UDP multicast APIs fix

fix #74, fix #7

libraries/ESP8266WiFi/src/WiFiUdp.cpp

@@ -142,22 +142,33 @@ int WiFiUDP::beginPacket(IPAddress ip, uint16_t port)
     return (_ctx->connect(addr, port)) ? 1 : 0;
 }
 
+int WiFiUDP::beginPacketMulticast(IPAddress multicastAddress, uint16_t port, 
+    IPAddress interfaceAddress, int ttl)
+{
+    ip_addr_t mcastAddr;
+    mcastAddr.addr = multicastAddress;
+    ip_addr_t ifaceAddr;
+    ifaceAddr.addr = interfaceAddress;
+
+    if (!_ctx) {
+        _ctx = new UdpContext;
+        _ctx->ref();
+    }
+    if (!_ctx->connect(mcastAddr, port)) {
+        return 0;
+    }
+    _ctx->setMulticastInterface(ifaceAddr);
+    _ctx->setMulticastTTL(ttl);
+    return 1;
+}
+
 int WiFiUDP::endPacket()
 {
     if (!_ctx)
         return 0;
 
     _ctx->send();
-    return 1;
-}
-
-int WiFiUDP::endPacketMulticast(IPAddress ip, uint16_t port)
-{
-    if (!_ctx)
-        return 0;
-    ip_addr_t addr;
-    addr.addr = (uint32_t) ip;
-    _ctx->send(&addr, port);
+    _ctx->disconnect();
     return 1;
 }
 

libraries/ESP8266WiFi/src/WiFiUdp.h

@@ -40,9 +40,13 @@ public:
 
   operator bool() const { return _ctx != 0; }
 
-  virtual uint8_t begin(uint16_t port);	// initialize, start listening on specified port. Returns 1 if successful, 0 if there are no sockets available to use
-  virtual void stop();  // Finish with the UDP socket
-  uint8_t beginMulticast(IPAddress interfaceAddr, IPAddress multicast, uint16_t port); // connect to a multicast group and listen on the given port
+  // initialize, start listening on specified port. 
+  // Returns 1 if successful, 0 if there are no sockets available to use
+  virtual uint8_t begin(uint16_t port);	
+  // Finish with the UDP connetion
+  virtual void stop();
+  // join a multicast group and listen on the given port
+  uint8_t beginMulticast(IPAddress interfaceAddr, IPAddress multicast, uint16_t port); 
 
   // Sending UDP packets
   
@@ -52,12 +56,19 @@ public:
   // Start building up a packet to send to the remote host specific in host and port
   // Returns 1 if successful, 0 if there was a problem resolving the hostname or port
   virtual int beginPacket(const char *host, uint16_t port);
+  // Start building up a packet to send to the multicast address
+  // multicastAddress - muticast address to send to
+  // interfaceAddress - the local IP address of the interface that should be used
+  //                    use WiFi.localIP() or WiFi.softAPIP() depending on the interface you need
+  // ttl              - multicast packet TTL (default is 1)
+  // Returns 1 if successful, 0 if there was a problem with the supplied IP address or port
+  virtual int beginPacketMulticast(IPAddress multicastAddress, 
+                                   uint16_t port, 
+                                   IPAddress interfaceAddress, 
+                                   int ttl = 1);
   // Finish off this packet and send it
   // Returns 1 if the packet was sent successfully, 0 if there was an error
   virtual int endPacket();
-  // Send the packet to a multicast address
-  // Returns 1 if the packet was sent successfully, 0 if there was an error
-  int endPacketMulticast(IPAddress ip, uint16_t port);
   // Write a single byte into the packet
   virtual size_t write(uint8_t);
   // Write size bytes from buffer into the packet

libraries/ESP8266WiFi/src/include/UdpContext.h

@@ -94,6 +94,21 @@ public:
         udp_disconnect(_pcb);
     }
 
+    void setMulticastInterface(ip_addr_t addr)
+    {
+        // newer versions of lwip have a macro to set the multicast ip
+        // udp_set_multicast_netif_addr(_pcb, addr);
+        _pcb->multicast_ip = addr;
+    }
+
+    void setMulticastTTL(int ttl)
+    {
+        // newer versions of lwip have an additional field (mcast_ttl) for this purpose
+        // and a macro to set it instead of direct field access
+        // udp_set_multicast_ttl(_pcb, ttl);
+        _pcb->ttl = ttl;
+    }
+
     size_t getSize() const
     {
         if (!_rx_buf)