Lab-1

Socket Programming

Perform the following tasks:

1. Develop a Root Transfer Protocol socket server. The server must wait for a client, serve that client, and then ends. Recall that an RTP client can make any number of requests but once an empty line is sent, the connection will be terminated and the server will shut down.
   
   Hint: It is always a good idea to separate the concerns. The management aspect of the server (listening on a port, waiting for a client, and server shutdown) should be in one class, the one with the main method. The request handling aspect of the server (streams, computing the square root, etc.) should be in a separate class, one called Handler. The following pattern is thus highly recommanded:

     1. Determine the port to listen on
     2. Handle or acknowledge exceptions
     3. handler = new Handler()
     4. serversocket = new ServerSocket(port)
     5. socket = serversocket.accept()
     6. handler.handle(socket)
     7. clean exit
   
     Handler class has handle(Socket socket) which:
     1. Get the raw I/O streams from socket
     2. Wrap the streams as appropriate
     3. Follow Protocol to generate a response to the request
     4. clean exit




2. Develop a network server according to the following specs:
   
   
   • Features
     Handles multiple clients but one at a time, has a log and a firewall, and delegates the handling of a connection to a separate class.
     
     
   • Firewall
     A connection is accepted only if it originated from the same IP address as that of the server.
     
     
   • Log
     For every connection, whether accepted or rejected by the firewall, a log entry is made. The entry consists of the following fields: the date and time at which the connection was made, the client's IP address, the client's port. The fields should be tab-delimited and the log should appear on standard output.
     
     
   • Shutdown
     The server should shut down when a file named running.txt in the server's directory ceases to exist. The start and shut-down events must be logged in the server's log. In terms of the pseudocode above, this means step #7 becomes: "if the file exists then go to step 4 else exit".
     
     
   • Protocol
     The connection handler uses a line-of-text, request-response protocol initiated by the client. The client is expected to start by sending a string of up to two digits representing a positive integer less than 100. If the received string does not meet this condition, the server returns the string Invalid!. Otherwise, it computes and returns a prime number with as many digits as specified in the client's request. In either case, the server terminates the connection after issuing its response; i.e. only one request is allowed per connection.
   
   
   Hint: There is no method in Java that generates such huge prime numbers but there is one that can determine, albeit not with certainty, if a given huge integer is prime.



3. Enhance the server developed in the previous question as follows:
   
   
   • Firewall
     In addition to accepting connections from the same IP, the server now accepts any IP that has been punched (see below).
     
     
   • Log
     A new entry: A log entry should be made whenever a connection is terminated. It should have the same fields as before plus the word terminated.
     
     
   • Protocol
     The client can now make multiple requests per connection. The request vocabulary now consists of four words: an integer as before, the word bye to end the connection, the word punch followed by a space followed by an IP to indicate that this IP address should be allowed, and the word plug followed by a space followed by an IP to indicate that this IP address should be removed from the list of allowed IPs. All words are case sensitive.
   
   Hint: Recall that the firewall and the log fall in the concern of the server manager, not the protocol handler. Hence, your handler class must be able to talk back to your server. You must arrange things so this is possible.

The following additional task is optional:

1. Enhance the server developed in the previous question by making it serve multiple clients at the same time.