Don't assume the InputStream is an DataInputStream in Spigot's case.

ProtocolLib/src/main/java/com/comphenix/protocol/injector/packet/ProxyPacketInjector.java

@@ -19,6 +19,7 @@ package com.comphenix.protocol.injector.packet;
 
 import java.io.DataInput;
 import java.io.DataInputStream;
+import java.io.InputStream;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.util.Map;
@@ -314,13 +315,13 @@ class ProxyPacketInjector implements PacketInjector {
 	}
 	
 	// Called from the ReadPacketModified monitor
-	public PacketEvent packetRecieved(PacketContainer packet, DataInputStream input, byte[] buffered) {
+	public PacketEvent packetRecieved(PacketContainer packet, InputStream input, byte[] buffered) {
 		if (playerInjection.canRecievePackets()) {
 			return playerInjection.handlePacketRecieved(packet, input, buffered);
 		}
 		
 		try {
-			Player client = playerInjection.getPlayerByConnection(input);
+			Player client = playerInjection.getPlayerByConnection((DataInputStream) input);
 
 			// Never invoke a event if we don't know where it's from
 			if (client != null) {

ProtocolLib/src/main/java/com/comphenix/protocol/injector/packet/ReadPacketModifier.java

@@ -19,6 +19,7 @@ package com.comphenix.protocol.injector.packet;
 
 import java.io.ByteArrayOutputStream;
 import java.io.DataInputStream;
+import java.io.InputStream;
 import java.lang.reflect.Method;
 import java.util.Map;
 
@@ -102,7 +103,7 @@ class ReadPacketModifier implements MethodInterceptor {
 		Object returnValue = null;
 		
 		// We need this in order to get the correct player
-		DataInputStream input = isReadPacketDataMethod ? (DataInputStream) args[0] : null;
+		InputStream input = isReadPacketDataMethod ? (InputStream) args[0] : null;
 		ByteArrayOutputStream bufferStream = null;
 		
 		// See if we need to buffer the read data

ProtocolLib/src/main/java/com/comphenix/protocol/injector/player/PlayerInjectionHandler.java

@@ -1,6 +1,7 @@
 package com.comphenix.protocol.injector.player;
 
 import java.io.DataInputStream;
+import java.io.InputStream;
 import java.lang.reflect.InvocationTargetException;
 import java.net.InetSocketAddress;
 import java.util.Set;
@@ -173,7 +174,7 @@ public interface PlayerInjectionHandler {
 	 * @param buffered - the buffered packet.
 	 * @return The packet event.
 	 */
-	public abstract PacketEvent handlePacketRecieved(PacketContainer packet, DataInputStream input, byte[] buffered);
+	public abstract PacketEvent handlePacketRecieved(PacketContainer packet, InputStream input, byte[] buffered);
 	
 	/**
 	 * Close any lingering proxy injections.

ProtocolLib/src/main/java/com/comphenix/protocol/injector/player/ProxyPlayerInjectionHandler.java

@@ -18,6 +18,7 @@
 package com.comphenix.protocol.injector.player;
 
 import java.io.DataInputStream;
+import java.io.InputStream;
 import java.lang.ref.WeakReference;
 import java.lang.reflect.InvocationTargetException;
 import java.net.InetSocketAddress;
@@ -656,7 +657,7 @@ class ProxyPlayerInjectionHandler implements PlayerInjectionHandler {
 	}
 	
 	@Override
-	public PacketEvent handlePacketRecieved(PacketContainer packet, DataInputStream input, byte[] buffered) {
+	public PacketEvent handlePacketRecieved(PacketContainer packet, InputStream input, byte[] buffered) {
 		throw new UnsupportedOperationException("Proxy injection cannot handle recieved packets.");
 	}
 	

ProtocolLib/src/main/java/com/comphenix/protocol/injector/spigot/DummyPlayerHandler.java

@@ -1,6 +1,7 @@
 package com.comphenix.protocol.injector.spigot;
 
 import java.io.DataInputStream;
+import java.io.InputStream;
 import java.lang.reflect.InvocationTargetException;
 import java.net.InetSocketAddress;
 import java.util.Set;
@@ -102,7 +103,7 @@ class DummyPlayerHandler implements PlayerInjectionHandler {
 	}
 
 	@Override
-	public PacketEvent handlePacketRecieved(PacketContainer packet, DataInputStream input, byte[] buffered) {
+	public PacketEvent handlePacketRecieved(PacketContainer packet, InputStream input, byte[] buffered) {
 		// Associate this buffered data
 		if (buffered != null) {
 			injector.saveBuffered(packet.getHandle(), buffered);