BundleNet

-- Minified CRC32 blob - MIT license - from here: https://raw.githubusercontent.com/davidm/lua-digest-crc32lua/master/lmod/digest/crc32lua.lua
do
    local type=type;local require=require;local setmetatable=setmetatable;local a=bit.bxor;local b=bit.bnot;local c=bit.band;local d=bit.brshift;local e=0xEDB88320;local function f(g)local h={}local i=setmetatable({},h)function h:__index(j)local k=g(j)i[j]=k;return k end;return i end;local l=f(function(m)local n=m;for o=1,8 do local p=c(n,1)n=d(n,1)if p==1 then n=a(n,e)end end;return n end)local function q(r,n)n=b(n or 0)local s=d(n,8)local t=l[a(n%256,r)]return b(a(s,t))end;local function u(v,n)n=n or 0;for m=1,#v do n=q(v:byte(m),n)end;return n end;function crc32(v,n)if type(v)=='string'then return u(v,n)else return q(v,n)end end
end

local function get_byte(num, byte)
    return bit.band(bit.brshift(num, byte * 8), 0xFF)
end

local function from_bytes(b)
    local n = 0
    for ix, byte in pairs(b) do
        n = bit.bor(n, bit.blshift(byte, (ix - 1) * 8))
    end
    return n
end

local side = settings.get "bundlenet.side" or "back"

local function send_raw(str)
    local i = 1
    for i = 1, math.ceil(#str / 2) do
        local first = str:byte(i * 2 - 1)
        local second = str:byte(i * 2) or 0
        local u16 = first * 256 + second
        rs.setBundledOutput(side, u16)
        sleep(0.1)
    end
    rs.setBundledOutput(side, 0)
end

local function receive_raw(length)
    local str = ""
    local count = 0
    os.pullEvent "redstone"
    while true do
        local u16 = rs.getBundledInput(side)
        local first = string.char(math.floor(u16 / 256))
        if not length and first == "\0" then break
        else
            count = count + 1
            str = str .. first
            if count == length then break end
            local second = string.char(u16 % 256)
            if not length and second == "\0" then break
            else
                count = count + 1
                str = str .. second
                if count == length then break end
            end
        end
        sleep(0.1)
    end
    return str
end

local function u32_to_string(u32)
    return string.char(get_byte(u32, 0), get_byte(u32, 1), get_byte(u32, 2), get_byte(u32, 3))
end

local function string_to_u32(str)
    return from_bytes{str:byte(1), str:byte(2), str:byte(3), str:byte(4)}
end

local function send(data)
    local length = u32_to_string(#data)
    local checksum = u32_to_string(crc32(data))
    print("len", length, "checksum", checksum)
    send_raw(length)
    send_raw(checksum)
    send_raw(data)
end

local function receive()
    local length = receive_raw(4)
    --sleep(0.1)
    local checksum = receive_raw(4)
    print("len", length, "checksum", checksum, "l", string_to_u32(length), "c", string_to_u32(checksum))
    --sleep(0.1)
    local data = receive_raw(string_to_u32(length))
    if crc32(data) ~= string_to_u32(checksum) then return false, "checksum mismatch", data end
    return true, data
end

local option = ...

if option == "send" then
    write "Send: "
    local text = read()
    send(text)
elseif option == "raw_receive" then
    print(receive_raw())
elseif option == "receive" then
    print(receive())
end

return { send = send, receive = receive }