/* FTP Commands *************************************************************/
/* Command summary:
 *
 *   ABOR - abort a file transfer
 *   ACCT - send account information
 *   APPE - append to a remote file
 *   CDUP - CWD to the parent of the current directory
 *   CWD  - change working directory
 *   DELE - delete a remote file
 *   HELP - return help on using the server
 *   LIST - list remote files
 *   MDTM - return the modification time of a file
 *   MKD  - make a remote directory
 *   MLSD - Standardized directory listing (instead of LIST)
 *   MLST - Standardized object listing (instead of LIST)
 *   MODE - set transfer mode
 *   NLST - name list of remote directory
 *   NOOP - do nothing
 *   PASS - send password
 *   PASV - enter passive mode
 *   PORT - open a data port
 *   PWD  - print working directory
 *   QUIT - terminate the connection
 *   REIN - reinitialize the connection
 *   RETR - retrieve a remote file
 *   REST - Sets the point at which a file transfer should start
 *   RMD  - remove a remote directory
 *   RNFR - rename from
 *   RNTO - rename to
 *   SITE - site-specific commands
 *   SIZE - return the size of a file
 *   STOR - store a file on the remote host
 *   STOU - store a file uniquely
 *   STRU - set file transfer structure
 *   STAT - return server status
 *   SYST - return system type
 *   TYPE - set transfer type
 *   USER - send username
 *
/* FTP Replies **************************************************************/
 *
 *   110 - Restart marker reply.
 *   120 - Service ready in nnn minutes.
 *   125 - Data connection already open; transfer starting.
 *   150 - File status okay; about to open data connection.
 *   200 - Command okay.
 *   202 - Command not implemented, superfluous at this site.
 *   211 - System status, or system help reply.
 *   212 - Directory status.
 *   213 - File status.
 *   214 - Help message.
 *   215 - NAME system type.
 *   220 - Service ready for new user.
 *   221 - Service closing control connection.
 *   225 - Data connection open; no transfer in progress.
 *   226 - Closing data connection.
 *   227 - Entering Passive Mode (h1,h2,h3,h4,p1,p2).
 *   230 - User logged in, proceed.
 *   250 - Requested file action okay, completed.
 *   257 - "PATHNAME" created.
 *   331 - User name okay, need password.
 *   332 - Need account for login.
 *   350 - Requested file action pending further information.
 *   421 - Service not available, closing control connection.
 *   425 - Can't open data connection.
 *   426 - Connection closed; transfer aborted.
 *   450 - Requested file action not taken.
 *   451 - Requested action aborted: local error in processing.
 *   452 - Requested action not taken.
 *   500 - Syntax error, command unrecognized.
 *   501 - Syntax error in parameters or arguments.
 *   502 - Command not implemented.
 *   503 - Bad sequence of commands.
 *   504 - Command not implemented for that parameter.
 *   530 - Not logged in.
 *   532 - Need account for storing files.
 *   550 - Requested action not taken.
 *   551 - Requested action aborted: page type unknown.
 *   552 - Requested file action aborted.
 *   553 - Requested action not taken.
 */