HW #3: Simplified HTTP on TCP

 CS 3700-001: Computer Networks
HW #3: Simplified HTTP on TCP
Submission: (1) Upload all source code (.java) files to both Blackboard and the Virtual Servers (cs3700a and cs3700b), AND
(2) set up and test java programs (.class files) on cs3700a and cs3700b (See Part II for details) **Submission will NOT be accepted after the cutoff deadline
An option of peer programming: You may choose to work on this assignment individually or in a team of two students. If you
choose to work in a team of two students, you must 1) add both team members’ first and last names as the comments on Blackboard
when submitting the .java files (both team members are required to submit the same .java files on Blackboard), and 2) put a team.txt
file including both team members’ names under your HW3/ on cs3700a (both team members are required to complete Task II under
both home directories on cs3700a). For grading, I will randomly pick the submission in one of the two home directories of the team
members on cs3700a and cs3700b, and then give both team members the same grade. If the team information is missing on
Blackboard or cs3700a, two or more submissions with similar source codes with just variable name/comment changes will be
considered to be a violation of the Integrity described in the course policies and both or all will be graded as 0.
Grading: Your programs will be graded via testing and points are associated with how much task it can complete. A program that
cannot be compiled or crashes while running will receive up to 5% of the total points. A submission of .java files that are similar to any
online Java program with only variable name changes will receive 0% of the total points.
Programming in Java is highly recommended, since all requirements in this assignment are guaranteed to be supported in Java. If
you choose to use any other language such as Python or C/C++, it is YOUR responsibility, before the cutoff deadline, to (2) set up the
compiling and running environment on cs3700a and cs3700b, (2) make sure that I can run/test your programs in your home directory
on cs3700a and cs3700b, and (3) provide a README file under HW3/ on cs3700a to include the commands that I need to use.
Part I (85%): Write a client program and a server program to implement the following simplified HTTP protocol based on TCP service.
Please make sure your program supports multiple clients. The webpage file CS3700.htm is provided. You may choose a port like 5678
and hard code it in both client and server programs. (Hints: for testing both programs on the same computer, you may want to put client
program and server program at two different directories. Do NOT hard code the file name “CS3700.htm”!)
• The ending signature of the entity body in the HTTP response message for the case “200 OK”:
o When the HTTP Server program sends a HTTP response message out, it pads four continuous blank lines, i.e., “\r\n\r\n\r\n\r\n”,
to the end of the .htm file as the ending signature of the entity body.
o When the HTTP Client program read the HTTP response message line by line, it counts the number of continuous lines that
are empty strings “” (NOT a null string). Once such number reaches 4, the entity body has been fully received.
o It is assumed that the .htm file does not include such ending signature (in the real practice, length of the entity body may be
included in the head line and used to determine the end of an entity body).
• HTTP Client Program:
1. Display messages on the standard output to ask the user to input the DNS name/ip of your HTTP server.
2. Buildup the TCP connection to your HTTP server with the Host Name input by User at the given port, and display the RTT of
establishing this TCP connection in millisecond (the difference between the moments right before and after creating the
socket object). Catch the exception, terminate the program, and display error messages on the standard output if any.
3. Display messages on the standard output to ask the user to input the HTTP method type, name of the htm file requested, HTTP
Version, and User-Agent, respectively (separately please!). (hint: all inputs can be strings.)
4. Use the above inputs from user to construct ONE HTTP request message and send it to the HTTP server program over the TCP
connection. Your HTTP request message only needs to include the following lines. (Hint: At the end of each line including
the last empty line, a “\r\n” is needed. The correctness of the format will be checked by the instructor.):
The request line (hint: the URL should include a ‘/’ in front of the htm file name)
The header line for the field “Host:”
The header line for the field “User-Agent:”
<empty line>
5. Receive and interpret the HTTP response message from the HTTP Server program line by line, display the RTT (File
Transmission Time may be included) of HTTP query in millisecond (the difference between the moment right before HTTP
request is sent and the moment right after HTTP response is received) as a single line (e.g., RTT = 1.089 ms), display the status
line and header lines of the HTTP response message on the standard output, and save the data in the entity body to a .htm file
to local directory if there is any. (Hint: (a) When one empty string “” (NOT a null string!) is read the FIRST TIME, it indicates
the header lines are over and the entity body is going to start next line if the case is “200 OK”.)
6. Display a message on the standard output to ask the User whether to continue. If yes, repeat steps 3 through 6. Otherwise, close
all i/o streams, TCP connection, and terminate the Client program.
• HTTP Server Program:
1. Listen to the given port and wait for a connection request from a HTTP Client.
2. Create a new thread for every incoming TCP connection request from a HTTP client.
3. Read, display to the standard output, and interpret incoming HTTP request message line by line
MSU Denver, M&CS CS 3700-001: Computer Networks, Spring 2020 Dr. Weiying Zhu
o If the method given in the request line is NOT “GET”, it is a “400 Bad Request” case
o If the file specified in the URL does not exit/cannot be open, it is a “404 Not Found” case
o Otherwise, it is a “200 OK” case
4. According to the case discovered above, construct ONE HTTP response message and send it to the HTTP client program over
the TCP connection. Your HTTP response message needs include the following lines using the HTTP message format. (Hint:
At the end of each line including those empty lines, a “\r\n” is needed.)
The status line
The header line for the field “Date:”
The header line for the field “Server: ”, you may use any value of your choice
<empty line>
Data read from the requested HTML file line by line … (hint: for the 200 OK case only)
<empty line>
<empty line>
<empty line>
<empty line>
5. Repeat Step 3 through 4 until a null is read. (Hint: this happens when THIS client closes the TCP connection.)
6. Close all i/o streams and the TCP socket for THIS Client, and terminate the thread for THIS client. (Hint: when this happens,
the parent thread is still alive doing Steps 1 and 2 forever, unless the Server process is killed/terminated.)
Part II (15%): Test your programs on the Virtual Servers in the cloud and your laptop/home computer.
Warning: to complete this part, especially when you work at home, you must first (1) connect to GlobalProtect using your NetID
account (please read “how to connect to GlobalProtect …” at https://msudenver.edu/vpn/); then (2) connect to the virtual servers
cs3700a and cs3700b using sftp and ssh command on MAC/Linux or PUTTY and PSFTP on Windows.
ITS only supports GlobalProtect on MAC and Windows machines. If your home computer has a different OS, it is your responsibility
to figure out how to connect to cs3700a and cs3700b for programming assignments and submit your work by the cutoff deadline. Such
issues cannot be used as an excuse to request any extension.
1. MAKE a directory “HW3” under your home directory on cs3700a.msdenver.edu and cs3700b.msudenver.edu, a subdirectory
“server” under “HW3” on cs3700a.msudenver.edu, and a subdirectory “client” under “HW3” on cs3700b.msudenver.edu.
2. UPLOAD and COMPILE the server program under “HW3/server” and the client program under “HW3/client” on the VMs.
3. TEST the server program running on cs3700a.msudenver.edu together with a client program running on your laptop or lab
computer and another client program, simultaneously, running on cs3700b.msudenver.edu to test all the possible cases.
4. SAVE a file named testResultsClient.txt under “HW3/client” on cs3700b.msudenver.edu, which captures the outputs of your client
program when you test it. You can use the following command to redirect the standard output (stdout) and the standard error (stderr)
to a file on UNIX, Linux, or Mac, and view the contents of the file
java prog_name_args | tee testResultsClient.txt //copy stdout to the .txt file
//if you want, you may also use “script” command instead of the “tee” command
//to write both stdin and stdout into testResultsClient.txt while testing your
//client program on cs3700a. For how to use “script”, see
// https://www.geeksforgeeks.org/script-command-in-linux-with-examples/
//or Google “script command in Linux” if the above link is broken.
cat file-name //display the file’s contents.