ReceiveString Returns Only the Immediately Available Data

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Demonstrates that Socket.ReceiveString returns only the text immediately available and not the entire response. The example connects to chilkatsoft.com over TLS and requests big_helloWorld.txt, a large text file of roughly 74,000 lines. A single ReceiveString call returns just the first portion of the response, and the example reports how many characters were received compared with the total size given by the response Content-Length header.

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.StringBuilder,
  Chilkat.Socket;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  socket: TSocket;
  bTls: Boolean;
  maxWaitMs: Integer;
  httpReq: string;
  responseText: string;
  sb: TStringBuilder;
  contentLength: string;

begin
  success := False;

  socket := TSocket.Create;

  //  Connect to chilkatsoft.com over TLS.
  bTls := True;
  maxWaitMs := 5000;
  success := socket.Connect('chilkatsoft.com',443,bTls,maxWaitMs);
  if (success = False) then
    begin
      WriteLn(socket.LastErrorText);
      Exit;
    end;

  socket.StringCharset := 'utf-8';

  //  Send an HTTP GET request for big_helloWorld.txt, a large text file of roughly 74,000 lines of
  //  "Hello World!".  This uses a minimal HTTP request only to exercise ReceiveString against a public
  //  server -- for real HTTP work, use the Chilkat Http, Rest, or HttpCurl classes instead.
  httpReq := 'GET /big_helloWorld.txt HTTP/1.1' + #13#10 + 'Host: chilkatsoft.com' + #13#10 + 'Connection: close' + #13#10 + #13#10;
  success := socket.SendString(httpReq);
  if (success = False) then
    begin
      WriteLn(socket.LastErrorText);
      Exit;
    end;

  //  Call ReceiveString a single time.  It returns only the text that is immediately available --
  //  typically just the first network packet -- and does NOT wait for the entire response to arrive.
  responseText := socket.ReceiveString();
  if (socket.LastMethodSuccess = False) then
    begin
      WriteLn(socket.LastErrorText);
      Exit;
    end;

  //  Load the received text into a StringBuilder so its length can be measured and the Content-Length
  //  header extracted.  The Content-Length header gives the total size, in bytes, of the response body.
  sb := TStringBuilder.Create;
  sb.Append(responseText);
  contentLength := sb.GetBetween('Content-Length: ',#13#10);
  if (sb.LastMethodSuccess = False) then
    begin
      WriteLn(sb.LastErrorText);
      Exit;
    end;

  //  Compare what this single ReceiveString returned against the full size of the expected response.
  //  The received amount is only a small fraction of the total.
  WriteLn('Characters received so far (headers + partial body): ' + sb.Length);
  WriteLn('Expected response body size (Content-Length): ' + contentLength + ' bytes');

  //  A single ReceiveString call returns whatever is currently available, so it cannot indicate whether
  //  the full response has arrived.  This makes it difficult to know when a response is complete: the
  //  application must either know how many bytes to expect (for example from a Content-Length header or
  //  an application-defined length prefix) and keep receiving until that many bytes are collected, or
  //  keep receiving until the peer closes the connection.


  socket.Free;
  sb.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.