How to set the timeout for a TcpClient

Question

I have a TcpClient which I use to send data to a listener on a remote computer  The remote computer will sometimes be on and sometimes off  Because of this  the TcpClient will fail to connect often  I want the TcpClient to timeout after one second  so it doesn t take much time when it can t connect to the remote computer  Currently  I use this code for the TcpClient   try       TcpClient client   new TcpClient  remotehost   this Port       client SendTimeout   1000       Byte   data   System Text Encoding Unicode GetBytes this Message       NetworkStream stream   client GetStream        stream Write data  0  data Length       data   new Byte 512       Int32 bytes   stream Read data  0  data Length       this Response   System Text Encoding Unicode GetString data  0  bytes        stream Close        client Close             FireSentEvent       Notifies of success   catch  Exception ex        FireFailedEvent ex     Notifies of failure     This works well enough for handling the task  It sends it if it can  and catches the exception if it can t connect to the remote computer  However  when it can t connect  it takes ten to fifteen seconds to throw the exception  I need it to time out in around one second  How would I change the time out time

User · Answer

If using async  amp  await and desire to use a time out without blocking  then an alternative and simpler approach from the answer provide by mcandal is to execute the connect on a background thread and await the result  For example   Task lt bool gt  t   Task Run      gt  client ConnectAsync ipAddr  port  Wait 1000    await t  if   t Result       Console WriteLine  Connect timed out       return     Set return an error code or throw here       Successful Connection - if we get to here    See the Task Wait MSDN article for more info and other examples

User · Answer

Here is a code improvement based on mcandal solution   Added exception catching for any exception generated from the client ConnectAsync task  e g  SocketException when server is unreachable   var timeOut   TimeSpan FromSeconds 5        var cancellationCompletionSource   new TaskCompletionSource lt bool gt      try       using  var cts   new CancellationTokenSource timeOut                 using  var client   new TcpClient                          var task   client ConnectAsync hostUri  portNumber                using  cts Token Register      gt  cancellationCompletionSource TrySetResult true                                  if  task    await Task WhenAny task  cancellationCompletionSource Task                                         throw new OperationCanceledException cts Token                                         throw exception inside  task   if any                  if  task Exception  InnerException    null                                        throw task Exception InnerException                                                                      catch  OperationCanceledException operationCanceledEx           connection timeout           catch  SocketException socketEx              catch  Exception ex

User · Answer

As Simon Mourier mentioned  it s possible to use ConnectAsync TcpClient s method with Task in addition and stop operation as soon as possible  For example         client   new TcpClient       Initialization of TcpClient CancellationToken ct   new CancellationToken       Required for  quot   Task   quot  method if  client ConnectAsync this ip  this port  Wait 1000  ct      Connect with timeout of 1 second               transfer      if  client    null            client Close       Close the connection and dispose a TcpClient object         Console WriteLine  quot Success quot            ct ThrowIfCancellationRequested       Stop asynchronous operation after successull connection    and transfer in needed           else       Console WriteLine  quot Connetion timed out quot              Also  I would recommended checking the AsyncTcpClient C  library with some examples provided like Server  lt  gt  Client

User · Answer

You would need to use the async BeginConnect method of TcpClient instead of attempting to connect synchronously  which is what the constructor does  Something like this   var client   new TcpClient    var result   client BeginConnect  remotehost   this Port  null  null    var success   result AsyncWaitHandle WaitOne TimeSpan FromSeconds 1     if   success        throw new Exception  Failed to connect           we have connected client EndConnect result

User · Answer

Set ReadTimeout or WriteTimeout property on the NetworkStream for synchronous reads writes   Updating OP s code   try       TcpClient client   new TcpClient  remotehost   this Port       Byte   data   System Text Encoding Unicode GetBytes this Message       NetworkStream stream   client GetStream        stream WriteTimeout   1000       lt ------- 1 second timeout     stream ReadTimeout   1000       lt ------- 1 second timeout     stream Write data  0  data Length       data   new Byte 512       Int32 bytes   stream Read data  0  data Length       this Response   System Text Encoding Unicode GetString data  0  bytes        stream Close        client Close             FireSentEvent       Notifies of success   catch  Exception ex           Throws IOException on stream read write timeout     FireFailedEvent ex     Notifies of failure

User · Answer

Another alternative using https   stackoverflow com a 25684549 3975786   var timeOut   TimeSpan FromSeconds 5        var cancellationCompletionSource   new TaskCompletionSource lt bool gt     try       using  var cts   new CancellationTokenSource timeOut                 using  var client   new TcpClient                          var task   client ConnectAsync hostUri  portNumber                using  cts Token Register      gt  cancellationCompletionSource TrySetResult true                                  if  task    await Task WhenAny task  cancellationCompletionSource Task                                         throw new OperationCanceledException cts Token                                                                       catch OperationCanceledException

User · Answer

Starting with  NET 4 5  TcpClient has a cool ConnectAsync method that we can use like this  so it s now pretty easy   var client   new TcpClient    if   client ConnectAsync  remotehost   remotePort  Wait 1000            connection failure

User · Answer

The answers above don t cover how to cleanly deal with a connection that has timed out  Calling TcpClient EndConnect  closing a connection that succeeds but after the timeout  and disposing of the TcpClient   It may be overkill but this works for me       private class State               public TcpClient Client   get  set            public bool Success   get  set               public TcpClient Connect string hostName  int port  int timeout                var client   new TcpClient               when the connection completes before the timeout it will cause a race           we want EndConnect to always treat the connection as successful if it wins         var state   new State   Client   client  Success   true             IAsyncResult ar   client BeginConnect hostName  port  EndConnect  state           state Success   ar AsyncWaitHandle WaitOne timeout  false            if   state Success     client Connected              throw new Exception  Failed to connect              return client             void EndConnect IAsyncResult ar                var state    State ar AsyncState          TcpClient client   state Client           try                       client EndConnect ar                     catch              if  client Connected  amp  amp  state Success              return           client Close

User · Answer

One thing to take note of is that it is possible for the BeginConnect call to fail before the timeout expires   This may happen if you are attempting a local connection    Here s a modified version of Jon s code             var client   new TcpClient            var result   client BeginConnect  remotehost   Port  null  null            result AsyncWaitHandle WaitOne TimeSpan FromSeconds 1            if   client Connected                        throw new Exception  Failed to connect                           we have connected         client EndConnect result

[c#] How to set the timeout for a TcpClient?

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