Lua - flushing input buffer during interactive terminal session - lua

Question

So I've got this lua test script for handling interactive user input in the terminal. It's working as expected, except I can't figure out a way to clear the input buffer between calls to io.read(1).
Before you say it, no, curses is not an option, nor is any third-party library. This script will (when it's done) be used on an embedded device with set firmware, so pure lua is the only option.
The code:
UP = 65
DOWN = 66
RIGHT = 67
LEFT = 68
local function sleep(seconds)
os.execute("sleep " .. tonumber(seconds));
end
local function write(String)
io.write(String);
io.flush();
end
local key = {
[27] = function()
group = (io.read(1)):byte();
if group == 91 then
direction = (io.read(1)):byte();
if direction == UP then return write("Up") end
if direction == DOWN then return write("Down") end
if direction == RIGHT then return write("Right") end
if direction == LEFT then return write("Left") end
return write("("..direction..")");
end
return write("("..direction..")");
end,
[113] = function() running = false end
}
running = true;
os.execute("stty raw -echo");
while running do
local k = io.read(1);
if k == 'w' then break end
k = k:byte();
if key[k] then key[k]();
else write('('..k..')') end
sleep(.25);
-- while io.read(1) ~= nil do end -- This blocks indefinitely
end
os.execute("stty sane")