dgram: introduce `reuseAddr` option

Introduce new signature for both `dgram.createSocket` method and
`dgram.Socket` constructor:

    dgram.createSocket(options, [listener])

Options should contain `type` property and may contain `reuseAddr`
property. When `reuseAddr` is `true` - SO_REUSEADDR will be issued on
socket on bind.

fix #7415

Signed-off-by: Fedor Indutny <fedor@indutny.com>

doc/api/dgram.markdown

@@ -22,8 +22,13 @@ You have to change it to this:
 
 
 ## dgram.createSocket(type, [callback])
+## dgram.createSocket(options, [callback])
 
 * `type` String. Either 'udp4' or 'udp6'
+* `options` Object. Should contain a `type` property and could contain
+  `reuseAddr` property. `false` by default.
+  When `reuseAddr` is `true` - `socket.bind()` will reuse address, even if the
+  other process has already bound a socket on it.
 * `callback` Function. Attached as a listener to `message` events.
   Optional
 * Returns: Socket object
@@ -41,7 +46,7 @@ with `socket.address().address` and `socket.address().port`.
 ## Class: dgram.Socket
 
 The dgram Socket class encapsulates the datagram functionality.  It
-should be created via `dgram.createSocket(type, [callback])`.
+should be created via `dgram.createSocket(...)`
 
 ### Event: 'message'
 

lib/dgram.js

@@ -22,6 +22,7 @@
 var assert = require('assert');
 var util = require('util');
 var events = require('events');
+var constants = require('constants');
 
 var UDP = process.binding('udp_wrap').UDP;
 
@@ -96,6 +97,11 @@ exports._createSocketHandle = function(address, port, addressType, fd) {
 function Socket(type, listener) {
   events.EventEmitter.call(this);
 
+  if (typeof type === 'object') {
+    var options = type;
+    type = options.type;
+  }
+
   var handle = newHandle(type);
   handle.owner = this;
 
@@ -105,6 +111,9 @@ function Socket(type, listener) {
   this.type = type;
   this.fd = null; // compatibility hack
 
+  // If true - UV_UDP_REUSEADDR flag will be set
+  this._reuseAddr = options && options.reuseAddr;
+
   if (util.isFunction(listener))
     this.on('message', listener);
 }
@@ -196,7 +205,11 @@ Socket.prototype.bind = function(/*port, address, callback*/) {
       if (!self._handle)
         return; // handle has been closed in the mean time
 
-      var err = self._handle.bind(ip, port || 0, /*flags=*/ 0);
+      var flags = 0;
+      if (self._reuseAddr)
+        flags |= constants.UV_UDP_REUSEADDR;
+
+      var err = self._handle.bind(ip, port || 0, flags);
       if (err) {
         self.emit('error', errnoException(err, 'bind'));
         self._bindState = BIND_STATE_UNBOUND;

src/node_constants.cc

@@ -1071,12 +1071,17 @@ void DefineSystemConstants(Handle<Object> target) {
 #endif
 }
 
+void DefineUVConstants(Handle<Object> target) {
+  NODE_DEFINE_CONSTANT(target, UV_UDP_REUSEADDR);
+}
+
 void DefineConstants(Handle<Object> target) {
   DefineErrnoConstants(target);
   DefineWindowsErrorConstants(target);
   DefineSignalConstants(target);
   DefineOpenSSLConstants(target);
   DefineSystemConstants(target);
+  DefineUVConstants(target);
 }
 
 }  // namespace node

test/simple/test-dgram-broadcast-multi-process.js

@@ -157,7 +157,10 @@ if (process.argv[2] !== 'child') {
     })(x);
   }
 
-  var sendSocket = dgram.createSocket('udp4');
+  var sendSocket = dgram.createSocket({
+    type: 'udp4',
+    reuseAddr: true
+  });
 
   // bind the address explicitly for sending
   // INADDR_BROADCAST to only one interface
@@ -201,7 +204,10 @@ if (process.argv[2] !== 'child') {
 
 if (process.argv[2] === 'child') {
   var receivedMessages = [];
-  var listenSocket = dgram.createSocket('udp4');
+  var listenSocket = dgram.createSocket({
+    type: 'udp4',
+    reuseAddr: true
+  });
 
   listenSocket.on('message', function(buf, rinfo) {
     // receive udp messages only sent from parent