(Delphi ActiveX) S3 Get Object Metadata, such as ETag

Demonstrates how to get an S3 object's metadata using a HEAD request.

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;
statusCode: Integer;
etag: WideString;

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 in the desired region.
// In this case we connect to S3 in the "us-west-2" region.
bTls := 1;
port := 443;
bAutoReconnect := 1;
success := rest.Connect('s3-us-west-2.amazonaws.com',port,bTls,bAutoReconnect);

// Provide AWS credentials.
authAws := TChilkatAuthAws.Create(Self);
authAws.AccessKey := 'AWS_ACCESS_KEY';
authAws.SecretKey := 'AWS_SECRET_KEY';
authAws.ServiceName := 's3';

// This particular bucket is in the Oregon region, as opposed to the US Standard,
// therefore the Region must be set appropriately.
// Also note that we connected to "s3-us-west-2.amazonaws.com".
authAws.Region := 'us-west-2';

success := rest.SetAuthAws(authAws.ControlInterface);

// Note: The above REST connection and setup of the AWS credentials
// can be done once.  After connecting, any number of REST calls can be made.
// The "auto reconnect" property passed to rest.Connect indicates that if
// the connection is lost, a REST method call will automatically reconnect
// if needed.
// --------------------------------------------------------------------------

// Set the bucket name via the HOST header.
// In this case, the bucket name is "chilkat.ocean".
// Note that the Host header should use "bucketName.s3.amazonaws.com", not "bucketName.s3-us-west-2.amazonaws.com"
rest.Host := 'chilkat.ocean.s3.amazonaws.com';

// Our object is "starfish.jpg".
// Get the metadata.
// Since we are sending a HEAD request, we shouldn't use any of the Full* methods.
// Instead, send the request, then just read the response header.
success := rest.SendReqNoBody('HEAD','/starfish.jpg');
if (success <> 1) then
  begin
    Memo1.Lines.Add(rest.LastErrorText);
    Exit;
  end;

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

// When successful, the S3 Storage service will respond with a 200 response code,
// with an XML body.  
if (statusCode <> 200) then
  begin
    // Examine the request/response to see what happened.
    Memo1.Lines.Add('response status code = ' + IntToStr(statusCode));
    Memo1.Lines.Add('response status text = ' + rest.ResponseStatusText);
    Memo1.Lines.Add('response header: ' + rest.ResponseHeader);
    Exit;
  end;

// The response header contains information about the S3 object.
// For example:

// 	HTTP/1.1 200 OK
// 	x-amz-id-2: GrV/hrB2EUkBlWc0h3JDdmVIrYDXfPC7CGvo/qSVRmYRPwilAOry8+4r2YWl4xJfa1HRYXrP808=
// 	x-amz-request-id: 4BDC6D6AEA0BDEF3
// 	Date: Mon, 13 May 2019 22:03:13 GMT
// 	Last-Modified: Mon, 10 Nov 2014 16:10:23 GMT
// 	ETag: "2e9c59dbf2662367dc97dfdda85da048"
// 	Accept-Ranges: bytes
// 	Content-Type: image/jpg
// 	Content-Length: 6229
// 	Server: AmazonS3

// Get the ETag response header value:
etag := rest.ResponseHdrByName('ETag');
Memo1.Lines.Add('ETag: ' + etag);
end;