Really Slow Redstone Networking

-- converts a value between 0 and 127 to bits, least significant bits first
local function to_bits(charbyte)
    if charbyte > 127 then error "invalid character" end
    local out = {}
    for i = 0, 6 do
        local bitmask = bit.blshift(1, i)
        local bit = bit.brshift(bit.band(bitmask, charbyte), i)
        table.insert(out, bit)
    end
    return out
end

local function from_bits(bit_table)
    local int = 0
    for i = 0, 6 do
        local index = i + 1 -- Lua...
        int = bit.bor(int, bit.blshift(bit_table[index], i))
    end
    return int
end

local rx_side = settings.get "rx_side" or "right"
local tx_side = settings.get "tx_side" or "left"

local function send(str)
    str = "\127" .. str
    for i = 1, #str do
        local byte = str:byte(i)
        for _, bit in ipairs(to_bits(byte)) do
            rs.setOutput(tx_side, bit == 1)
            sleep(0.1)
        end
    end
    rs.setOutput(tx_side, false)
end

local function receive(char_callback)
    local str = ""
    repeat
        os.pullEvent "redstone"
    until rs.getInput(rx_side)
    while true do
        local bits = {}
        for i = 0, 6 do
            if rs.getInput(rx_side) then
                table.insert(bits, 1)
            else
                table.insert(bits, 0)
            end
            sleep(0.1)
        end
        local char = string.char(from_bits(bits))
        if char == "\0" then break end
        if char ~= "\127" and char_callback then char_callback(char) end
        str = str .. char
    end
    return str:sub(2)
end

local w, h = term.getSize()
local send_window = window.create(term.current(), 1, h, w, 1)
local message_window = window.create(term.current(), 1, 1, w, h - 1)

local function exec_in_window(w, f)
    local x, y = term.getCursorPos()
    local last = term.redirect(w)
    f()
    term.redirect(last)
    w.redraw()
    term.setCursorPos(x, y)
end

local function write_char(txt)
    exec_in_window(message_window, function()
        write(txt)
    end)
end

local function sender()
    term.redirect(send_window)
    term.setBackgroundColor(colors.lightGray)
    term.setTextColor(colors.white)
    term.clear()
    while true do
        local msg = read()
        send(msg)
    end
end

local function receiver()
    while true do
        receive(write_char)
        write_char "\n"
    end
end

parallel.waitForAll(sender, receiver)