Secure DNS

-- Function to load DNS entries from the /DNS directory
local function loadDNS()
    local dns = {}
    for _, file in ipairs(fs.list("/DNS")) do
        local f = fs.open("/DNS/" .. file, "r")
        local ip = f.readAll()
        f.close()
        dns[file] = ip
    end
    return dns
end

-- Function to log DNS connections
local function logConnection(url, ip)
    local logFile = fs.open("dns_log.txt", "a")
    logFile.writeLine("URL: " .. url .. ", IP: " .. ip .. ", Time: " .. textutils.formatTime(os.time(), true))
    logFile.close()
end

-- Function to load the stored password from /DNS/locked.cfg
local function loadPassword()
    local filePath = "/DNS/locked.cfg"
    if fs.exists(filePath) then
        local file = fs.open(filePath, "r")
        local password = file.readAll()
        file.close()
        return password
    end
    return nil  -- No password file found
end

-- Function to handle DNS requests
local function handleDNSRequest(dns, senderID, url)
    local storedPassword = loadPassword()
    if storedPassword then
        rednet.send(senderID, "PASSWORD_REQUIRED")  -- Ask for the password

        local timer = os.startTimer(10)  -- Wait for 10 seconds for a response
        while true do
            local event, id, message = os.pullEvent()
            if event == "rednet_message" and id == senderID then
                if message == storedPassword then
                    if dns[url] then
                        rednet.send(senderID, dns[url])
                        logConnection(url, dns[url])
                    else
                        rednet.send(senderID, "404_NOT_FOUND")
                    end
                else
                    rednet.send(senderID, "AUTH_FAILED")
                end
                break
            elseif event == "timer" and id == timer then
                rednet.send(senderID, "TIMEOUT")
                break
            end
        end
    else
        if dns[url] then
            rednet.send(senderID, dns[url])
            logConnection(url, dns[url])
        else
            rednet.send(senderID, "404_NOT_FOUND")
        end
    end
end

-- Automatically find and open the first available modem
local function openModem()
    local sides = {"top", "bottom", "left", "right", "front", "back"}
    for _, side in ipairs(sides) do
        if peripheral.isPresent(side) and peripheral.getType(side) == "modem" then
            rednet.open(side)
            return side
        end
    end
    print("Error: No modem found.")
    return nil
end

-- Main DNS server function
local function runDNSServer()
    local modemSide = openModem()
    if not modemSide then return end

    local dns = loadDNS()
    print("DNS Server is running on " .. modemSide .. " modem. Listening for requests...")

    while true do
        local senderID, url = rednet.receive()
        handleDNSRequest(dns, senderID, url)
    end
end

-- Main execution
runDNSServer()