Delphi DLL

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. Delphi DLL

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
rest: HCkRest;
bTls: Boolean;
port: Integer;
bAutoReconnect: Boolean;
authAws: HCkAuthAws;
statusCode: Integer;
etag: PWideChar;

begin
success := False;

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

rest := CkRest_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 := CkRest_Connect(rest,'s3-us-west-2.amazonaws.com',port,bTls,bAutoReconnect);

// Provide AWS credentials.
authAws := CkAuthAws_Create();
CkAuthAws_putAccessKey(authAws,'AWS_ACCESS_KEY');
CkAuthAws_putSecretKey(authAws,'AWS_SECRET_KEY');
CkAuthAws_putServiceName(authAws,'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".
CkAuthAws_putRegion(authAws,'us-west-2');

success := CkRest_SetAuthAws(rest,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"
CkRest_putHost(rest,'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 := CkRest_SendReqNoBody(rest,'HEAD','/starfish.jpg');
if (success <> True) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

// Now get the response header.
statusCode := CkRest_ReadResponseHeader(rest);
if (statusCode < 0) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    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 = ' + CkRest__responseStatusText(rest));
    Memo1.Lines.Add('response header: ' + CkRest__responseHeader(rest));
    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 := CkRest__responseHdrByName(rest,'ETag');
Memo1.Lines.Add('ETag: ' + etag);

CkRest_Dispose(rest);
CkAuthAws_Dispose(authAws);

end;