diff --git a/src/fr/univ/lyon1/client/Client.java b/src/fr/univ/lyon1/client/Client.java
index 33afdfe..abb6001 100644
--- a/src/fr/univ/lyon1/client/Client.java
+++ b/src/fr/univ/lyon1/client/Client.java
@@ -1,51 +1,39 @@
 package fr.univ.lyon1.client;
 
+import fr.univ.lyon1.common.Channel;
 import fr.univ.lyon1.common.Message;
-import fr.univ.lyon1.common.User;
+import fr.univ.lyon1.common.command.Command;
+import fr.univ.lyon1.common.command.CommandType;
+import fr.univ.lyon1.common.exception.ChatException;
+import fr.univ.lyon1.common.exception.UnknownCommand;
 
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.net.Socket;
+import java.util.ArrayList;
 import java.util.List;
 
 public class Client {
     private final int port;
     private final String address;
+    private final String username;
+    private final String password;
     protected final Socket socket;
     protected final ObjectOutputStream out;
     private ObjectInputStream in;
+    private List<Channel> channels = new ArrayList<>();
     protected boolean started = false;
 
-    public Client(String address, int port, String uuid, String password) throws Exception {
+
+    public Client(String address, int port, String username, String password) throws Exception {
         this.address = address;
         this.port = port;
+        this.username = username;
+        this.password = password;
         socket = new Socket(address, port);
         out = new ObjectOutputStream(socket.getOutputStream());
-        while (!this.auth(uuid, password));
-        out.writeObject("listUsers");
-        out.flush();
-        out.writeObject("join general");
-        out.flush();
-    }
-
-    public boolean auth(String uuid, String password) throws IOException {
         getIn();
-
-        out.writeUTF(uuid);
-        out.flush();
-        out.writeUTF(password);
-        out.flush();
-
-        String response = in.readUTF();
-        System.out.println(response);
-
-        if (response.startsWith("err:"))
-            return false;
-        else if (response.equals("logged"))
-            return true;
-        else
-            throw new IOException("Uk message");
     }
 
     public void disconnectedServer() throws IOException {
@@ -60,7 +48,7 @@ public class Client {
     public String sendMessage(String content) {
 
         try {
-            out.writeObject(new Message(content));
+            out.writeObject(new Command(CommandType.message, List.of(new Message(content, channels.get(0)))));
             out.flush();
         } catch (IOException e) {
             System.err.println("Fail to send message !");
@@ -70,26 +58,51 @@ public class Client {
         return content;
     }
 
-    public Message messageReceived(Message msg) {
-        System.out.println();
-        System.out.println(msg);
-        return msg;
+    public void action(Object data) throws IOException {
+        if (data instanceof Command)
+            command((Command) data);
+        else if (data instanceof ChatException)
+            ((ChatException) data).printStackTrace();
+        else {
+            out.writeObject(new UnknownCommand());
+            out.flush();
+        }
     }
 
-    public void action(Object data) {
-        if (data instanceof Message)
-            messageReceived((Message) data);
-        else if (data instanceof List) {
-            List<Object> tmpList = (List<Object>) data;
-            if (tmpList.get(0) instanceof User) {
-                List<User> users = (List<User>) data;
-                for (User u : users) {
-                    System.out.println(u);
-                }
-            }
+    private void command(Command cmd) throws IOException {
+        switch (cmd.getType()) {
+            case login -> commandLogin();
+            case message -> commandMessage(cmd);
+            case list -> commandList(cmd);
+            case join -> commandJoin(cmd);
         }
     }
 
+    private void commandLogin() throws IOException {
+        out.writeObject(new Command(CommandType.list, null));
+        out.flush();
+        out.writeObject(new Command(CommandType.join, List.of("general")));
+        out.flush();
+    }
+
+    protected void commandMessage(Command cmd) {
+        System.out.println();
+        System.out.println(cmd.getArgs().get(0));
+    }
+
+    private void commandList(Command cmd) {
+        List<Object> users = cmd.getArgs();
+        for (Object u : users) {
+            System.out.println(u);
+        }
+    }
+
+    private void commandJoin(Command cmd) {
+        Channel chan = (Channel) cmd.getArgs().get(0);
+        channels.add(chan);
+        System.out.println("You join "+chan);
+    }
+
     public void run() throws InterruptedException, IOException {
         if (started)
             return;
@@ -102,6 +115,9 @@ public class Client {
 
         started = true;
 
+        out.writeObject(new Command(CommandType.login, List.of(username, password)));
+        out.flush();
+
         clientSendThread.join();
         socket.close();
         clientReceiveThread.interrupt();
diff --git a/src/fr/univ/lyon1/client/ClientReceive.java b/src/fr/univ/lyon1/client/ClientReceive.java
index f71a9f1..4f5aa9d 100644
--- a/src/fr/univ/lyon1/client/ClientReceive.java
+++ b/src/fr/univ/lyon1/client/ClientReceive.java
@@ -46,7 +46,11 @@ public class ClientReceive implements Runnable {
             if (data == null)
                 break;
 
-            this.client.action(data);
+            try {
+                this.client.action(data);
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
         }
 
         try {
diff --git a/src/fr/univ/lyon1/common/Message.java b/src/fr/univ/lyon1/common/Message.java
index f179891..29d6786 100644
--- a/src/fr/univ/lyon1/common/Message.java
+++ b/src/fr/univ/lyon1/common/Message.java
@@ -24,9 +24,10 @@ public class Message implements Serializable {
         this.content = content;
     }
 
-    public Message(String content) {
+    public Message(String content, Channel channel) {
         this.uuid = UUID.randomUUID();
         this.content = content;
+        this.channel = channel;
     }
 
     public Message repley(User user, String content) {
diff --git a/src/fr/univ/lyon1/common/command/Command.java b/src/fr/univ/lyon1/common/command/Command.java
new file mode 100644
index 0000000..d3e5ea6
--- /dev/null
+++ b/src/fr/univ/lyon1/common/command/Command.java
@@ -0,0 +1,23 @@
+package fr.univ.lyon1.common.command;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+
+public class Command implements Serializable {
+    private final CommandType type;
+    private final List<Object> args;
+
+    public Command(CommandType type, List<Object> args) {
+        this.type = type;
+        this.args = args;
+    }
+
+    public CommandType getType() {
+        return type;
+    }
+
+    public List<Object> getArgs() {
+        return new ArrayList<>(args);
+    }
+}
diff --git a/src/fr/univ/lyon1/common/command/CommandType.java b/src/fr/univ/lyon1/common/command/CommandType.java
new file mode 100644
index 0000000..6e36acc
--- /dev/null
+++ b/src/fr/univ/lyon1/common/command/CommandType.java
@@ -0,0 +1,27 @@
+package fr.univ.lyon1.common.command;
+
+import java.io.Serializable;
+
+public enum CommandType implements Serializable {
+    login("login", "Login to the server"),
+    message("message", "Send a message"),
+    join("join", "Join a channel"),
+    leave("leave", "Leave a channel"),
+    list("list", "List all users"),
+    listChannels("listChannels", "List all channels");
+
+    private final String name;
+    private final String description;
+    CommandType(String name, String description) {
+        this.name = name;
+        this.description = description;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+}
diff --git a/src/fr/univ/lyon1/common/exception/ChatException.java b/src/fr/univ/lyon1/common/exception/ChatException.java
new file mode 100644
index 0000000..7749e46
--- /dev/null
+++ b/src/fr/univ/lyon1/common/exception/ChatException.java
@@ -0,0 +1,7 @@
+package fr.univ.lyon1.common.exception;
+
+public class ChatException extends Exception {
+    public ChatException(String message) {
+        super(message);
+    }
+}
diff --git a/src/fr/univ/lyon1/common/exception/LoginInvalid.java b/src/fr/univ/lyon1/common/exception/LoginInvalid.java
new file mode 100644
index 0000000..b412ec0
--- /dev/null
+++ b/src/fr/univ/lyon1/common/exception/LoginInvalid.java
@@ -0,0 +1,7 @@
+package fr.univ.lyon1.common.exception;
+
+public class LoginInvalid extends ChatException {
+    public LoginInvalid(String message) {
+        super(message);
+    }
+}
diff --git a/src/fr/univ/lyon1/common/exception/LoginRequired.java b/src/fr/univ/lyon1/common/exception/LoginRequired.java
new file mode 100644
index 0000000..72060ec
--- /dev/null
+++ b/src/fr/univ/lyon1/common/exception/LoginRequired.java
@@ -0,0 +1,7 @@
+package fr.univ.lyon1.common.exception;
+
+public class LoginRequired extends ChatException {
+    public LoginRequired() {
+        super("Login required");
+    }
+}
diff --git a/src/fr/univ/lyon1/common/exception/UnknownCommand.java b/src/fr/univ/lyon1/common/exception/UnknownCommand.java
new file mode 100644
index 0000000..32a7c29
--- /dev/null
+++ b/src/fr/univ/lyon1/common/exception/UnknownCommand.java
@@ -0,0 +1,9 @@
+package fr.univ.lyon1.common.exception;
+
+import fr.univ.lyon1.common.command.Command;
+
+public class UnknownCommand extends ChatException {
+    public UnknownCommand() {
+        super("Command unknown");
+    }
+}
diff --git a/src/fr/univ/lyon1/gui/ClientGUI.java b/src/fr/univ/lyon1/gui/ClientGUI.java
index cb19ab2..18acf9e 100644
--- a/src/fr/univ/lyon1/gui/ClientGUI.java
+++ b/src/fr/univ/lyon1/gui/ClientGUI.java
@@ -2,22 +2,21 @@ package fr.univ.lyon1.gui;
 
 import fr.univ.lyon1.client.Client;
 import fr.univ.lyon1.client.ClientReceive;
-import fr.univ.lyon1.common.Message;
+import fr.univ.lyon1.common.command.Command;
 
 import java.io.IOException;
 
 public class ClientGUI extends Client {
     private final MainGui gui;
 
-    public ClientGUI(MainGui gui, String address, int port) throws IOException, InterruptedException, Exception {
+    public ClientGUI(MainGui gui, String address, int port) throws Exception {
         super(address, port, null, null);
         this.gui = gui;
     }
 
     @Override
-    public Message messageReceived(Message msg) {
-        gui.receiveMessage(msg.toString());
-        return msg;
+    protected void commandMessage(Command cmd) {
+        gui.receiveMessage(cmd.getArgs().get(0).toString());
     }
 
     @Override
diff --git a/src/fr/univ/lyon1/server/ConnectedClient.java b/src/fr/univ/lyon1/server/ConnectedClient.java
index 3f583d7..74ce713 100644
--- a/src/fr/univ/lyon1/server/ConnectedClient.java
+++ b/src/fr/univ/lyon1/server/ConnectedClient.java
@@ -3,6 +3,12 @@ package fr.univ.lyon1.server;
 import fr.univ.lyon1.common.Channel;
 import fr.univ.lyon1.common.Message;
 import fr.univ.lyon1.common.User;
+import fr.univ.lyon1.common.command.Command;
+import fr.univ.lyon1.common.command.CommandType;
+import fr.univ.lyon1.common.exception.ChatException;
+import fr.univ.lyon1.common.exception.LoginInvalid;
+import fr.univ.lyon1.common.exception.LoginRequired;
+import fr.univ.lyon1.common.exception.UnknownCommand;
 import fr.univ.lyon1.server.models.ChannelModel;
 import fr.univ.lyon1.server.models.UserModel;
 
@@ -11,6 +17,7 @@ import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.net.Socket;
+import java.util.Collections;
 import java.util.List;
 
 public class ConnectedClient implements Runnable {
@@ -26,77 +33,67 @@ public class ConnectedClient implements Runnable {
         this.server = server;
         this.socket = socket;
         this.out = new ObjectOutputStream(socket.getOutputStream());
-
-        System.out.println("New user try to auth");
-        while (!this.auth());
-    }
-
-    private boolean auth() throws IOException {
-        if (in == null)
-            in = new ObjectInputStream(socket.getInputStream());
-
-        String username = in.readUTF();
-        System.out.println("username: "+username);
-        String password = in.readUTF();
-        System.out.println("Pass: "+password);
-
-        if (username.isEmpty() || password.isEmpty()) {
-            out.writeUTF("err: Login required");
-            out.flush();
-            return false;
-        }
-
-        UserModel user = UserModel.get(username);
-
-        if (user == null)
-            out.writeUTF("err: Username not found !");
-        else if (!user.checkPassword(password))
-            out.writeUTF("err: Password invalid !");
-        else {
-            out.writeUTF("logged");
-            out.flush();
-            this.user = user;
-            return  true;
-        }
-        out.flush();
-
-        return false;
+        this.in = new ObjectInputStream(socket.getInputStream());
     }
 
     public Message sendMessage(Message message) throws IOException {
-        out.writeObject(message);
+        out.writeObject(new Command(CommandType.message, List.of(message)));
         out.flush();
         return message;
     }
 
-    private void actionMessage(Object data) throws IOException, ClassNotFoundException {
-        Message msg = (Message) data;
+    private void actionCommand(Command command) throws IOException, ChatException {
+        CommandType type = command.getType();
+        if (user == null && type != CommandType.login)
+            throw new LoginRequired();
 
-        if (msg.getContent().startsWith("/"))
-            command(msg);
-        else {
-            msg.setSender(this.user);
-            server.broadcastMessage(msg, id);
+        switch (command.getType()) {
+            case login -> commandLogin(command);
+            case message -> commandMessage(command);
+            case list -> commandList();
+            case join -> commandJoin(command);
         }
     }
 
-    private void command(Message msg) throws IOException {
-        String content = msg.getContent();
-        if (content.equals("/list")) {
-            List<User> users = server.getUsers();
-            sendMessage(msg.repley(Server.getServerUser(), "Total: "+users.toArray().length + "\n" + String.join(", ", users.stream().map(User::getUsername).toList())));
-        } else if (content.startsWith("/join"))
-            actionJoinChannel(content);
+    private void commandLogin(Command cmd) throws IOException, ChatException {
+        List<Object> args = cmd.getArgs();
+
+        String username = (String) args.get(0);
+        System.out.println("username: "+username);
+        String password = (String) args.get(1);
+        System.out.println("Pass: "+password);
+
+        if (username.isEmpty() || password.isEmpty())
+            throw new LoginInvalid("Invalid args");
+
+        UserModel user = UserModel.get(username);
+
+        if (user == null)
+            throw new LoginInvalid("Username not found");
+        else if (!user.checkPassword(password))
+            throw new LoginInvalid("Password invalid");
+        else {
+            out.writeObject(new Command(CommandType.login, null));
+            out.flush();
+            this.user = user;
+            System.out.println("Client "+user.getUsername()+" is connected !");
+        }
     }
 
-    private void actionListUsers() throws IOException {
-        out.writeObject(server.getUsers());
+    private void commandMessage(Command cmd) {
+        Message msg = (Message) cmd.getArgs().get(0);
+        msg.setSender(this.user);
+        // ToDo: Check the user channel
+        server.broadcastMessage(msg, id);
+    }
+
+    private void commandList() throws IOException {
+            out.writeObject(new Command(CommandType.list, Collections.singletonList(server.getUsers())));
         out.flush();
     }
 
-    private void actionJoinChannel(String msg) throws IOException {
-        String name = msg.replaceAll("^(/?join) ", "");
-        System.out.println(name);
+    private void commandJoin(Command cmd) throws IOException {
+        String name = (String) cmd.getArgs().get(0);
         ChannelModel chan = ChannelModel.get(name);
 
         if (chan == null) {
@@ -106,7 +103,7 @@ public class ConnectedClient implements Runnable {
             if (!chan.have(user))
                 chan.addUser(user);
 
-        out.writeObject(chan);
+        out.writeObject(new Command(CommandType.join, List.of((Channel) chan)));
         out.flush();
 
         server.broadcastMessage(new Message(chan, Server.getServerUser(), user.getUsername()+" joined the channel !"), -1);
@@ -115,19 +112,18 @@ public class ConnectedClient implements Runnable {
     public void run() {
         try {
             while (true) {
-
                 Object data = in.readObject();
                 if (data == null)
                     break;
 
-                if (data instanceof Message)
-                    actionMessage(data);
-                else if (data instanceof String) {
-                    String msg = (String) data;
-                    if (data.equals("listUsers"))
-                        actionListUsers();
-                    else if (((String) data).startsWith("join"))
-                        actionJoinChannel(msg);
+                try {
+                    if (data instanceof Command)
+                        actionCommand((Command) data);
+                    else
+                        throw new UnknownCommand();
+                } catch (ChatException e) {
+                    out.writeObject(e);
+                    out.flush();
                 }
             }
         } catch (IOException | ClassNotFoundException e) {
diff --git a/src/fr/univ/lyon1/server/Server.java b/src/fr/univ/lyon1/server/Server.java
index 9ab29d6..8bf6058 100644
--- a/src/fr/univ/lyon1/server/Server.java
+++ b/src/fr/univ/lyon1/server/Server.java
@@ -23,9 +23,6 @@ public class Server {
 
     public ConnectedClient addClient(ConnectedClient newClient) {
         clients.add(newClient);
-
-        System.out.println("Client "+newClient.getUser().getUsername()+" is connected !");
-
         return newClient;
     }
 
diff --git a/src/module-info.java b/src/module-info.java
index b6f9ef6..670c9b7 100644
--- a/src/module-info.java
+++ b/src/module-info.java
@@ -8,5 +8,6 @@ module fr.univ.lyon1.gui {
     requires org.mariadb.jdbc;
 
     opens fr.univ.lyon1.gui to javafx.fxml;
+    exports fr.univ.lyon1.common.command;
     exports fr.univ.lyon1.gui;
 }
\ No newline at end of file