Fix 1.20.2->1.20 if run on the backend

Author: kennytv

common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_20to1_20_2/Protocol1_20To1_20_2.java

@@ -27,6 +27,7 @@
 import com.viaversion.viaversion.api.minecraft.entities.Entity1_19_4Types;
 import com.viaversion.viaversion.api.protocol.packet.Direction;
 import com.viaversion.viaversion.api.protocol.packet.PacketWrapper;
+import com.viaversion.viaversion.api.protocol.packet.ServerboundPacketType;
 import com.viaversion.viaversion.api.protocol.packet.State;
 import com.viaversion.viaversion.api.rewriter.EntityRewriter;
 import com.viaversion.viaversion.api.rewriter.ItemRewriter;
@@ -44,6 +45,7 @@
 import com.viaversion.viaversion.protocols.protocol1_20_2to1_20.packet.ServerboundConfigurationPackets1_20_2;
 import com.viaversion.viaversion.protocols.protocol1_20_2to1_20.packet.ServerboundPackets1_20_2;
 import java.util.UUID;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 public final class Protocol1_20To1_20_2 extends BackwardsProtocol<ClientboundPackets1_20_2, ClientboundPackets1_19_4, ServerboundPackets1_20_2, ServerboundPackets1_19_4> {
 
@@ -70,17 +72,18 @@ protected void registerPackets() {
         });
 
         registerClientbound(State.LOGIN, ClientboundLoginPackets.GAME_PROFILE.getId(), ClientboundLoginPackets.GAME_PROFILE.getId(), wrapper -> {
-            final ServerboundLoginPackets ackPacket = ServerboundLoginPackets.LOGIN_ACKNOWLEDGED;
-            wrapper.create(ackPacket).sendToServer(Protocol1_20To1_20_2.class);
-
             // We can't set the internal state to configuration here as protocols down the line will expect the state to be play
+            // Add this *before* sending the ack since the server might immediately answer
             wrapper.user().put(new ConfigurationPacketStorage());
+            wrapper.create(ServerboundLoginPackets.LOGIN_ACKNOWLEDGED).sendToServer(Protocol1_20To1_20_2.class);
+            // TODO Client needs to be set to CONFIGURATION state
         });
 
         registerClientbound(State.CONFIGURATION, ClientboundConfigurationPackets1_20_2.FINISH_CONFIGURATION.getId(), ClientboundConfigurationPackets1_20_2.FINISH_CONFIGURATION.getId(), wrapper -> {
             wrapper.cancel();
-            wrapper.create(ServerboundConfigurationPackets1_20_2.FINISH_CONFIGURATION).sendToServer(Protocol1_20To1_20_2.class);
             wrapper.user().get(ConfigurationPacketStorage.class).setFinished(true);
+            wrapper.create(ServerboundConfigurationPackets1_20_2.FINISH_CONFIGURATION).sendToServer(Protocol1_20To1_20_2.class);
+            // TODO Client needs to be set to PLAY phase
         });
 
         registerServerbound(State.LOGIN, ServerboundLoginPackets.HELLO.getId(), ServerboundLoginPackets.HELLO.getId(), wrapper -> {
@@ -96,6 +99,7 @@ protected void registerPackets() {
             // TODO: Check whether all the necessary data for the join game packet is always expected by the client or if we need to cache it from the initial login
             final PacketWrapper configAcknowledgedPacket = wrapper.create(ServerboundPackets1_20_2.CONFIGURATION_ACKNOWLEDGED);
             configAcknowledgedPacket.sendToServer(Protocol1_20To1_20_2.class);
+            // TODO Client needs to be set to CONFIGURATION state
 
             wrapper.user().put(new ConfigurationPacketStorage());
         });
@@ -159,6 +163,16 @@ public void transform(final Direction direction, final State state, final Packet
         }
     }
 
+    @Override
+    protected @Nullable ServerboundPackets1_19_4 configurationAcknowledgedPacket() {
+        return null;
+    }
+
+    @Override
+    protected @Nullable ServerboundPacketType finishConfigurationPacket() {
+        return null;
+    }
+
     @Override
     public void init(final UserConnection connection) {
         addEntityTracker(connection, new EntityTrackerBase(connection, Entity1_19_4Types.PLAYER));