Artificially create a connection timeout error

Question

I ve had a bug in our software that occurs when I receive a connection timeout  These errors are very rare  usually when my connection gets dropped by our internal network   How can I generate this kind of effect artificially so I can test our software    If it matters the app is written in C   MFC using CAsyncSocket classes   Edit   I ve tried using a non-existent host  and I get the socket error      WSAEINVAL  10022  Invalid argument   My next attempt was to use Alexander s suggestion of connecting to a different port  e g  81  on my own server though   That worked great  Exactly the same as a dropped connection  60 second wait  then error   Thank you

User · Answer

You can try to connect to one of well-known Web sites on a port that may not be available from outside - 200 for example  Most of firewalls work in DROP mode and it will simulate a timeout for you

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Plug in your network cable into a switch which has no other connection cables  That should work imho

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For me easiest way was adding static route on office router based on destination network  Just route traffic to some unresponsive host  e g  your computer  and you will get request timeout   Best thing for me was that static route can be managed over web interface and enabled disabled easily

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The following URL always gives a timeout  and combines the best of  Alexander and  Emu s answers above   http   example com 81  Using example com 81 is an improvement on Alexander s answer because example com is reserved by the DNS standard  so it will always be unreachable  unlike google com 81  which may change if Google feels like it  Also  because example com is defined to be unreachable  you won t be flooding Google s servers   I d say it s an improvement over  emu s answer because it s a lot easier to remember

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Depending on what firewall software you have installed available  you should be able to block the outgoing port and depending on how your firewall is setup it should just drop the connection request packet  No connection request  no connection  timeout ensues  This would probably work better if it was implemented at a router level  they tend to drop packets instead of sending resets  or whatever the equivalent is for the situation  but there s bound to be a software package that d do the trick too

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How about a software solution   Install SSH server on the application server  Then  use socket tunnel to create a link between your local port and the remote port on the application server  You can use ssh client tools to do so  Have your client application connect to your mapped local port instead  Then  you can break the socket tunnel at will to simulate the connection timeout

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You might install Microsoft Loopback driver that will create a separate interface for you  Then you can connect on it to some service of yours  your own host   Then in Network Connections you can disable enable such interface

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I had issues along the same lines you do   In order to test the software behavior  I just unplugged the network cable at the appropriate time   I had to set a break-point right before I wanted to unplug the cable     If I were doing it again  I d put a switch  a normally closed momentary push button one  in a network cable     If the physical disconnect causes a different behavior  you could connect your computer to a cheap hub and put the switch I mentioned above between your hub and the main network   -- EDIT -- In many cases you ll need the network connection working until you get to a certain point in your program  THEN you ll want to disconnect using one of the many suggestions offered

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There are services available which allow you to artificially create origin timeouts by calling an API where you specify how long the server will take to respond  Server Timeout on macgyver is an example of such a service   For example if you wanted to test a request that takes 15 seconds to respond you would simply make a post request to the macgyver API   JSON Payload          timeout length   15000     API Response  After 15 seconds           response    ok      Server Timeout program on macgyver https   askmacgyver com explore program server-timeout 3U4s6g6u

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There are a couple of tactics I ve used in the past to simulate networking issues    Pull out the network cable Switch off the switch  ideally with the switch that the computer is plugged into still being powered so the machine maintains it s  network connection   between your machine and the  target  machine Run firewall software on the target machine that silently drops received data   One of these ideas might give you some means of artifically generating the scenario you need

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The technique I use frequently to simulate a random connection timeout is to use ssh local port forwarding    ssh -L 12345 realserver com 80 localhost   This will forward traffic on localhost 12345 to realserver com 80 You can loop this around in your own local machine as well  if you want   ssh -L 12345 localhost 8080 localhost   So you can point your application at your localhost and custom port  and the traffic will get routed to the target host port  Then you can exit out of this shell  you may also need to ctrl c the shell after you exit  and it will kill the forwarding which causes your app to see a connection loss

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You can use the Python REPL to simulate a timeout while receiving data  i e  after a connection has been established successfully   Nothing but a standard Python installation is needed   Python 2 7 4  default  Apr  6 2013  19 54 46   MSC v 1500 32 bit  Intel   on win32 Type  help    copyright    credits  or  license  for more information   gt  gt  gt  import socket  gt  gt  gt  s   socket socket socket AF INET  socket SOCK STREAM           gt  gt  gt  s bind   localhost   9000    gt  gt  gt  s listen 0   gt  gt  gt   clientsocket  address    s accept     Now it waits for an incoming connection  Connect whatever you want to test to localhost 9000  When you do  Python will accept the connection and accept   will return it  Unless you send any data through the clientsocket  the caller s socket should time out during the next recv

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Plenty of good answers but the cleanest solution seems to be this service  http   httpstat us 504 sleep 60000  You can configure the timeout duration  up to 230 seconds  and eventual return code

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If you are on a unix machine  you can start a port listening using netcat   nc -l 8099   Then  modify you service to call whatever it usually does to that port e g  http   localhost 8099 some sort of endpoint  Then  your service will open the connection and write data  but will never get a response  and so will give you a Read Time Out  rather than Connection Refused

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Connect to a non-routable IP address  such as 10 255 255 1

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10 0 0 0 10 255 255 255 172 16 0 0 172 31 255 255 192 168 0 0 192 168 255 255   All these are non-routable

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I would like to point everybody s attention to pathod  With a config  taken from their examples  of 200 b 100 dr you ll get a connection that randomly drops

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The easiest thing would be to drop your connection using CurrPorts   However  in order to unit test your exception handling code  perhaps you should consider abstracting your network connection code  and write a stub  mock or decorator which throws exceptions on demand  You will then be able to test the application error-handling logic without having to actually use the network

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Despite it isn t completely clear which one the OP wants to test  there s a difference between attempting a connection to a non-existent host port and a timeout of an already established connection  I would go with Rob and wait until the connection is working and then pull the cable  Or - for convenience - have a virtual machine working as the test server  with bridged networking  and just deactivating the virtual network interface once the connection is established

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Connect to an existing host but to a port that is blocked by the firewall that simply drops TCP SYN packets  For example  www google com 81

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If you want to use an active connection you can also use http   httpbin org delay    where   is the time you want their server to wait before sending a response  As long as your timeout is shorter than the delay     should simulate the effect  I ve successfully used it with the python requests package   You may want to modify your request if you re sending anything sensitive - no idea what happens to the data sent to them

[networking] Artificially create a connection timeout error

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