Add a serializer for reading and writing ItemStacks to byte arrays.

To aid discoverability, we add a short-cut to this serializer in
PacketContainer, next to the getByteArrays() method.

ProtocolLib/src/main/java/com/comphenix/protocol/events/PacketContainer.java

@@ -51,6 +51,7 @@ import com.comphenix.protocol.reflect.cloning.ImmutableDetector;
 import com.comphenix.protocol.reflect.cloning.AggregateCloner.BuilderParameters;
 import com.comphenix.protocol.reflect.instances.DefaultInstances;
 import com.comphenix.protocol.utility.MinecraftReflection;
+import com.comphenix.protocol.utility.StreamSerializer;
 import com.comphenix.protocol.wrappers.BukkitConverters;
 import com.comphenix.protocol.wrappers.ChunkPosition;
 import com.comphenix.protocol.wrappers.WrappedDataWatcher;
@@ -235,6 +236,14 @@ public class PacketContainer implements Serializable {
 	public StructureModifier<byte[]> getByteArrays() {
 		return structureModifier.withType(byte[].class);
 	}
+	
+	/**
+	 * Retrieve a serializer for reading and writing ItemStacks stored in a byte array.
+	 * @return A instance of the serializer.
+	 */
+	public StreamSerializer getByteArraySerializer() {
+		return new StreamSerializer();
+	}
 
 	/**
 	 * Retrieves a read/write structure for every int array field.

ProtocolLib/src/main/java/com/comphenix/protocol/utility/StreamSerializer.java

@@ -0,0 +1,73 @@
+package com.comphenix.protocol.utility;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.lang.reflect.Method;
+
+import org.bukkit.inventory.ItemStack;
+
+import com.comphenix.protocol.reflect.FuzzyReflection;
+
+/**
+ * Utility methods for reading and writing Minecraft objects to streams.
+ * 
+ * @author Kristian
+ */
+public class StreamSerializer {
+	// Cached methods
+	private static Method readItemMethod;
+	private static Method writeItemMethod;
+
+	/**
+	 * Read or deserialize an item stack from an underlying input stream.
+	 * <p>
+	 * To supply a byte array, wrap it in a {@link java.io.ByteArrayInputStream ByteArrayInputStream} 
+	 * and {@link java.io.DataInputStream DataInputStream}. 
+	 * 
+	 * @param input - the target input stream.
+	 * @return The resulting item stack.
+	 * @throws IOException If the operation failed due to reflection or corrupt data.
+	 */
+	public ItemStack deserializeItemStack(DataInputStream input) throws IOException {
+		if (readItemMethod == null)
+			readItemMethod = FuzzyReflection.fromClass(MinecraftReflection.getPacketClass()).
+								getMethodByParameters("readPacket", 
+										MinecraftReflection.getItemStackClass(), 
+										new Class<?>[] {DataInputStream.class});
+		try {
+			Object nmsItem = readItemMethod.invoke(null, input);
+			
+			// Convert back to a Bukkit item stack
+			return MinecraftReflection.getBukkitItemStack(nmsItem);
+			
+		} catch (Exception e) {
+			throw new IOException("Cannot read item stack.", e);
+		}
+	}
+	
+	/**
+	 * Write or serialize an item stack to the given output stream.
+	 * <p>
+	 * To supply a byte array, wrap it in a {@link java.io.ByteArrayOutputStream ByteArrayOutputStream} 
+	 * and {@link java.io.DataOutputStream DataOutputStream}. 
+	 * 
+	 * @param output - the target output stream.
+	 * @param stack - the item stack that will be written.
+	 * @throws IOException If the operation fails due to reflection problems.
+	 */
+	public void serializeItemStack(DataOutputStream output, ItemStack stack) throws IOException {
+		Object nmsItem = MinecraftReflection.getMinecraftItemStack(stack);
+		
+		if (writeItemMethod == null)
+			writeItemMethod = FuzzyReflection.fromClass(MinecraftReflection.getPacketClass()).
+								getMethodByParameters("writePacket", new Class<?>[] { 
+										MinecraftReflection.getItemStackClass(), 
+										DataOutputStream.class });
+		try {
+			writeItemMethod.invoke(null, nmsItem, output);
+		} catch (Exception e) {
+			throw new IOException("Cannot write item stack " + stack, e);
+		}
+	}
+}