Pascal (Lazarus/Delphi)

S3 Get Object Metadata, such as ETag

See more Amazon S3 (new) Examples

Demonstrates how to get an S3 object's metadata using a HEAD request. Pascal (Lazarus/Delphi)

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.Rest,
  Chilkat.AuthAws;

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

procedure RunDemo;
var
  success: Boolean;
  rest: TRest;
  bTls: Boolean;
  port: Integer;
  bAutoReconnect: Boolean;
  authAws: TAuthAws;
  statusCode: Integer;
  etag: string;

begin
  success := False;

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

  rest := TRest.Create;

  //  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 := True;
  port := 443;
  bAutoReconnect := True;
  success := rest.Connect('s3-us-west-2.amazonaws.com',port,bTls,bAutoReconnect);

  //  Provide AWS credentials.
  authAws := TAuthAws.Create;
  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);

  //  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 <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  Now get the response header.
  statusCode := rest.ReadResponseHeader();
  if (statusCode < 0) then
    begin
      WriteLn(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.
      WriteLn('response status code = ' + statusCode);
      WriteLn('response status text = ' + rest.ResponseStatusText);
      WriteLn('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');
  WriteLn('ETag: ' + etag);


  rest.Free;
  authAws.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.