# TCP/IP disconnect not handled correctly **URL:** \ **Category:** Robot Controller\ **Created:** [September 13, 2010, 1:16pm UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795 "2010-09-13T13:16:53Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![jeroen](https://dub1.discourse-cdn.com/flex005/user_avatar/tech-community.robotics.abb.com/jeroen/32/3305_2.png) [@jeroen](https://tech-community.robotics.abb.com/u/jeroen)\ **Post date:** [September 13, 2010, 1:16pm UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/1 "2010-09-13T13:16:53Z")
Hi, I have a TCP/IP connection between my robot to a control program running on a PC. The code below runs in a separate semi-static task. If I physically disconnect the robot (plug out cable), after a while this task crashes on the SocketSend function call shown below. The socket\_status keeps reporting SOCKET\_CONNECTED however. How can I fix/work around this? Regards, ! -------------------------------------------------------------------------------- ! Send status to client. ! -------------------------------------------------------------------------------- TRAP TrapStatus VAR socketStatus sockStat; sockStat:=SocketGetStatus(client\_socket); IF sockStat=SOCKET\_CONNECTED THEN ! Send status to client. SocketSend client\_socketStr:=Status+ByteToStr(13Char)+ByteToStr(10Char); ELSE ! Connection lost? ! … ENDIF ! Acknowledge. SetDO doStatus,0; RETURN; ERROR !TryNext; ! Acknowledge. SetDO doStatus,0; RETURN; ENDTRAP ---
**Author:** ![Henrik\_Berlin](https://dub1.discourse-cdn.com/flex005/user_avatar/tech-community.robotics.abb.com/henrik_berlin/32/1011_2.png) [@Henrik\_Berlin](https://tech-community.robotics.abb.com/u/Henrik_Berlin)\ **Post date:** [September 17, 2010, 4:04pm UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/2 "2010-09-17T16:04:00Z")
Moved to RobotWare forum. ---
**Author:** ![James\_NC](https://avatars.discourse-cdn.com/v4/letter/j/db5fbb/32.png) [@James\_NC](https://tech-community.robotics.abb.com/u/James_NC)\ **Post date:** [September 24, 2010, 9:46pm UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/3 "2010-09-24T21:46:45Z")
I’ve been working through this myself, and I think I can help. SOCKET\_CONNECTED will be true unless the client or server explicitly closes the connection. However, if the cable is unplugged, you should be getting a Timeout Error. You can handle error with the following error catcher: ERROR IF ERRNO=ERR\_SOCK\_TIMEOUT THEN … Just be careful not to spend too much time in your TRAP, as I believe code ignores any other interrupts while inside a TRAP. ---
**Author:** ![lubosko105](https://avatars.discourse-cdn.com/v4/letter/l/ecccb3/32.png) [@lubosko105](https://tech-community.robotics.abb.com/u/lubosko105)\ **Post date:** [January 24, 2012, 9:57pm UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/4 "2012-01-24T21:57:41Z")
Hallo jeroen. In your topic I see you are writing TCP communication. I want to make TCP server on the server side. Do you know if is posible to start new thread with socket (returned by SocketAccept fnc) ? Your code looks working like this. thanks for help. ---
**Author:** ![jeroen](https://dub1.discourse-cdn.com/flex005/user_avatar/tech-community.robotics.abb.com/jeroen/32/3305_2.png) [@jeroen](https://tech-community.robotics.abb.com/u/jeroen)\ **Post date:** [January 26, 2012, 8:04am UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/5 "2012-01-26T08:04:06Z")
What exactly do you mean by a new thread? I don’t think you can make a server with a thread for each connection; you just have to handle all connections in the same task. In my application I just need to handle a single connection. I have a ServerStart procedure: PROC ServerStart(bool Recover) IF Recover THEN Log “ServerStart with recovery need”; SocketClose server\_socket; SocketClose client\_socket; ELSE Log “ServerStart without the need for recovery”; ENDIF SocketCreate server\_socket; SocketBind server\_socket, IPAddress, IPPort; SocketListen server\_socket; Log “Wait for connection”; SocketAccept server\_socket, client\_socketClientAddress:=client\_ipTime:=WAIT\_MAX; Log "Connection with " + client\_ip; ERROR IF ERRNO=ERR\_SOCK\_TIMEOUT THEN Log “ERR\_SOCK\_TIMEOUT”; Retry; ELSEIF ERRNO=ERR\_SOCK\_CLOSED THEN Log “ERR\_SOCK\_CLOSED”; Return; ELSE Log “Unknown error” ENDIF ENDPROC And in the main loop I handle the server like: ServerStart(FALSE); – Some more initialization WHILE TRUE DO SocketReceive client\_socket Str:=ReceiveTime:=nHeartbeatTimeout; Log Receive; ! Process data ENDWHILE ERROR IF ERRNO=ERR\_SOCK\_TIMEOUT THEN Log “Timeout”; ! Close connection and restart. ServerStart(TRUE); Retry; ELSEIF ERRNO=ERR\_SOCK\_CLOSED THEN Log “Socket closed by peer!”; ServerStart(TRUE); Retry; ELSE Log “Unknown error”; ENDIF ENDPROC ---
**Author:** ![niggos](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@niggos](https://tech-community.robotics.abb.com/u/niggos)\ **Post date:** [February 10, 2012, 12:29am UTC](https://tech-community.robotics.abb.com/t/tcp-ip-disconnect-not-handled-correctly/3795/6 "2012-02-10T00:29:38Z")
Hi there! I’m quiet new to RAPID, but I spent some time on developing a TCP-based communication from client-PC to server-IRC5. just a thought: If you have the option “Multitasking” installed, you can use some additional tasks for separate server sockets that listen continously for incoming data. @jeroen: You can try to use _ResetRetrycount;_ in your error handling rigth after ServerStart(TRUE); The standard number of retry counts is 4 (configurable somewhere …), so after four times of handling the same error, the Retry; will not be executed and the loop/proc will come to end/be finished. hope this might help!?