Proposed fix for issue 243, adding DNS to the Ethernet library. Uses a slightly modified version of the agreed API as the host/port parameters have been moved from the Client constructor to the Client::connect methods. This means it's possible for errors to be returned if the DNS lookup fails and also reduces the RAM footprint of the Client class as it no longer needs to store the host/port for later use in Client::connect.

libraries/Ethernet/Dns.h

@@ -0,0 +1,41 @@
+// Arduino DNS client for WizNet5100-based Ethernet shield
+// (c) Copyright 2009-2010 MCQN Ltd.
+// Released under Apache License, version 2.0
+
+#ifndef DNSClient_h
+#define DNSClient_h
+
+#include <Udp.h>
+
+class DNSClient
+{
+public:
+    // ctor
+    void begin(const IPAddress& aDNSServer);
+
+    /** Convert a numeric IP address string into a four-byte IP address.
+        @param aIPAddrString IP address to convert
+        @param aResult IPAddress structure to store the returned IP address
+        @result 1 if aIPAddrString was successfully converted to an IP address,
+                else error code
+    */
+    int inet_aton(const char *aIPAddrString, IPAddress& aResult);
+
+    /** Resolve the given hostname to an IP address.
+        @param aHostname Name to be resolved
+        @param aResult IPAddress structure to store the returned IP address
+        @result 1 if aIPAddrString was successfully converted to an IP address,
+                else error code
+    */
+    int getHostByName(const char* aHostname, IPAddress& aResult);
+
+protected:
+    uint16_t BuildRequest(const char* aName);
+    uint16_t ProcessResponse(int aTimeout, IPAddress& aAddress);
+
+    IPAddress iDNSServer;
+    uint16_t iRequestId;
+    UDP iUdp;
+};
+
+#endif