TCP Socket - nonexisting IP problem

mapmusic · **Joined:** Tue Oct 30, 2012 4:23 am **Posts:** 22

Hello Network experts,

I need check possibility of connect before running some code on TCP SOcket.
I use TCP socket example from Reference Guide, which works well on IPs which are available.
I got into problem, when I try to connect to nonexisting IP.
Problem is when I am connecting there, in "While" part I have

IsConnetcted= False

and

LastErrorCode=0

, so code is cycling .
Have you any tip to check this in code ?

Thanks

Martin

My Code:

Function TCP_Connect(xIP as string, xPort as integer) As Boolean
  Dim start, stop as Integer
  Dim conn as Boolean
  Dim TCPSocket1 as TCPSocket
  TCPSocket1 = New TCPSocket
  TCPSocket1.Address = xIP
  TCPSocket1.Port = xPort
  TCPSocket1.Connect
  start = Ticks
  While Not TCPSocket1.IsConnected
    If TCPSocket1.LastErrorCode <> 0 then
      StatusBar.text = "Socket Error: " + str(TCPSocket1.LastErrorCode)
      Exit
    End If
    TCPSocket1.Poll
  Wend
  stop = Ticks
  If TCPSocket1.IsConnected then
    StatusBar.text= "Socket Connected in " + Str(stop - start) + " ticks"
    conn = true
  Else
    StatusBar.text= "Socket failed to connect. It took " + Str(stop - start) + _
      " ticks to figure that out"
    conn= false
  End If
  TCPSocket1.Close
  StatusBar.text= "Socket closed"
  return conn
End Function

pony · **Posted:** Tue Feb 05, 2013 10:31 am

Add a timeout value after which to give up.
NOTE - Ticks can roll over, so add some error checking

Function TCP_Connect(xIP as string, xPort as integer) As Boolean
  Dim start, stop as Integer
  Dim conn as Boolean
  Dim TCPSocket1 as TCPSocket
  TCPSocket1 = New TCPSocket
  TCPSocket1.Address = xIP
  TCPSocket1.Port = xPort
  TCPSocket1.Connect
  start = Ticks
  dim timeout as Integer = 180 //3 seconds
  While Not TCPSocket1.IsConnected
    If TCPSocket1.LastErrorCode <> 0 then
      StatusBar.text = "Socket Error: " + str(TCPSocket1.LastErrorCode)
      Exit
    End If
    TCPSocket1.Poll
    if Ticks > start +timeout then //did 3 seconds elapse
      StatusBar.text= "Timed out" //we time out, dang!
      conn = false//no connection
      exit//exit the loop
    end
  Wend
  stop = Ticks
  If TCPSocket1.IsConnected then
    StatusBar.text= "Socket Connected in " + Str(stop - start) + " ticks"
    conn = true
  Else
    StatusBar.text= "Socket failed to connect. It took " + Str(stop - start) + _
      " ticks to figure that out"
    conn= false
  End If
  TCPSocket1.Close
  StatusBar.text= "Socket closed"
  return conn
End Function

mapmusic · **Joined:** Tue Oct 30, 2012 4:23 am **Posts:** 22

Thanks pony,

It is good idea to check for connection only for 3 seconds. I will implement

But Is there any way to check IP by ping it ?
Maybe it could be better before opening any socket.

Thanks

M.

pony · **Posted:** Tue Feb 05, 2013 11:17 am

mapmusic wrote:

Thanks pony,

It is good idea to check for connection only for 3 seconds. I will implement

But Is there any way to check IP by ping it ?
Maybe it could be better before opening any socket.

Thanks

M.

You could spawn a shell and issue a ping.

Not all devices answer to ICMP pings.

I don't know what you are connecting to, but I can envisage an instance were a remote IP answered to a ping, but did not have the service you want running on it (ping a web server, but Apache or IIS etc isnt running).
For my network applications, I'm not interested if they are replying to a ping or not. I'm only interested in the service I wish to connect to.

mapmusic · **Joined:** Tue Oct 30, 2012 4:23 am **Posts:** 22

I agree, that ping is not way to check if service is working.
(I am connecting to software with TCP services on 2 ports and I can ping this software)
But I am finding way to avoid 2 subroutines (each 3 seconds) if not needed.

Anyway thanks for tips.

M.

msssltd · **Posted:** Wed Feb 06, 2013 3:48 am

Does this help?

Sub Form1.Button1.Action
  TCPSocket1.Address = "localhost"
  TCPSocket1.Port = 1023
  
  TCPSocket2.Address = "localhost"
  TCPSocket2.Port = 1024
  
  //Fail early.
  Dim fSuccess as boolean
  If TCPSocket1.Connect(3000) Then
    If TCPSocket2.Connect(3000) then
      fSuccess = true
    End if
  End if
  
  If not fSuccess then
    // .IsConnected can tells us which socket failed
    // .LastErrorCode can tell us what went wrong
    Return
  End if
  
  //All connected up.
End Sub

//Add a module to your project and add the following method
Function Connect(extends tcp as TCPSocket, time_out_ms as integer) as boolean
  Dim time_out as double = time_out_ms * 1000
  Dim start_ms as double = Microseconds
  
  tcp.Connect
  Do
    tcp.Poll
  Loop until tcp.IsConnected or (Microseconds - start_ms > time_out)
  
  Return tcp.IsConnected
End Function

mapmusic · **Joined:** Tue Oct 30, 2012 4:23 am **Posts:** 22

Thanks msssltd,

Tip from pony also worked fine, but I used your modified code. (Extends is cool ... it is new for me

)

Thanks guys for solve my problem !

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TCP Socket - nonexisting IP problem