CS 372 Introduction to Computer Networks Programming Assignment 2


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Design and implement a simple file transfer system, i.e., create a file transfer server and a file
transfer client. Write the ftserver and the ftclient programs. The final version of your
programs must accomplish the following tasks:
1. ftserver starts on Host A, and validates command-line parameters
2. ftserver waits on for a client request.
3. ftclient starts on Host B, and validates any pertinent command-line parameters.
(, , , ,
, etc…)
4. ftserver and ftclient establish a TCP control connection on . (For
the remainder of this description, call this connection P)
5. ftserver waits on connection P for ftclient to send a command.
6. ftclient sends a command (-l (list) or -g (get)) on connection P.
7. ftserver receives command on connection P.
If ftclient sent an invalid command
• ftserver sends an error message to ftclient on connection P, and ftclient
displays the message on-screen.
• ftserver initiates a TCP data connection with ftclient on .
(Call this connection Q)
• If ftclient has sent the -l command, ftserver sends its directory to ftclient
on connection Q, and ftclient displays the directory on-screen.
• If ftclient has sent -g , ftserver validates FILENAME, and
– sends the contents of FILENAME on connection Q. ftclient saves the
file in the current default directory (handling “duplicate file name” error
if necessary), and displays a “transfer complete” message on-screen
– sends an appropriate error message (“File not found”, etc.) to ftclient on
connection P, and ftclient displays the message on-screen.
• ftserver closes connection Q (don’t leave open sockets!).
8. ftclient closes connection P (don’t leave open sockets!) and terminates.
9. ftserver repeats from 2 (above) until terminated by a supervisor (SIGINT).
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Program Requirements:
• ftserver must be written in C.
• ftclient must be written in Java or Python.
• Of course, your program must be well-modularized and well-documented.
• Your programs must run on a flip server: (flip1, flip2, flip3).engr.oregonstate.edu
o Probably the best way to do this is to use SSH Secure Shell, Putty, or another
terminal emulator to log onto access.engr.oregonstate.edu using your ENGR
username/password and note which flip you get.
o It will be easiest if you bring up two instances of the shell on the separate flip
servers and use one to run the server, and the other to run the client (this is how I
will be testing!).
• You may not use sendfile or any other predefined function that makes the problem trivial.
• Your program should be able to send a complete text file. You are not required to handle
an “out of memory” error. Separate grading for short text files and long text files.
• Use the directories in which the programs are running. Don’t hard-code any directories
that might be inaccessible to the graders.
• Combine all program files into one *.zip archive (no .7z or .gz allowed). The .zip file
should not contain any folders – only files!
• If you use additional include-files or make-files, be sure to include them in your .zip file.
• Create a README containing detailed instructions on how to compile and run your
server and client.
• Be absolutely sure to cite any references and credit any collaborators. I’m sick of giving
failing grades for people not doing this.
There are many possibilities for extra credit. All extra credit must be documented and
referenced in your program description and README.txt to receive any credit. Here are a
few ideas to get you started:
• Make your server multi-threaded.
• Implement username/password access to the server.
• Allow client to change directory on the server.
• Transfer files additional to text files (e.g. binary files) (a text file with a non-.txt
extension doesn’t count.
• etc…
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• Beej’s Guide will be helpful. It has many things you’ll need for this assignment.
• Don’t hard-code the port numbers
• Don’t use the well-known FTP port numbers, or 30021 or 30020, as these will be
probably in use (by network services or other students).
• We will test your system with text files only (unless your README specifies additional
file types), one very large and one small.
• If you implement extra credit features, be sure to fully describe those features, and how
to use them, in your README, or you won’t receive any extra credit.
• Programs will be accepted up to 48 hours late with a 10% penalty per 24-hour period.
Example Execution:
SERVER (flip1) CLIENT (flip2)
Input to console Output Input to Console Output
> ftserver 30021
Server open on 30021
> ftclient flip1 30021 –l 30020
Connection from flip2.
List directory requested
on port 30020.
Sending directory
contents to flip2:30020
Receiving directory
structure from
> ftclient flip1 30021 –g
shortfile.txt 30020
Connection from flip2.
File “shortfile.txt”
requested on port 30020.
Sending “shortfile.txt”
to flip2:30020
from flip1:30020
File transfer
> ftclient flip1 30021 –g
longfileee.txt 30020
Connection from flip2.
File “longfileee.txt”
requested on port 30020.
File not found. Sending
error message to
flip1:30021 says