PaperMC / PaperMC/Paper

EntityKnockbackByEntityEvent is called twice if triggered by a player doing a strong knockback attack.

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status: needs triage type: bug version: 1.21.3
Dominant language
Java
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Description

Expected behavior

EntityKnockbackByEntityEvent would be called a single time every time an entity was hit.

Observed/Actual behavior

EntityKnockbackByEntityEvent is called twice if it is triggered by a player who does a sprinting attack.

Steps/models to reproduce

Create a Paper plugin, register an EntityKnockbackByEntity listener and broadcast a debug message every time it runs.

Punch an entity like a mob or an animal without sprinting. It should broadcast the debug message once.

Now punch the entity again while sprinting. It'll now broadcast the debug message twice.

Plugin and Datapack List

knockbackEventTest

Paper version

This server is running Paper version 1.21.3-29-master@be886cf (2024-11-15T09:07:14Z) (Implementing API version 1.21.3-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.3-25-1ef4c0e (MC: 1.21.3)

Other

No response

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the sprinting-attack case with a Paper plugin that listens for EntityKnockbackByEntityEvent, comparing it with a normal attack. Trace where the event is dispatched during the strong knockback path; done means each entity hit causes exactly one event while preserving the normal behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
api, game-dev
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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