Programming assignment P3

In this assignment you will design and implement a simple client-server protocol, called the TIME protocol. The TIME protocol has only one message type, called a GETTIME message. When a client sends a GETTIME request to a server, the server responds with a GETTIME response containing the current time of day, and the client should then print a description of this response in the terminal window. The time of day need only be specified to the nearest second. The server program must be multi-threaded: that is, it must process each request in a new thread, using a similar design to the web server in assignment P2.

As with our previous client-server examples, the server program will take exactly 1 command line argument, specifying the port on which it will be listening. The client program will take exactly 2 command line arguments, specifying the name of the machine on which the server is running, and the port on which the server is listening. Following is an example of the outputs when the server is running on the machine blackbird.dickinson.edu, and the client is run on the machine albatross.dickinson.edu.

First, we start the server on blackbird:

  blackbird:/tmp jmac$ java TimeServerP3 56765

Then, we run the client on albatross:

  albatross:/tmp jmac$ java TimeClientP3 blackbird 56765
  TimeServer at blackbird says time is 15:20:19

Your solution should contain exactly 2 files, called TimeServerP3.java and TimeClientP3.java. If you define any other classes, add them to one of these files as we did with the MyHttpRequest class in assignment P2. Submit your code to Web-CAT by first making a zip file of these two Java files.

Extra credit

For a small amount of extra credit on this assignment (at most 5% of the total score), you can implement an additional message type for the TIME protocol: the SETTIME message. When the client sends a SETTIME request to the server, it provides a new value for the current time, specified with hours, minutes, and seconds (the server will not keep track of the date). On receiving a SETTIME request, the server resets its clock to the requested time, and responds to the client with a message confirming that the SETTIME request has been performed. Subsequent GETTIME requests should return times that correctly reflect the most recent SETTIME.

To achieve this, the client program must accept an additional optional parameter. If this parameter is present, it should be in the format HH:MM:SS, representing the time in hours, minutes, and seconds, where the hours are specified using the 24-hour clock. If the extra parameter is present, the client program performs a SETTIME request, otherwise it performs a GETTIME request.

For example, assume that the server has been started on blackbird.dickinson.edu as above. Then just as before, we might run the client on albatross.dickinson.edu. Issuing a GETTIME produces the same behavior as before (assuming the current time is around 3:20 p.m.):

  albatross:/tmp jmac$ java TimeClientP3 blackbird 56765
  TimeServer at blackbird says time is 15:20:19

We might then issue a SETTIME, setting the server's time to 9:45 a.m.:

  albatross:/tmp jmac$ java TimeClientP3 blackbird 56765 09:45:00
  TimeServer at blackbird completed SETTIME request

Finally, we wait for exactly 100 seconds and issue another GETTIME:

  albatross:/tmp jmac$ java TimeClientP3 blackbird 56765
  TimeServer at blackbird says time is 09:46:40

Note that the server's time is now 100 seconds later than the 9:45 a.m. to which it was set, 100 seconds ago.

A note on the implementation: do not attempt to reset the system clock on the machine where the server is running. Instead, the server should merely remember the offset between its own "virtual" clock, and the system clock.