Added DHCP-based chat server example

libraries/Ethernet/examples/DhcpChatServer/DhcpChatServer.ino

@@ -0,0 +1,80 @@
+/*
+ DHCP Chat  Server
+ 
+ A simple server that distributes any incoming messages to all
+ connected clients.  To use telnet to  your device's IP address and type.
+ You can see the client's input in the serial monitor as well.
+ Using an Arduino Wiznet Ethernet shield. 
+ 
+ THis version attempts to get an IP address using DHCP
+ 
+ Circuit:
+ * Ethernet shield attached to pins 10, 11, 12, 13
+ 
+ created 21 May 2011
+ by Tom Igoe
+ Based on ChatServer example by David A. Mellis
+ 
+ */
+
+#include <SPI.h>
+#include <Ethernet.h>
+
+// Enter a MAC address and IP address for your controller below.
+// The IP address will be dependent on your local network.
+// gateway and subnet are optional:
+byte mac[] = { 
+  0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x02 };
+IPAddress ip(192,168,1, 177);
+IPAddress gateway(192,168,1, 1);
+IPAddress subnet(255, 255, 0, 0);
+
+// telnet defaults to port 23
+Server server(23);
+boolean gotAMessage = false; // whether or not you got a message from the client yet
+
+void setup() {
+   // open the serial port
+  Serial.begin(9600);
+  // start the Ethernet connection:
+  Serial.println("Trying to get an IP address using DHCP");
+  if (Ethernet.begin(mac) == 0) {
+    Serial.println("Failed to configure Ethernet using DHCP");
+    // initialize the ethernet device not using DHCP:
+    Ethernet.begin(mac, ip, gateway, subnet);
+  }
+  // print your local IP address:
+  Serial.print("My IP address: ");
+  ip = Ethernet.localIP();
+  for (byte thisByte = 0; thisByte < 4; thisByte++) {
+    // print the value of each byte of the IP address:
+    Serial.print(ip[thisByte], DEC);
+    Serial.print("."); 
+  }
+  Serial.println();
+  // start listening for clients
+  server.begin();
+ 
+}
+
+void loop() {
+  // wait for a new client:
+  Client client = server.available();
+
+  // when the client sends the first byte, say hello:
+  if (client) {
+    if (!gotAMessage) {
+      Serial.println("We have a new client");
+      client.println("Hello, client!"); 
+      gotAMessage = true;
+    }
+
+    // read the bytes incoming from the client:
+    char thisChar = client.read();
+    // echo the bytes back to the client:
+    server.write(thisChar);
+    // echo the bytes to the server as well:
+    Serial.print(thisChar);
+  }
+}
+