netrouter.lua

local component = require("component")
local event = require("event")
local szn = require("serialization")


dnstablefile = io.open("dns.table", "r")
dnstableraw = dnstablefile:read("*a")
print("Serialized DNS table: " .. dnstableraw)
dns = szn.unserialize(dnstableraw)

netport = 1000
dnsport = 53
component.modem.open(netport)
component.modem.open(dnsport)
if not component.modem.isOpen(netport) then
  print("ERROR: could not open netport!")
  os.exit()
end
if not component.modem.isOpen(dnsport) then
  print("ERROR: could not open dnsport!")
  os.exit()
end


function dnsResolve(resolveName, dnstable)
  local resolveAddr = nil

  for i, row in pairs(dnstable) do
    if row.hostname == resolveName then
      resolveAddr = row.addr
    end
  end
  return resolveAddr
end

function dnsLookup(lookupAddr, dnstable)
  local lookupName = nil

  for i, row in pairs(dnstable) do
    if row.addr == lookupAddr then
      lookupName = row.hostname
    end
  end
  return lookupName
end

function parsePacket(packet)
  local pktDest = packet[1]
  local pktMesg = packet[2]
  return pktDest, pktMesg
end

function parseDNS(packet)
  -- pktType list:
  --   LOOKUP  -- format: msg={type="LOOKUP", addr}
  --   RESOLVE -- format: msg={type="RESOLVE", hostname}
  return packet[1], packet[2]
end


while true do
  print()
  print("pulling!")
  local _, _, devFrom, pPort,_, msg = event.pull("modem")

  -- dns packet format: {"LOOKUP" | "RESOLVE", addr/hostname}
  -- dns response packet: (RE stands for response) {"LOOKUP_RE" | "RESOLVE_RE", returned addr/hostname}
  if pPort == dnsport then
    print("RECEIVED PACKET ON DNSPORT:")
    local pDNStype, pDNScontent = parseDNS(szn.unserialize(msg))
    print("From: " .. devFrom)
    print("Type: " .. pDNStype)
    print("Content: " .. pDNScontent)

    if pDNStype == "LOOKUP" then
      print("Running DNS lookup...")
      local pDNSname = dnsLookup(pDNScontent, dns)
      print("Found hostname: " .. pDNSname)
      local lookupRePkt = {"LOOKUP_RE", pDNSname}
      print("Sending LOOKUP_RE packet to " .. devFrom)
      component.modem.send(devFrom, dnsport, szn.serialize(lookupRePkt))


    elseif pDNStype == "RESOLVE" then
      print("Running DNS resolve...")
      local pDNSaddr = dnsResolve(pDNScontent, dns)
      print("Found address: " .. pDNSaddr)
      local resolveRePkt = {"RESOLVE_RE", pDNSaddr}
      print("Sending RESOLVE_RE packet to " .. devFrom)
      component.modem.send(devFrom, dnsport, szn.serialize(resolveRePkt))

    else
      print("Invalid DNS command")
    end

  elseif pPort == netport then
    -- parse received packet
    -- packet format: {"destination_hostname", "data"}
    -- packet response: "SUCCESS" | "FAILURE"
    local pDest, pMsg = parsePacket(szn.unserialize(msg))
    local pDestAddr = dnsResolve(pDest, dns)
    print("RECEIVED PACKET ON NETPORT:")
    print("From: " .. devFrom .. " (" .. dnsLookup(devFrom, dns) .. ")")
    print("Destination: " .. pDest .. " (" .. pDestAddr .. ")")
    print("Message: " .. pMsg)
    print("Forwarding message to " .. pDestAddr .. "...")
    component.modem.send(pDestAddr, netport, pMsg)
    component.modem.send(devFrom, netport, "SUCCESS")
  else
    print("Port was neither netport nor dnsport! This shouldn't happen, is a port open that shouldn't be?")
  end
end