• thechoer takes as arguments a tcp port and a udp port to which it will listen to incoming connection requests and incoming udp packets, respectively:

		thechoer <tcp-port> <udp-port>

• thechoer must be able to handle up to 7 outgoing tcp connections at the same time. Feel free to increase your limit to be more than 7. We shall only test your program for up to 7 outgoing connections. By "outgoing connections", we mean the connections in which the process under consideration is on the client side.
• thechoer operates somewhat like a shell. It keeps taking user's commands, at the same time watches incoming connection requests and data packets. When appropriate, thechoer prints out diagnostic information to stdout and goes back to the prompt mode to accept user's inputs.
• below is a description of all commands thechoer is supposed to handle, along with the description of associated actions :
  • info: print out its IP address, host name, TCP port, UDP port. For example:

		IP address         hostname           upd port      tcp port
		192.168.0.3 (funny.cse.buffalo.edu)     4892           43444

• connect <ip-address> <tcp-port>: try to establish a tcp connection to <ip-address> at port <tcp-port>. For example

		connect 192.168.0.3 99999

the two sides then report that the connection is indeed established.

• show: show all existing outgoing tcp connections in the following format:

		conn. ID |      IP       |     hostname         | local port | remote port
		---------------------------------------------------------------------------------
		   1     | 192.168.0.1   | abc.cse.buffalo.edu  | 1234       | 1235
		   2     | 192.168.0.2   | def.cse.buffalo.edu  | 1453       | 98234
		   3     | 192.168.0.3   | ghi.cse.buffalo.edu  | 1233       | 09823
		   4     | 192.168.0.4   | xyz.cse.buffalo.edu  | 1235       | 0823

• send <conn-id> <message>: send to the connection whose id is <conn-id> the <message> that follows. For example,

		send 3 Oh! This assignment is a piece of cake.

• sendto <ip-address> <udp-port> <message>: send <message> as a udp datagram to <ip-address> at <udp-poprt>.
• disconnect <conn-id>: disconnect the tcp connection whose id is <conn-id>.
• the rest of the user's inputs should be reported as "unknown command"
• for each message thechoer sends out, the process (which is an instance of thechoer) attaches is process ID (PID) along. Feel free to use any packet format you want to encapsulate the PID and the message. Make sure that, if you send the PID as an integer, then you must take care of the little-endian/big-endian issue.
• up on receiving a TCP connection request from someone, thechoer spawns a child process to handle the new request. It prints out something like

		got Conn. request from 192.168.0.2, child 19534 handling it.

• The child process just echoes whatever it receives and quits when the connection is closed by the client. Recall that the child process has to attach its PID to the message it is echoing. Moreover, it reports the following for each message that it aches:

		echoing "message"
			to: IP   = <ip-address>
		        type = tcp

		        PID  = <my-pid>

here, "message" is the message that it is echoing, <ip-address> is the ip address of the other end, and <my-pid> is the child's process id.

• If thechoer gets a UDP packet from someone, it aches the message and prints

		echoing "message"
			to: IP   = <ip-address>
		        type = udp
		        PID  = <my-pid>

• If a process gets an echoed message back, it prints

		got echoed message "message"
			from: IP   = <ip-address>
		          type = udp (or tcp)
		          PID  = <peer-pid>

the meaning of each field should be clear.

• Your program MUST use select for I/O multiplexing of tcp sockets, udp socket, and stdin.
• Lastly, the program should fix the problem of the UDP_Echo example. Read the README file in that example for more details.