Removed all entity ID rewriting logic.

This was all a no-op anyway, and should the need for this arise again,
it is trivial to re-add. However, Velocity does not need this, and
probably will never need it. Let's have the complexity go away.

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -86,11 +86,7 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
             connection.getMinecraftConnection().close();
             return;
         }
-
+        connection.getPlayer().getConnection().write(buf.retain());
-        ClientPlaySessionHandler playerHandler =
-                (ClientPlaySessionHandler) connection.getPlayer().getConnection().getSessionHandler();
-        ByteBuf remapped = playerHandler.getIdRemapper().remap(buf, ProtocolConstants.Direction.CLIENTBOUND);
-        connection.getPlayer().getConnection().write(remapped);
     }
 
     @Override

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -8,7 +8,6 @@ import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import com.velocitypowered.proxy.protocol.packet.*;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
-import com.velocitypowered.proxy.protocol.remap.EntityIdRemapper;
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import com.velocitypowered.proxy.util.ThrowableUtils;
 import io.netty.buffer.ByteBuf;
@@ -33,7 +32,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
     private boolean spawned = false;
     private final List<UUID> serverBossBars = new ArrayList<>();
     private final Set<String> clientPluginMsgChannels = new HashSet<>();
-    private EntityIdRemapper idRemapper;
 
     public ClientPlaySessionHandler(ConnectedPlayer player) {
         this.player = player;
@@ -127,8 +125,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
     @Override
     public void handleUnknown(ByteBuf buf) {
-        ByteBuf remapped = idRemapper.remap(buf, ProtocolConstants.Direction.SERVERBOUND);
+        player.getConnectedServer().getMinecraftConnection().write(buf.retain());
-        player.getConnectedServer().getMinecraftConnection().write(remapped);
     }
 
     @Override
@@ -152,7 +149,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             // nothing special to do here
             spawned = true;
             player.getConnection().delayedWrite(joinGame);
-            idRemapper = EntityIdRemapper.getMapper(joinGame.getEntityId(), player.getConnection().getProtocolVersion());
         } else {
             // Ah, this is the meat and potatoes of the whole venture!
             //
@@ -167,7 +163,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             // Most notably, by having the client accept the join game packet, we can work around the need to perform
             // entity ID rewrites, eliminating potential issues from rewriting packets and improving compatibility with
             // mods.
-            idRemapper.setServerEntityId(joinGame.getEntityId());
             player.getConnection().delayedWrite(joinGame);
             int tempDim = joinGame.getDimension() == 0 ? -1 : 0;
             player.getConnection().delayedWrite(new Respawn(tempDim, joinGame.getDifficulty(), joinGame.getGamemode(), joinGame.getLevelType()));
@@ -250,10 +245,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
         return clientPluginMsgChannels;
     }
 
-    public EntityIdRemapper getIdRemapper() {
-        return idRemapper;
-    }
-
     public void setLastPing(long lastPing) {
         this.lastPingID = lastPing;
         this.lastPingSent = System.currentTimeMillis();

proxy/src/main/java/com/velocitypowered/proxy/protocol/remap/EntityIdRemapper.java

@@ -1,29 +0,0 @@
-package com.velocitypowered.proxy.protocol.remap;
-
-import com.velocitypowered.proxy.protocol.ProtocolConstants;
-import io.netty.buffer.ByteBuf;
-
-/**
- * Represents a protocol-specific entity ID remapper for certain Minecraft packets. This is mostly required to support
- * old versions of Minecraft. For Minecraft 1.8 clients and above, Velocity can use a more efficient method based on
- * sending JoinGame packets multiple times.
- */
-public interface EntityIdRemapper {
-    /**
-     * Remaps the entity IDs in this packet so that they apply to the player.
-     * @param original the packet to remap
-     * @param direction the direction of the packet
-     * @return a remapped packet, which may either be a retained version of the original buffer or an entirely new buffer
-     */
-    ByteBuf remap(ByteBuf original, ProtocolConstants.Direction direction);
-
-    int getClientEntityId();
-
-    int getServerEntityId();
-
-    void setServerEntityId(int id);
-
-    static EntityIdRemapper getMapper(int eid, int protocolVersion) {
-        return NoopEntityIdRemapper.INSTANCE;
-    }
-}

proxy/src/main/java/com/velocitypowered/proxy/protocol/remap/NoopEntityIdRemapper.java

@@ -1,32 +0,0 @@
-package com.velocitypowered.proxy.protocol.remap;
-
-import com.velocitypowered.proxy.protocol.ProtocolConstants;
-import io.netty.buffer.ByteBuf;
-
-public class NoopEntityIdRemapper implements EntityIdRemapper {
-    public static final NoopEntityIdRemapper INSTANCE = new NoopEntityIdRemapper();
-
-    private NoopEntityIdRemapper() {
-
-    }
-
-    @Override
-    public ByteBuf remap(ByteBuf original, ProtocolConstants.Direction direction) {
-        return original.retain();
-    }
-
-    @Override
-    public int getClientEntityId() {
-        return 0;
-    }
-
-    @Override
-    public int getServerEntityId() {
-        return 0;
-    }
-
-    @Override
-    public void setServerEntityId(int id) {
-
-    }
-}