add custom on_punch for mob arrows

api.lua

@@ -6,7 +6,7 @@ local use_cmi = minetest.global_exists("cmi")
 
 mobs = {
 	mod = "redo",
-	version = "20180908",
+	version = "20180909",
 	intllib = S,
 	invis = minetest.global_exists("invisibility") and invisibility or {},
 }
@@ -3309,7 +3309,7 @@ function mobs:register_arrow(name, def)
 		hit_node = def.hit_node,
 		hit_mob = def.hit_mob,
 		drop = def.drop or false, -- drops arrow as registered item when true
-		collisionbox = {0, 0, 0, 0, 0, 0}, -- remove box around arrows
+		collisionbox = def.collisionbox or {0, 0, 0, 0, 0, 0},
 		timer = 0,
 		switch = 0,
 		owner_id = def.owner_id,
@@ -3319,6 +3319,9 @@ function mobs:register_arrow(name, def)
 
 		on_activate = def.on_activate,
 
+		on_punch = def.on_punch or function(self, hitter, tflp, tool_capabilities, dir)
+		end,
+
 		on_step = def.on_step or function(self, dtime)
 
 			self.timer = self.timer + 1

api.txt

@@ -396,6 +396,8 @@ This function registers a arrow for mobs with the attack type shoot.
        'rotate'       integer value in degrees to rotate arrow
        'on_step'      is a custom function when arrow is active, nil for
                       default.
+       'on_punch'     is a custom function when arrow is punched, nil by default
+       'collisionbox' is hitbox table for arrow, {0,0,0,0,0,0} by default.
 
 
 Spawn Eggs