Delphi ActiveX

HTTP GET -- Read Response from Stream

Demonstrates how to send an HTTP GET for a web page, and then read the response from a Stream. The purpose is to fulfill a situation such as the following: "I have a URL and just want the <head> </head> portion of the HTML. This would avoid having to download a potentially enormous web page just to get at header information, such as the <styles>."

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uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Integer;
rest: TChilkatRest;
url: TChilkatUrl;
bAutoReconnect: Integer;
responseStatusCode: Integer;
errResponse: WideString;
bodyStream: TChilkatStream;
readResponseBodyTask: IChilkatTask;
sbBody: TChilkatStringBuilder;
exitLoop: Integer;
bodyText: WideString;
maxWaitMs: Integer;

begin
success := 0;

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

rest := TChilkatRest.Create(Self);

// In this example, we'll get the web page at http://www.nytimes.com/pages/business/index.html
// The domain is "www.nytimes.com", and the path is "/pages/business/index.html"

// If we have only the full URL to begin with, it can be loaded into the Chilkat URL object to
// access the parts:
url := TChilkatUrl.Create(Self);
url.ParseUrl('http://www.nytimes.com/pages/business/index.html');

bAutoReconnect := 1;
success := rest.Connect(url.Host,url.Port,url.Ssl,bAutoReconnect);

// Send the GET request (This sends the GET request, but does not read the response.)
success := rest.SendReqNoBody('GET',url.Path);
if (success <> 1) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

// Read the response header.
responseStatusCode := rest.ReadResponseHeader();
if (responseStatusCode < 0) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

Memo1.Lines.Add('Response status code = ' + IntToStr(responseStatusCode));

// We expect a 200 response status.
if (responseStatusCode <> 200) then
  begin

    // If the response status code is not 200, we could check for a redirect status code and 
    // then follow it, read the entire response (as shown here), or just call rest.Disconnect
    errResponse := rest.ReadRespBodyString();
    if (rest.LastMethodSuccess <> 1) then
      begin
        Memo1.Lines.Add(rest.LastErrorText);
      end
    else
      begin
        Memo1.Lines.Add(errResponse);
      end;

    Exit;
  end;

bodyStream := TChilkatStream.Create(Self);
// Set a 10 second read timeout for the stream. 
// (Give up if no data arrives within 10 seconds after calling a read method.)
bodyStream.ReadTimeoutMs := 10000;

// Create a background thread task to read the response body (which feeds
// it to the bodyStream object.)
readResponseBodyTask := rest.ReadRespBodyStreamAsync(bodyStream.ControlInterface,1);

// Start the task. 
success := readResponseBodyTask.Run();

// Read the HTTP response body until the "</head>" is seen, or until
// the end-of-stream is reached.

sbBody := TChilkatStringBuilder.Create(Self);
exitLoop := 0;
while not exitLoop and (bodyStream.EndOfStream <> 1) do
  begin

    bodyText := bodyStream.ReadString();
    if (bodyStream.LastMethodSuccess = 1) then
      begin
        sbBody.Append(bodyText);
        if (sbBody.Contains('</head>',0)) then
          begin
            exitLoop := 1;
          end;
      end
    else
      begin
        exitLoop := 1;
      end;

  end;

// Cancel the remainder of the task...
readResponseBodyTask.Cancel();

// Ensure we're disconnected from the server.
maxWaitMs := 50;
rest.Disconnect(maxWaitMs);

Memo1.Lines.Add('----');
Memo1.Lines.Add(sbBody.GetAsString());
Memo1.Lines.Add('----');
Memo1.Lines.Add('Successfully received the body up to the desired point.');
end;