streamline auto bind

README.md

@@ -114,7 +114,9 @@ Options include:
   // Optionally pass in your own UDP socket to use.
   socket: udpSocket,
   // Optionally pass in array of { host, port } to add to the routing table if you know any peers
-  nodes: [{ host, port }, ...]
+  nodes: [{ host, port }, ...],
+  // Optionally pass a port you prefer to bind to instead of a random one
+  bind: 0
 }
 ```
 
@@ -128,9 +130,9 @@ Your DHT routing id is `hash(publicIp + publicPort)` and will be autoconfigured
 Wait for the node to be fully bootstrapped etc.
 You don't have to wait for this method, but can be useful during testing.
 
-#### `await node.bind(port)`
+#### `await node.bind([preferredPort])`
 
-Bind to a specific UDP port instead of a random one.
+Wait for the underlying socket to bind. If you prefer a specific port you can specify it here.
 
 #### `node.id`
 

index.js

@@ -66,6 +66,7 @@ class DHT extends EventEmitter {
     this.table = new Table(opts.id || randomBytes(32))
 
     this.rpc = new RPC({
+      bind: opts.bind,
       maxWindow: opts.maxWindow,
       socket: opts.socket,
       onwarning: opts.onwarning,
@@ -93,7 +94,6 @@ class DHT extends EventEmitter {
     this._nat = new NatAnalyzer(opts.natSampleSize || 16)
     this._onrow = (row) => row.on('full', (node) => this._onfullrow(node, row))
     this._rotateSecrets = false
-    this._bound = false
     this._secrets = [
       Buffer.alloc(32),
       Buffer.alloc(32)
@@ -105,11 +105,7 @@ class DHT extends EventEmitter {
     sodium.randombytes_buf(this._secrets[1])
 
     this.table.on('row', this._onrow)
-
-    this.rpc.socket.on('listening', () => {
-      this._bound = true
-      this.emit('listening')
-    })
+    this.rpc.socket.on('listening', () => this.emit('listening'))
 
     if (opts.nodes) {
       for (const node of opts.nodes) this.addNode(node)
@@ -198,9 +194,7 @@ class DHT extends EventEmitter {
       this._resolveSampled = null
     }
 
-    if (!this._bound) {
-      await bind(this.rpc.socket, 0)
-    }
+    await this.rpc.bind()
 
     this.emit('ready')
   }
@@ -676,24 +670,3 @@ function compare (id, a, b) {
 function randomOffset (n) {
   return n - ((Math.random() * 0.5 * n) | 0)
 }
-
-function bind (socket, port) {
-  return new Promise((resolve, reject) => {
-    socket.bind(port)
-
-    socket.on('error', onerror)
-    socket.on('listening', ondone)
-
-    function onerror (err) {
-      socket.removeListener('error', onerror)
-      socket.removeListener('listening', ondone)
-      reject(err)
-    }
-
-    function ondone () {
-      socket.removeListener('error', onerror)
-      socket.removeListener('listening', ondone)
-      resolve()
-    }
-  })
-}

lib/rpc.js

@@ -9,6 +9,9 @@ module.exports = class RPC {
     this._tick = 0
     this._w = 0
     this._win = [0, 0, 0, 0]
+    this._bind = opts.bind || 0
+    this._bound = false
+    this._binding = null
 
     this.maxWindow = opts.maxWindow || 80 // ~100 per second burst, ~80 per second avg
     this.maxRetries = 3
@@ -45,31 +48,41 @@ module.exports = class RPC {
     return this.socket.address()
   }
 
-  bind (port) {
-    return new Promise((resolve, reject) => {
-      const s = this.socket
+  bind (port = this._bind) {
+    if (this._binding) return this._binding
 
-      if (s.listen) {
-        s.listen(port)
-      } else {
-        s.bind(port)
-      }
+    const defaultPort = this._bind
+
+    this._binding = new Promise((resolve, reject) => {
+      const s = this.socket
 
+      s.bind(port)
       s.on('listening', onlistening)
       s.on('error', onerror)
 
       function onlistening () {
+        this._bound = true
+
         s.removeListener('listening', onlistening)
         s.removeListener('error', onerror)
         resolve()
       }
 
       function onerror (err) {
+        // retry on any port if preferred port is unavail
+        if (port === defaultPort && port !== 0) {
+          port = 0
+          s.bind(0)
+          return
+        }
+
         s.removeListener('listening', onlistening)
         s.removeListener('error', onerror)
         reject(err)
       }
     })
+
+    return this._binding
   }
 
   destroy () {
@@ -93,8 +106,12 @@ module.exports = class RPC {
     return this.socket
   }
 
-  request (m, opts) {
-    if (this.destroyed) return Promise.reject(new Error('RPC socket destroyed'))
+  async request (m, opts) {
+    if (this.destroyed) throw new Error('RPC socket destroyed')
+
+    const socket = (opts && opts.socket) || this.socket
+
+    if (!this._bound && socket === this.socket) await this.bind()
 
     if (this._drainInterval === null) {
       this._drainInterval = setInterval(this._drain.bind(this), 750)
@@ -113,7 +130,7 @@ module.exports = class RPC {
     return new Promise((resolve, reject) => {
       const total = this._win[0] + this._win[1] + this._win[2] + this._win[3]
       const req = {
-        socket: (opts && opts.socket) || this.socket,
+        socket,
         timeout: 2,
         expectOk: !!(opts && opts.expectOk !== false),
         tries: (opts && opts.retry === false) ? this.maxRetries : 0,

test.js

@@ -1,4 +1,5 @@
 const tape = require('tape')
+const dgram = require('dgram')
 const DHT = require('./')
 
 tape('make tiny swarm', async function (t) {
@@ -255,10 +256,39 @@ tape('addNode / nodes option', async function (t) {
   bootstrap.destroy()
 })
 
+tape('set bind', async function (t) {
+  const port = await freePort()
+
+  const a = new DHT({ bind: port })
+  await a.ready()
+
+  t.same(a.address().port, port, 'bound to explicit port')
+
+  const b = new DHT({ bind: port })
+  await b.ready()
+
+  t.notSame(b.address().port, port, 'bound to different port as explicit one is taken')
+
+  a.destroy()
+  b.destroy()
+})
+
 function destroy (list) {
   for (const node of list) node.destroy()
 }
 
+function freePort () {
+  return new Promise(resolve => {
+    const socket = dgram.createSocket('udp4')
+
+    socket.bind(0)
+    socket.on('listening', function () {
+      const { port } = socket.address()
+      socket.close(() => resolve(port))
+    })
+  })
+}
+
 async function makeSwarm (n) {
   const node = new DHT()
   await node.bind(0)