Add config option for blocking and fix crash due to synchronization

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

@@ -116,23 +116,27 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI {
             if (connection != null) {
                 for (Field field : connection.getClass().getDeclaredFields()) {
                     field.setAccessible(true);
-                    Object value = field.get(connection);
+                    final Object value = field.get(connection);
                     if (value instanceof List) {
                         // Inject the list
                         field.set(connection, new ListWrapper((List) value) {
                             @Override
                             public void handleAdd(Object o) {
-                                if (o instanceof ChannelFuture) {
-                                    inject((ChannelFuture) o);
+                                synchronized (value) {
+                                    if (o instanceof ChannelFuture) {
+                                        inject((ChannelFuture) o);
+                                    }
                                 }
                             }
                         });
                         // Iterate through current list
-                        for (Object o : (List) value) {
-                            if (o instanceof ChannelFuture) {
-                                inject((ChannelFuture) o);
-                            } else {
-                                break; // not the right list.
+                        synchronized (value) {
+                            for (Object o : (List) value) {
+                                if (o instanceof ChannelFuture) {
+                                    inject((ChannelFuture) o);
+                                } else {
+                                    break; // not the right list.
+                                }
                             }
                         }
                     }
@@ -221,6 +225,10 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI {
         return getConfig().getBoolean("suppress-metadata-errors", false);
     }
 
+    public boolean isShieldBlocking() {
+        return getConfig().getBoolean("shield-blocking", true);
+    }
+
     public boolean isAutoTeam() {
         // Collision has to be enabled first
         if (!isPreventCollision()) return false;

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

@@ -16,6 +16,7 @@ import us.myles.ViaVersion.util.PacketUtil;
 import java.io.IOException;
 
 public class IncomingTransformer {
+    private final ViaVersionPlugin plugin = (ViaVersionPlugin) ViaVersion.getInstance();
     private final ConnectionInfo info;
     private boolean startedBlocking = false;
 
@@ -34,7 +35,7 @@ public class IncomingTransformer {
         if (packet.getPacketID() != -1) {
             packetID = packet.getPacketID();
         }
-        if (ViaVersion.getInstance().isDebug()) {
+        if (plugin.isDebug()) {
             if (packet != PacketType.PLAY_PLAYER_POSITION_LOOK_REQUEST && packet != PacketType.PLAY_KEEP_ALIVE_REQUEST && packet != PacketType.PLAY_PLAYER_POSITION_REQUEST && packet != PacketType.PLAY_PLAYER_LOOK_REQUEST) {
                 System.out.println("Direction " + packet.getDirection().name() + " Packet Type: " + packet + " New ID: " + packetID + " Original: " + original + " Size: " + input.readableBytes());
             }
@@ -267,7 +268,7 @@ public class IncomingTransformer {
             output.writeByte(face);
             PacketUtil.readVarInt(input);
 
-            ItemStack inHand = ViaVersionPlugin.getHandItem(info);
+            ItemStack inHand = plugin.getHandItem(info);
             try {
                 ItemSlotRewriter.ItemStack item = ItemSlotRewriter.ItemStack.fromBukkit(inHand);
                 ItemSlotRewriter.fixIdsFrom1_9To1_8(item);
@@ -291,8 +292,8 @@ public class IncomingTransformer {
             output.writeLong(-1L);
             output.writeByte(255);
             // write item in hand
-            ItemStack inHand = ViaVersionPlugin.getHandItem(info);
-            if (inHand != null) {
+            ItemStack inHand = plugin.getHandItem(info);
+            if (inHand != null && plugin.isShieldBlocking()) {
                 if (inHand.getType().name().endsWith("SWORD")) {
                     // blocking?
                     if (hand == 0) {

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

@@ -830,17 +830,18 @@ public class OutgoingTransformer {
             if (entry.getOldID() == 0) {
                 // Byte
                 byte data = (byte) entry.getValue();
-
-                if ((data & 0x10) == 0x10) {
-                    if (validBlocking.contains(entityID)) {
-                        ItemSlotRewriter.ItemStack shield = new ItemSlotRewriter.ItemStack();
-                        shield.id = 442;
-                        shield.amount = 1;
-                        shield.data = 0;
-                        sendSecondHandItem(entityID, shield);
+                if (entityID != info.getEntityID() && plugin.isShieldBlocking()) {
+                    if ((data & 0x10) == 0x10) {
+                        if (validBlocking.contains(entityID)) {
+                            ItemSlotRewriter.ItemStack shield = new ItemSlotRewriter.ItemStack();
+                            shield.id = 442;
+                            shield.amount = 1;
+                            shield.data = 0;
+                            sendSecondHandItem(entityID, shield);
+                        }
+                    } else {
+                        sendSecondHandItem(entityID, null);
                     }
-                } else {
-                    sendSecondHandItem(entityID, null);
                 }
             }
         }

src/main/resources/config.yml

@@ -10,3 +10,5 @@ prevent-collision: true
 auto-team: true
 # When enabled if certain metadata can't be read we won't tell you about it
 suppress-metadata-errors: false
+# When enabled 1.9 will be able to block by using shields
+shield-blocking: true