(Delphi ActiveX) REST Follow Redirects

Demonstrates how to follow a 302/303 redirect response.

Chilkat for Delphi Downloads Chilkat ActiveX DLL for Delphi Chilkat non-ActiveX DLL for Delphi * The examples here use the ActiveX DLL.

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
rest: TChilkatRest;
bTls: Integer;
port: Integer;
bAutoReconnect: Integer;
success: Integer;
responseText: WideString;
statusCode: Integer;
redirectUrl: IChilkatUrl;

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

rest := TChilkatRest.Create(Self);

bTls := 1;
port := 443;
bAutoReconnect := 1;
success := rest.Connect('chilkatsoft.com',port,bTls,bAutoReconnect);
if (success <> 1) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

// Send a POST to a URL that will respond with a 302 redirect..
rest.AddQueryParam('firstName','John');
rest.AddQueryParam('lastName','Doe');
responseText := rest.FullRequestFormUrlEncoded('POST','/echoPost302.asp');
if (rest.LastMethodSuccess <> 1) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

statusCode := rest.ResponseStatusCode;

// Examine the response status code
if (statusCode < 300) then
  begin
    Memo1.Lines.Add('Not a redirect.');
    Memo1.Lines.Add(responseText);
    Exit;
  end;

if (statusCode > 399) then
  begin
    Memo1.Lines.Add('Error response: Status code = ' + IntToStr(statusCode));
    Memo1.Lines.Add(responseText);
    Exit;
  end;

Memo1.Lines.Add('Redirect status code = ' + IntToStr(statusCode));

// The response header will contain a Location field with the redirect URL, such as this:
// Location: http://www.chilkatsoft.com/echoPostFinal.asp

// The response status code determines how the client should behave.
// Here are some common possibilities:

// 301: Moved Permanently
// This and all future requests should be directed to the given URI.  (Keep the original HTTP method for the redirect.  In this case, the 
// original request was a POST, so we POST to the redirect URL.)

// 302: Found (aka Object Moved aka Moved Temporarily)
// This is the most popular redirect code, but also an example of industrial practice contradicting the standard. HTTP/1.0 specification (RFC 1945 ) required the client
// to perform a temporary redirect (the original describing phrase was �Moved Temporarily�), but popular browsers implemented it as a 303 See Other. Therefore, HTTP/1.1
// added status codes 303 and 307 to disambiguate between the two behaviors. However, the majority of Web applications and frameworks still use the 302 status code
// as if it were the 303.

// 303: See Other
// The response to the request can be found under another URI using a GET method. When received in response to a PUT, it should be assumed that the server has
// received the data and the redirect should be issued with a separate GET message.

// 307: Temporary Redirect
// In this occasion, the request should be repeated with another URI, but future requests can still use the original URI. In contrast to 303, the request method
// should not be changed when reissuing the original request. For instance, a POST request must be repeated using another POST request.

Memo1.Lines.Add(rest.ResponseHeader);

redirectUrl := rest.RedirectUrl();
if (rest.LastMethodSuccess = 0) then
  begin
    Memo1.Lines.Add('No Location header found for redirect.');
    Exit;
  end;

// Prep for the redirect..
rest.ClearAllParts();

// Disconnect and re-connect.  
// (This can be skipped if both the host and SSL/TLS conditions are the same.)
rest.Disconnect(100);
success := rest.Connect(redirectUrl.Host,redirectUrl.Port,redirectUrl.Ssl,bAutoReconnect);
if (success <> 1) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

if ((statusCode = 301) or (statusCode = 307)) then
  begin
    // Redirect using a POST, sending the same params to the new destination
    rest.AddQueryParam('firstName','John');
    rest.AddQueryParam('lastName','Doe');
    responseText := rest.FullRequestFormUrlEncoded('POST',redirectUrl.Path);
    if (rest.LastMethodSuccess <> 1) then
      begin
        Memo1.Lines.Add(rest.LastErrorText);
        Exit;
      end;
  end;

if ((statusCode = 302) or (statusCode = 303)) then
  begin
    // Redirect using a GET, sending the query params found in the redirect URL.
    responseText := rest.FullRequestFormUrlEncoded('GET',redirectUrl.PathWithQueryParams);
    if (rest.LastMethodSuccess <> 1) then
      begin
        Memo1.Lines.Add(rest.LastErrorText);
        Exit;
      end;
  end;

// Show the final status code and the response text.
Memo1.Lines.Add('Final status code = ' + IntToStr(rest.ResponseStatusCode));

Memo1.Lines.Add('Final response text (HTML, XML, JSON, or whatever..)');
Memo1.Lines.Add(responseText);
end;