Assignment 1: A Multi-Threaded Web Server

Programming Assignment 1:
A Multi-Threaded Web Server
In this assignment, you will learn the basics of socket programming for TCP
connections in Python: how to create a socket, bind it to a specific address and port,
as well as send and receive a HTTP packet. You will also learn some basics of HTTP
header format.
You will develop a web server that handles one HTTP request at a time. Your web
server should accept and parse the HTTP request, get the requested file from the
server’s file system, create an HTTP response message consisting of the requested
file preceded by header lines, and then send the response directly to the client. If the
requested file is not present in the server, the server should send an HTTP “404 Not
Found” message back to the client. Further, you will implement a multithreaded
server that is capable of serving multiple requests simultaneously.
What to Hand in
You will hand in a zip file containing:
1. The complete server code (all source file)
2. The screen shots of your client (ex: a browser), verifying that you actually
receive the contents of the HTML file from the server.
3. A brief report about “how your design your code”, “result and discussion”,
“conclusion”.
Grading Criteria:
a. Submitting all required files (even with a non-compiling code): 40%.
b. A reasonable attempt and a reasonable code that doesn’t compile: 50%
c. A reasonable program/code, which runs successfully, but doesn’t give the
correct output: 70% (ex: no “404 Not Found” message.)
d. A successful program with the correct output, but not fulfilling all
requirements: 90% (ex: the multithreaded function do not work well.)
e. A submission fulfilling all the requirements: 100%
Code
This assignment is divided into two steps.
• Step A: Below you will find the skeleton code for the Web server. You are to
complete the skeleton code. The places where you need to fill in code are 
marked with #Fill in start and #Fill in end. Each place may
require one or more lines of code.
• Step B: To implement the multithreaded server, you need to add thread
module to the Web server (in Step A).
Running the Server
Put an HTML file (e.g., HelloWorld.html) in the same directory that the server is in.
Run the server program. Determine the IP address of the host that is running the
server (e.g., 128.238.251.26). From another host, open a browser and provide the
corresponding URL. For example:
http://128.238.251.26:6789/HelloWorld.html
‘HelloWorld.html’ is the name of the file you placed in the server directory. Note
also the use of the port number after the colon. You need to replace this port number
with whatever port you have used in the server code. In the above example, we have
used the port number 6789. The browser should then display the contents of
HelloWorld.html. If you omit ":6789", the browser will assume port 80 and you will
get the web page from the server only if your server is listening at port 80.
Then try to get a file that is not present at the server. You should get a “404 Not
Found” message.
Skeleton Python Code for the Web Server
#import socket module
from socket import *
import sys # In order to terminate the program
serverSocket = socket(AF_INET, SOCK_STREAM)
#Prepare a sever socket
#Fill in start
#Fill in end
while True:
#Establish the connection
print('Ready to serve...')
connectionSocket, addr = #Fill in start #Fill in end
try:
message = #Fill in start #Fill in end
filename = message.split()[1]
f = open(filename[1:])
outputdata = #Fill in start #Fill in end
#Send one HTTP header line into socket
#Fill in start
#Fill in end
#Send the content of the requested file to the client
for i in range(0, len(outputdata)):
connectionSocket.send(outputdata[i].encode())
connectionSocket.send("\r\n".encode())
connectionSocket.close()
except IOError:
#Send response message for file not found
#Fill in start
#Fill in end
#Close client socket
#Fill in start
#Fill in end
serverSocket.close()
sys.exit()#Terminate the program after sending the corresponding data
Multithreaded Server
Currently, the web server handles only one HTTP request at a time. Implement a
multithreaded server that is capable of serving multiple requests simultaneously.
Using threading, first create a main thread in which your modified server listens for
clients at a fixed port. When it receives a TCP connection request from a client, it
will set up the TCP connection through another port and services the client request
in a separate thread. There will be a separate TCP connection in a separate thread
for each request/response pair.
You need to complete the code from the skeleton Python code above. You will
import thread module to start. The example of code is listed below. More lines of
code are needed.
# import thread module
from _thread import *
import threading
# A lock object is created by
print_lock = threading.Lock()
Optional Exercises
Instead of using a browser, write your own HTTP client to test your server. Your
client will connect to the server using a TCP connection, send an HTTP request to
the server, and display the server response as an output. You can assume that the
HTTP request sent is a GET method. The client should take command line
arguments specifying the server IP address or host name, the port at which the server
is listening, and the path at which the requested object is stored at the server. The
following is an input command format to run the client.
client.py server_host server_port filename