add knockback handler

server/player/handler.go

@@ -53,6 +53,8 @@ type Handler interface {
 	// the original cause of the immunity frame. In this case, the damage is
 	// reduced but the player is still knocked back.
 	HandleHurt(ctx *Context, damage *float64, immune bool, attackImmunity *time.Duration, src world.DamageSource)
+	// HandleKnockBack handles the player being knocked back. ctx.Cancel() may be called to cancel knockback.
+	HandleKnockBack(ctx *Context, src *mgl64.Vec3, force, height *float64)
 	// HandleDeath handles the player dying to a particular damage cause.
 	HandleDeath(p *Player, src world.DamageSource, keepInv *bool)
 	// HandleRespawn handles the respawning of the player in the world. The spawn position passed may be
@@ -192,6 +194,7 @@ func (NopHandler) HandleAttackEntity(*Context, world.Entity, *float64, *float64,
 func (NopHandler) HandleExperienceGain(*Context, *int)                                     {}
 func (NopHandler) HandlePunchAir(*Context)                                                 {}
 func (NopHandler) HandleHurt(*Context, *float64, bool, *time.Duration, world.DamageSource) {}
+func (NopHandler) HandleKnockBack(*Context, *mgl64.Vec3, *float64, *float64)               {}
 func (NopHandler) HandleHeal(*Context, *float64, world.HealingSource)                      {}
 func (NopHandler) HandleFoodLoss(*Context, int, *int)                                      {}
 func (NopHandler) HandleDeath(*Player, world.DamageSource, *bool)                          {}

server/player/player.go

@@ -715,6 +715,11 @@ func (p *Player) KnockBack(src mgl64.Vec3, force, height float64) {
 // knockBack is an unexported function that is used to knock the player back. This function does not check if the player
 // can take damage or not.
 func (p *Player) knockBack(src mgl64.Vec3, force, height float64) {
+	ctx := event.C(p)
+	if p.Handler().HandleKnockBack(ctx, &src, &force, &height); ctx.Cancelled() {
+		return
+	}
+
 	velocity := p.Position().Sub(src)
 	velocity[1] = 0