Added new method to UDP to take a hostname rather than an IP address. Part of issue 243

Author: amcewen

libraries/Ethernet/Udp.cpp

@@ -30,6 +30,7 @@
 #include "socket.h"
 #include "Ethernet.h"
 #include "Udp.h"
+#include "Dns.h"
 
 /* Constructor */
 UDP::UDP() : _sock(MAX_SOCK_NUM) {}
@@ -74,6 +75,22 @@ void UDP::stop()
   _sock = MAX_SOCK_NUM;
 }
 
+int UDP::beginPacket(const char *host, uint16_t port)
+{
+  // Look up the host first
+  int ret = 0;
+  DNSClient dns;
+  IPAddress remote_addr;
+
+  dns.begin(Ethernet.dnsServerIP());
+  ret = dns.getHostByName(host, remote_addr);
+  if (ret == 1) {
+    return beginPacket(remote_addr, port);
+  } else {
+    return ret;
+  }
+}
+
 int UDP::beginPacket(IPAddress ip, uint16_t port)
 {
   _offset = 0;

libraries/Ethernet/Udp.h

@@ -60,6 +60,9 @@ class UDP : public Stream {
   // Start building up a packet to send to the remote host specific in ip and port
   // Returns 1 if successful, 0 if there was a problem with the supplied IP address or port
   int beginPacket(IPAddress ip, uint16_t port);
+  // 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
+  int beginPacket(const char *host, uint16_t port);
   // Finish off this packet and send it
   // Returns 1 if the packet was sent successfully, 0 if there was an error
   int endPacket();