Ultimate++ Components Files

Ftp class is a U++ client side implementation of the File Transfer Protocol (FTP) as specified in RFC 959, with several advanced capabilities: 

- Support for IPv6 and NATs, as specified in RFC 2428.
- Support for ftp over TLS/SSL (FTPS), as specified in RFC 2228.
- Support for feature negotiation mechanism as specifien in RFC 2389.
- Support for multithreading, using worker threads. 
- Support for parsing UNIX and DOS style directory listings.
- Support for extending the functionality of Ftp class, using the low-level SendCommand() method.
- Support for transfer restart (resume) mechanism, as specified in RFC 3959.

ToDo:
--------
- Proxy support (using NetworkProxy).
- Refactoring and optimization of FtpAsyncIO.

History:
--------
(13-07-2017):   Ftp package, version 1.2.1.
                Transfer restart mechanism fixed. It now properly handles failed or aborted transfer.
(02-06-2017):   REST and APPE commands are implemented. See RFC 3659 for more informations.
                Accordingly, Ftp::Append(), Ftp::Restart(), Ftp::GetRestartPos(), Ftp:Request::Restart(), 
                Ftp::Request::DeleteFailed(), and Ftp::Result::IsRestarted() methods are added. 
                It is now possible to restart a failed transfer.             
(01-06-2017):   GetSize() method is added to Ftp class.
(21-04-2017):   Ftp::Request::UserData() and Ftp::Result::GetUserData() methods are added. 
                These methods allow passing user data/messages through worker threads a convenient way.
                Ftp::Request::Priority() method implemented. This method allows user to pre-set a priority level for given worker thread.
(17-04-2017):   FtpAsyncIO and related helper functions refactored. Ftp threads are limited to max 256 slots per process.
(16-04-2017):   Ftp::DirEntry further refactored. Directory listing parser moved to DirEntry::Parser() function.
                Multithreaded convenience functions now check whether the MT infrastructure is available.
                Accordingly ifdef/define preprocessor commands to check MT are removed.
(15-04-2017):   Ftp::DirEntry now properly handles pathnames with whitespaces.
(14-04-2017):   NAMESPACE_UPP and END_UPP_NAMESPACE macros removed.
                Ftp convenience functions are re-written, using an objective approach. (Sugggested by Klugier)
                As a result, two new helper class added to the package: Ftp::Request and Ftp::Result.
                Ftp:DirEnty refactored.
                Possible race condition in AbortWorker() is fixed.
(12-04-2017):   FTP package, version 1.1 
                GetFeatures() method is added. Thıs method implements the FEAT command. See RFC 2389 for details.
(09-04-2017):   FtpAsyncIO: Data buffer size used by FileStream is set to 5 MB (default was 4k) in order to reduce  disk I/O.
                Ftp[Async]Put/Get methods' parameter list order changed.  
(07-04-2017):   FTP package, version 1.0 
                This version brings concurrent file transfers, using Upp's multithreading infrastructure.
(04-04-2017):   FtpAsyncGet() and FtpAsyncPut() convenience functions are added to the package.
                These helper functions simplify asynchronous file transfers while retaining the flexibility and features of Ftp class.
                Slight API changes for better integration with GUI apps. Ftp::Type (ASCII|BINARY) and Ftp::Mode (PASSIVE|ACTIVE) enums made private.
                (See Get() and Put() documentation for API changes.)
                Documentation updated accordingly.
(02-04-2017):   Fixed Ftp::TransferData(): The server reply for failed transfers is now properly handled.
                Control connection now checks if the socket is open.
(06-03-2017):   Ftp package, version 0.9 
                GetReplyAsXml() method is added. This method simplifies the parsing of FTP protocol messages and internal messages.
(30-01-2017):   From now on FTP package requires at least C++11.
(20-01-2015):   Fixed Active mode IPV6 data connection. Improved FTPS. From now on, Ftp class supports also TLS. (As long as it is supported by U++ Core/SSL package)
(07-01-2015):   Ftp package, version 0.8
                Added basic FTPS (SSL) support. FTPS is limited to passive mode connections and can only be invoked per ftp session (latter is a security measure).
(29-12-2014):   Possible namspace clash fixed (Thanks Klugier!).
(25-12-2014):   Ftp package, version 0.7
                FtpGet() and FtpPut() convenience functions are added to the package. These helper functions simplify ftp transfers while retaining flexibility and features of Ftp class.
(24-12-2014):   Complete rewrite of Ftp class. (API breakage). 
                Ftp class from now on supports IPv6 and adjustable data chunk size. 
                Abort() sequence is refined.
(12-05-2014):   Fixed DecodePath() method and download/upload start marker code 125 is now properly handled.
(08-05-2014):   Added Noop() method. Useful for keeping connections alive.
(07-05-2014):   This is the first public beta.