Attaching custom methods - C# Discussion Boards

Alper Camel18-Apr-05 1:44

18-Apr-05 1:44

Thank you for your reply!

Ok. I got it. I need admin account.

Actually My problem is ;

I wrote a small server (listens tcp port),
when a client's cable unplugged, I want my server detect this,
and says this client is disconnected,

Do you know how can I do it?

thank you very much...

Dave Kreskowiak18-Apr-05 4:57

18-Apr-05 4:57

The server cannot detect this at all. As I put in your other post, PING'ing the client is not a reliable method considering the client might be behind a firewall or NAT that won't let ICMP traffic through it.

The only thing you can do is build in a "keep alive" where the client must send these "keep alive" requests to the server every so often. If the server stops receiving these requests from the client within a specified time period, it can assume that the client is no longer connected.

I don't know how much traffic or how many clients you're expecting, but this has scalability limitations. If you get enough clients connected, you could conceivably have 80%, or more, of the traffic going to the server just "keep alive"'s, resulting in very slow performance.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Anonymous18-Apr-05 21:14

Anonymous

18-Apr-05 21:14

That's Right. but my problem is that my clients may anyone. I mean. any client who knows my server IP and Port Number can connect to my server.
that is clients cannot send me message that they are online or something.. because they don't know the way I search them...
They can only send me string messages and my server display it on the received screen.. (of sure incoming messages are token as bytes no problem at this fact at all)..

As a result, server has to detect which clients are online or not! by a way ping or something..

By this way , I know that all the work done by server and server has much work to do.. But I have to...

Thank you very much for reply..
Greetings....
Alper.
Software Developer.

Dave Kreskowiak19-Apr-05 2:21

19-Apr-05 2:21

Your client may be anyone, anywhere on the planet?

Since you're trying to determine if the client disconnects unexpectedly, I'm assuming that you have to keep state information for the duration of the client session. Is this correct?

Are you writing a client piece to this also? If so, then you could include code that would send a "keep alive" request back to the server so the server knows it's still connected. After a certain timeout, if no "keep alive" request has been received by the server, you can assume the client either lost communication or terminated the client for some reason.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Alper Camel19-Apr-05 4:13

19-Apr-05 4:13

Unfortunately I'm writing only the Server Part,
and the clients are electronic cards that
has the client code in their EP-ROM and flash memory.

If their battery gets low or power-off my or their network cable unplugged, my server has to detect it.

Because the memory is very important for the EP-ROM based electronic cards client. Any Keep-Alive Send code couldnt be added into the clients.

Again Thank you very much...

Dave Kreskowiak19-Apr-05 14:59

Re: Attaching custom methods

19-Apr-05 14:59

You could have put that little tidbit into your original post!

Now, your options are extremely limited...

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Attaching custom methods

Enishi18-Apr-05 1:29

Enishi

18-Apr-05 1:29

Hi, im new to C# and have a problem when i must assign methods to objects i create in execution mode.
while in design mode u can create a timer and then double click on it and there u go, but how can i attach a method to a timer i have created in execution time?

<br />
using System.Timers;<br />
<br />
Timer t = new timer(30000);<br />
t.enabled=true;<br />
//but how i tell the timer what method or event to raise when its interval elapses?<br />

Ty for ur time.

MoustafaS18-Apr-05 2:42

MoustafaS

18-Apr-05 2:42

Timer t = new Timer(new TimerCallBack(Your Method));
and then handle all the rest

Re: Attaching custom methods

Sebastian Schneider18-Apr-05 3:09

Sebastian Schneider

18-Apr-05 3:09

Declare your Timer

[code]
System.Timers.Timer myTimer = new System.Timers.Timer(1000);
// 1000 is the Interval used by the Timer in ms, i.e. the time between two "Timer.Elapsed" Events
[/code]

Then add an EventHandler

[code]
myTimer.Elapsed +=new System.Timers.ElapsedEventHandler(myTimer_Elapsed);
// Note: In VS.NET 2003, as soon as you type the +=, VS will ask you to press
// TAB. If you do, it will code-complete everything else, even the Delegate's
// body if you press TAB again.
[/code]

Now, on each Elapsed-Event, the Delegate will be executed

[code]
//If you are not using VS.NET, this is what the delegate should look like:
private void myTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{

}
[/code]

Re: Attaching custom methods

Enishi18-Apr-05 21:38

Enishi

18-Apr-05 21:38

TY a lot for your help and examples, it works perfect now.

Networking

Alper Camel18-Apr-05 1:12

18-Apr-05 1:12

I have a tcp server, when a client connects, then let its cable unplugged!
Then How can server detect that it is disconnected?

Thanks all!

Re: Networking

Dave Kreskowiak18-Apr-05 4:51

18-Apr-05 4:51

It can't. The only thing it can do is assume that the client dropped the connection without closing it, because of a complete lack of communication for a specified timeout period.

Or, with a little more thought, the server can try and PING the client every so often to see if it is still alive. This has it's problems too considering the client might be behind a firewall that won't let ICMP packets through.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Re: Networking

BambooMoon18-Apr-05 5:46

BambooMoon

18-Apr-05 5:46

It isn't really true that the server can't detect that the client disconnected. But the server can't detect it just by sitting there. I had some code somewhere that managed this by having the server periodically switch the socket to nonblocking mode and try to do a read in peek mode. Note that the receive in peek mode might return WSAEWOULDBLOCK if the socket is still live and there is nothing to read on it. But if the socket is closed, it will not return an exception. That is why I preload the bytes[] array with some data that I can then compare the read result against, of course assuming that I would never expect the read to contain that exact byte pattern. There might be a better way, but this worked fine for me.

try
{
// Try doing a dummy read to see if the socket is still alive
bytes[0] = 0xf;
bytes[1] = 0xe;
bytes[2] = 0xd;
bytes[3] = 0xc;
socket.Blocking = false;
socket.Receive(bytes, 0, 4, SocketFlags.Peek);
socket.Blocking = true;
if (bytes[0] == 0xf && bytes[1] == 0xe && bytes[2] == 0xd && bytes[3] == 0xc)
{
// The sender has shut down the socket
bexitreadloop = true;
socket.Close();
form1.DisplaySocketStatusMessage("Lost connection with sender");
break;
}
}
catch (SocketException e)
{
socket.Blocking = true;
int code = e.ErrorCode;
if (e.ErrorCode != WSAEWOULDBLOCK)
{
bexitreadloop = true;
socket.Close();
form1.DisplaySocketStatusMessage("Socket error on read");
break;
}
}

Re: Networking

Alper Camel18-Apr-05 21:47