Loss message in Socket Async mode

[rockdale]

Hi, all

Did not find a .Net Communication forum to post.

I am soing a client/server message system and using C#.net socket and
Async mode.

Pretty much as described in article

http://www.developerfusion.co.uk/show/3997/3/

But I have a big issue with this approach and I am not what did I do
wrong.

the client send message so quick that when I loss the second message.

I need to call endReceive in my Callback function and process the first
message, now the second message is arrived and since I have not call
beginReceive, then, I loss the second message.

Am I doing wrong or is that unavoidable?

Thanks in advance
-rockdale




--------------------------------------------------------------
source code from the article is attached.
byte[] m_DataBuffer = new byte [1024];
IAsyncResult m_asynResult;
public AsyncCallback pfnCallBack ;
public Socket m_socClient;
// create the socket...
public void OnConnect()
{
m_socClient = new Socket
(AddressFamily.InterNetwork,SocketType.Stream ,ProtocolType.Tcp );
// get the remote IP address...
IPAddress ip = IPAddress.Parse ("10.10.120.122");
int iPortNo = 8221;
//create the end point
IPEndPoint ipEnd = new IPEndPoint (ip.Address,iPortNo);
//connect to the remote host...
m_socClient.Connect ( ipEnd );
//watch for data ( asynchronously )...
WaitForData();
}
public void WaitForData()
{
if ( pfnCallBack == null )
pfnCallBack = new AsyncCallback (OnDataReceived);
// now start to listen for any data...
m_asynResult =
m_socClient.BeginReceive
(m_DataBuffer,0,m_DataBuffer.Length,SocketFlags.None,pfnCallBack,null);
}
public void OnDataReceived(IAsyncResult asyn)
{
//end receive...
int iRx = 0 ;
iRx = m_socClient.EndReceive (asyn);
char[] chars = new char[iRx + 1];
System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
int charLen = d.GetChars(m_DataBuffer, 0, iRx, chars, 0);
System.String szData = new System.String(chars);
WaitForData();
}

 

[Peter Duniho]

[...]
But I have a big issue with this approach and I am not what did I do
wrong.

the client send message so quick that when I loss the second message.

I need to call endReceive in my Callback function and process the first
message, now the second message is arrived and since I have not call
beginReceive, then, I loss the second message.

Am I doing wrong or is that unavoidable?

It's not only not unavoidable, it's impossible. When you are using TCP,
delivery of the data, in the correct order, is guaranteed unless some error
occurs on the network connection.

I think it's more likely that you don't understand that TCP doesn't know
anything about "messages". This is probably the number one mistake people
new to network programming make, especially those who haven't read the
documentation carefully.

TCP is a byte stream. You put bytes in one end, they come out the other.
There is no guarantee that the bytes will be "chunked" in the same
arrangement when receiving as they were when sending. They will always be
in the correct order, but the divisions between the groups of data may be in
different places, or removed altogether, or it may even happen that new
divisions are inserted.

In your case, probably the first and second transmissions are being combined
into a single transmission before being sent. Then your receiving code
receives them both at the same time. Given that I see nothing in your
receiving code that attempts to figure out where one ends and the next
starts, this seems especially likely to me.

Pete

 

[rockdale]

Thanks for the reply and sorry for the double posts.

Yes, I am very new to network programming. And the problem I have is
exactly what you suspected. I read the bytes based on my msg size
(stored in the 8th byte in my message header) and then I stopped, I
should continue to read the rest bytes since the second message is just
followed as you said.

Thanks
-rockdale

[...]
But I have a big issue with this approach and I am not what did I do
wrong.

the client send message so quick that when I loss the second message.

I need to call endReceive in my Callback function and process the first
message, now the second message is arrived and since I have not call
beginReceive, then, I loss the second message.

Am I doing wrong or is that unavoidable?

It's not only not unavoidable, it's impossible. When you are using TCP,
delivery of the data, in the correct order, is guaranteed unless some error
occurs on the network connection.

I think it's more likely that you don't understand that TCP doesn't know
anything about "messages". This is probably the number one mistake people
new to network programming make, especially those who haven't read the
documentation carefully.

TCP is a byte stream. You put bytes in one end, they come out the other.
There is no guarantee that the bytes will be "chunked" in the same
arrangement when receiving as they were when sending. They will always be
in the correct order, but the divisions between the groups of data may be in
different places, or removed altogether, or it may even happen that new
divisions are inserted.

In your case, probably the first and second transmissions are being combined
into a single transmission before being sent. Then your receiving code
receives them both at the same time. Given that I see nothing in your
receiving code that attempts to figure out where one ends and the next
starts, this seems especially likely to me.

Pete