Bug#2845 client fails to reconnect if using TCP/IP

- Detect that connection to server has been broken in "net_clear". Since 
  net_clear is always called before we send command to server, we can be sure
  that server has not received the command.


mysql-test/r/wait_timeout.result:
  Update test result
mysql-test/t/wait_timeout-master.opt:
  Decrease wait_timeout value to avoid unneccessary sleeps
mysql-test/t/wait_timeout.test:
  Test that same error message is returned when disconnected regardless of connection is socket or TCP
  Decrease sleep times
sql/net_serv.cc:
  Make "net_clear" detect if connection with server has been broken by 
  performing a select. If the select returns that there are data to read but
  no data can be read, that means the connection is broken. Signal disconnected
  to "write" functions by setting error to 2.

mysql-test/r/wait_timeout.result

@@ -6,3 +6,11 @@ ERROR HY000: MySQL server has gone away
 select 3;
 3
 3
+select 1;
+1
+1
+select 2;
+ERROR HY000: MySQL server has gone away
+select 3;
+3
+3

mysql-test/t/wait_timeout-master.opt

---wait-timeout=2
+--wait-timeout=1

mysql-test/t/wait_timeout.test

@@ -3,9 +3,25 @@
 #
 --disable_reconnect
 select 1;
-# wait_timeout is 2, so we should get disconnected now
---sleep 5
+# wait_timeout is 1, so we should get disconnected now
+--sleep 2
+# When the connection is closed in this way, the error code should
+# be consistent see bug#2845 for an explanation
 --error 2006
 select 2;
 --enable_reconnect
 select 3;
+
+# Do the same test as above on a TCP connection
+connect (con1,127.0.0.1,root,,test,$MASTER_MYPORT,);
+--disable_reconnect
+select 1;
+# wait_timeout is 1, so we should get disconnected now
+--sleep 2
+# When the connection is closed in this way, the error code should
+# be consistent see bug#2845 for an explanation
+--error 2006
+select 2;
+--enable_reconnect
+select 3;
+disconnect con1;

sql/net_serv.cc

@@ -194,30 +194,93 @@ my_bool net_realloc(NET *net, ulong length)
   DBUG_RETURN(0);
 }
 
-	/* Remove unwanted characters from connection */
+
+/*
+  Check if there is any data to be read from the socket
+
+  SYNOPSIS
+    net_data_is_ready()
+    sd   socket descriptor
+
+  DESCRIPTION
+    Check if there is any data to be read from the socket.
+
+  RETURN VALUES
+    0	No data to read
+    1	Data or EOF to read
+*/
+
+static my_bool net_data_is_ready(my_socket sd)
+{
+  fd_set sfds;
+  struct timeval tv;
+  int res;
+
+  FD_ZERO(&sfds);
+  FD_SET(sd, &sfds);
+
+  tv.tv_sec= tv.tv_usec= 0;
+
+  if ((res= select(sd+1, &sfds, NULL, NULL, &tv)) < 0)
+    return FALSE;
+  else
+    return test(res ? FD_ISSET(sd, &sfds) : 0);
+}
+
+
+/*
+  Remove unwanted characters from connection
+  and check if disconnected
+
+  SYNOPSIS
+    net_clear()
+    net			NET handler
+
+  DESCRIPTION
+    Read from socket until there is nothing more to read. Discard
+    what is read.
+
+    If there is anything when to read 'net_clear' is called this
+    normally indicates an error in the protocol.
+
+    When connection is properly closed (for TCP it means with
+    a FIN packet), then select() considers a socket "ready to read",
+    in the sense that there's EOF to read, but read() returns 0.
+
+*/
 
 void net_clear(NET *net)
 {
+  int count;
   DBUG_ENTER("net_clear");
-#if !defined(EXTRA_DEBUG) && !defined(EMBEDDED_LIBRARY)
+#if !defined(EMBEDDED_LIBRARY)
+  while(net_data_is_ready(net->vio->sd))
   {
-    int count;					/* One may get 'unused' warn */
-    my_bool old_mode;
-    if (!vio_blocking(net->vio, FALSE, &old_mode))
+    /* The socket is ready */
+    if ((count= vio_read(net->vio, (char*) (net->buff),
+                         (uint32) net->max_packet)) > 0)
     {
-      while ((count = vio_read(net->vio, (char*) (net->buff),
-			       (uint32) net->max_packet)) > 0)
-	DBUG_PRINT("info",("skipped %d bytes from file: %s",
-			   count, vio_description(net->vio)));
-      vio_blocking(net->vio, TRUE, &old_mode);
+      DBUG_PRINT("info",("skipped %d bytes from file: %s",
+                         count, vio_description(net->vio)));
+#ifdef EXTRA_DEBUG
+      fprintf(stderr,"skipped %d bytes from file: %s\n",
+              count, vio_description(net->vio));
+#endif
+    }
+    else
+    {
+      DBUG_PRINT("info",("socket ready but only EOF to read - disconnected"));
+      net->error= 2;
+      break;
     }
   }
-#endif /* EXTRA_DEBUG */
+#endif
   net->pkt_nr=net->compress_pkt_nr=0;		/* Ready for new command */
   net->write_pos=net->buff;
   DBUG_VOID_RETURN;
 }
 
+
 	/* Flush write_buffer if not empty. */
 
 my_bool net_flush(NET *net)