Secure DNS

-- Function to log connections
local function logConnection(id, message)
    local logFile = "dns_log.txt"
    local file = fs.open(logFile, "a")
    file.writeLine("ID: " .. id .. " - " .. message .. " - " .. textutils.formatTime(os.time(), true))
    file.close()
end

-- Function to check if an ID is blocked
local function isBlocked(id)
    local blockFile = "/blocked/" .. tostring(id) .. ".txt"
    return fs.exists(blockFile)
end

-- Function to load website IP from file
local function loadWebsiteIP(url)
    local filePath = "/DNS/" .. url
    if not fs.exists(filePath) then
        return nil
    end
    local file = fs.open(filePath, "r")
    local ip = file.readAll()
    file.close()
    return ip
end

-- Function to authenticate request
local function authenticateRequest(token)
    local validToken = "YOUR_SECURE_TOKEN"  -- Replace with your secure token
    return token == validToken
end

-- Open modem
local modemSide = "back"  -- Change to the side your modem is connected to
rednet.open(modemSide)

print("DNS server is running...")

while true do
    -- Wait for a DNS request
    local senderID, request = rednet.receive()
    logConnection(senderID, "Requested: " .. request)

    -- Extract token and URL from the request
    local token, url = string.match(request, "([^:]+):(.+)")

    -- Validate and authenticate request
    if not authenticateRequest(token) then
        rednet.send(senderID, "ERROR 403: Unauthorized Access")
        logConnection(senderID, "Unauthorized access")
    elseif isBlocked(senderID) then
        rednet.send(senderID, "ERROR 403: Your IP address has been blocked from this DNS Network")
        logConnection(senderID, "Blocked")
    else
        -- Look up the IP address for the requested URL
        local ip = loadWebsiteIP(url)
        if ip then
            rednet.send(senderID, ip)
            logConnection(senderID, "Sent IP: " .. ip)
        else
            rednet.send(senderID, "404_NOT_FOUND")
            logConnection(senderID, "URL not found")
        end
    end
end