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EE450 Socket Programming Project
Part 1
Fall 2021
Due Date:
Sunday, October 17, 2021 11:59PM
(Hard Deadline, Strictly Enforced)
OBJECTIVE
The objective of project is to familiarize you with UNIX socket programming. It is an individual
assignment and no collaborations are allowed. Any cheating will result in an automatic F in
the course (not just in the assignment). If you have any doubts/questions email the TA your
questions, come by TA’s office hours, or ask during the weekly discussion session. You can ask
TAs any question about the content of the project, but TAs have the right to reject your
request for debugging.
PROBLEM STATEMENT
In this part of the project, you will implement client-server socket programming using TCP. Clients
would like to ask Main server which state a city is located in. A client sends a city name to Main
server and Main server will search in its database and reply to the client with a state name.
Figure 1
The detailed operations to be performed by all the parties are described with the help of Figure 1.
There are in total 3 communication endpoints, which are run in 3 individual terminal windows:
● Client 1 and Client 2: represent two different users, send queries to main server
● Main server: store information, search, send responses to clients
You are highly encouraged to use Beej’s Guide to Network Programming to complete this
assignment. You can use code from Beej’s Guide as a starting point (remember to mention any
code you take directly from other sources like Beej’s Guide in the README and your comments).
The full process can be roughly divided into three phases, and their communication and
computation steps are as follows:
Bootup
1. [Computation]: Main server read the file list.txt and store the information.
2. [Communication]: Main server process wait for client processes to connect
Client 1
Client 2
Main
server
TCP
TCP
3. [Computation]: Two clients are run and ask the user to input a city name.
Query
1. [Communication]: Each client then establishes a TCP connection to the Main server and
sends its queries (the city name) to the Main server.
○ A client can terminate itself only after it receives a reply from the server (in the
Reply phase).
○ Main server may be connected to both clients at the same time.
2. [Computation]: Once the Main server receives the queries, it decodes the queries and
searches in the list with the received country name, obtaining the corresponding backend
server ID.
Reply
1. [Communication]: Main server prepares a reply message and sends the result to the
appropriate client.
2. [Communication]: Clients receive the reply message from Main server and display it.
Clients should keep active for further inputted queries, until the program is manually killed
(Ctrl-C).
The format of list.txt is as follows.

,,

,,

,,

Example list.txt:
California
Los Angeles,San Diego
Illinois
Chicago,Peoria,Springfield
Texas
Austin,Dallas,Houston

Assumptions on the list.txt file:
1. City and state names are letters. The length of a city name can vary from 1 letter to at most
20 letters. States and cities may contain both capital and lowercase letters and can contain
white spaces.
2. Cities associated to the same state will be on the same line and delimited by commas.
3. There is no additional empty line(s) at the beginning or the end of the file. That is, the
whole list.txt do not contain any empty lines.
4. For simplicity, there is no overlap of city names among different states.
5. For a given state, there may be repeated city names.
6. list.txt will not be empty.
7. A state server will have at least one city name, and at most 100 city names.
An example list.txt is provided for you as a reference and for testing. A different list.txt will be
used for grading, so you are advised to prepare your own files for testing purposes.
Source Code Files
Your implementation should include the source code files described below:
1. servermain: You must name your code file: servermain.c or servermain.cc or
servermain.cpp (all small letters). Also, you must name the corresponding header file (if
you have one; it is not mandatory) servermain.h (all small letters).
2. client: The name for this piece of code must be client.c or client.cc or client.cpp (all small
letters) and the header file (if you have one; it is not mandatory) must be called client.h
(all small letters). There should be only one client file!!!
Note: Your compilation should generate separate executable files for each of the components listed
above.
DETAILED EXPLANATION
Phase 1 -- Bootup
Main server program first boots up in this phase. While booting up, the servers must display a boot
up message on the terminal. The format of the boot up message for Main server is given in the onscreen
message table at the end of the document. As the boot up message indicates, Main server
must listen on the appropriate port for incoming packets/connections.
As described in the previous section, the main server needs to read the text file and store the
information. There are many ways to store the information, such as dictionary, array, vector, etc.
You need to decide which format to use based on the requirement of the problem. You can use
any format if it can give you correct results.
Once the server programs have booted up, two client programs run. Each client displays a boot up
message as indicated in the onscreen messages table. Note that the client code takes no input
argument from the command line. The format for running the client code is:
./client
After running it, it should display messages to ask the user to enter a query country name (e.g.,
implement using std::cin):
./client
Client is up and running.
Enter City Name:
For example, if the client 1 is booted up and asks for a state for city Dallas, then the terminal
displays like this after user types “Dallas” as the input:
./client
Client is up and running.
Enter City Name: Dallas
The main server has its unique port number specified in “PORT NUMBER ALLOCATION”
section with the source and destination IP address as localhost/127.0.0.1. Clients use dynamic ports.
Clients and Main server are required to print out on-screen messages after executing each action
as described in the “ON SCREEN MESSAGES” section. These messages will help with grading
if the process did not execute successfully. Missing some of the on-screen messages might result
in misinterpretation that your process failed to complete. Please follow the exact format when
printing the on-screen messages.
Phase 2 -- Query
After booting up, Clients establish TCP connections with Main server. After successfully
establishing the connection, Clients send the input city name to Main server. Once this is sent,
Clients should print a message in a specific format. Repeat the same steps for Client 2.
Main server then receives requests from two Clients. If the city name is not found, the Main server
will print out a message (see the “On Screen Messages” section) and return to standby.
For a server to receive requests from several clients at the same time, the function fork() should
be used for the creation of a new process. fork() function is used for creating a new process, which
is called child process, which runs concurrently with the process that makes the fork() call (parent
process).
For a TCP server, when an application is listening for stream-oriented connections from other hosts,
it is notified of such events and must initialize the connection using accept(). After the connection
with the client is successfully established, the accept() function returns a non-zero descriptor for a
socket called the child socket. The server can then fork off a process using fork() function to
handle connection on the new socket and go back to wait on the original socket. Note that the
socket that was originally created, that is the parent socket, is going to be used only to listen to the
client requests, and it is not going to be used for computation or communication between client
and Main server. Child sockets that are created for a parent socket have the identical well-known
port number and IP address at the server side, but each child socket is created for a specific client.
Through using the child socket with the help of fork(), the server can handle the two clients without
closing any one of the connections.
Once the Main server receives the queries, it decodes the queries and searches in the list with the
received city name, finding the corresponding state ID.
Phase 3 -- Reply
At the end of Phase 2, the Main server should have the result ready. The result is the state name
that the city is associated with. The result should be sent back to the corresponding client using
TCP. The client will print out the city name and then print out the messages for a new request as
follows:
...
City Dallas is located in state Texas.
-----Start a new query-----
Enter city name:
See the ON SCREEN MESSAGES table for an example output table.
PORT NUMBER ALLOCATION
The ports to be used by the client and the servers are specified in the following table:
Table 1. Static and Dynamic assignments for TCP and UDP ports
Process Dynamic Ports Static Ports
Main Server TCP(with client): 33xxx
Client 1 TCP
Client 2 TCP
NOTE: xxx is the last 3 digits of your USC ID. For example, if the last 3 digits of your USC ID
are “319”, you should use the port: 33319 for the Main Server, etc. Port number of all processes
print port number of their own.
ON SCREEN MESSAGES
Table 2. Main Server on-screen messages
Event On-screen Messages
Booting up (only while starting): Main server is up and running.
Upon reading the state lists: Main server has read the state list from list.txt.
Print the results of which city is
located in which country:
(Repeated cities should be
printed only once)
:



:


Upon receiving the input from the
client:
Main server has received the request on city
from client using TCP over port

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