lnet TLTCPComponent not triggering receive event?
lazarus / 38-Networking and Web Programming

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Awesome Programmer · 2015-03-16 18:09

I don't understand why this is happening. I am using  lnet
TLTCPComponent to communicate through network connection. I have set
up its OnReceive event. However, it just won't fire when it receives
message back from another computer. What is going on?

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taazz · 2015-03-17 05:54

Quote from: reltek on March 16, 2015, 07:09:57 pm  I don't understand
why this is happening. I am using  lnet TLTCPComponent to communicate
through network connection. I have set up its OnReceive event.
However, it just won't fire when it receives message back from another
computer. What is going on?

WE will not understand either if you don provide something look at and
grind our teeth against. In general are you sure you are not using
localhost(127.0.0.1) as the listening address? do you set the
listening address correctly to start with?

In other news I prefer more other types of libraries so post some code
and people that use it will be able to tell you what is wrong with it.

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Awesome Programmer · 2015-03-17 19:27

Hi Taazz,

I wrote a test program to talk to a device connected to the Network.

I simply dropped the lnet TLTCPComponent on the form and did the
following.

Code: [Select]type
  TForm1 = class(TForm)
        net1:TLTCPComponent;
        Timer1:TTimer;   //Set for 30 milliseconds
        procedure FormCreate(Sender:TObject);
        procedure net1receive(aSocket:TLSocket);
        procedure Timer1Timer(Sender:TObject);
  private
  public
  end;

procedure TForm1.FormCreate(Sender:TObject);
begin
      Timer1.Interval := 30; //milliseconds
      net1.connect('192.168.1.31',10002);
      Timer1.Enabled := true;
end;

procedure TForm1.net1receive(aSocket:TLSocket);
var
     rbyte:array[0..3] of byte;
begin
     asocket.Get(rbyte, sizeof(rbyte));
end;

procedure TForm1.Timer1Timer(Sender:TObject);
var
bbyte: array[0..3] of byte;
begin
     bbyte[0] := $FF;
     bbyte[1] :=$01;
     bbyte[2] :=$03;

     net1.send(bbyte, sizeof(bbyte), net1.iterator);
end;

This demo program works as expected. It is able to send and receive
data, but when I do the same on an actual program I am working on or
developing I see NO RESPONSE at all from the device. I probed its
TCP/IP communication using wireshark. My pc is sending data but
nothing comes back and so the OnReceive doesn't see anything to
trigger on. What could be the difference between this demo code and my
other program especially when I am doing exactly the SAMETHING.

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taazz · 2015-03-18 03:19

it looks like its not a problem with lnet but with the external device
you are using. Things to try out.

1) make sure that the machine can accept multiple connection from the
same computer.
2) make sure that one and only one program connects to the machine.
3) make sure the machine is active and responsive (aka reset it).

And there my ideas end, I would need to have knowledge about the
external machine and its details before trying to make any assumption
of what might have gone wrong.

PS.
I know that you have probably done all of the above a couple of times
already but with out any farther knowledge I can't help and I doubt if
any one else can either.

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Awesome Programmer · 2015-03-25 15:38

Figured out why my receive event didn't trigger. I also use Synaser
for Serial communication along with lNet. Somehow they interfered with
each other. Once I made the serial and Network communication
selectable, it is working now.