The first programming project is meant to introduce you to socket programming, as well as the Unix software development environment (gcc, make, etc.). You may find it useful to refer to this document for socket programming (Beej's Guide to Network Programming).
Your task will be to write a TCP Proxy. You'll learn how to write both client and server code in this homework.
A TCP proxy server is a server that acts as an intermediary between a client and another server, called the destination server. Clients establish connections to the TCP proxy server, which then establishes a connection to the destination server. The proxy server sends data received from the client to the destination server and forwards data received from the destination server to the client. Interestingly, the TCP proxy server is actually both a server and a client. It is a server to its client and a client to its destination server.
The proxy server you will build for this homework will be invoked at the command line as follows:
# ./tcp_proxy destination-host destination-port listen-port
For example, to redirect all connections to port 3000 on your local machine to yahoo's web server, run:
# ./tcp_proxy www.yahoo.com 80 3000
The proxy server will accept a single connection from a client and forward it using a single connection to the server. During the connection, the proxy will not accept any other connections.
prompt> scp -i ~/.euca/id-rsa-kp-vs442-test tcp_proxy.tar.gz ubuntu@XX.XX.XX.XX:~/ prompt> ssh -i ~/.euca/id-rsa-kp-vs442-test ubuntu@XX.XX.XX.XX # tar -xzf tcp_proxy.tar.gz # cd tcp_proxy # make gcc -pthread -o tcp_proxy tcp_proxy.cFirst, make sure that you save your work before terminating your instance, either by placing it in a bucket, using a version control system like (CVS, SVN, Git, darcs, etc.), or simply fetching it back on your machine. To fetch it back on your machine, follow the steps:
# cd .. (come outside the dir tcp_proxy) # tar -czf tcp_proxy.tar.gz tcp_proxy --exclude=".git" prompt> scp -i ~/.euca/id-rsa-kp-vs442-test ubuntu@XX.XX.XX.XX:tcp_proxy.tar.gz .
tcp_proxy. To test it, type, for example:
# ./tcp_proxy www.yahoo.com 80 1234Now you should test your program using telnet. In the new window, run:
# telnet localhost 1234 Trying ::1... telnet: connect to address ::1: Connection refused Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Connection closed by foreign host. #The message "Connected to localhost" says that your proxy accepted a TCP connection, but then immediately closed it, since the proxy is not fully implemented. You must finish implementing the proxy. You are free to use any basic C library, or you can design your own data structures. It is possible to complete the assignment without using any other external libraries or data structures.
You should test your proxy to make sure that it continues to forward data even when some connections aren't responding. Here's one test you should be able to pass.
First, run the proxy and point it at fireless.cs.cornell.edu's HTTP port:
# ./tcp_proxy fireless.cs.cornell.edu 80 1234Now, in another window, use telnet to fetch /big through the proxy:
# telnet localhost 1234 Trying ::1... telnet: connect to address ::1: Connection refused Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. GET /courses/2014fa/cs5413/labs/bigWatch the data go by for a while, then interrupt the output by typing ''control-] RETURN'', after which telnet should stop and print telnet>. Now check that the proxy hasn't been hung because telnet isn't reading data; suspend your telnet by typing ''
zRETURN'', wait for 10 seconds, and fetch something else:
telnet> z Suspended # telnet localhost 1234 Trying ::1... telnet: connect to address ::1: Connection refused Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. GET /courses/2014fa/cs5413/labs/small You got it! Connection closed by foreign host.If you see "You got it!," your program passes the test.
# tar -czf tcp_proxy.tar.gz tcp_proxy --exclude=".git"To turn in your distribution, upload the
tcp_proxy.tar.gzfile on CMS.
man socketgives you the man page for the socket system call.
ulimitcommand before you will see the core files being created (e.g.
ulimit -c unlimited). You can examine the core files with
gdbin order to learn what went wrong --- this is an invaluable tool. You can start by typing
gdb program program.core, and then typing the gdb command
backtrace. GDB will in turn return a trace pointing to where your program has crashed.