public/subjects/net-cat/net-cat.en.md

net-cat

Objectives

This project consists on recreating the NetCat in a Server-Client Architecture that can run in a server mode on a specified port listening for incoming connections, and it can be used in client mode, trying to connect to a specified port and transmitting information to the server.

• NetCat, nc system command, is a computer network utility for reading from and writing to network connections using TCP or UDP. It is used for anything involving TCP, UDP, or UNIX-domain sockets, it is able to open TCP connections, send UDP packages, listen on arbitrary TCP and UDP ports...

• To see more information about NetCat inspect the manual man nc.

Here is a simple example of connection and transmission between Server-Client by creating a TCP socket between server and client.

• Open two terminals, one for the server and the other for Client.

  • Use the following commands for the server side :

    stuednt$ mawk -W interactive '$0="\033[1;32mServer: \033[0m"$0' | nc -l -p <port>
    Client: Hello it's the CLIENT talking
    hello there
    
    

  • Use the following commands for the client side :

    stuednt$ mawk -W interactive '$0="\033[1;32mClient: \033[0m"$0' | nc <host ip> <port>
    Hello it's the CLIENT talking
    Server: Hello there
    
    

  • To see the host IP use the command ifconfig on the server host machine.

Your project must work in a similar way that NetCat works, in other words, you must create a group chat. The project must present :

• TCP or UDP connection between server and multiple clients (relation of 1 to many). The type of connection must be established by using a flag, just like nc, by default it uses TCP connection, but if you want to use UDP connection present the flag -u.
• Each Client must have an user name.
• Clients must be able to send messages to the chat.
• Messages sent, must be identified by the time that was sent and the user name of who sent the message.
• If a Client joins the chat, all the previous messages sent to the chat must be uploaded to the new Client.
• If a Client connects to the server, the rest of the Clients must be informed by the server that the Client joined the group.
• If a Client exits the chat, the rest of the Clients must be informed by the server that the Client left.
• All Clients must receive the messages sent by other Clients.
• If a Client leaves the chat, the rest of the Clients must not disconnect.

This project will help you learn about :

• Manipulation of structures.
• Net-Cat
• TCP/UDP
  • TCP/UDP connection
  • TCP/UDP socket
• Channels
• Goroutines
• IP and ports

Hints

• Try to find out more about the flags -u, -p and -l.

Instructions

• Your project must be written in Go.
• Your project must use TCP or UDP.
• The code must respect the good practices.
• It is recommended that the code should present a test file for the server connection and the client connection.
• You have to be able to handle the errors from server side and client side.

Usage

Here is a simple example of a group chat :

• Server side :

student$ ./net-cat -p 8080
listening on port 8080....

• Two Clients running at the same time

• Client 2 :

student$ ./net-cat 192.168.1.123 8080
welcome, you are connected

enter user name : client2
your name is client2

client2 joined the chat...
client1 joined the chat...

hello
client2 at 18:12- hello
client1 at 18:13- hello man
how are you?
client2 at 18:15- how are you?
client1 left the chat...

• Client 1 :

stuednt$ ./net-cat 192.168.1.123 8080
wellcome, you are connected

enter user name : client1
your name is client1

client2 joined the chat...
client1 joined the chat...

client2 at 18:12- hello
hello man
client1 at 18:13- hello man
client2 at 18:15- how are you?
^C