Assignment 2 Computer Science 441 solution


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1 Objective
The objective of this assignment is to practice server side network programming with TCP.
Specifically, you will implement a multi-threaded web server to serve web objects to HTTP
clients over the Internet.
2 Overview
In this assignment, you will implement a simple web server from scratch. The server should
support non-persistent HTTP (as in HTTP 1.0). This means that once an HTTP request is served,
the server closes the TCP connection. To inform the client that the connection is closed, include
the header line “connection:close” in the server response.
Your server is only required to handle GET requests. It has to check if the requested object is
available, and if so return a copy of the object to the client. As this simplified version of a web
server deals with GET only, your program needs to return responses with the following status
codes only:
• 200 OK
• 400 Bad Request
• 404 Not Found
Your web server should be able to handle more than one connection simultaneously. To handle
multiple connections, the server has to be multi-threaded. In the main thread, the server listens
on a fixed port. When it receives a TCP connection request, it sets up a TCP connection through
another socket and services the request in a separate worker thread. That is, once the server
accepts a connection, it will spawn a new thread to parse the incoming HTTP request, transmit
the object, etc. A high-level description of the functionality of the main and worker thread is
described in Algorithms 1 and 2.
Algorithm 1 Main Thread.
1: while not stopped do
2: Listen for connection requests
3: Accept new connection request from client
4: Spawn a new worker thread to handle the new connection
5: end while
All the requested web pages are in the current directory where your web server is running, i.e.,
the current directory is the web server root directory.
Assignment 2 CPSC 441
Algorithm 2 Worker Thread.
1: Parse the HTTP request
2: Ensure well-formed request (return error otherwise)
3: Determine if requested object exists (return error otherwise)
4: Transmit the content of the object over the existing connection
5: Close the connection
Write a Java class named WebServer, which extends the Java class Thread and includes the
following public methods:
• WebServer(int port)
This is the default constructor. The parameter port specifies the port at which the web
server listens.
• void shutdown()
Informs the web server to shut down, clean up and exit.
Your implementation should include exception handling code to deal with all checked exceptions in your program. Print exception messages to standard system output. A simple tester
class, named Tester, is provided so that you can see how we are going to run your server.
• You are not allowed to change the signature of the methods provided to you. You can
however define other methods or classes in order to complete the program.
• You are not allowed to use class URL or URLConnection or their subclasses for this assignment. Ask the instructor if you are in doubt about any specific Java classes that you want
to use in your program.