Address issue #10 for multicast with multi-homed systems

Author: CJLove

README.md

@@ -52,7 +52,7 @@ The UdpSocket class has the following interface for managing the UDP socket:
 UdpSocket(CallbackImpl &callback, SocketOpt *options = nullptr);
 
 // Start a multicast socket
-SocketRet startMcast(const char *mcastAddr, uint16_t port);
+SocketRet startMcast(const char *mcastAddr, uint16_t port, const char *localIpAddr = nullptr);
 
 // Start a unicast client/server socket
 SocketRet startUnicast(const char *remoteAddr, uint16_t localPort, uint16_t port)

examples/mcastApp.cpp

@@ -9,7 +9,7 @@
 class McastApp {
 public:
     // UDP Multicast
-    McastApp(const char *multicastAddr, uint16_t port);
+    McastApp(const char *multicastAddr, uint16_t port, const char *localIface);
 
     virtual ~McastApp() = default;
 
@@ -21,8 +21,8 @@ class McastApp {
     sockets::UdpSocket<McastApp> m_mcast;
 };
 
-McastApp::McastApp(const char *multicastAddr, uint16_t port) : m_mcast(*this) {
-    sockets::SocketRet ret = m_mcast.startMcast(multicastAddr, port);
+McastApp::McastApp(const char *multicastAddr, uint16_t port, const char *localIface) : m_mcast(*this) {
+    sockets::SocketRet ret = m_mcast.startMcast(multicastAddr, port, localIface);
     if (ret.m_success) {
         std::cout << "Connected to mcast group " << multicastAddr << ":" << port << "\n";
     } else {
@@ -45,28 +45,32 @@ void McastApp::onReceiveData(const char *data, size_t size) {
 }
 
 void usage() {
-    std::cout << "McastApp -m <mcastAddr> -p <port>\n";
+    std::cout << "McastApp -m <mcastAddr> -p <port> -[-l <localAddr>]\n";
 }
 
 int main(int argc, char **argv) {
     int arg = 0;
     const char *addr = nullptr;
+    const char *local = nullptr;
     uint16_t port = 0;
-    while ((arg = getopt(argc, argv, "m:p:?")) != EOF) { // NOLINT
+    while ((arg = getopt(argc, argv, "m:p:l:?")) != EOF) { // NOLINT
         switch (arg) {
         case 'm':
             addr = optarg;
             break;
         case 'p':
             port = static_cast<uint16_t>(std::stoul(optarg));
             break;
+        case 'l':
+            local = optarg;
+            break;
         case '?':
             usage();
             exit(1);    // NOLINT
         }
     }
 
-    auto *app = new McastApp(addr, port);
+    auto *app = new McastApp(addr, port, local);
 
     while (true) {
         std::string data;

include/sockets-cpp/UdpSocket.h

@@ -68,7 +68,7 @@ class UdpSocket {
      * @param port - port number to listen/connect to
      * @return SocketRet - indication that multicast setup was successful
      */
-    SocketRet startMcast(const char *mcastAddr, uint16_t port) {
+    SocketRet startMcast(const char *mcastAddr, uint16_t port, const char *localIpAddr = nullptr) {
         SocketRet ret;
 
         int result = m_socketCore.Initialize();
@@ -164,7 +164,11 @@ class UdpSocket {
         //
         struct ip_mreq mreq { };
         inet_pton(AF_INET,mcastAddr,&mreq.imr_multiaddr);
-        mreq.imr_interface.s_addr = htonl(INADDR_ANY);
+        if (localIpAddr) {
+            inet_pton(AF_INET, localIpAddr, &mreq.imr_interface.s_addr);
+        } else {
+            mreq.imr_interface.s_addr = htonl(INADDR_ANY);
+        }
         if (m_socketCore.SetSockOpt(m_fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, reinterpret_cast<char *>(&mreq), sizeof(mreq)) < 0) {
             ret.m_success = false;
 #if defined(FMT_SUPPORT)
@@ -177,6 +181,25 @@ class UdpSocket {
             return ret;
         }
 
+        struct in_addr addr;
+        if (localIpAddr) {
+            inet_pton(AF_INET, localIpAddr, &addr.s_addr);
+        } else {
+            mreq.imr_interface.s_addr = htonl(INADDR_ANY);
+        }
+        if (m_socketCore.SetSockOpt(m_fd, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr)) < 0)
+        {
+            ret.m_success = false;
+#if defined(FMT_SUPPORT)
+            ret.m_msg = fmt::format("Error: setsockopt(IP_MULTICAST_IF) failed: errno {}", errno);
+#else
+            std::array<char,MSG_SIZE> msg;
+            (void)snprintf(msg.data(),msg.size(),"Error: setsockopt(IP_MULTICAST_IF) failed: %d", errno);
+            ret.m_msg = msg.data();
+#endif
+            return ret;
+        }
+
         m_thread = std::thread(&UdpSocket::ReceiveTask, this);
         ret.m_success = true;
         return ret;

test/test_UdpSocket.cpp

@@ -196,7 +196,7 @@ TEST(UdpSocket,mcast_start_stop)
     MockSocketCore &core = app.m_socket.getCore();
 
     EXPECT_CALL(core, Socket(_,_,_)).WillOnce(Return(4));
-    EXPECT_CALL(core, SetSockOpt(_,_,_,_,_)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0));
+    EXPECT_CALL(core, SetSockOpt(_,_,_,_,_)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0));
     EXPECT_CALL(core,Bind(_,_,_)).WillOnce(Return(0));
     EXPECT_CALL(core, Close(_)).WillOnce(Return(0));
     EXPECT_CALL(core, Select(_,_,_,_,_)).WillRepeatedly(Return(0));
@@ -207,6 +207,23 @@ TEST(UdpSocket,mcast_start_stop)
     app.m_socket.finish();
 }
 
+TEST(UdpSocket,mcast_start_stop_local)
+{
+    UdpTestApp app;
+    MockSocketCore &core = app.m_socket.getCore();
+
+    EXPECT_CALL(core, Socket(_,_,_)).WillOnce(Return(4));
+    EXPECT_CALL(core, SetSockOpt(_,_,_,_,_)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0)).WillOnce(Return(0));
+    EXPECT_CALL(core,Bind(_,_,_)).WillOnce(Return(0));
+    EXPECT_CALL(core, Close(_)).WillOnce(Return(0));
+    EXPECT_CALL(core, Select(_,_,_,_,_)).WillRepeatedly(Return(0));
+    auto ret = app.m_socket.startMcast("224.0.0.1",5000,"127.0.0.1");
+    EXPECT_EQ(true,ret.m_success);
+
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    app.m_socket.finish();
+}
+
 TEST(UdpSocket,finish_close_failure)
 {
     UdpTestApp app;