Make the protocol dissector heuristic (#14335)

util/wireshark/minetest.lua

@@ -1280,14 +1280,15 @@ do
 
 	function p_minetest.dissector(buffer, pinfo, tree)
 
-		-- Add Minetest tree item and verify the ID
-		local t = tree:add(p_minetest, buffer(0,8))
-		t:add(f_id, buffer(0,4))
+		-- Defer if payload doesn't have Minetest's magic number
 		if buffer(0,4):uint() ~= minetest_id then
-			t:add_expert_info(PI_UNDECODED, PI_WARN, "Invalid ID, this is not a Minetest packet")
-			return
+			return false
 		end
 
+		-- Add Minetest tree item
+		local t = tree:add(p_minetest, buffer(0,8))
+		t:add(f_id, buffer(0,4))
+
 		-- ID is valid, so replace packet's shown protocol
 		pinfo.cols.protocol = "Minetest"
 		pinfo.cols.info = "Minetest"
@@ -1339,12 +1340,11 @@ do
 		end
 
 		pinfo.cols.info:append(" (" .. reliability_info .. ")")
+		return true
 
 	end
 
-	-- FIXME Is there a way to let the dissector table check if the first payload bytes are 0x4f457403?
-	DissectorTable.get("udp.port"):add(30000, p_minetest)
-	DissectorTable.get("udp.port"):add(30001, p_minetest)
+	p_minetest:register_heuristic("udp", p_minetest.dissector)
 end