Exercício

Implementar um protocolo da camada de aplicação para distribuir arquivos de texto. O protocolo é bem simples e está especificado abaixo::

• Upon connection clients must send a password.
• Clients can ask to access a text file located on the server.
• If they do not gain authorisation, all their requests are denied.
• The connection to a client is closed when they quit.

• 101 PASSWD <string>
• 102 ACCESS <filename>
• 103 QUIT

• 901 OK
• 902 UNKNOWN
• 903 UNAUTHORISED
• 904 NOT FOUND
• 905 EOF

The commands may give rise to different responses:

• In response to the command 101 PASSWD the server will return 901 OK if correct; and 903 UNAUTHORISED if incorrect. Use a fixed, hard-coded password for the exercise.
• In response to the command 102 ACCESS the server will return 903 UNAUTHORISED if a correct password has not been provided already; 904 NOT FOUND if the file does not exist; or if the file exists then the server should return 901 OK; followed by the file, line by line; followed by a 905 EOF.
• In response to the command 103 QUIT the server should respond 901 OK then close its various connection handling objects. The client should close its connection handlers on receiving the OK.
• If the command is not recognised the server should respond with 902 UNKNOWN.