add explanatory comment regarding IP_MULTICAST_LOOP, remove cout debug msg

diff --git a/libs/midi++2/ipmidi_port.cc b/libs/midi++2/ipmidi_port.cc
index a8b11b1ae5f396fa708176cb6947eb805cab7b1e..fd5cb9a2395e727a457dda57104038439ea0429b 100644 (file)
--- a/libs/midi++2/ipmidi_port.cc
+++ b/libs/midi++2/ipmidi_port.cc
@@ -235,14 +235,36 @@ IPMIDIPort::open_sockets (int base_port, const string& ifname)
        int loop = 0;
 
 #ifdef PLATFORM_WINDOWS
+
+       /* https://msdn.microsoft.com/en-us/library/windows/desktop/ms739161%28v=vs.85%29.aspx
+        *
+        * ------------------------------------------------------------------------------
+        * Note The Winsock version of the IP_MULTICAST_LOOP option is
+        * semantically different than the UNIX version of the
+        * IP_MULTICAST_LOOP option:
+        *
+        * In Winsock, the IP_MULTICAST_LOOP option applies only to the receive path.
+        * In the UNIX version, the IP_MULTICAST_LOOP option applies to the send path.
+        *
+        * For example, applications ON and OFF (which are easier to track than
+        * X and Y) join the same group on the same interface; application ON
+        * sets the IP_MULTICAST_LOOP option on, application OFF sets the
+        * IP_MULTICAST_LOOP option off. If ON and OFF are Winsock
+        * applications, OFF can send to ON, but ON cannot sent to OFF. In
+        * contrast, if ON and OFF are UNIX applications, ON can send to OFF,
+        * but OFF cannot send to ON.
+        * ------------------------------------------------------------------------------
+        *
+        * Alles klar? Gut! 
+        */
+
        const int target_sock = sockin;
 #else
        const int target_sock = sockout;
 #endif
 
        if (::setsockopt (target_sock, IPPROTO_IP, IP_MULTICAST_LOOP, (char *) &loop, sizeof (loop)) < 0) {
-               //::perror("setsockopt(IP_MULTICAST_LOOP)");
-               cout << "Cannot set loopback status\n";
+               ::perror("setsockopt(IP_MULTICAST_LOOP)");
                return false;
        }
 
@@ -271,7 +293,7 @@ IPMIDIPort::open_sockets (int base_port, const string& ifname)
                return false;
        }
 #endif
-       cout << "ipmidi ports setup!!!!!!!\n";
+
        return true;
 }