Safe Debug Library

--[[
    Safe Debug
    tesla1889
    Public Domain
--]]
local no_good_info = {}
do
    local baseLevel = 0
    local info = debug.getinfo(baseLevel)
    while info do
        no_good_info[info] = true   -- get collection of protected info
        baseLevel = (baseLevel + 1)
    end
end
local db = {}   --  move unsandboxed debug here
for k,v in pairs(debug) do
    db[k] = v
    debug[k] = nil
end
--  debug.debug = db.debug  --  not completely sure what to protect here, so I'll comment it out
debug.gethook = function()
    return db.gethook() --  ensure no optional values are passed
end
debug.getinfo = function(n,m)
    local raw = db.getinfo(n)
    if no_good_info[raw]
        then error("debug.getinfo: level out of range")
    end
    local mask = {
        currentline = false,
        func = false,
        linedefined = false,
        name = false,
        namewhat = false,
        nups = false,
        short_src = false,
        source = false,
        what = false
    }
    if m then
        if (type(m) ~= "string")
            then error("debug.getinfo: string mask expected")
        end
        local len = #m
        for n = 1,len do
            local c = string.sub(m,n,n)
            if  (c == "n") then
                mask.name = true
                mask.namewhat = true
            elseif  (c == "f") then
                mask.func = true
            elseif  (c == "S") then
                mask.linedefined = true
                mask.short_src = true
                mask.source = true
                mask.what = true
            elseif  (c == "l") then
                mask.currentline = true
            elseif  (c == "u") then
                mask.nups = true
            else
                error("debug.getinfo: invalid mask option '" .. c .. "'")
            end
        end
    else
        mask = {
            currentline = true,
            func = true,
            linedefined = true,
            name = true,
            namewhat = true,
            nups = true,
            short_src = true,
            source = true,
            what = true
        }
    end
    local info = {}
    for k,v in pairs(raw) do
        if mask[k]
            then info[k] = v
        end
    end
    return info
end
debug.getlocal = function(n,l)
    if (type(n) == "function")  --  restrict getlocal to functions
        then return db.getlocal(n,l)
    end
end
local meta_critical = {
    --  insert all values with metatables you don't want accessible
}
do
    local t,c = {},#meta_critical
    for n = 1,c
        do t[meta_critical[n]] = true
    end
    meta_critical = t
end
debug.getmetatable = function(obj)
    if (not meta_critical[obj])
        then return db.getmetatable(obj)
    end
end
--  leave out debug.getregistry
debug.getupvalue = db.getupvalue    --  safe
--  leave out debug.getuservalue
debug.sethook = db.sethook  --  safe
--  leave out debug.setlocal
debug.setmetatable = function(obj)
    if (not meta_critical[obj])
        then return db.setmetatable(obj)
    end
end
local fn_critical = {
    --  insert all functions that you want to protect
}
do
    local t,c = {},#fn_critical
    for n = 1,c
        do t[fn_critical[n]] = true
    end
    fn_critical = t
end
debug.setupvalue = function(f,u,v)
    if (not fn_critical[f])
        then return db.setupvalue(f,u,v)
    end
end
--  leave out debug.setuservalue
debug.traceback = db.traceback  --  a string of info never hurt anyone
debug.upvalueid = db.upvalueid  --  safe
debug.upvaluejoin = function(f1,n1,f2,n2)
    if (not (fn_critical[fl] or fn_critical[f2]))
        then return db.upvaluejoin(f1,n1,f2,n2)
    end
end