feat: compatibility with go-libp2p-mdns (#80)

Adds an additional mdns poller to interop with go-libp2p until both implementations comply with the new spec, https://github.com/libp2p/specs/blob/4c5a459ae8fb9a250e5f87f0c64fadaa7997266a/discovery/mdns.md.

Author: Alan Shaw

.gitignore

@@ -3,6 +3,7 @@ docs
 **/*.log
 test/repo-tests*
 **/bundle.js
+.nyc_output
 
 # Logs
 logs

README.md

@@ -33,9 +33,10 @@ mdns.start(() => setTimeout(() => mdns.stop(() => {}), 20 * 1000))
 
 - options
   - `peerInfo` - PeerInfo to announce
-  - `broadcast` - (true/false) announce our presence through mDNS, default false
+  - `broadcast` - (true/false) announce our presence through mDNS, default `false`
   - `interval` - query interval, default 10 * 1000 (10 seconds)
   - `serviceTag` - name of the service announce , default 'ipfs.local`
+  - `compat` - enable/disable compatibility with go-libp2p-mdns, default `true`
 
 ## MDNS messages
 

package.json

@@ -10,7 +10,7 @@
   ],
   "scripts": {
     "lint": "aegir lint",
-    "coverage": "aegir coverage",
+    "coverage": "nyc --reporter=lcov --reporter=text npm run test:node",
     "test": "aegir test -t node",
     "test:node": "aegir test -t node",
     "release": "aegir release -t node --no-build",
@@ -35,11 +35,11 @@
   "homepage": "https://github.com/libp2p/js-libp2p-mdns",
   "devDependencies": {
     "aegir": "^18.2.2",
-    "async": "^2.6.2",
     "chai": "^4.2.0",
     "dirty-chai": "^2.0.1"
   },
   "dependencies": {
+    "async": "^2.6.2",
     "debug": "^4.1.1",
     "libp2p-tcp": "~0.13.0",
     "multiaddr": "^6.0.6",

src/compat/constants.js

@@ -0,0 +1,6 @@
+'use strict'
+
+exports.SERVICE_TAG = '_ipfs-discovery._udp'
+exports.SERVICE_TAG_LOCAL = `${exports.SERVICE_TAG}.local`
+exports.MULTICAST_IP = '224.0.0.251'
+exports.MULTICAST_PORT = 5353

src/compat/index.js

@@ -0,0 +1,60 @@
+'use strict'
+
+// Compatibility with Go libp2p MDNS
+
+const EE = require('events')
+const parallel = require('async/parallel')
+const Responder = require('./responder')
+const Querier = require('./querier')
+
+class GoMulticastDNS extends EE {
+  constructor (peerInfo) {
+    super()
+    this._started = false
+    this._peerInfo = peerInfo
+    this._onPeer = this._onPeer.bind(this)
+  }
+
+  start (callback) {
+    if (this._started) {
+      return callback(new Error('MulticastDNS service is already started'))
+    }
+
+    this._started = true
+    this._responder = new Responder(this._peerInfo)
+    this._querier = new Querier(this._peerInfo.id)
+
+    this._querier.on('peer', this._onPeer)
+
+    parallel([
+      cb => this._responder.start(cb),
+      cb => this._querier.start(cb)
+    ], callback)
+  }
+
+  _onPeer (peerInfo) {
+    this.emit('peer', peerInfo)
+  }
+
+  stop (callback) {
+    if (!this._started) {
+      return callback(new Error('MulticastDNS service is not started'))
+    }
+
+    const responder = this._responder
+    const querier = this._querier
+
+    this._started = false
+    this._responder = null
+    this._querier = null
+
+    querier.removeListener('peer', this._onPeer)
+
+    parallel([
+      cb => responder.stop(cb),
+      cb => querier.stop(cb)
+    ], callback)
+  }
+}
+
+module.exports = GoMulticastDNS

src/compat/querier.js

@@ -0,0 +1,176 @@
+'use strict'
+
+const assert = require('assert')
+const EE = require('events')
+const MDNS = require('multicast-dns')
+const Multiaddr = require('multiaddr')
+const PeerInfo = require('peer-info')
+const PeerId = require('peer-id')
+const nextTick = require('async/nextTick')
+const log = require('debug')('libp2p:mdns:compat:querier')
+const { SERVICE_TAG_LOCAL, MULTICAST_IP, MULTICAST_PORT } = require('./constants')
+
+class Querier extends EE {
+  constructor (peerId, options) {
+    super()
+    assert(peerId, 'missing peerId parameter')
+    options = options || {}
+    this._peerIdStr = peerId.toB58String()
+    // Re-query every 60s, in leu of network change detection
+    options.queryInterval = options.queryInterval || 60000
+    // Time for which the MDNS server will stay alive waiting for responses
+    // Must be less than options.queryInterval!
+    options.queryPeriod = Math.min(
+      options.queryInterval,
+      options.queryPeriod == null ? 5000 : options.queryPeriod
+    )
+    this._options = options
+    this._onResponse = this._onResponse.bind(this)
+  }
+
+  start (callback) {
+    this._handle = periodically(() => {
+      // Create a querier that queries multicast but gets responses unicast
+      const mdns = MDNS({ multicast: false, interface: '0.0.0.0', port: 0 })
+
+      mdns.on('response', this._onResponse)
+
+      mdns.query({
+        id: nextId(), // id > 0 for unicast response
+        questions: [{ name: SERVICE_TAG_LOCAL, type: 'PTR', class: 'IN' }]
+      }, null, {
+        address: MULTICAST_IP,
+        port: MULTICAST_PORT
+      })
+
+      return {
+        stop: callback => {
+          mdns.removeListener('response', this._onResponse)
+          mdns.destroy(callback)
+        }
+      }
+    }, {
+      period: this._options.queryPeriod,
+      interval: this._options.queryInterval
+    })
+
+    nextTick(() => callback())
+  }
+
+  _onResponse (event, info) {
+    const answers = event.answers || []
+    const ptrRecord = answers.find(a => a.type === 'PTR' && a.name === SERVICE_TAG_LOCAL)
+
+    // Only deal with responses for our service tag
+    if (!ptrRecord) return
+
+    log('got response', event, info)
+
+    const txtRecord = answers.find(a => a.type === 'TXT')
+    if (!txtRecord) return log('missing TXT record in response')
+
+    let peerIdStr
+    try {
+      peerIdStr = txtRecord.data[0].toString()
+    } catch (err) {
+      return log('failed to extract peer ID from TXT record data', txtRecord, err)
+    }
+
+    if (this._peerIdStr === peerIdStr) {
+      return log('ignoring reply to myself')
+    }
+
+    let peerId
+    try {
+      peerId = PeerId.createFromB58String(peerIdStr)
+    } catch (err) {
+      return log('failed to create peer ID from TXT record data', peerIdStr, err)
+    }
+
+    PeerInfo.create(peerId, (err, info) => {
+      if (err) return log('failed to create peer info from peer ID', peerId, err)
+
+      const srvRecord = answers.find(a => a.type === 'SRV')
+      if (!srvRecord) return log('missing SRV record in response')
+
+      log('peer found', peerIdStr)
+
+      const { port } = srvRecord.data || {}
+      const protos = { A: 'ip4', AAAA: 'ip6' }
+
+      const multiaddrs = answers
+        .filter(a => ['A', 'AAAA'].includes(a.type))
+        .reduce((addrs, a) => {
+          const maStr = `/${protos[a.type]}/${a.data}/tcp/${port}`
+          try {
+            addrs.push(new Multiaddr(maStr))
+            log(maStr)
+          } catch (err) {
+            log(`failed to create multiaddr from ${a.type} record data`, maStr, port, err)
+          }
+          return addrs
+        }, [])
+
+      multiaddrs.forEach(addr => info.multiaddrs.add(addr))
+      this.emit('peer', info)
+    })
+  }
+
+  stop (callback) {
+    this._handle.stop(callback)
+  }
+}
+
+module.exports = Querier
+
+/**
+ * Run `fn` for a certain period of time, and then wait for an interval before
+ * running it again. `fn` must return an object with a stop function, which is
+ * called when the period expires.
+ *
+ * @param {Function} fn function to run
+ * @param {Object} [options]
+ * @param {Object} [options.period] Period in ms to run the function for
+ * @param {Object} [options.interval] Interval in ms between runs
+ * @returns {Object} handle that can be used to stop execution
+ */
+function periodically (fn, options) {
+  let handle, timeoutId
+  let stopped = false
+
+  const reRun = () => {
+    handle = fn()
+    timeoutId = setTimeout(() => {
+      handle.stop(err => {
+        if (err) log(err)
+        if (!stopped) {
+          timeoutId = setTimeout(reRun, options.interval)
+        }
+      })
+      handle = null
+    }, options.period)
+  }
+
+  reRun()
+
+  return {
+    stop (callback) {
+      stopped = true
+      clearTimeout(timeoutId)
+      if (handle) {
+        handle.stop(callback)
+      } else {
+        callback()
+      }
+    }
+  }
+}
+
+const nextId = (() => {
+  let id = 0
+  return () => {
+    id++
+    if (id === Number.MAX_SAFE_INTEGER) id = 1
+    return id
+  }
+})()

src/compat/responder.js

@@ -0,0 +1,97 @@
+'use strict'
+
+const OS = require('os')
+const assert = require('assert')
+const MDNS = require('multicast-dns')
+const log = require('debug')('libp2p:mdns:compat:responder')
+const TCP = require('libp2p-tcp')
+const nextTick = require('async/nextTick')
+const { SERVICE_TAG_LOCAL } = require('./constants')
+
+const tcp = new TCP()
+
+class Responder {
+  constructor (peerInfo) {
+    assert(peerInfo, 'missing peerInfo parameter')
+    this._peerInfo = peerInfo
+    this._peerIdStr = peerInfo.id.toB58String()
+    this._onQuery = this._onQuery.bind(this)
+  }
+
+  start (callback) {
+    this._mdns = MDNS()
+    this._mdns.on('query', this._onQuery)
+    nextTick(() => callback())
+  }
+
+  _onQuery (event, info) {
+    const multiaddrs = tcp.filter(this._peerInfo.multiaddrs.toArray())
+    // Only announce TCP for now
+    if (!multiaddrs.length) return
+
+    const questions = event.questions || []
+
+    // Only respond to queries for our service tag
+    if (!questions.some(q => q.name === SERVICE_TAG_LOCAL)) return
+
+    log('got query', event, info)
+
+    const answers = []
+    const peerServiceTagLocal = `${this._peerIdStr}.${SERVICE_TAG_LOCAL}`
+
+    answers.push({
+      name: SERVICE_TAG_LOCAL,
+      type: 'PTR',
+      class: 'IN',
+      ttl: 120,
+      data: peerServiceTagLocal
+    })
+
+    // Only announce TCP multiaddrs for now
+    const port = multiaddrs[0].toString().split('/')[4]
+
+    answers.push({
+      name: peerServiceTagLocal,
+      type: 'SRV',
+      class: 'IN',
+      ttl: 120,
+      data: {
+        priority: 10,
+        weight: 1,
+        port,
+        target: OS.hostname()
+      }
+    })
+
+    answers.push({
+      name: peerServiceTagLocal,
+      type: 'TXT',
+      class: 'IN',
+      ttl: 120,
+      data: [Buffer.from(this._peerIdStr)]
+    })
+
+    multiaddrs.forEach((ma) => {
+      const proto = ma.protoNames()[0]
+      if (proto === 'ip4' || proto === 'ip6') {
+        answers.push({
+          name: OS.hostname(),
+          type: proto === 'ip4' ? 'A' : 'AAAA',
+          class: 'IN',
+          ttl: 120,
+          data: ma.toString().split('/')[2]
+        })
+      }
+    })
+
+    log('responding to query', answers)
+    this._mdns.respond(answers, info)
+  }
+
+  stop (callback) {
+    this._mdns.removeListener('query', this._onQuery)
+    this._mdns.destroy(callback)
+  }
+}
+
+module.exports = Responder