Re: Error when converting to use UDP - C# Discussion Boards

27-Aug-02 14:34

Hello,

For a school assignment I have to make a little client and server that send a file using either TCP or UDP (depending on the selection of the user).

I found these two little sample programs that could teach me what I need, the problem is that if a change the server and client to use UDP (and datagrams) an exception is thrown in the server at the Listen call.

The programs are here:

ms-help://MS.VSCC/MS.MSDNVS/cpguide/html/cpconnon-blockingserversocketexample.htm[^]

ms-help://MS.VSCC/MS.MSDNVS/cpguide/html/cpconnon-blockingclientsocketexample.htm[^]

Any ideas?? Also, how can I make the server accept multiple connections at a time? I know I have to create a thread for each connection, but where and how??

Thanks,

-- LuisR

──────────────
  Luis Alonso Ramos
  Chihuahua, Mexico
  www.luisalonsoramos.com

"Do not worry about your difficulties in mathematics, I assure you that mine are greater." -- Albert Einstein

Michael Mac28-Aug-02 2:15

28-Aug-02 2:15

Luis Alonso Ramos wrote:
The problem is that if a change the server and client to use UDP (and datagrams) an exception is thrown in the server at the Listen call.

UPD datagrams support up to 64 KB messages without fragmentation.
If you want to send a bigger portion simply turn on it

socket.SetSocketOption( SocketOptionLevel.Udp, SocketOptionName.DontFragment, false);

Another case in which an exception could be thrown is that the default buffer is too small to receive such a big datagram. For example, in UdpClient it's set to 8KB.

socket.SetSocketOption( SocketOptionLevel.Udp, SocketOptionName.SendLowWater, 1024 * 128 /*128KB*/);
socket.SetSocketOption( SocketOptionLevel.Udp, SocketOptionName.SendBuffer, 1024 * 128 /*128KB*/);

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Luis Alonso Ramos28-Aug-02 3:04

28-Aug-02 3:04

I tried adding those lines after the creation of the socket, and they throw exceptions (of invalid argument type.)

Anyway, I don't try to send more than 64 KB at a time, it's just a simple 19 byte message.

Any idea why the server will not start listening??

-- LuisR

──────────────
  Luis Alonso Ramos
  Chihuahua, Mexico
  www.luisalonsoramos.com

"Do not worry about your difficulties in mathematics, I assure you that mine are greater." -- Albert Einstein

Michael Mac28-Aug-02 3:51

28-Aug-02 3:51

Could you give the exception's description and its type. It could help.

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Luis Alonso Ramos28-Aug-02 4:14

28-Aug-02 4:14

Yes, this is the exception:

System.Net.Sockets.SocketException: The attempted operation is not supported for
 the type of object referenced
   at System.Net.Sockets.Socket.Listen(Int32 backlog)
   at AsynchronousSocketListener.StartListening() in d:\projects\asyncsock\server\server.cs:line 49

The socket is created like this:

Socket listener = new Socket(AddressFamily.InterNetwork,
    SocketType.Dgram, ProtocolType.Udp);

Thanks,

-- LuisR

──────────────
  Luis Alonso Ramos
  Chihuahua, Mexico
  www.luisalonsoramos.com

"Do not worry about your difficulties in mathematics, I assure you that mine are greater." -- Albert Einstein

Russell Morris28-Aug-02 4:36

Russell Morris

28-Aug-02 4:36

From what I remember, UDP is a connectionless protocol. Unlike TCP, UDP has no notion of an explicit 'connection' being made to a server socket, which is most likely why this exception is being thrown.

TCP is designed to guaruntee data delivery or to notify the sender and receiver of a delivery failure. In order to do this it keeps alot of state behind the scenes, thus necessitating the 'connection' metaphor.

UDP, however, is much more like IP in that it is a "best effort" delivery protocol. If you send data over UDP, it will most likely get their in good shape. However, it's up to the person reading from the UDP stream to figure out whether or not the data they got has been corrupted.

Long story short - there is no such thing as a 'Connection' or a 'Listen socket' in UDP. If you want to send a data packet via UDP, you specify the data you want to send along with the IP address and port # you want to send it to. You do this for every send() call. Same type of thing with receive() on UDP. You don't connect to a server socket like you would with TCP, you just recv() on a specific port # and wait for someone to send a UDP packet to that port.

My only experience with writing UDP code is in straight C on Unix, so I'm not sure how this would be implemented in the .NET FCL...

--
Russell Morris

"Have you gone mad Frink? Put down that science pole!"

Luis Alonso Ramos28-Aug-02 4:44

28-Aug-02 4:44

Russell Morris wrote:
You don't connect to a server socket like you would with TCP, you just recv() on a specific port # and wait for someone to send a UDP packet to that port.

So, that is why there is no UdpListener class?? For an UDP server I just start an UdpClient class and call receive on certain port, and it will block until some one calls send on that port?

-- LuisR

──────────────
  Luis Alonso Ramos
  Chihuahua, Mexico
  www.luisalonsoramos.com

"Do not worry about your difficulties in mathematics, I assure you that mine are greater." -- Albert Einstein

Quick Question

Alex Korchemniy27-Aug-02 8:57

Alex Korchemniy

27-Aug-02 8:57

My application needs to support multiple displays. How do I programmaticly move a window/form to a certain displays (monitor)?

If I need to do this with win32 api, what would be the function?

leppie27-Aug-02 9:38

27-Aug-02 9:38

As long as child forms can move outside the main window, it should have multiple monitor support.

I did note somewhere (cant remember where though) than the position you use is as if the no.1 monitor is the centre monitor in an imaginart monitor grid.
So in my case, 2nd monitor being on the left, the bottom left corner would be (-1024, 768) top right (0,0). Not so sure though Unsure | :~

Hope you understand Smile | :)

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Andy Smith27-Aug-02 9:55

Andy Smith

27-Aug-02 9:55

You should be able to get all the info you need about screen points from the System.Windows.Forms.Screen class

leppie27-Aug-02 11:30

27-Aug-02 11:30

hehe, maybe there Dead | X|

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Christian Graus27-Aug-02 12:06

Christian Graus

27-Aug-02 12:06

AK wrote:
If I need to do this with win32 api, what would be the function?

I presume you meant to ask this in the C++ forum ? If you're asking about C#, you don't need the API at all. Check out James' and my Code Project screensaver, it supports multimonitor in C#.

Christian

We're just observing the seasonal migration from VB to VC. Most of these birds will be killed by predators or will die of hunger. Only the best will survive - Tomasz Sowinski 29-07-2002 ( on the number of newbie posters in the VC forum )

Cats, and most other animals apart from mad cows can write fully functional vb code. - Simon Walton - 6-Aug-2002

Thanks

Alex Korchemniy27-Aug-02 14:58

Alex Korchemniy

27-Aug-02 14:58

What I basicly needed was to get the a form to show up on all the displays center on the screen. This is what I did:

1. Create a form for every screen.
2. Set the location of the form to the screen points (w/ offset to make it centered)
3. Assign all the events to the same event handler. (So all the forms are uniform)
4. Show all the forms.
5. When I get input from the form - all forms are closed.

Thanks for helping me out.

Cursor Blink Rate

Nnamdi Onyeyiri27-Aug-02 8:52

27-Aug-02 8:52

There is a setting in windows control panel that allows you to set how fast this happens, i wondered if anyone knew how to discover it, so i am not hard coding it.

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

Destructor problem

leppie27-Aug-02 7:55

27-Aug-02 7:55

Hi all,

I have implemented a destructor, and although the destructor gets called and I can step thru the functions, there is this one function that does not "respond". It gets called and returns, but does not do (it does nothing) what its meant to do. Frown | :(

I can however assign the same function to a button and it works without any problems.

~CD()
{
  this.Stop(); //this does not work correctly
  //clean up unmanged resources
  _Free(); // I know this gets called as the program exits correctly
}

Any suggestions? Confused | :confused:

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Michael Mac27-Aug-02 8:15

27-Aug-02 8:15

Maybe the resources which Stop function uses are freed before the function is called.

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leppie27-Aug-02 9:40

27-Aug-02 9:40

Nope, not it, I have tried calling the unmanaged dll directly with the same effect Frown | :(

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Michael Mac27-Aug-02 11:38

27-Aug-02 11:38

If you post Stop function's code it'll be simplier to come up with a solution. Smile | :)

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Michael Mac27-Aug-02 11:41

27-Aug-02 11:41

But first do what Nnamdi Onyeyiri advises.
I agree with him. WTF | :WTF:

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Nnamdi Onyeyiri27-Aug-02 21:15

27-Aug-02 21:15

Michael Mac wrote:
But first do what Nnamdi Onyeyiri advises.
I agree with him.

ahhh c'mon, i do know thing or two.

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

Michael Mac28-Aug-02 0:15

28-Aug-02 0:15

I meant I'm a WTF | :WTF:

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Nnamdi Onyeyiri27-Aug-02 8:49

27-Aug-02 8:49

try overriding the Dispose method, a wise person once told me this is a better way of doing it.

Suspicious | :suss: Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."

David Stone27-Aug-02 11:49

David Stone

27-Aug-02 11:49

I believe you may be referring to this man. Big Grin | :-D

David Stone

But Clinton wasn't a predictable, boring, aging, lying, eloquent, maintainer-of-the-status-quo. He was a predictable, boring-but-trying-to-look-hip, aging-and-fat-but-seemingly-oblivious-to-it, lying-but-in-sadly-blatant-ways, not-eloquent-but-trying-to-make-up-for-it-by-talking-even-more, bringer-in-of-scary-and-potentially-dangerous-new-policies. And there was also Al Gore. It just wasn't *right*.

Shog⁹

Nnamdi Onyeyiri27-Aug-02 11:51