Assignment 5: Socket Programming

Due by: Friday, March 21, 2025 at 11:59 p.m.

In this assignment, you'll use tools to retrieve network addresses based on domain names and do some simple socket programming.

As with all the assignments and projects in this course, it's recommended that you do the stages in the order given. Try to get the MIN unit tests passing before moving on to the FULL ones. Likewise, try to get the MIN integration tests passing before moving on to the FULL ones.

First, download the archive given below and unzip it into an appropriate directory.

Useful Functions and Types

In addition to general I/O functions like read(), write(), and close(), consult the C documentation or man pages for the following functions:

  • socket()
  • connect()
  • getaddrinfo()
  • freeaddrinfo()
  • inet_ntop()

A number of struct types will also be necessary. Be sure to consult Chapter 4 of the textbook for more information about the following structs:

  • struct addrinfo
  • struct sockaddr
  • struct sockaddr_in
  • struct sockaddr_in6

Stage 1: Gathering and Interpreting Network Information

Make the following edits in client.c and main.c. This portion of the assignment is focused on providing the basic functionality of the nslookup utility. After completing this implementation, you can compare your output with that of nslookup.

  1. Implement addr_string() to convert an IP address into the correct format, either IPv4 dotted decimal or IPv6 colon hexadecimal. If the server parameter is NULL, return "no address information". All returned strings must be dynamically allocated because the caller will free() them.
  2. Use addr_string() as part of the implementation of serv_string() to display more information about the server described by the server parameter. While addr_string() only formats the address, serv_string() also displays information about the transport and network layer protocols.
  3. Implement get_server_list() to use DNS to resolve the human-readable hostname. Note that the proto string can be a name (such as "http") or a number formatted as a string (such as "80"), but the logic of your implementation should not need to examine that parameter explicitly.
  4. Complete the designated portion of main() to support command-line queries of servers. If protocol is 53 (DNS) or 67 (DHCP), use UDP instead of TCP.

Stage 2: Client Sockets

Implement the web() function in client.c to create a socket and connect to an HTTP server, based on the following requirements:

  1. After opening the socket and connecting, send the message "GET foo HTTP/1.0" where "foo" is the file specified in the arguments. Recall that HTTP requires all header lines to end in CRLF ("\r\n") and the header as a whole to end with an additional CRLF.
  2. Read the response, printing the first line, which should be the HTTP status code, and the value set in the Content-Type header line. Doing so will require looking through multiple lines, and it may be useful to use strtok() to split strings. Make sure to strip the CRLF from both the returned result and type strings.
  3. Return NULL if any errors occur.
  4. Be sure to clean up any resources, such as dynamically allocated data or open sockets.

Turn In

First, run make clean to remove all of the executable and object files from your directory structure. Then, zip up the contents of your project directory in either a .zip or a .tar.xz file. Upload this archive to Brightspace. Your assignment must be submitted by Friday, March 21, 2025 at 11:59 p.m. Grace days are not available for assignments.

All work must be done within assigned teams, though you may discuss general concepts with your classmates. Please refer to the course policies if you have any questions about academic integrity. If you have trouble with the assignment, I am always available for assistance.

Under no circumstances should any member of one team look at the code written by another team. Tools will be used to detect code similarity automatically.

Code that does not compile will automatically score zero points.

Grading

Your grade will be determined by the following categories.

Category Description Weight
Unit Tests Your solution passes the 11 unit tests. 55%
Integration Tests Your solution passes the nine integration tests. 45%

Credits

This assignment is based on material from CS 361 by Michael S. Kirkpatrick. This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.