(Delphi DLL) Fetch S3 Object Metadata

Demonstrates how to get the metadata for an S3 object using the REST API.

The HEAD operation retrieves metadata from an object without returning the object itself. This operation is useful if you are interested only in an object's metadata. To use HEAD, you must have READ access to the object.

A HEAD request has the same options as a GET operation on an object. The response is identical to the GET response except that there is no response body.

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

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
rest: HCkRest;
bTls: Boolean;
port: Integer;
bAutoReconnect: Boolean;
success: Boolean;
authAws: HCkAuthAws;
responseStatusCode: Integer;
i: Integer;
numHeaders: Integer;
sbName: HCkStringBuilder;

begin
// 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 using the correct region (in this example, "us-west-2")
bTls := True;
port := 443;
bAutoReconnect := True;
success := CkRest_Connect(rest,'s3-us-west-2.amazonaws.com',port,bTls,bAutoReconnect);

// Provide AWS credentials for the REST call.
authAws := CkAuthAws_Create();
CkAuthAws_putAccessKey(authAws,'AWS_ACCESS_KEY');
CkAuthAws_putSecretKey(authAws,'AWS_SECRET_KEY');
CkAuthAws_putServiceName(authAws,'s3');
// Make sure the Region agrees with the region in the Connect.
CkAuthAws_putRegion(authAws,'us-west-2');
success := CkRest_SetAuthAws(rest,authAws);

// User-defined metadata are name/value pairs, and are returned in the HTTP response header.
// Metadata header names begin with "x-amz-meta-" to distinguish them from other HTTP headers.
// Note that Amazon S3 stores user-defined metadata keys in lowercase.

// Set the bucket name via the HOST header.
// In this case, the bucket name is "chilkat.ocean".
CkRest_putHost(rest,'chilkat.ocean.s3.amazonaws.com');

// Send the HEAD request.
success := CkRest_SendReqNoBody(rest,'HEAD','/seahorse.jpg');
if (success <> True) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

// Read the response header.
responseStatusCode := CkRest_ReadResponseHeader(rest);
if (responseStatusCode < 0) then
  begin
    Memo1.Lines.Add(CkRest__lastErrorText(rest));
    Exit;
  end;

Memo1.Lines.Add('Response status code = ' + IntToStr(responseStatusCode));
if (responseStatusCode <> 200) then
  begin
    Memo1.Lines.Add(CkRest__responseHeader(rest));
    Memo1.Lines.Add('Object does not exist.');
    Exit;
  end;

// Show the full response header that was received:
Memo1.Lines.Add('Response header:');
Memo1.Lines.Add(CkRest__responseHeader(rest));
Memo1.Lines.Add('--');

// Here is an example response header:

// 	x-amz-id-2: uS4Flff04M8x5YWajU231TP0ClBL19mMhuyfU5ZVQd6NsUHXVhHK+H3b0sjxY98Fujet1ejhyzk=
// 	x-amz-request-id: 27950009AA8E68AA
// 	Date: Mon, 23 Jan 2017 20:12:58 GMT
// 	Last-Modified: Fri, 20 Jan 2017 00:22:57 GMT
// 	ETag: "a8551f0a5437f43a796fca7623ee9232"
// 	x-amz-meta-species: big-belly seahorse
// 	x-amz-meta-genus: Hippocampus
// 	x-amz-meta-habitat: shallow tropical and temperate waters
// 	Accept-Ranges: bytes
// 	Content-Type: image/jpg
// 	Content-Length: 24388
// 	Server: AmazonS3

// Examine particular response headers (the object metadata headers..)
Memo1.Lines.Add('x-amz-meta-species: ' + CkRest__responseHdrByName(rest,'x-amz-meta-species'));
Memo1.Lines.Add('x-amz-meta-genus: ' + CkRest__responseHdrByName(rest,'x-amz-meta-genus'));
Memo1.Lines.Add('x-amz-meta-habitat: ' + CkRest__responseHdrByName(rest,'x-amz-meta-habitat'));
Memo1.Lines.Add('--');

// It is possible to iterate over the header fields to find all x-amz-meta* headers
i := 0;
numHeaders := CkRest_getNumResponseHeaders(rest);
sbName := CkStringBuilder_Create();
while i < numHeaders do
  begin
    CkStringBuilder_SetString(sbName,CkRest__responseHdrName(rest,i));
    if (CkStringBuilder_StartsWith(sbName,'x-amz-meta',False) = True) then
      begin
        Memo1.Lines.Add(CkStringBuilder__getAsString(sbName) + ': ' + CkRest__responseHdrValue(rest,i));
      end;
    i := i + 1;
  end;

// The output:

// 	x-amz-meta-species: big-belly seahorse
// 	x-amz-meta-genus: Hippocampus
// 	x-amz-meta-habitat: shallow tropical and temperate waters

CkRest_Dispose(rest);
CkAuthAws_Dispose(authAws);
CkStringBuilder_Dispose(sbName);

end;