vallentin/hook.lua

Module for hooking and intercepting function calls

hook.lua

Module for hooking and intercepting function calls.

Hooks can be added to any function. If multiple hooks are added to a single function, then each hook is executed in the order they have been added. If any hook returns anything other than nil, the execution of further hooks and the actual (intercepted) function is stopped. The returned values of the hook is returned to the original caller of the function.

Developed and tested using Lua 5.1 and Lua 5.2.

API References

The following references are based on hook.lua being included using local hook = require("hook").

hook.add(func, hook)

Adds a hook to a function, the hook is a function which will be called prior to the actual (intercepted) function.

If a function has multiple hooks added, each hook will be executed in the order they have been added.

If any hook returns anything other than nil, the execution of further hooks and the actual (intercepted) function is stopped. The returned values of the hook is returned to the original caller of the function.

hook.call(func, ...)

Executes each hooked function, until a hook returns anything other than nil. Then the returned values of the hook is returned to the original caller of hook.call().

The varargs would be the hooked function's parameters. As when calling the hooked function, the arguments is what will be passed through the varargs.

hook.remove(func, hook)

Remove a hook from a function.

hook.clear(func)

Removes all hooks from a function.

hook.count(func)

Counts the amount of hooks a function has (Note that the same hook can be added multiple times).

hook.gethooks(func)

Returns an array (indexed table), containing all the hooks.

Example

local hook = require("hook")


local function test(msg)
	print("test(\"" .. tostring(msg) .. "\")")
end


local function testHook(msg)
	print("testHook(\"" .. tostring(msg) .. "\")")
	
	if msg == "stop" then
		return true
	end
end

local function testHook2(msg)
	print("testHook2(\"" .. tostring(msg) .. "\")")
end


test = hook.add(test, testHook)
test = hook.add(test, testHook2)


print(hook.count(test))
-- Prints:
-- 2


for i, hook in ipairs(hook.gethooks(test)) do
	print("Hook #" .. i .. ": " .. tostring(hook))
end
-- Prints:
-- Hook #1: function: ........
-- Hook #2: function: ........


test("Hello World")
-- Prints:
-- testHook("Hello World")
-- testHook2("Hello World")
-- test("Hello World")


test("stop")
-- Prints:
-- testHook("stop")


hook.call(test, "Hooks Only")
-- Prints:
-- testHook("Hooks Only")
-- testHook2("Hooks Only")


-- Best for performance:
test = hook.remove(test, testHook)

-- Also works:
hook.remove(test, testHook)


test("Hello Again")
-- Prints:
-- testHook2("Hello Again")
-- test("Hello Again")


-- Best for performance:
test = hook.clear(test)

-- Also works:
hook.clear(test)

License

This module is shared under the MIT license, and is therefore free to use, share, distribute and modify. See LICENSE for more details.