nodejs · lostnet · Jul 23, 2016 · Jul 24, 2016 · Aug 2, 2016 · Aug 5, 2016
diff --git a/doc/api/dgram.md b/doc/api/dgram.md
@@ -370,6 +370,84 @@ added: v0.6.9
 Sets or clears the `SO_BROADCAST` socket option.  When set to `true`, UDP
 packets may be sent to a local interface's broadcast address.
 
+### socket.setMulticastInterface(multicastInterface)
+<!-- YAML
+added: REPLACEME
+-->
+
+* `multicastInterface` {String}
+
+*Note: All references to scope in this section are refering to
+[IPv6 Zone Indices][], which are defined by [RFC 4007][]. In string form, an IP
+with a scope index is written as `'IP%scope'` where scope is an interface name or
+interface number.*
+
+Sets the default outgoing multicast interface of the socket to a chosen
+interface or back to system interface selection. The `multicastInterface` must
+be a valid string representation of an IP from the socket's family.
+
+For IPv4 sockets, this should be the IP configured for the desired physical
+interface. All packets sent to multicast on the socket will be sent on the
+interface determined by the most recent successful use of this call.
+
+For IPv6 sockets, `multicastInterface` should include a scope to indicate the
+interface as in the examples that follow. In IPv6, individual `send` calls can
+also use explicit scope in addresses, so only packets sent to a multicast
+address without specifying an explicit scope are affected by the most recent
+successful use of this call.
+
+#### Examples: IPv6 Outgoing Multicast Interface
+
+On most systems, where scope format uses the interface name:
+
+```js
+const socket = dgram.createSocket('udp6');
+
+socket.bind(1234, () => {
+  socket.setMulticastInterface('::%eth1');
+});
+```
+
+On Windows, where scope format uses an interface number:
+
+```js
+const socket = dgram.createSocket('udp6');
+
+socket.bind(1234, () => {
+  socket.setMulticastInterface('::%2');
+});
+```
+
+#### Example: IPv4 Outgoing Multicast Interface
+All systems use an IP of the host on the desired physical interface:
+```js
+const socket = dgram.createSocket('udp4');
+
+socket.bind(1234, () => {
+  socket.setMulticastInterface('10.0.0.2');
+});
+```
+
+#### Call Results
+
+A call on a socket that is not ready to send or no longer open may throw a *Not
+running* [`Error`][].
+
+If `multicastInterface` can not be parsed into an IP then an *EINVAL*
+[`System Error`][] is thrown.
+
+On IPv4, if `multicastInterface` is a valid address but does not match any
+interface, or if the address does not match the family then
+a [`System Error`][] such as `EADDRNOTAVAIL` or `EPROTONOSUP` is thrown.
+
+On IPv6, most errors with specifying or omiting scope will result in the socket
+continuing to use (or returning to) the system's default interface selection. 
+
+A socket's address family's ANY address (IPv4 `'0.0.0.0'` or IPv6 `'::'`) can be
+used to return control of the sockets default outgoing interface to the system
+for future multicast packets.
+
+
 ### socket.setMulticastLoopback(flag)
 <!-- YAML
 added: v0.3.8
@@ -512,4 +590,7 @@ and `udp6` sockets). The bound address and port can be retrieved using
 [`socket.address().address`]: #dgram_socket_address
 [`socket.address().port`]: #dgram_socket_address
 [`socket.bind()`]: #dgram_socket_bind_port_address_callback
+[`System Error`]: errors.html#errors_class_system_error
 [byte length]: buffer.html#buffer_class_method_buffer_bytelength_string_encoding
+[IPv6 Zone Indices]: https://en.wikipedia.org/wiki/IPv6_address#Link-local_addresses_and_zone_indices
+[RFC 4007]: https://tools.ietf.org/html/rfc4007 
diff --git a/lib/dgram.js b/lib/dgram.js
@@ -563,6 +563,21 @@ Socket.prototype.setMulticastLoopback = function(arg) {
 };
 
 
+Socket.prototype.setMulticastInterface = function(interfaceAddress) {
+  this._healthCheck();
+
+  if (typeof interfaceAddress !== 'string') {
 static void IsIP(const FunctionCallbackInfo<Value>& args) { 
 exports.isIP = cares.isIP; 
 static void IsIP(const FunctionCallbackInfo<Value>& args) { 
 exports.isIP = cares.isIP; 
+    throw new errors.TypeError('ERR_INVALID_ARG_TYPE',
+                               'interfaceAddress',
+                               'string');
+  }
+
+  const err = this._handle.setMulticastInterface(interfaceAddress);
+  if (err) {
+    throw errnoException(err, 'setMulticastInterface');
+  }
+};
+
 Socket.prototype.addMembership = function(multicastAddress,
                                           interfaceAddress) {
   this._healthCheck();

diff --git a/src/udp_wrap.cc b/src/udp_wrap.cc
@@ -130,6 +130,7 @@ void UDPWrap::Initialize(Local<Object> target,
                       GetSockOrPeerName<UDPWrap, uv_udp_getsockname>);
   env->SetProtoMethod(t, "addMembership", AddMembership);
   env->SetProtoMethod(t, "dropMembership", DropMembership);
+  env->SetProtoMethod(t, "setMulticastInterface", SetMulticastInterface);
   env->SetProtoMethod(t, "setMulticastTTL", SetMulticastTTL);
   env->SetProtoMethod(t, "setMulticastLoopback", SetMulticastLoopback);
   env->SetProtoMethod(t, "setBroadcast", SetBroadcast);
@@ -238,6 +239,22 @@ X(SetMulticastLoopback, uv_udp_set_multicast_loop)
 
 #undef X
 
+void UDPWrap::SetMulticastInterface(const FunctionCallbackInfo<Value>& args) {
+  UDPWrap* wrap;
+  ASSIGN_OR_RETURN_UNWRAP(&wrap,
+                          args.Holder(),
+                          args.GetReturnValue().Set(UV_EBADF));
+
+  CHECK_EQ(args.Length(), 1);
+  CHECK(args[0]->IsString());
+
+  Utf8Value iface(args.GetIsolate(), args[0]);
+
+  const char* iface_cstr = *iface;
+
+  int err = uv_udp_set_multicast_interface(&wrap->handle_, iface_cstr);
+  args.GetReturnValue().Set(err);
+}
 
 void UDPWrap::SetMembership(const FunctionCallbackInfo<Value>& args,
                             uv_membership membership) {

diff --git a/src/udp_wrap.h b/src/udp_wrap.h
@@ -50,6 +50,8 @@ class UDPWrap: public HandleWrap {
   static void RecvStop(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void AddMembership(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void DropMembership(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void SetMulticastInterface(
+      const v8::FunctionCallbackInfo<v8::Value>& args);
   static void SetMulticastTTL(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void SetMulticastLoopback(
       const v8::FunctionCallbackInfo<v8::Value>& args);

diff --git a/test/internet/test-dgram-multicast-multi-process.js b/test/internet/test-dgram-multicast-multi-process.js
@@ -29,6 +29,7 @@ const assert = require('assert');
 const dgram = require('dgram');
 const fork = require('child_process').fork;
 const LOCAL_BROADCAST_HOST = '224.0.0.114';
+const LOCAL_HOST_IFADDR = '0.0.0.0';
 const TIMEOUT = common.platformTimeout(5000);
 const messages = [
   Buffer.from('First message to send'),
@@ -159,6 +160,7 @@ if (process.argv[2] !== 'child') {
     sendSocket.setBroadcast(true);
     sendSocket.setMulticastTTL(1);
     sendSocket.setMulticastLoopback(true);
+    sendSocket.setMulticastInterface(LOCAL_HOST_IFADDR);
   });
 
   sendSocket.on('close', function() {
@@ -198,7 +200,7 @@ if (process.argv[2] === 'child') {
   });
 
   listenSocket.on('listening', function() {
-    listenSocket.addMembership(LOCAL_BROADCAST_HOST);
+    listenSocket.addMembership(LOCAL_BROADCAST_HOST, LOCAL_HOST_IFADDR);
 
     listenSocket.on('message', function(buf, rinfo) {
       console.error('[CHILD] %s received "%s" from %j', process.pid,