Sockets. Most modern operating systems use the socket abstraction to manage interprocess communication connections. As we've seen, a socket is similar to a file descriptor. The following system calls all operate on sockets:

• socket() - Create and return the file descriptor (a small integer) of a new socket. The socket's address family, connection type and protocol type are specified in the call.
• sendto() - Send a message through a socket to a specific destination.
• recv() - Receive a message into a local buffer.

Your task:

1. Write a program to access the time server on network hosts and print the results.

   The Time Protocol is documented in an RFC. Note that there are several "network time" protocols. Look for the one that uses port 37. Look up the RFC to find out the details such as the message format for the Time Protocol. [Do you see the error in this RFC?]

2. Rewrite your program to broadcast a request to all timeservers listening on your workstation's local network. You'll need to:
   • Use recvfrom() to return the address of the remote host as well as the data value.
   • Put recvfrom() in an infinite loop to watch for multiple returns (you'll need to use ctrl-C to terminate your program).

   Identify the responding host and print the time in each response. Use gethostbyaddr(), getnameinfo(), or getipnodebyaddr() to print the responding host's mnemonic name (rather than IP address number).

3. While not required, see if you can print the date and time in a human readable form, e.g. Fri Sep 12 11:53:00 2003.