Pascal (Lazarus/Delphi)

Streaming Download Large File to the Local Filesystem

See more Azure Cloud Storage Examples

Downloads a large file in a streaming fashion to the local filesystem. 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.AuthAzureStorage,
  Chilkat.Stream;

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

procedure RunDemo;
var
  success: Boolean;
  rest: TRest;
  bTls: Boolean;
  port: Integer;
  bAutoReconnect: Boolean;
  azAuth: TAuthAzureStorage;
  responseStatusCode: Integer;
  bodyStream: TStream;
  errResponse: string;

begin
  success := False;

  //  Azure File Service Example: Downloads a large file to the local filesystem using a Chilkat stream.
  //  See:  https://docs.microsoft.com/en-us/rest/api/storageservices/get-file

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

  rest := TRest.Create;

  //  Connect to the Azure Storage Blob Service
  bTls := True;
  port := 443;
  bAutoReconnect := True;
  //  In this example, the storage account name is "chilkat".
  success := rest.Connect('chilkat.file.core.windows.net',port,bTls,bAutoReconnect);
  if (success <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  Provide Azure Cloud credentials for the REST calls.
  azAuth := TAuthAzureStorage.Create;
  azAuth.AccessKey := 'AZURE_ACCESS_KEY';
  //  The account name used here should match the 1st part of the domain passed in the call to Connect (above).
  azAuth.Account := 'chilkat';
  azAuth.Scheme := 'SharedKey';
  azAuth.Service := 'File';
  //  This causes the "x-ms-version: 2021-08-06" header to be automatically added.
  azAuth.XMsVersion := '2021-08-06';
  success := rest.SetAuthAzureStorage(azAuth);

  //  Note: The application does not need to explicitly set the following
  //  headers: x-ms-date, Authorization.  These headers
  //  are automatically set by Chilkat.

  //  When streaming a download to the local filesystem or directed elsewhere,
  //  the complete HTTP GET operation must be broken into parts.
  //  For example, an HTTP GET consists of sending the request, followed by reading the response header,
  //  and then finally the response body.  We'll want to read the response header, and then based
  //  on the information received (such as success or failure), either read the response body
  //  as an error message, or as the file data.

  //  Send the HTTP GET request to download the file.
  //  The share is named "pip".
  success := rest.SendReqNoBody('GET','/pip/somethingBig.zip');
  if (success <> True) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  //  Read the response header.
  responseStatusCode := rest.ReadResponseHeader();
  if (responseStatusCode < 0) then
    begin
      WriteLn(rest.LastErrorText);
      Exit;
    end;

  WriteLn('Response status code = ' + responseStatusCode);

  //  We expect a 200 response status if the file data is coming.
  //  Otherwise, we'll get a string response body with an error message(or no response body).
  if (responseStatusCode = 200) then
    begin

      bodyStream := TStream.Create;

      //  The stream's sink will be a file.
      bodyStream.SinkFile := 'qa_output/somethingBig.zip';

      //  Read the response body to the stream.  Given that we've
      //  set the stream's sink to a file, it will stream directly
      //  to the file.
      success := rest.ReadRespBodyStream(bodyStream,True);
      if (success <> True) then
        begin
          WriteLn(rest.LastErrorText);
          Exit;
        end;

      WriteLn('Successfully received the large file.');

    end
  else
    begin
      errResponse := rest.ReadRespBodyString();
      if (rest.LastMethodSuccess <> True) then
        begin
          WriteLn(rest.LastErrorText);
        end
      else
        begin
          WriteLn(errResponse);
        end;
    end;


  rest.Free;
  azAuth.Free;
      bodyStream.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.