Q: create a hookfunction in lua

Question

I want do a hookfunction for lua :

For explain i want hook the params and return the params when function called, like this :

function func1(x, y)
  print(tonumber(x) + tonumber(y))
end

a = hookfunction(func1, function(...)    -- a = old function
  local args = { ... }
  print("Argument 1 =>", args[1])
  print("Argument 2 =>", args[2])
  return a(...)
end)

func1(12, 5)

Output : 

Argument 1 => 12
Argument 2 => 5
17

Answer 1

There's two different things you can do. You can either create a wrapper just for that function, or you can actually set a debugging hook in the Lua runtime. Here's how you'd create a wrapper:

function func1(x, y)
  print(tonumber(x) + tonumber(y))
end

function wrapfunction(a)    -- a = old function
  return function(...)
    local args = { ... }
    print("Argument 1 =>", args[1])
    print("Argument 2 =>", args[2])
    return a(...)
  end
end
func1 = wrapfunction(func1)

func1(12, 5)

And here's how you'd set a debugging hook:

function func1(x, y)
  print(tonumber(x) + tonumber(y))
end

function hookfunction(event)
  if debug.getinfo(2, 'f').func == func1 then
    print("Argument 1 =>", select(2, debug.getlocal(2, 1)))
    print("Argument 2 =>", select(2, debug.getlocal(2, 2)))
  end
end
debug.sethook(hookfunction, 'c')

func1(12, 5)