local co_yield = coroutine.yield

local co_create = coroutine.create

local co_status = coroutine.status

local co_resume = coroutine.resume

local select = select

-- Reimplemented coroutine.wrap, returning "nil, err" if the coroutine cannot

-- be resumed. This protects user code from inifite loops when doing things like

-- repeat

--   local chunk, err = res.body_reader()

--   if chunk then -- <-- This could be a string msg in the core wrap function.

--     ...

--   end

-- until not chunk

local co_wrap = function(func)

    local co = co_create(func)

    if not co then

        return nil, "could not create coroutine"

    else

        return function(...)

            if co_status(co) == "suspended" then

                return select(2, co_resume(co, ...))

            else

                return nil, "can't resume a " .. co_status(co) .. " coroutine"

            end

        end

    end

end