Possibility to add 'isCompatible' with other types. Fixes crashes on a 1.8 server

src/main/java/us/myles/ViaVersion/api/PacketWrapper.java

@@ -117,7 +117,7 @@ public class PacketWrapper {
             }
         } else {
             Pair<Type, Object> read = readableObjects.poll();
-            if (read.getKey().equals(type)) {
+            if (read.getKey().equals(type) || (type.isCompatibleWith(read.getKey()) && type.getOutputClass().equals(read.getKey().getOutputClass()))) {
                 return (T) read.getValue();
             } else {
                 if (type == Type.NOTHING) {
@@ -173,7 +173,7 @@ public class PacketWrapper {
         packetValues.addAll(readableObjects);
         readableObjects.clear();
         // If the buffer has readable bytes, copy them.
-        if(inputBuffer.readableBytes() > 0){
+        if (inputBuffer.readableBytes() > 0) {
             passthrough(Type.REMAINING_BYTES);
         }
     }

src/main/java/us/myles/ViaVersion/api/type/Type.java

@@ -10,6 +10,8 @@ import us.myles.ViaVersion.api.minecraft.item.Item;
 import us.myles.ViaVersion.api.type.types.*;
 import us.myles.ViaVersion.api.type.types.minecraft.*;
 
+import java.util.HashSet;
+import java.util.Set;
 import java.util.UUID;
 
 @Getter
@@ -68,6 +70,7 @@ public abstract class Type<T> implements ByteBufReader<T>, ByteBufWriter<T> {
     /* Actual Class */
 
     private final Class<? super T> outputClass;
+    private final Set<Class<? extends Type>> compatibilities;
     private final String typeName;
 
     public Type(Class<? super T> outputClass) {
@@ -77,6 +80,19 @@ public abstract class Type<T> implements ByteBufReader<T>, ByteBufWriter<T> {
     public Type(String typeName, Class<? super T> outputClass) {
         this.outputClass = outputClass;
         this.typeName = typeName;
+        this.compatibilities = new HashSet<>();
+    }
+
+    public void addCompatibility(Class<? extends Type> claz) {
+        compatibilities.add(claz);
+    }
+
+    public void addCompatibility(Type claz) {
+        addCompatibility(claz.getClass());
+    }
+
+    public boolean isCompatibleWith(Type claz) {
+        return compatibilities.contains(claz.getClass());
     }
 
     @Override

src/main/java/us/myles/ViaVersion/protocols/protocolsnapshotto1_9_3/MetaListSnapshotType.java

@@ -3,6 +3,7 @@ package us.myles.ViaVersion.protocols.protocolsnapshotto1_9_3;
 import io.netty.buffer.ByteBuf;
 import us.myles.ViaVersion.api.minecraft.metadata.Metadata;
 import us.myles.ViaVersion.api.type.Type;
+import us.myles.ViaVersion.protocols.protocol1_9to1_8.Protocol1_9TO1_8;
 import us.myles.ViaVersion.protocols.protocol1_9to1_8.metadata.NewType;
 
 import java.util.ArrayList;
@@ -11,6 +12,7 @@ import java.util.List;
 public class MetaListSnapshotType extends Type<List<Metadata>> {
     public MetaListSnapshotType() {
         super(List.class);
+        addCompatibility(Protocol1_9TO1_8.METADATA_LIST);
     }
 
     @Override

src/main/java/us/myles/ViaVersion/protocols/protocolsnapshotto1_9_3/MetaSnapshotType.java

@@ -3,11 +3,13 @@ package us.myles.ViaVersion.protocols.protocolsnapshotto1_9_3;
 import io.netty.buffer.ByteBuf;
 import us.myles.ViaVersion.api.minecraft.metadata.Metadata;
 import us.myles.ViaVersion.api.type.Type;
+import us.myles.ViaVersion.protocols.protocol1_9to1_8.Protocol1_9TO1_8;
 import us.myles.ViaVersion.protocols.protocol1_9to1_8.metadata.NewType;
 
 public class MetaSnapshotType extends Type<Metadata> {
     public MetaSnapshotType() {
         super(Metadata.class);
+        addCompatibility(Protocol1_9TO1_8.METADATA);
     }
 
     @Override