Missing server-side check in enderman teleport

The bug

The client tries to teleport endermen as well. This can cause particles and teleportation sounds to appear at the wrong position or the enderman might be away for a short moment before its position is re-synchronized.

How to reproduce

1. Summon an enderman
2. Punch it in Creative mode
   → It will disappear for a short moment

Code analysis

Partwise by Franz Reiter

Based on 1.12 decompiled using MCP 9.40 PRE 1

The method net.minecraft.entity.monster.EntityEnderman.teleportRandomly() is called client-side as well which can result in different results since the random number generators are not synchronized. Additionally this method is called when the hurt animation is displayed client-side by dealing 0 unblockable damage to the enderman.

This could be solved by either adding an "is server" check in the method EntityEnderman.teleportRandomly() or maybe even better in the method net.minecraft.entity.monster.EntityEnderman.attackEntityFrom(DamageSource, float).