## 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 :
```console
stuednt$ mawk -W interactive '$0="\033[1;32mServer: \033[0m"$0' | nc -l -p < port >
Client: Hello it's the CLIENT talking
hello there
```
- Use the following commands for the client side :
```console
stuednt$ 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 ](https://linuxize.com/post/netcat-nc-command-with-examples/ )
- [TCP/UDP ](https://www.privateinternetaccess.com/blog/2018/12/tcp-vs-udp-understanding-the-difference/ )
- TCP/UDP connection
- TCP/UDP socket
- [Channels ](https://tour.golang.org/concurrency/2 )
- [Goroutines ](https://tour.golang.org/concurrency/1 )
- IP and [ports ](https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers )
### 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** ](https://public.01-edu.org/subjects/good-practices.en ).
- 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 :
```console
student$ ./net-cat -p 8080
listening on port 8080....
```
- Two Clients running at the same time
- Client 2 :
```console
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 :
```console
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
```
