feat: use nextState on packet write to change states to ensure proper synchronization

src/main/java/net/minestom/server/listener/manager/PacketListenerManager.java

@@ -128,6 +128,13 @@ public final class PacketListenerManager {
             // Packet is likely invalid
             MinecraftServer.getExceptionManager().handleException(e);
         }
+
+        // If the packet intends to switch state, do it now.
+        var nextState = packet.nextState();
+        if (nextState != null && state != nextState) {
+            System.out.println("CHANGE CLIENT STATE TO " + nextState);
+            connection.setClientState(nextState);
+        }
     }
 
     /**

src/main/java/net/minestom/server/listener/preplay/HandshakeListener.java

@@ -40,7 +40,7 @@ public final class HandshakeListener {
     public static void listener(@NotNull ClientHandshakePacket packet, @NotNull PlayerConnection connection) {
         String address = packet.serverAddress();
         // Bungee support (IP forwarding)
-        if (BungeeCordProxy.isEnabled() && connection instanceof PlayerSocketConnection socketConnection && packet.nextState() == 2) {
+        if (BungeeCordProxy.isEnabled() && connection instanceof PlayerSocketConnection socketConnection && packet.intent() == 2) {
             final String[] split = address.split("\00");
 
             if (split.length == 3 || split.length == 4) {
@@ -110,7 +110,7 @@ public final class HandshakeListener {
             ((PlayerSocketConnection) connection).refreshServerInformation(address, packet.serverPort(), packet.protocolVersion());
         }
 
-        switch (packet.nextState()) {
+        switch (packet.intent()) {
             case 1 -> {
                 connection.setClientState(ConnectionState.STATUS);
                 connection.setServerState(ConnectionState.STATUS);

src/main/java/net/minestom/server/listener/preplay/LoginListener.java

@@ -220,9 +220,7 @@ public final class LoginListener {
         }
     }
 
-    public static void loginAckListener(@NotNull ClientLoginAcknowledgedPacket packet, @NotNull PlayerConnection connection) {
+    public static void loginAckListener(@NotNull ClientLoginAcknowledgedPacket ignored, @NotNull PlayerConnection connection) {
-        connection.setClientState(ConnectionState.CONFIGURATION);
-
         CONNECTION_MANAGER.registerPlayer(connection.getPlayer());
 
         // Registry data
@@ -262,7 +260,6 @@ public final class LoginListener {
         AsyncUtils.runAsync(() -> {
             //todo event
 
-            connection.setServerState(ConnectionState.PLAY);
             connection.sendPacket(new FinishConfigurationPacket());
         });
     }

src/main/java/net/minestom/server/network/ConnectionManager.java

@@ -217,10 +217,10 @@ public final class ConnectionManager {
                     player.setUuid(eventUuid);
                 }
             }
-            // Send login success packet
+
+            // Send login success packet (and switch to configuration phase)
             LoginSuccessPacket loginSuccessPacket = new LoginSuccessPacket(player.getUuid(), player.getUsername(), 0);
             playerConnection.sendPacket(loginSuccessPacket);
-            playerConnection.setServerState(ConnectionState.CONFIGURATION);
         });
     }
 

src/main/java/net/minestom/server/network/NetworkBufferTypes.java

@@ -240,7 +240,7 @@ final class NetworkBufferTypes {
                         // Kotlin - https://discord.com/channels/706185253441634317/706186227493109860/1163703658341478462
                         buffer.write(BYTE, (byte) NBTType.TAG_End.getOrdinal());
                     } else {
-                        buffer.write(BYTE, (byte) NBTType.TAG_Compound.getOrdinal());
+                        buffer.write(BYTE, (byte) value.getID().getOrdinal());
                         nbtWriter.writeRaw(value);
                     }
                 } catch (IOException e) {
@@ -265,7 +265,10 @@ final class NetworkBufferTypes {
                     buffer.nbtReader = nbtReader;
                 }
                 try {
-                    return nbtReader.read();
+                    byte tagId = buffer.read(BYTE);
+                    if (tagId == NBTType.TAG_End.getOrdinal())
+                        return NBTEnd.INSTANCE;
+                    return nbtReader.readRaw(tagId);
                 } catch (IOException | NBTException e) {
                     throw new RuntimeException(e);
                 }

src/main/java/net/minestom/server/network/packet/client/ClientPacket.java

@@ -1,6 +1,8 @@
 package net.minestom.server.network.packet.client;
 
+import net.minestom.server.network.ConnectionState;
 import net.minestom.server.network.NetworkBuffer;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents a packet received from a client.
@@ -8,4 +10,8 @@ import net.minestom.server.network.NetworkBuffer;
  * Packets are value-based, and should therefore not be reliant on identity.
  */
 public interface ClientPacket extends NetworkBuffer.Writer {
+
+    default @Nullable ConnectionState nextState() {
+        return null;
+    }
 }

src/main/java/net/minestom/server/network/packet/client/configuration/ClientFinishConfigurationPacket.java

@@ -1,8 +1,10 @@
 package net.minestom.server.network.packet.client.configuration;
 
+import net.minestom.server.network.ConnectionState;
 import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.packet.client.ClientPacket;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public record ClientFinishConfigurationPacket() implements ClientPacket {
 
@@ -14,4 +16,8 @@ public record ClientFinishConfigurationPacket() implements ClientPacket {
     public void write(@NotNull NetworkBuffer writer) {
     }
 
+    @Override
+    public @NotNull ConnectionState nextState() {
+        return ConnectionState.PLAY;
+    }
 }

src/main/java/net/minestom/server/network/packet/client/handshake/ClientHandshakePacket.java

@@ -8,7 +8,7 @@ import org.jetbrains.annotations.NotNull;
 import static net.minestom.server.network.NetworkBuffer.*;
 
 public record ClientHandshakePacket(int protocolVersion, @NotNull String serverAddress,
-                                    int serverPort, int nextState) implements ClientPacket {
+                                    int serverPort, int intent) implements ClientPacket {
 
     public ClientHandshakePacket {
         if (serverAddress.length() > getMaxHandshakeLength()) {
@@ -30,7 +30,7 @@ public record ClientHandshakePacket(int protocolVersion, @NotNull String serverA
         }
         writer.write(STRING, serverAddress);
         writer.write(UNSIGNED_SHORT, serverPort);
-        writer.write(VAR_INT, nextState);
+        writer.write(VAR_INT, intent);
     }
 
     private static int getMaxHandshakeLength() {

src/main/java/net/minestom/server/network/packet/client/login/ClientLoginAcknowledgedPacket.java

@@ -1,8 +1,10 @@
 package net.minestom.server.network.packet.client.login;
 
+import net.minestom.server.network.ConnectionState;
 import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.packet.client.ClientPacket;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public record ClientLoginAcknowledgedPacket() implements ClientPacket {
 
@@ -14,4 +16,8 @@ public record ClientLoginAcknowledgedPacket() implements ClientPacket {
     public void write(@NotNull NetworkBuffer writer) {
     }
 
+    @Override
+    public @NotNull ConnectionState nextState() {
+        return ConnectionState.CONFIGURATION;
+    }
 }

src/main/java/net/minestom/server/network/packet/server/ServerPacket.java

@@ -4,6 +4,7 @@ import net.minestom.server.network.ConnectionState;
 import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.player.PlayerConnection;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents a packet which can be sent to a player using {@link PlayerConnection#sendPacket(SendablePacket)}.
@@ -21,4 +22,9 @@ public non-sealed interface ServerPacket extends NetworkBuffer.Writer, SendableP
      */
     int getId(@NotNull ConnectionState state);
 
+    // If not null, the server will switch state immediately after sending this packet
+    default @Nullable ConnectionState nextState() {
+        return null;
+    }
+
 }

src/main/java/net/minestom/server/network/packet/server/configuration/FinishConfigurationPacket.java

@@ -5,6 +5,7 @@ import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.packet.server.ServerPacket;
 import net.minestom.server.network.packet.server.ServerPacketIdentifier;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public record FinishConfigurationPacket() implements ServerPacket {
 
@@ -20,4 +21,9 @@ public record FinishConfigurationPacket() implements ServerPacket {
     public int getId(@NotNull ConnectionState state) {
         return ServerPacketIdentifier.CONFIGURATION_FINISH_CONFIGURATION;
     }
+
+    @Override
+    public @NotNull ConnectionState nextState() {
+        return ConnectionState.PLAY;
+    }
 }

src/main/java/net/minestom/server/network/packet/server/login/LoginSuccessPacket.java

@@ -5,6 +5,7 @@ import net.minestom.server.network.NetworkBuffer;
 import net.minestom.server.network.packet.server.ServerPacket;
 import net.minestom.server.network.packet.server.ServerPacketIdentifier;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.UUID;
 
@@ -27,4 +28,9 @@ public record LoginSuccessPacket(@NotNull UUID uuid, @NotNull String username, i
     public int getId(@NotNull ConnectionState state) {
         return ServerPacketIdentifier.LOGIN_SUCCESS;
     }
+
+    @Override
+    public @NotNull ConnectionState nextState() {
+        return ConnectionState.CONFIGURATION;
+    }
 }

src/main/java/net/minestom/server/network/player/PlayerConnection.java

@@ -166,7 +166,7 @@ public abstract class PlayerConnection {
      * @return the server connection state
      */
     public @NotNull ConnectionState getServerState() {
-        return clientState;
+        return serverState;
     }
 
     public PlayerPublicKey playerPublicKey() {

src/main/java/net/minestom/server/network/player/PlayerSocketConnection.java

@@ -379,9 +379,16 @@ public class PlayerSocketConnection extends PlayerConnection {
             }
         }
         try (var hold = ObjectPool.PACKET_POOL.hold()) {
-            var buffer = PacketUtils.createFramedPacket(getServerState(), hold.get(), serverPacket, compressed);
+            var state = getServerState();
+            var buffer = PacketUtils.createFramedPacket(state, hold.get(), serverPacket, compressed);
             System.out.println("SEND " + getServerState() + " cls=" + serverPacket.getClass().getSimpleName() + " id=" + serverPacket.getId(getServerState()));
             writeBufferSync(buffer, 0, buffer.limit());
+
+            var nextState = serverPacket.nextState();
+            if (nextState != null && state != nextState) {
+                System.out.println("CHANGE SERVER STATE TO " + nextState);
+                setServerState(nextState);
+            }
         }
     }