Use UDP unconnected sockets

UDP connected sockets are limited to commuinicating with one
host and port.

Author: gdsports

src/EthernetUdp.cpp

@@ -106,9 +106,8 @@ int EthernetUDP::beginPacket(IPAddress ip, uint16_t port)
 
   ip_addr_t ipaddr;
 
-  if(ERR_OK != udp_connect( _udp.pcb, u8_to_ip_addr(rawIPAddress(ip), &ipaddr), port)) {
-    return 0;
-  }
+  _sendtoIP = ip;
+  _sendtoPort = port;
 
   udp_recv(_udp.pcb, &udp_receive_callback, &_udp);
   stm32_eth_scheduler();
@@ -122,12 +121,8 @@ int EthernetUDP::endPacket()
     return 0;
   }
 
-  // A remote IP & port must be connected to udp pcb. Call ::beginPacket before.
-  if((udp_flags(_udp.pcb) & UDP_FLAGS_CONNECTED) != UDP_FLAGS_CONNECTED) {
-    return 0;
-  }
-
-  if(ERR_OK != udp_send(_udp.pcb, _data)) {
+  ip_addr_t ipaddr;
+  if(ERR_OK != udp_sendto(_udp.pcb, _data, u8_to_ip_addr(rawIPAddress(_sendtoIP), &ipaddr), _sendtoPort)) {
     _data = stm32_free_data(_data);
     return 0;
   }

src/EthernetUdp.h

@@ -50,6 +50,8 @@ class EthernetUDP : public UDP {
   uint16_t _port; // local port to listen on
   IPAddress _remoteIP; // remote IP address for the incoming packet whilst it's being processed
   uint16_t _remotePort; // remote port for the incoming packet whilst it's being processed
+  IPAddress _sendtoIP;  // the remote IP address set by beginPacket
+  uint16_t _sendtoPort; // the remote port set by beginPacket
 
   struct pbuf *_data;     //pbuf for data to send
   struct udp_struct _udp; //udp settings