    if (!this._listenRelays.has(id)) {
+      return
+    }
+
+    this._removeListenRelay(id)
+  }
+
+  /**
+   * Attempt to listen on the given relay connection.
+   * @private
+   * @param {Connection} connection connection to the peer
+   * @param {string} id peer identifier string
+   * @return {Promise<void>}
+   */
+  async _addListenRelay (connection, id) {
+    // Check if already listening on enough relays
+    if (this._listenRelays.size >= this.maxListeners) {
+      return
+    }
+
+    // Create relay listen addr
+    let listenAddr, remoteMultiaddr
+
+    try {
+      const remoteAddrs = this._peerStore.addressBook.get(connection.remotePeer)
+      // TODO: HOP Relays should avoid advertising private addresses!
+      remoteMultiaddr = remoteAddrs.find(a => a.isCertified).multiaddr // Get first announced address certified
+    } catch (_) {
+      log.error(`${id} does not have announced certified multiaddrs`)
+      return
+    }
+
+    if (!remoteMultiaddr.protoNames().includes('p2p')) {
+      listenAddr = `${remoteMultiaddr.toString()}/p2p/${connection.remotePeer.toB58String()}/p2p-circuit`
+    } else {
+      listenAddr = `${remoteMultiaddr.toString()}/p2p-circuit`
+    }
+
+    // Attempt to listen on relay
+    this._listenRelays.add(id)
+
+    try {
+      await this._transportManager.listen([multiaddr(listenAddr)])
+      // TODO: push announce multiaddrs update
+      // await this._libp2p.identifyService.pushToPeerStore()
+    } catch (err) {
+      log.error(err)
+      this._listenRelays.delete(id)
+    }
+  }
+
+  /**
+   * Remove listen relay.
+   * @private
+   * @param {string} id peer identifier string.
+   * @return {void}
+   */
+  _removeListenRelay (id) {
+    if (this._listenRelays.delete(id)) {
+      // TODO: this should be responsibility of the connMgr
+      this._listenOnAvailableHopRelays([id])
+    }
+  }
+
+  /**
+   * Try to listen on available hop relay connections.
+   * The following order will happen while we do not have enough relays.
+   * 1. Check the metadata store for known relays, try to listen on the ones we are already connected.
+   * 2. Dial and try to listen on the peers we know that support hop but are not connected.
+   * 3. Search the network.
+   * @param {Array<string>} [peersToIgnore]
+   * @return {Promise<void>}
+   */
+  async _listenOnAvailableHopRelays (peersToIgnore = []) {
+    // TODO: The peer redial issue on disconnect should be handled by connection gating
+    // Check if already listening on enough relays
+    if (this._listenRelays.size >= this.maxListeners) {
+      return
+    }
+
+    const knownHopsToDial = []
+
+    // Check if we have known hop peers to use and attempt to listen on the already connected
+    for (const [id, metadataMap] of this._peerStore.metadataBook.data.entries()) {
+      // Continue to next if listening on this or peer to ignore
+      if (this._listenRelays.has(id) || peersToIgnore.includes(id)) {
+        continue
+      }
+
+      const supportsHop = metadataMap.get(hopMetadataKey)
+
+      // Continue to next if it does not support Hop
+      if (!supportsHop || uint8ArrayToString(supportsHop) !== hopMetadataValue) {
+        continue
+      }
+
+      const peerId = PeerId.createFromCID(id)
+      const connection = this._connectionManager.get(peerId)
+
+      // If not connected, store for possible later use.
+      if (!connection) {
+        knownHopsToDial.push(peerId)
+        continue
+      }
+
+      await this._addListenRelay(connection, id)
+
+      // Check if already listening on enough relays
+      if (this._listenRelays.size >= this.maxListeners) {
+        return
+      }
+    }
+
+    // Try to listen on known peers that are not connected
+    for (const peerId of knownHopsToDial) {
+      const connection = await this._libp2p.dial(peerId)
+      await this._addListenRelay(connection, peerId.toB58String())
+
+      // Check if already listening on enough relays
+      if (this._listenRelays.size >= this.maxListeners) {
+        return
+      }
+    }
+
+    // TODO: Try to find relays to hop on the network
+  }
+}
+
+module.exports = AutoRelay

src/circuit/circuit/hop.js

@@ -116,6 +116,33 @@ module.exports.hop = async function hop ({
   throw errCode(new Error(`HOP request failed with code ${response.code}`), Errors.ERR_HOP_REQUEST_FAILED)
 }
 
+/**
+ * Performs a CAN_HOP request to a relay peer, in order to understand its capabilities.
+ * @param {object} options
+ * @param {Connection} options.connection Connection to the relay
+ * @returns {Promise<boolean>}
+ */
+module.exports.canHop = async function canHop ({
+  connection
+}) {
+  // Create a new stream to the relay
+  const { stream } = await connection.newStream([multicodec.relay])
+  // Send the HOP request
+  const streamHandler = new StreamHandler({ stream })
+  streamHandler.write({
+    type: CircuitPB.Type.CAN_HOP
+  })
+
+  const response = await streamHandler.read()
+  await streamHandler.close()
+
+  if (response.code !== CircuitPB.Status.SUCCESS) {
+    return false
+  }
+
+  return true
+}
+
 /**
  * Creates an unencoded CAN_HOP response based on the Circuits configuration
  *

src/circuit/index.js

@@ -1,16 +1,18 @@
 'use strict'
 
+const debug = require('debug')
+const log = debug('libp2p:circuit')
+log.error = debug('libp2p:circuit:error')
+
 const mafmt = require('mafmt')
 const multiaddr = require('multiaddr')
 const PeerId = require('peer-id')
 const withIs = require('class-is')
 const { CircuitRelay: CircuitPB } = require('./protocol')
 
-const debug = require('debug')
-const log = debug('libp2p:circuit')
-log.error = debug('libp2p:circuit:error')
 const toConnection = require('libp2p-utils/src/stream-to-ma-conn')
 
+const AutoRelay = require('./auto-relay')
 const { relay: multicodec } = require('./multicodec')
 const createListener = require('./listener')
 const { handleCanHop, handleHop, hop } = require('./circuit/hop')
@@ -35,11 +37,19 @@ class Circuit {
     this._libp2p = libp2p
     this.peerId = libp2p.peerId
     this._registrar.handle(multicodec, this._onProtocol.bind(this))
+
+    // Create autoRelay if enabled
+    this._autoRelay = this._options.autoRelay.enabled && new AutoRelay({ libp2p, ...this._options.autoRelay })
   }
 
-  async _onProtocol ({ connection, stream, protocol }) {
+  async _onProtocol ({ connection, stream }) {
     const streamHandler = new StreamHandler({ stream })
     const request = await streamHandler.read()
+
+    if (!request) {
+      return
+    }
+
     const circuit = this
     let virtualConnection
 
@@ -163,7 +173,7 @@ class Circuit {
     // Called on successful HOP and STOP requests
     this.handler = handler
 
-    return createListener(this, options)
+    return createListener(this._libp2p, options)
   }
 
   /**

src/circuit/listener.js

@@ -8,13 +8,23 @@ const log = debug('libp2p:circuit:listener')
 log.err = debug('libp2p:circuit:error:listener')
 
 /**
- * @param {*} circuit
+ * @param {Libp2p} libp2p
  * @returns {Listener} a transport listener
  */
-module.exports = (circuit) => {
+module.exports = (libp2p) => {
   const listener = new EventEmitter()
   const listeningAddrs = new Map()
 
+  // Remove listeningAddrs when a peer disconnects
+  libp2p.connectionManager.on('peer:disconnect', (connection) => {
+    const deleted = listeningAddrs.delete(connection.remotePeer.toB58String())
+
+    if (deleted) {
+      // TODO push announce multiaddrs update
+      // libp2p.identifyService.pushToPeerStore()
+    }
+  })
+
   /**
    * Add swarm handler and listen for incoming connections
    *
@@ -24,7 +34,7 @@ module.exports = (circuit) => {
   listener.listen = async (addr) => {
     const addrString = String(addr).split('/p2p-circuit').find(a => a !== '')
 
-    const relayConn = await circuit._dialer.connectToPeer(multiaddr(addrString))
+    const relayConn = await libp2p.dial(multiaddr(addrString))
     const relayedAddr = relayConn.remoteAddr.encapsulate('/p2p-circuit')
 
     listeningAddrs.set(relayConn.remotePeer.toB58String(), relayedAddr)

src/config.js

@@ -63,6 +63,10 @@ const DefaultConfig = {
       hop: {
         enabled: false,
         active: false
+      },
+      autoRelay: {
+        enabled: false,
+        maxListeners: 2
       }
     },
     transport: {}

src/identify/index.js

@@ -131,13 +131,12 @@ class IdentifyService {
 
   /**
    * Calls `push` for all peers in the `peerStore` that are connected
-   *
-   * @param {PeerStore} peerStore
+   * @returns {void}
    */
-  pushToPeerStore (peerStore) {
+  pushToPeerStore () {
     const connections = []
     let connection
-    for (const peer of peerStore.peers.values()) {
+    for (const peer of this.peerStore.peers.values()) {
       if (peer.protocols.includes(MULTICODEC_IDENTIFY_PUSH) && (connection = this.connectionManager.get(peer.id))) {
         connections.push(connection)
       }

src/index.js

@@ -438,7 +438,7 @@ class Libp2p extends EventEmitter {
 
     // Only push if libp2p is running
     if (this.isStarted() && this.identifyService) {
-      this.identifyService.pushToPeerStore(this.peerStore)
+      this.identifyService.pushToPeerStore()
     }
   }
 
@@ -456,13 +456,14 @@ class Libp2p extends EventEmitter {
 
     // Only push if libp2p is running
     if (this.isStarted() && this.identifyService) {
-      this.identifyService.pushToPeerStore(this.peerStore)
+      this.identifyService.pushToPeerStore()
     }
   }
 
   async _onStarting () {
-    // Listen on the provided transports
-    await this.transportManager.listen()
+    // Listen on the provided transports for the provided addresses
+    const addrs = this.addressManager.getListenAddrs()
+    await this.transportManager.listen(addrs)
 
     // Start PeerStore
     await this.peerStore.start()

src/peer-store/address-book.js

@@ -270,7 +270,7 @@ class AddressBook extends Book {
    *
    * @override
    * @param {PeerId} peerId
-   * @returns {Array<data>}
+   * @returns {Array<Address>|undefined}
    */
   get (peerId) {
     if (!PeerId.isPeerId(peerId)) {

src/transport-manager.js

@@ -139,11 +139,10 @@ class TransportManager {
    * Starts listeners for each listen Multiaddr.
    *
    * @async
+   * @param {Array<Multiaddr>} addrs addresses to attempt to listen on
    */
-  async listen () {
-    const addrs = this.libp2p.addressManager.getListenAddrs()
-
-    if (addrs.length === 0) {
+  async listen (addrs) {
+    if (!addrs || addrs.length === 0) {
       log('no addresses were provided for listening, this node is dial only')
       return
     }