Lazarus Pascal

Fetch a Chunk of Messages, Tracking Failures

Demonstrates the Chilkat Imap.FetchChunk2 method, which downloads a run of messages by sequence number and reports which succeeded and which failed. The arguments are the starting sequence number, the count, a MessageSet that receives the failed IDs, a MessageSet that receives the successfully-fetched IDs, and the EmailBundle. This example fetches the first chunk of messages and reports the success and failure counts.

Background: When bulk-downloading a large mailbox, individual messages can occasionally fail to fetch (a corrupt message on the server, a transient error) without failing the whole operation. FetchChunk2 is designed for that reality: it returns a partial EmailBundle plus two MessageSet objects so your code can log or retry exactly the messages that did not come through, rather than aborting the entire sync.

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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.EmailBundle,
  Chilkat.Imap,
  Chilkat.MessageSet;

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

procedure RunDemo;
var
  success: Boolean;
  imap: TImap;
  numMessages: Integer;
  count: Integer;
  failedSet: TMessageSet;
  fetchedSet: TMessageSet;
  bundle: TEmailBundle;

begin
  success := False;

  //  Demonstrates the Imap.FetchChunk2 method, which downloads a run of messages by sequence
  //  number and reports which succeeded and which failed.  The 1st argument is the starting
  //  sequence number, the 2nd is the count, the 3rd receives the failed IDs, the 4th receives
  //  the successfully-fetched IDs, and the 5th is the EmailBundle.

  imap := TImap.Create;

  imap.Ssl := True;
  imap.Port := 993;

  success := imap.Connect('imap.example.com');
  if (success = False) then
    begin
      WriteLn(imap.LastErrorText);
      Exit;
    end;
  success := imap.Login('user@example.com','myPassword');
  if (success = False) then
    begin
      WriteLn(imap.LastErrorText);
      Exit;
    end;

  numMessages := imap.SelectMailbox('Inbox');
  if (numMessages < 0) then
    begin
      WriteLn(imap.LastErrorText);
      Exit;
    end;

  //  Fetch messages 1..25 (or fewer if the mailbox is smaller).
  count := 25;
  if (count > numMessages) then
    begin
      count := numMessages;
    end;

  failedSet := TMessageSet.Create;
  fetchedSet := TMessageSet.Create;
  bundle := TEmailBundle.Create;
  success := imap.FetchChunk2(1,count,failedSet,fetchedSet,bundle);
  if (success = False) then
    begin
      WriteLn(imap.LastErrorText);
      Exit;
    end;

  WriteLn('Fetched: ' + fetchedSet.Count);
  WriteLn('Failed:  ' + failedSet.Count);

  success := imap.Disconnect();
  if (success = False) then
    begin
      WriteLn(imap.LastErrorText);
      Exit;
    end;


  imap.Free;
  failedSet.Free;
  fetchedSet.Free;
  bundle.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.