Fix potential protocol mismatch and exploit for plugin message channel

src/main/java/net/minestom/server/entity/Player.java

@@ -7,6 +7,7 @@
 import net.kyori.adventure.identity.Identified;
 import net.kyori.adventure.identity.Identity;
 import net.kyori.adventure.inventory.Book;
+import net.kyori.adventure.key.Key;
 import net.kyori.adventure.pointer.Pointers;
 import net.kyori.adventure.resource.ResourcePackCallback;
 import net.kyori.adventure.resource.ResourcePackInfo;
@@ -904,8 +905,20 @@ public void sendMessage(final @NotNull Identity source, final @NotNull Component
      *
      * @param channel the message channel
      * @param data    the message data
+     * @deprecated Use {@link #sendPluginMessage(Key, byte[])} instead.
      */
+    @Deprecated(forRemoval = true, since = "1.5.0")
     public void sendPluginMessage(@NotNull String channel, byte @NotNull [] data) {
+        sendPluginMessage(Key.key(channel), data);
+    }
+
+    /**
+     * Sends a plugin message to the player.
+     *
+     * @param channel the message channel
+     * @param data    the message data
+     */
+    public void sendPluginMessage(@NotNull Key channel, byte @NotNull [] data) {
         sendPacket(new PluginMessagePacket(channel, data));
     }
 
@@ -916,7 +929,9 @@ public void sendPluginMessage(@NotNull String channel, byte @NotNull [] data) {
      *
      * @param channel the message channel
      * @param message the message
+     * @deprecated Use {@link #sendPluginMessage(Key, byte[])} instead.
      */
+    @Deprecated(forRemoval = true, since = "1.5.0")
     public void sendPluginMessage(@NotNull String channel, @NotNull String message) {
         sendPluginMessage(channel, message.getBytes(StandardCharsets.UTF_8));
     }

src/main/java/net/minestom/server/network/packet/server/common/PluginMessagePacket.java

@@ -1,5 +1,6 @@
 package net.minestom.server.network.packet.server.common;
 
+import net.kyori.adventure.key.Key;
 import net.minestom.server.MinecraftServer;
 import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.packet.server.ServerPacket;
@@ -9,15 +10,15 @@
 import static net.minestom.server.network.NetworkBuffer.RAW_BYTES;
 import static net.minestom.server.network.NetworkBuffer.STRING;
 
-public record PluginMessagePacket(String channel,
+public record PluginMessagePacket(Key channel,
                                   byte[] data) implements ServerPacket.Configuration, ServerPacket.Play {
     public PluginMessagePacket(@NotNull NetworkBuffer reader) {
-        this(reader.read(STRING), reader.read(RAW_BYTES));
+        this(Key.key(reader.read(STRING)), reader.read(RAW_BYTES));
     }
 
     @Override
     public void write(@NotNull NetworkBuffer writer) {
-        writer.write(STRING, channel);
+        writer.write(STRING, channel.asString());
         writer.write(RAW_BYTES, data);
     }
 
@@ -41,6 +42,6 @@ public int playId() {
     public static @NotNull PluginMessagePacket getBrandPacket() {
         final String brandName = MinecraftServer.getBrandName();
         final byte[] data = NetworkBuffer.makeArray(networkBuffer -> networkBuffer.write(STRING, brandName));
-        return new PluginMessagePacket("minecraft:brand", data);
+        return new PluginMessagePacket(Key.key("minecraft:brand"), data);
     }
 }