rootdns

--[[
    Root DNS server.
    By Mitchfizz05. Licensed under the GNU General Pubic License v3.
]]

term.clear()
term.setCursorPos(1,1)

print("Root DNS server starting...")

-- Scan for modem.
print("Scanning for modem...")
local modemSide = nil
for n,side in ipairs(rs.getSides()) do
    if peripheral.getType(side) == "modem" then
        -- Modem detected!
        modemSide = side
        break
    end
end

if modemSide == nil then
    -- No modem detected. Exit program.
    print("No modem detected.")
    return
end

-- Open modem.
rednet.open(modemSide)
print("Opened modem on the " .. modemSide .. " side.")

-- Scan for other root DNS servers.
print("Scanning for other DNS servers...")
rednet.broadcast("dns.search")
local timer = os.startTimer(1)
while true do
    local e,id,msg,proto = os.pullEvent()
    if e == "rednet_message" then
        if msg == "dns.pong" then
            -- Another DNS server found!
            print("Other DNS servers found on the network!")
            print("Only 1 DNS server can be on a network at once.")
            return
        end
    elseif e == "timer" and id == timer then
        break
    end
end
print("No other DNS servers found.")

-- Stores all current domain names.
domains  = {}

-- Load domains from file.
print("Reading DNS file...")
local file = fs.open("data/zones", "r")
if not file then
    -- Fatal error! Zonefile cannot be read!
    print("Fatal error! Zonefile cannot be read!")
    return
end

-- Iterate through lines.
local line = ""
while true do
    -- Read line.
    line = file:readLine()

    -- Check that the line was read.
    if not line then
        break
    end

    -- Split the domain record.
    local domain = string.sub(line, 0, string.find(line, ":") - 1)
    local target = string.sub(line, string.find(line, ":") + 1)

    -- Register the domain into the domains array.
    domains[domain] = target
end

-- Close the zonefile.
file:close()

-- Server started.
print("Root DNS server started!")

-- Begin rednet loop.
while true do
    local id,msg = rednet.receive()
    if msg == "ping" then
        -- Ping request.
        rednet.send(id, "pong")
    elseif msg == "dns.search" then
        -- DNS server scan.
        rednet.send(id, "dns.pong")
    elseif string.sub(msg, 0, #"dns.lookup:") == "dns.lookup:" then
        -- DNS lookup.
        local domain = string.sub(msg, #"dns.lookup:" + 1)

        print("Request to lookup domain: " .. domain)

        -- Check that the domain name exists.
        if (domains[domain]) then
            rednet.send(id, "dns.probe:" .. domains[domain])
        else
            -- Domain doesn't exist!
            rednet.send(id, "dns.probe.failed")
        end
    end
end