doesn't pick lowest numbered socket in available()

improved EthernetServer::available() such that it will not always pick the
lowest numbered socket

Author: sauerburger

libraries/Ethernet/src/EthernetServer.cpp

@@ -52,17 +52,22 @@ EthernetClient EthernetServer::available()
 {
   accept();
 
-  for (int sock = 0; sock < MAX_SOCK_NUM; sock++) {
-    EthernetClient client(sock);
-    if (EthernetClass::_server_port[sock] == _port) {
+  // increment _sock to avoid returning the same socket again
+  _sock = (_sock + 1) % MAX_SOCK_NUM;
+
+  for (int i = 0; i < MAX_SOCK_NUM; i++) {
+    EthernetClient client(_sock);
+    if (EthernetClass::_server_port[_sock] == _port) {
       uint8_t s = client.status();
       if (s == SnSR::ESTABLISHED || s == SnSR::CLOSE_WAIT) {
         if (client.available()) {
-          // XXX: don't always pick the lowest numbered socket.
+          // doesn't always pick the lowest numbered socket, because of _sock +
+          // 1 at the beginning
           return client;
         }
       }
     }
+    _sock = (_sock + 1) % MAX_SOCK_NUM;
   }
 
   return EthernetClient(MAX_SOCK_NUM);

libraries/Ethernet/src/EthernetServer.h

@@ -10,6 +10,7 @@ public Server {
 private:
   uint16_t _port;
   void accept();
+  int _sock = -1; 
 public:
   EthernetServer(uint16_t);
   EthernetClient available();