Add it so when you're on 1.9 you can block using shields. Also change ConnectionInfo to use lombok.

src/main/java/us/myles/ViaVersion/ConnectionInfo.java

@@ -1,14 +1,16 @@
 package us.myles.ViaVersion;
 
 import io.netty.buffer.ByteBuf;
-import io.netty.channel.*;
+import io.netty.channel.ChannelHandler;
 import io.netty.channel.socket.SocketChannel;
+import lombok.Getter;
+import lombok.Setter;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
 import us.myles.ViaVersion.packets.State;
 
-import java.util.UUID;
+@Getter
-
+@Setter
 public class ConnectionInfo {
     private final SocketChannel channel;
     private Object lastPacket;
@@ -17,6 +19,7 @@ public class ConnectionInfo {
     private String openWindow;
     private int protocol = 0;
     private int compression = 0;
+    private int entityID;
     private boolean active = true;
     private String username;
 
@@ -24,64 +27,19 @@ public class ConnectionInfo {
         this.channel = socketChannel;
     }
 
-    public int getProtocol() {
-        return protocol;
-    }
-
-    public void setProtocol(int protocol) {
-        this.protocol = protocol;
-    }
-
-    public State getState() {
-        return state;
-    }
-
-    public void setState(State state) {
-        this.state = state;
-    }
-
-    public int getCompression() {
-        return compression;
-    }
-
-    public void setCompression(int compression) {
-        this.compression = compression;
-    }
-
-    public Object getLastPacket() {
-        return lastPacket;
-    }
-
-    public void setLastPacket(Object lastPacket) {
-        this.lastPacket = lastPacket;
-    }
-
-    public java.util.UUID getUUID() {
-        return UUID;
-    }
-
-    public void setUUID(UUID UUID) {
-        this.UUID = UUID;
-    }
-
     public Player getPlayer() {
         return UUID == null ? null : Bukkit.getPlayer(UUID);
     }
 
-    public SocketChannel getChannel() {
-        return channel;
-    }
-
-    public boolean isActive() {
-        return active;
-    }
-
     public void setActive(boolean active) {
         this.active = active;
     }
 
-    public void sendRawPacket(final ByteBuf packet) {
+    public void sendRawPacket(final ByteBuf packet, boolean currentThread) {
         final ChannelHandler handler = channel.pipeline().get("encoder");
+        if (currentThread) {
+            channel.pipeline().context(handler).writeAndFlush(packet);
+        } else {
             channel.eventLoop().submit(new Runnable() {
                 @Override
                 public void run() {
@@ -89,24 +47,13 @@ public class ConnectionInfo {
                 }
             });
         }
-
-    public String getOpenWindow() {
-        return openWindow;
     }
 
-    public void setOpenWindow(String openWindow) {
+    public void sendRawPacket(final ByteBuf packet) {
-        this.openWindow = openWindow;
+        sendRawPacket(packet, false);
     }
 
     public void closeWindow() {
         this.openWindow = null;
     }
-
-    public String getUsername() {
-        return username;
-    }
-
-    public void setUsername(String username) {
-        this.username = username;
-    }
 }

src/main/java/us/myles/ViaVersion/transformers/IncomingTransformer.java

@@ -17,6 +17,7 @@ import java.io.IOException;
 
 public class IncomingTransformer {
     private final ConnectionInfo info;
+    private boolean startedBlocking = false;
 
     public IncomingTransformer(ConnectionInfo info) {
         this.info = info;
@@ -87,6 +88,11 @@ public class IncomingTransformer {
         }
         if (packet == PacketType.PLAY_PLAYER_DIGGING) {
             int status = input.readByte() & 0xFF; // unsign
+            if (status == 5 && startedBlocking) {
+                // stopped blocking
+                startedBlocking = false;
+                sendSecondHandItem(null);
+            }
             if (status == 6) { // item swap
                 throw new CancelException();
             }
@@ -95,6 +101,13 @@ public class IncomingTransformer {
             output.writeBytes(input);
             return;
         }
+        if (packet == PacketType.PLAY_HELD_ITEM_CHANGE_REQUEST) {
+            if (startedBlocking) {
+                // stopped blocking
+                startedBlocking = false;
+                sendSecondHandItem(null);
+            }
+        }
         if (packet == PacketType.PLAY_CLICK_WINDOW) {
             // if placed in new slot, reject :)
             int windowID = input.readUnsignedByte();
@@ -268,6 +281,7 @@ public class IncomingTransformer {
             return;
         }
         if (packet == PacketType.PLAY_USE_ITEM) {
+            int hand = PacketUtil.readVarInt(input);
             output.clear();
             PacketUtil.writeVarInt(PacketType.PLAY_PLAYER_BLOCK_PLACEMENT.getPacketID(), output);
             // Simulate using item :)
@@ -275,6 +289,22 @@ public class IncomingTransformer {
             output.writeByte(255);
             // write item in hand
             ItemStack inHand = ViaVersionPlugin.getHandItem(info);
+            if (inHand != null) {
+                if (inHand.getType().name().endsWith("SWORD")) {
+                    // blocking?
+                    if (hand == 0) {
+                        if (!startedBlocking) {
+                            startedBlocking = true;
+                            ItemSlotRewriter.ItemStack shield = new ItemSlotRewriter.ItemStack();
+                            shield.id = 442;
+                            shield.amount = 1;
+                            shield.data = 0;
+                            sendSecondHandItem(shield);
+                        }
+                        throw new CancelException();
+                    }
+                }
+            }
             try {
                 ItemSlotRewriter.ItemStack item = ItemSlotRewriter.ItemStack.fromBukkit(inHand);
                 ItemSlotRewriter.fixIdsFrom1_9To1_8(item);
@@ -296,4 +326,18 @@ public class IncomingTransformer {
         }
         output.writeBytes(input);
     }
+
+    private void sendSecondHandItem(ItemSlotRewriter.ItemStack o) {
+        ByteBuf buf = info.getChannel().alloc().buffer();
+        PacketUtil.writeVarInt(PacketType.PLAY_ENTITY_EQUIPMENT.getNewPacketID(), buf);
+        PacketUtil.writeVarInt(info.getEntityID(), buf);
+        PacketUtil.writeVarInt(1, buf); // slot
+        // write shield
+        try {
+            ItemSlotRewriter.writeItemStack(o, buf);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        info.sendRawPacket(buf);
+    }
 }

src/main/java/us/myles/ViaVersion/transformers/OutgoingTransformer.java

@@ -1,15 +1,12 @@
 package us.myles.ViaVersion.transformers;
 
 import io.netty.buffer.ByteBuf;
-import io.netty.buffer.ByteBufInputStream;
-import io.netty.buffer.ByteBufOutputStream;
 import org.bukkit.entity.EntityType;
 import org.json.simple.JSONObject;
 import org.json.simple.parser.JSONParser;
 import org.json.simple.parser.ParseException;
 import org.spacehq.mc.protocol.data.game.chunk.Column;
 import org.spacehq.mc.protocol.util.NetUtil;
-import org.spacehq.opennbt.NBTIO;
 import org.spacehq.opennbt.tag.builtin.ByteTag;
 import org.spacehq.opennbt.tag.builtin.CompoundTag;
 import org.spacehq.opennbt.tag.builtin.StringTag;
@@ -26,8 +23,6 @@ import us.myles.ViaVersion.util.EntityUtil;
 import us.myles.ViaVersion.util.PacketUtil;
 import us.myles.ViaVersion.util.ReflectionUtil;
 
-import java.io.DataInputStream;
-import java.io.DataOutputStream;
 import java.io.IOException;
 import java.util.*;
 
@@ -566,6 +561,7 @@ public class OutgoingTransformer {
         if (packet == PacketType.PLAY_JOIN_GAME) {
             int id = input.readInt();
             clientEntityTypes.put(id, EntityType.PLAYER);
+            info.setEntityID(id);
             output.writeInt(id);
             output.writeBytes(input);
             return;
@@ -798,9 +794,31 @@ public class OutgoingTransformer {
             return;
         }
         List<MetadataRewriter.Entry> list = MetadataRewriter.readMetadata1_8(type, input);
+        for (MetadataRewriter.Entry entry : list) {
+            handleMetadata(entityID, entry, type);
+        }
         MetadataRewriter.writeMetadata1_9(type, list, output);
     }
 
+    private void handleMetadata(int entityID, MetadataRewriter.Entry entry, EntityType type) {
+        // This handles old IDs
+        if (type == EntityType.PLAYER) {
+            if (entry.getOldID() == 0) {
+                // Byte
+                byte data = (byte) entry.getValue();
+                if ((data & 0x10) == 0x10) {
+                    ItemSlotRewriter.ItemStack shield = new ItemSlotRewriter.ItemStack();
+                    shield.id = 442;
+                    shield.amount = 1;
+                    shield.data = 0;
+                    sendSecondHandItem(entityID, shield);
+                } else {
+                    sendSecondHandItem(entityID, null);
+                }
+            }
+        }
+    }
+
 
     private UUID getUUID(int id) {
         if (uuidMap.containsKey(id)) {
@@ -812,4 +830,18 @@ public class OutgoingTransformer {
         }
     }
 
+    private void sendSecondHandItem(int entityID, ItemSlotRewriter.ItemStack o) {
+
+        ByteBuf buf = info.getChannel().alloc().buffer();
+        PacketUtil.writeVarInt(PacketType.PLAY_ENTITY_EQUIPMENT.getNewPacketID(), buf);
+        PacketUtil.writeVarInt(entityID, buf);
+        PacketUtil.writeVarInt(1, buf); // slot
+        // write shield
+        try {
+            ItemSlotRewriter.writeItemStack(o, buf);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        info.sendRawPacket(buf, true);
+    }
 }