Help with lNET OnReceive Event
lazarus / 38-Networking and Web Programming

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epergola · 2009-06-19 01:00

Hi

I have exhausted all searches possibles in vain, so I hope to find
some help here. (Found quite a bit on SendMessage, basically nothing
on Receive).
I have a Lazarus app that communicates via lnet ltcpcomponent with a
tcpserversocket (Delphi) on the LAN server.
The LTCP component is installed on an lnet_form (LTCP_Form), which is
used by several other forms to communicate with the server.
I want to do something like this:
The client app:
  Form1
    send_message_to_server(my specs)
    the servers returns data (pure string format)
    when  the entire response from the server is captured on the
    OnRececive event of the TLCP, fill up a grid in Form2,
    Form2.showmodal.
so i try to put a function in Form1, something like this:
  ret_string:= LTCP_Form.process(myspecs); //this should         
                           //sendmessage(myspecs) and return
                          //in ret_string the Result of ONReceive
  if ret_string <> '' then begin
    Form2.fillgrid(ret_string);
    form2showmodal;
  end;
I know (more or less) how to ensure that 'myspecs' is sent completely
in the  SendMessage on the TLCP_Form.
My problem is with: HOW do I know that  ret_string is the
complete message returned from the remote server?
In my test, it appears that ret_string is almost always still empty
at that point, because ON Receive has not been triggered yet.
How do I ensure that I get the WHOLE message retrieved by OnReceive
before I proceed with
  Form2.fillgrid()?
I had thought of making the process() function (inside TLCP_Form)
something like this:
   SendMessage (My specs);
   LTCPOnReceive;  // call the onreceive, which will go in loop until
                          // the entire message is red,and ONLY then
                          // the next linewill execute and returns
control
                         //  to Form1.
   Result := receive_message; //ok now return, make possible
                                        // Form2.fillgrid()
But I have 2 problems:
1.LTCPOnReceive takes an argument asocket. What can I pass as   
   asocket? The LTCPComponent does not have a 'asocket' member.
2.How do  I ensure that the OnReceive event does not terminate  
   until the WHOLE message from the remote server TCP server
   has been read (the messages from the server are all
   pure ascii strings terminating with 'END:'.
I would greatly appreciate any help.

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Michael · 2009-07-02 22:19

There is a limit to the size of the data that the socket will receive
at once, I don't know how large it is.  You will need to make sure
your OnReceive procedure appends its data to your buffer until you
find the 'END:' terminator indicating that the data transmission is
complete



Code: [Select]//this would be a sockets OnReceive procedure
procedure TfrmMain.tnSocketReceive(aSocket: TLSocket);
var
    sData: String;
begin

    if (tnSocket.GetMessage( sData ) > 0) then begin
        //check to see if the data chuck has the terminator
        If ContainsEndOfTransmission( sData ) then begin
            //if it does, we are done, append our last chuck and
process the global buffer
            CompleteTheTransfer( sData );
        end else begin
            //otherwise, keep appending data to the buffer
            AppendToTheBuffer( sData );
        end;
    end;
end;