Detecting socket closed on TcpClient

[Michael Kennedy [UB]]

Hi,

I have a project using the TcpClient and its associated NetworkStream.
Everything works well except for one condition which I haven't found any
information about dealing with:

How do I detected when the socket connection was closed on the
server-side?

That is, if my client connects to the server and everything is initialized
correctly the system runs well. But how can I tell if the server is shut
down or otherwise closes my connection without my involvement (that is
without my calling close on the TcpClient)?

Thanks,
Michael

Michael Kennedy
United Binary

http://www.unittesting.com

[Michael Kennedy [UB]]

Re: Detecting socket closed on TcpClient

Hello,

Thanks for the response. I was afraid that that was the case. I am using
try/catches to catch the errors but I would like to be able to let the user
know if the connection was closed by the server.

I know this can be done using straight winsock / Win32 API sockets and C++.
Is there an equivalent in .NET? Can this functionality be accessed using
some sort of interop along side the TcpClient (short of just using the C++
sockets via interop of course).

Thanks,
Michael

"Tian Min Huang" <timhuang@onlin e.microsoft.com > wrote in message
news:cDoCK8tZDH A.2108@cpmsftng xa06.phx.gbl...[color=blue]
> Hello Michael,
>
> Thanks for your post.
>[color=green][color=darkred]
> >> But how can I tell if the server is shutdown or otherwise closes my[/color][/color]
> connection without my involvement?
>
> I suggest you to use try-catch statement to catch the exceptions thrown
> from tcp operations. Generally speaking, the client side will not be
> notified when the connection was damanged on the server-side until it[/color]
fails[color=blue]
> to communicate with the service. For example, when the connection is
> somehow not available, it will throw the following exception if you call
> NetworkStream:: Write or NetworkStream:: Read on client side:
>
> Unhandled Exception: System.IO.IOExc eption: Unable to read data from the
> transport connection. ---> System.Net.Sock ets.SocketExcep tion: An existing
> connection was forcibly closed by the remote host
>
> Hope this helps.
>
> Regards,
>
> HuangTM
> Microsoft Online Partner Support
> MCSE/MCSD
>
> Get Secure! ¨C www.microsoft.com/security
> This posting is provided ¡°as is¡± with no warranties and confers no[/color]
rights.[color=blue]
>[/color]

[Chris Langsenkamp]

Re: Detecting socket closed on TcpClient

On my solution I send some sort of 'bye' message to the client telling it the connection is being dropped, and I do so from the server with no expectation of response. The client is coded such that receiveing that from the server is the end of things. Your server connection is dropped for only a few reasons, one of which you can't control inside your program (ISP/connectivity failure), the rest should be app errors that you should be able to trap and kick out your bye messages as the server does it's finishing work. The key is making sure the server can't by any means abruptly halt, but must terminate gracefully, and telling all the clients is part of that. Even so, the client must be insulated from connectivity failings because certainly the clients are much more likely to have them than the server (i.e. dialup drop) which is no different to the client than the server hanging up - the read/write fails and client must deal with it.

Chris Langsenkamp
Chat Live at http://www.cleverchat.net
--------------------------------------------------------------------------------

"Michael Kennedy [UB]" <mkennedy@REMOV ETHIS.unitedbin ary.com> wrote in message news:%235xOuz$Z DHA.2548@TK2MSF TNGP09.phx.gbl. ..
Hello,

Thanks for the response. I was afraid that that was the case. I am using
try/catches to catch the errors but I would like to be able to let the user
know if the connection was closed by the server.

I know this can be done using straight winsock / Win32 API sockets and C++.
Is there an equivalent in .NET? Can this functionality be accessed using
some sort of interop along side the TcpClient (short of just using the C++
sockets via interop of course).

Thanks,
Michael

"Tian Min Huang" <timhuang@onlin e.microsoft.com > wrote in message
news:cDoCK8tZDH A.2108@cpmsftng xa06.phx.gbl...[color=blue]
> Hello Michael,
>
> Thanks for your post.
>[color=green][color=darkred]
> >> But how can I tell if the server is shutdown or otherwise closes my[/color][/color]
> connection without my involvement?
>
> I suggest you to use try-catch statement to catch the exceptions thrown
> from tcp operations. Generally speaking, the client side will not be
> notified when the connection was damanged on the server-side until it[/color]
fails[color=blue]
> to communicate with the service. For example, when the connection is
> somehow not available, it will throw the following exception if you call
> NetworkStream:: Write or NetworkStream:: Read on client side:
>
> Unhandled Exception: System.IO.IOExc eption: Unable to read data from the
> transport connection. ---> System.Net.Sock ets.SocketExcep tion: An existing
> connection was forcibly closed by the remote host
>
> Hope this helps.
>
> Regards,
>
> HuangTM
> Microsoft Online Partner Support
> MCSE/MCSD
>
> Get Secure! ¨C www.microsoft.com/security
> This posting is provided ¡°as is¡± with no warranties and confers no[/color]
rights.[color=blue]
>[/color]

[Michael Kennedy [UB]]

Re: Detecting socket closed on TcpClient

Hi,

Thanks for the info. I know about interporating with the API using PInvoke.
But what I was asking for was a .NET way of acheiving the same
functionality. This limitation is not important enough for me to build whole
wrapper classes for the winsock API.

Also, I do catch the exceptions and they do contain the information about
the socket being closed. However, what I need is some way to determine if
the socket has been closed without traffic to the server. Consider that the
client connects to the server and everything is good. Sits there idle for
awhile, then the server is shutdown. Now the client will sit there for an
indefinite period of time (until it tries to talk again) before it knows the
server is gone.

Our C++ apps which use the Win32 API are notified immediately when the
server is shutdown. I was asking if there is the same functionality in the
..NET sockets. I guess the answer is no.

Thanks again,
Michael


"Tian Min Huang" <timhuang@onlin e.microsoft.com > wrote in message
news:KoKcfM2aDH A.1996@cpmsftng xa06.phx.gbl...[color=blue]
> Hello Michael,
>
> Thanks for your reply. I'd like to share the following information with[/color]
you:[color=blue]
>
> 1. According to the SocketException , it's clearly indicate that the
> connection was closed by the server.
> "System.Net.Soc kets.SocketExce ption: An existing connection was forcibly
> closed by the remote host"
>
> 2. You can also call winsock APIs directly by using Platform Invoke.[/color]
Please[color=blue]
> refer to the following MSDN article:
>
> Consuming Unmanaged DLL Functions
>[/color]
http://msdn.microsoft.com/library/de...us/cpguide/htm[color=blue]
> l/cpconconsumingu nmanageddllfunc tions.asp
>
> Hope this helps.
>
> Regards,
>
> HuangTM
> Microsoft Online Partner Support
> MCSE/MCSD
>
> Get Secure! ¨C www.microsoft.com/security
> This posting is provided ¡°as is¡± with no warranties and confers no[/color]
rights.[color=blue]
>
>[/color]

[Tian Min Huang]

Re: Detecting socket closed on TcpClient

Hi Michael,

Thanks for your response. I am now performing further research on this
issue, and will come back with my information.

Have a nice day!

Regards,

HuangTM
Microsoft Online Partner Support
MCSE/MCSD

Get Secure! ¨C www.microsoft.com/security
This posting is provided ¡°as is¡± with no warranties and confers no rights.

[Tian Min Huang]

Re: Detecting socket closed on TcpClient

Hello Michael,

Now I'd like to share the following information with you. Generally
speaking, we should set the SO_KEEPALIVE option (by using setsockopt) to
monitor the connection. Please refer to the following KB article:

How to Determine Loss of Client/Server Connection

http://support.microsoft.com/default.aspx?scid=kb;en-us;140325

In .NET Framework, please refer to the corresponding KeepAlive option:

SocketOptionNam e Enumeration

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/

frlrfsystemnets ocketssocketopt ionnameclasstop ic.asp

Please feel free to let me know if you have any problems or concerns.

Have a nice day!

Regards,

HuangTM
Microsoft Online Partner Support
MCSE/MCSD

Get Secure! ¨C www.microsoft.com/security
This posting is provided ¡°as is¡± with no warranties and confers no rights.

[Michael Kennedy [UB]]

Re: Detecting socket closed on TcpClient

Hi,

Thanks for the response. That does look like it might be helpful to me. I'll
let you know how it goes.

Thanks,
Michael


"Tian Min Huang" <timhuang@onlin e.microsoft.com > wrote in message
news:FOUGBD8bDH A.1996@cpmsftng xa06.phx.gbl...[color=blue]
> Hello Michael,
>
> Now I'd like to share the following information with you. Generally
> speaking, we should set the SO_KEEPALIVE option (by using setsockopt) to
> monitor the connection. Please refer to the following KB article:
>
> How to Determine Loss of Client/Server Connection
> http://support.microsoft.com/default...b;en-us;140325
>
> In .NET Framework, please refer to the corresponding KeepAlive option:
>
> SocketOptionNam e Enumeration
>[/color]
http://msdn.microsoft.com/library/de...us/cpref/html/[color=blue]
> frlrfsystemnets ocketssocketopt ionnameclasstop ic.asp
>
> Please feel free to let me know if you have any problems or concerns.
>
> Have a nice day!
>
> Regards,
>
> HuangTM
> Microsoft Online Partner Support
> MCSE/MCSD
>
> Get Secure! ¨C www.microsoft.com/security
> This posting is provided ¡°as is¡± with no warranties and confers no[/color]
rights.[color=blue]
>
>[/color]