Pascal (Lazarus/Delphi)

AWS S3 File Streaming Upload

See more Amazon S3 (new) Examples

Demonstrates how to do a streaming upload from a file to the AWS S3 storage service. The AWS authorization presents some difficulties when the REST request body is to be streamed from a file (or from some other source). The issue is that the SHA-256 hash of the file data must be calculated. There are only two possible ways to do this: (1) stream the file into memory in its entirety and calculate the SHA-256 hash prior to uploading, or (2) pre-calculate the SHA-256 in a streaming fashion, and then provide it to the AWS authentication object.

If the application does NOT pre-compute the SHA-256, then Chilkat (internally) is forced to stream into memory, calculate the SHA-256, and then upload from the in-memory copy of the file.

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.AuthAws,
  Chilkat.Rest,
  Chilkat.Stream,
  Chilkat.Crypt2;

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

procedure RunDemo;
var
  success: Boolean;
  crypt: TCrypt2;
  fileToUploadPath: string;
  hashStr: string;
  rest: TRest;
  bTls: Boolean;
  port: Integer;
  bAutoReconnect: Boolean;
  authAws: TAuthAws;
  fileStream: TStream;
  responseStr: string;

begin
  success := False;

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

  //  This first part is optional.  AWS authentication requires
  //  the SHA-256 hash of the request body (i.e. the contents of the file
  //  to be uploaded).  We can choose to pre-calculate the SHA-256 in a streaming fashion
  //  and then provide it to the authenticator object.  This way, if the file is
  //  extremely large, it never needs to completely reside in memory.
  crypt := TCrypt2.Create;
  crypt.EncodingMode := 'hex';
  crypt.HashAlgorithm := 'sha-256';
  fileToUploadPath := 'qa_data/xml/hamlet.xml';
  hashStr := crypt.HashFileENC(fileToUploadPath);

  rest := TRest.Create;

  //  Connect to the Amazon AWS REST server.
  bTls := True;
  port := 443;
  bAutoReconnect := True;
  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 := TAuthAws.Create;
  authAws.AccessKey := 'AWS_ACCESS_KEY';
  authAws.SecretKey := 'AWS_SECRET_KEY';
  authAws.ServiceName := 's3';
  //  Provide the pre-computed SHA-256 here:
  authAws.PrecomputedSha256 := hashStr;

  success := rest.SetAuthAws(authAws);

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

  fileStream := TStream.Create;
  fileStream.SourceFile := fileToUploadPath;

  //  Upload to the S3 Storage service.
  //  If the application provided the SHA-256 hash of the file contents (as shown above)
  //  then file is streamed and never has to completely reside in memory.
  //  If the application did NOT provide the SHA-256, then Chilkat will (internally) 
  //  load the entire file into memory, calculate the SHA-256, and then upload.
  responseStr := rest.FullRequestStream('PUT','/hamlet.xml',fileStream);
  if (rest.LastMethodSuccess <> True) 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 (rest.ResponseStatusCode = 200) then
    begin
      WriteLn(responseStr);
      WriteLn('File uploaded.');
    end
  else
    begin
      //  Examine the request/response to see what happened.
      WriteLn('response status code = ' + rest.ResponseStatusCode);
      WriteLn('response status text = ' + rest.ResponseStatusText);
      WriteLn('response header: ' + rest.ResponseHeader);
      WriteLn('response body: ' + responseStr);
      WriteLn('---');
      WriteLn('LastRequestStartLine: ' + rest.LastRequestStartLine);
      WriteLn('LastRequestHeader: ' + rest.LastRequestHeader);
    end;


  crypt.Free;
  rest.Free;
  authAws.Free;
  fileStream.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.