hotfix

Lua 5.2/5.3 hotfix. Hot update functions and keep old data.

Usage

local hotfix = require("hotfix")
hotfix.hotfix_module("mymodule.sub_module")

helper/hotfix_helper.lua is an example to hotfix modified modules using lfs.

hotfix_module(module_name)

hotfix_module() uses package.searchpath(module_name, package.path) to search the path of module. The module is loaded and the returned value is updated to package.loaded[module_name]. If the returned value is nil, then package.loaded[module_name] is assigned to true. hotfix_module() returns the final value of package.loaded[module_name].

Functons are updated to new ones but old upvalues are kept. Old tables are kept and new fields are inserted. All references to old functions are replaced to new ones.

The module may change any global variables if it want to.

Local variable which is not referenced by _G is not updated.

-- test.lua: return { function func() return "old" end }
local test = require("test")  -- referenced by _G.package.loaded["test"]
local func = test.func        -- is not upvalue nor is referenced by _G
-- test.lua: return { function func() return "new" end }
require("hotfix").hotfix_module("test")
test.func()  -- "new"  
func()       -- "old"

Todo: Replace functions of local variables in all threads using:

debug.getlocal ([thread,] f, local)
debug.setlocal ([thread,] level, local, value)

Why not protect the global variables

We can protect the glocal variables on loading.

[1] uses a read only ENV to load. local env = {} setmetatable(env, { __index = _G }) load(chunk, check_name, 't', env)

But it can not stop indirect write. Global variables may be changed. In the following example, t is OK but math.sin is changed.

Lua 5.3.2  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> math.sin(123)
-0.45990349068959
> do
>> local _ENV = setmetatable({}, {__index = _G})
>> t = 123
>> math.sin = print
>> end
> t
nil
> math.sin(123)
123

[2] uses a fake ENV to load and ignores all operations. In this case, we can not init new local variables.

local M = {}
+ local log = require("log")  -- Can not require!
function M.foo()
+    log.info("test")
end
return M

Another problem is the new function's _ENV is not the real ENV. Following test will fail because set_global() has a protected ENV.

log("New upvalue which is a function set global...")
run_test([[
        local M = {}
        function M.foo() return 12345 end
        return M
    ]],
    function() assert(nil == global_test) end,
    [[
        local M = {}
        local function set_global() global_test = 11111 end
        function M.foo()
            set_global()
        end
        return M
    ]],
    function()
        assert(nil == test.foo())
        assert(11111 == global_test)  -- FAIL!
        global_test = nil
    end)

How to run test

Run main.lua in test dir. main.lua will write a test.lua file and hotfix it. main.lua will write log to log.txt.

D:\Jinq\Git\hotfix\test>..\..\..\tools\lua-5.3.2_Win64_bin\lua53
Lua 5.3.2  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> require("main").run()
main.lua:80: assertion failed!

Unexpected update

log function is changed from print() to an empty function. The hotfix will replace all print() to an empty function which is totally unexpected.

local M = {}
local log = print
function M.foo() log("Old") end
return M

local M = {}
local log = function() end
function M.foo() log("Old") end
return M

hotfix.add_protect{print} can protect print function from being replaced. But it also means that log can not be updated.

Reference

• [1] hotfix by tickbh
  https://github.com/tickbh/td_rlua/blob/11523931b0dd271ad4c5e9c532a9d3bae252a264/td_rlua/src/hotfix.rs
  http://www.cnblogs.com/tickbh/articles/5459120.html (In Chinese)
  Lua 5.2/5.3.

  Can only update global functions.

local M = {}
+ function M.foo() end  -- Can not add M.foo().
return M

• [2] lua_hotupdate
  https://github.com/asqbtcupid/lua_hotupdate
  Lua 5.1.

  Using a fake ENV, the module's init statements result in noop.