How to intercept and modify Packet44UpdateAttributes in ProtocolLib 2.5.1. This example modifies the sprint speed to be 200% faster.

UpdateAttributes.java

package com.comphenix.example;

import java.util.List;
import java.util.Set;
import java.util.UUID;

import org.bukkit.plugin.java.JavaPlugin;
import com.comphenix.protocol.Packets;
import com.comphenix.protocol.ProtocolLibrary;
import com.comphenix.protocol.events.ConnectionSide;
import com.comphenix.protocol.events.PacketAdapter;
import com.comphenix.protocol.events.PacketEvent;
import com.comphenix.protocol.wrappers.WrappedAttribute;
import com.comphenix.protocol.wrappers.WrappedAttributeModifier;
import com.comphenix.protocol.wrappers.WrappedAttributeModifier.Operation;
import com.google.common.collect.Sets;

public class UpdateAttributes extends JavaPlugin {
    private static final UUID SPRITING_SPEED = UUID.fromString("662a6b8d-da3e-4c1c-8813-96ea6097278d");
    private static final UUID SUPER_SPRINTING = UUID.fromString("d64c79c2-a459-446c-9308-409e1b6b3340");
    
    @Override
    public void onEnable() {
        ProtocolLibrary.getProtocolManager().addPacketListener(
            new PacketAdapter(this, ConnectionSide.SERVER_SIDE, Packets.Server.UPDATE_ATTRIBUTES) {
                public void onPacketSending(PacketEvent event) {
                    List<WrappedAttribute> list = event.getPacket().getAttributeCollectionModifier().read(0);
                    
                    for (int i = 0; i < list.size(); i++) {
                        WrappedAttribute attribute = list.get(i);
                        
                        // See if we should add the super sprinting attribute
                        if (attribute.hasModifier(SPRITING_SPEED) && !attribute.hasModifier(SUPER_SPRINTING)) {
                            Set<WrappedAttributeModifier> modifiers = Sets.newHashSet(attribute.getModifiers());

                            // Add the new super sprinting too
                            modifiers.add(WrappedAttributeModifier.newBuilder().
                                    name("Super Sprinting").
                                    uuid(SUPER_SPRINTING).
                                    amount(2).
                                    operation(Operation.ADD_PERCENTAGE).build());
 
                            list.set(i, attribute.withModifiers(modifiers));
                        }
                    }
                    
                    event.getPacket().getAttributeCollectionModifier().write(0, list);
                }
            }
        );
    }
}