Update page 'Protocol'

Protocol.md

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-Protocol wiki
+# Protocol
+
+The protocol used is based on **TCP** connections for maximum security.  
+At the moment, it doesn't use **TLS** but plan to in a near future.
+
+## Packet
+
+A simple packet looks like this:
+
+| Command | Argument 1 | Argument 2 |
+| :-----: | :--------: | :--------: |
+|  PING   |   Hello    |   World!   |
+
+- **Command** - Always represent a single **uppercase** word as a command
+- **Arguments** - Represent a **semicolon-delimited** list of arguments
+
+Since all is a string, it is represented as:
+
+```md
+PING
+Hello;World!\n
+```
+
+Notice the `\n` at the end, it is used to show the end of the packet.  
+So, in one line, the packet is: `PING\nHello;World!\n`
+
+## ID
+
+Since the broker need to know the destination of a packet, we add an id as an argument:
+
+| Command | Argument 1 | Argument 2 | Argument 3 |
+| :-----: | :--------: | :--------: | :--------: |
+|  PING   |     ID     |   Hello    |   World!   |
+
+- **ID** - a 64 bit unsigned integer
+
+Here is the string representation:
+
+```md
+PING
+ID;Hello;World!\n
+```
+
+The consequence is that the first argument is **always** used for the **ID**
+
+## Byte Representation
+
+A packet need to be sent as **bytes**, here are the rules to send a packet:
+
+- The first **4** bytes are the total byte length of the packet as a 32 bit unsigned integer
+- The string representation of the packet is encoded in **UTF-8**
+
+We must send the byte-length since UTF-8 is variable in size, we can't send the characters count.
+
+A simple example to read a packet in C#:
+
+```cs
+// _stream is a connected NetworkStream
+
+// Length
+byte[] buffer = new byte[4];
+_stream.Read(buffer, 0, buffer.Length);
+
+uint length = BitConverter.ToUInt32(buffer, 0);
+
+// Data
+buffer = new byte[length];
+_stream.Read(buffer, 0, buffer.Length);
+
+string[] packet = Encoding.UTF8.GetString(buffer).Split('\n');
+
+// Parse
+string command = packet[0];
+string[] arguments = packet[1].Split(';');
+```
+
+And here an example to write a packet in C#:
+
+```cs
+// _stream is a connected NetworkStream
+
+// Command
+string command = "PING";
+uint id = "457545645";
+string argument1 = "Hello";
+string argument2 = "World!";
+string packet = command + "\n" + id.ToString() + ";" + argument1 + ";" + argument2 + "\n";
+
+byte[] data = Encoding.UTF8.GetBytes(packet); // Convert to UTF-8 bytes
+
+_stream.Write(BitConverter.GetBytes(data.Length), 0, 4); // Send the length
+_stream.Write(data, 0, data.Length); // Send the packet
+```
+
+## Commands
+
+Each command is described in a dedicated page
+
+- TODO