(Delphi ActiveX) REST Read Response with Stream API

Demonstrates how to make a REST call that returns a binary body, and to receive the body through a stream API.

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;
authAws: TChilkatAuthAws;
responseStatusCode: Integer;
errResponse: WideString;
bodyStream: TChilkatStream;
readResponseBodyTask: IChilkatTask;
nextChunk: Array of Byte;

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

rest := TChilkatRest.Create(Self);

// Connect to the Amazon AWS REST server.
bTls := 1;
port := 443;
bAutoReconnect := 1;
success := rest.Connect('s3.amazonaws.com',port,bTls,bAutoReconnect);

// ----------------------------------------------------------------------------
// Important: For buckets created in regions outside us-east-1,
// there are three important changes that need to be made.
// See Working with S3 Buckets in Non-us-east-1 Regions for the details.
// ----------------------------------------------------------------------------

// Provide AWS credentials for the REST call.
authAws := TChilkatAuthAws.Create(Self);
authAws.AccessKey := 'AWS_ACCESS_KEY';
authAws.SecretKey := 'AWS_SECRET_KEY';
authAws.ServiceName := 's3';
success := rest.SetAuthAws(authAws.ControlInterface);

// Set the bucket name via the HOST header.
// In this case, the bucket name is "chilkat100".
rest.Host := 'chilkat100.s3.amazonaws.com';

// Send the request to download the JPG.
success := rest.SendReqNoBody('GET','/starfish.jpg');
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 the JPG data is coming.
// Otherwise, we'll get a string response body with an error message(or no response body).
if (responseStatusCode <> 200) then
  begin
    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();

// The application can now read the bodyStream...
while (bodyStream.EndOfStream <> 1) do
  begin

    // Read the next chunk of bytes (whatever is immediately available,
    // or wait for more data (up to 10 seconds because we set the stream's ReadTimeoutMs property)
    nextChunk := bodyStream.ReadBytes();
    if (bodyStream.LastMethodSuccess <> 1) then
      begin
        Memo1.Lines.Add('Failed to receive more response data.');
        // Make sure the background task is aborted/cancelled.
        success := readResponseBodyTask.Cancel();

        Exit;
      end;

    // OK.. the app has the next chunk of the body, and may do whatever it wishes with it...
  end;

Memo1.Lines.Add('Successfully received the entire response body.');
end;