Delphi ActiveX

Receive a 4-byte Length Prefix from a Socket

Demonstrates Socket.ReceiveCount, which reads a four-byte length prefix as a signed 32-bit integer. A return value of -1 indicates failure.

Background. Reading the length prefix first tells the application exactly how many bytes to read for the message body, which is a reliable way to know when a full message has arrived.

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var
success: Integer;
socket: TChilkatSocket;
bTls: Integer;
maxWaitMs: Integer;
messageLength: Integer;

begin
success := 0;

socket := TChilkatSocket.Create(Self);

//  Connect to the server using TLS.
bTls := 1;
maxWaitMs := 5000;
success := socket.Connect('example.com',5000,bTls,maxWaitMs);
if (success = 0) then
  begin
    Memo1.Lines.Add(socket.LastErrorText);
    Exit;
  end;

//  Read a four-byte length prefix as a signed 32-bit integer (network byte order by default).  A
//  return value of -1 indicates failure.
messageLength := socket.ReceiveCount();
if (messageLength < 0) then
  begin
    Memo1.Lines.Add(socket.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('The peer will send ' + IntToStr(messageLength) + ' bytes.');