Add upsteam multicast compatibility APIs (#821)

Fixes #747 while remaining ESP8266 compatible

Author: earlephilhower

libraries/WiFi/src/WiFiUdp.cpp

@@ -38,7 +38,7 @@ template<>
 WiFiUDP* SList<WiFiUDP>::_s_first = 0;
 
 /* Constructor */
-WiFiUDP::WiFiUDP() : _ctx(0) {
+WiFiUDP::WiFiUDP() : _ctx(0), _multicast(false) {
     WiFiUDP::_add(this);
 }
 
@@ -48,6 +48,7 @@ WiFiUDP::WiFiUDP(const WiFiUDP& other) {
         _ctx->ref();
     }
     WiFiUDP::_add(this);
+    _multicast = other._multicast;
 }
 
 WiFiUDP& WiFiUDP::operator=(const WiFiUDP& rhs) {
@@ -97,6 +98,12 @@ uint8_t WiFiUDP::beginMulticast(IPAddress interfaceAddr, IPAddress multicast, ui
     return 1;
 }
 
+uint8_t WiFiUDP::beginMulticast(IPAddress addr, uint16_t port) {
+    auto ret = beginMulticast(IP_ADDR_ANY, addr, port);
+    _multicast = true;
+    return ret;
+}
+
 /*  return number of bytes available in the current packet,
     will return zero if parsePacket hasn't been called yet */
 int WiFiUDP::available() {
@@ -137,7 +144,13 @@ int WiFiUDP::beginPacket(IPAddress ip, uint16_t port) {
         _ctx = new UdpContext;
         _ctx->ref();
     }
-    return (_ctx->connect(ip, port)) ? 1 : 0;
+    auto ret = (_ctx->connect(ip, port)) ? 1 : 0;
+    if (_multicast) {
+        _ctx->setMulticastInterface(IP_ADDR_ANY);
+        _ctx->setMulticastTTL(255);
+    }
+    return ret;
+
 }
 
 int WiFiUDP::beginPacketMulticast(IPAddress multicastAddress, uint16_t port,

libraries/WiFi/src/WiFiUdp.h

@@ -44,9 +44,12 @@ class WiFiUDP : public UDP, public SList<WiFiUDP> {
 
     // initialize, start listening on specified port.
     // Returns 1 if successful, 0 if there are no sockets available to use
-    uint8_t begin(uint16_t port) override;
+    virtual uint8_t begin(uint16_t port) override;
+    // initialize, start listening on specified multicast IP address and port. Returns 1 if successful, 0 if there are no sockets available to use
+    virtual uint8_t beginMulticast(IPAddress, uint16_t) override;
+
     // Finish with the UDP connection
-    void stop() override;
+    virtual void stop() override;
     // join a multicast group and listen on the given port
     uint8_t beginMulticast(IPAddress interfaceAddr, IPAddress multicast, uint16_t port);
 
@@ -110,4 +113,6 @@ class WiFiUDP : public UDP, public SList<WiFiUDP> {
     static void stopAll();
     static void stopAllExcept(WiFiUDP * exC);
 
+private:
+    bool _multicast;
 };