TwSocket Udp Client how to receive Bytes Properly ?

[Skullcode 0]

i use Twsocket as udp Client that is communicating with udpserver 

 

the server sends data in Bytes and the client should Receive This Data in Bytes as well

 

i have tried the following based on what i see in the Demo Sample of OverbyteIcsUdpLstn Demo

 

procedure TMainForm.WSocketDataAvailable(Sender: TObject; Error: Word);
var
aBytes : Tbytes;
begin
wsocket.Receive(aBytes, length(aBytes));
//...
end;

 but this freezes the application and immediately crashed

[Lajos Juhász 293]

First you've to initialize aBytes. Try something like this:

 

setLength(aBytes, 1024);

wsocket.Receive(aBytes, length(aBytes));

 

 

[FPiette 383]

Response of Lajos is correct.

But anyway, it is better to use a fixed size array as buffer to avoid allocation freeing a dynamic array as each data packet is coming. So write something like this instead:

procedure TMainForm.WSocketDataAvailable(Sender: TObject; Error: Word);
const
    BUF_SIZE = 1000; // Or whatever size fits your needs
var
    ABytes : array [0..BUF_SIZE] of bytes;
    Len    : Integer;
begin
    Len := WSocket.Receive(@ABytes[0], BUF_SIZE);
    if Len = 0 then
        Exit;
    if Len < 0 then begin
        ShowMessage('Error receiving data');
        Exit;
    end;
    // Process data...
end;

 

Edited November 20, 2020 by FPiette

[aehimself 396]

Just a small heads-up; binary transfer requires different handling than text. See

 

 

 

Edited November 23, 2020 by aehimself

[Angus Robertson 574]

The onDataAvailable event has knowledge of the data being received, unless you set LineMode to true, you just read all data into a buffer and process it later.  If binary data is not received, that is an application error. 

 

Angus