CHEN Yule 2018011660 28th, Oct.

An FTP server written in C and running with GNU/Linux.

GCC version: 9.3.0

USER, PASS, RETR, STOR, QUIT, SYST, TYPE, PORT, PASV, MKD, CWD, PWD, LIST, RMD, RNFR, RNTO, SIZE and REST.

• Invalid command line arguments when starting the server.
• FTP commands' syntax errors in parameters or arguments.
• Those exceptions occurring when calling those socket APIs, like socket(), listen(), bind(), accept(), and so on.

The server adopts multiple processes to manage multiple processes. Parent process keeps listening for incoming connections, until it is forced to terminate. Every time a new client requests to connect, parent process forks a new child process to deal with this client. A child process will terminate when it receives a QUIT command.

When receiving a REST command, the server would set a breakpoint for the next file transfer. Upon receiving next RETR / STOR command, the server would resume transmission from the breakpoint.

• Upon receiving a PASV command, the server requires the client to establish a data connection immediately, before the following RETR / STOR commands.
• When sending or receiving files in response to RETR and STOR commands from a client, the server ignores all control commands (including QUIT) from that particular client until the data connection is completed.
• It's not suggested to name directories and files using special characters like spaces. If so, FTP commands about these directories and files are more likely to be rejected.
• Upon receiving a LIST command, the server obtains directory and file information using shell command ls -l. The format of ls's results depends on the server's operating system type.

This FTP client is written in Python 3.

The file FanTastiP.py provides a class named FTP, which is used to perform the most basic tasks of FTP clients, like sending FTP commands defined by RFC959 to FTP servers, and receiving replies from FTP servers. FTP class provides rarely exception control mechanism.

The file FantasticFTP.py provides a class named FantasticFTP, inherited FTP class, which is used to implemented an FTP client GUI using the Tkinter GUI toolkit. FantasticFTP also provides reliable exception control mechanism; when an FantasticFTP object calls FTP class's method, it always adopts try / except mechanism to catch potential exceptions.

• IP address entry, port entry, and Connect / Disconnect button

• Command prompt, where green words denote commands and purple words denote responses.

• Server working directory window

  The 4 buttons in the upper left corner: "back to the parent directory", "create a new directory", "remove a directory", and "rename a directory or file".

  Double click a directory inside the window to change working directory.

  

• Download / Upload buttons &Task window

  

• Wrong formats of IP address or port number. When users give IP addresses or port numbers passwords with wrong formats, the client will force users to try again.
• Non-standardized responses of LIST command. A standardized response format of LIST command is something like “d-wxrwxr-x 2 ftp dir_name 1024 Sep 5 13:43”. If file and directory information received after a LIST command is not standardized, the client will exit.
• Illegal directory operations, such as deleting non-empty directory, creating new directory with an illegal directory name, moving files to a non-existent directory when renaming, and so on.
• Connection exceptions. When a connection is closed unexpectedly, the client cannot perform almost operations anymore, and will open an error-showing pop-up window to remind users to reconnect.
• File transfer exceptions, such as downloading a non-existent file, uploading a file without server directory's writing permissions

• Download: Before sending a "RETR filename" command, the client would first check if filename exists in the local directory. If it does, the client would get its size and send a "REST size" command to tell the server this breakpoint. Finally, the client sends a RETR commands.
• Upload: Before sending a "STOR filename" command, the client would first send a "SIZE filename" command to ask the server how much of the transfer has been down. If the SIZE command's response is "213 size", then the client would send a "REST size" command to tell the server this breakpoint. Finally, the client sends a STOR commands.

• The client only supports connections with the server's IP address. That is, without knowing the target IP address, it cannot establish a connection.
• The client supports anonymous logins. An empty username would lead to an anonymous login.
• The client only supports file transfer in binary mode.
• When transferring a file, the client blocks most of the GUI's buttons.