LNET UDP send data stream problem
lazarus / 38-Networking and Web Programming

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MaartenJB · 2015-06-14 09:53

Hi, I've got a problem sending udp data from a stream with lnet udp.
I've made two examples, the first one is just sending an integer,
which works just fine. In the second one I place the Integer inside a
stream, when I send it, the data is not correct. (examening packets
with wireshark packet sniffer)

Working code:
Code: [Select]var
  TestInt : Integer;
  sHost : String;
begin
  sHost := '169.254.8.237';
  TestInt := 123456789;
  udpServer.Connect(sHost, 8888);
  udpServer.Send(TestInt, SizeOf(Integer), sHost);
  udpServer.Disconnect(False);
end;

Not working:
Code: [Select]var
  TestInt : Integer;
  sHost : String;
  TestStream : TMemoryStream;
begin
  sHost := '169.254.8.237';
  TestInt := 123456789;

  TestStream := TMemoryStream.Create;
  try
    TestStream.WriteBuffer(TestInt, SizeOf(Integer));
    TestStream.Position:=0;
    udpServer.Connect(sHost, 8888);
    udpServer.Send(TestStream, TestStream.Size, sHost);
    udpServer.Disconnect(False);
//    TestStream.SaveToFile('abc.bin'); // when I look in this saved
file, the data is fine
  finally
    TestStream.Free;
  end;
end; 

Do I need to do something else when sending a stream?

Thanks in advance,

Maarten

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benohb · 2015-06-15 15:04

TestStream is class .... not data


Code: [Select]TestStream.Memory

is pointer to first byte of data



Code: [Select]udpServer.Send(TestStream.Memory, TestStream.Size,
sHost);


Check 


Code:
[Select]writeln(Integer(TestStream.Memory^))TestStream.Position:=10;;
The result is TestInt Value

+ TestStream.Position:=0; not needed

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MaartenJB · 2015-06-15 19:20

Hi benohb,

Thanks for that valuable lesson! It's working now 

(I need to use the ^ sign when using udp.send() aswell, like the
writeln() example)

Thanks again!