--Decode a string like "de ad be ef" into a binary string (in this case -
--four-byte 0xDEADBEEF.)
function unhex(str)
    str = string.gsub (str, "(%x%x) ?",
        function(h) return string.char(tonumber(h,16)) end)
    return str
end

--Convert an IPv4 address like 127.0.0.1 to four-byte binary string.
function ipv4_to_hex(ip)
    ret = ""
    for v in ip:gmatch("(%d%d?%d?)[.]?") do --at least one digit, maybe a dot.
        if ret == nil then
            break
        end
        ret = ret .. string.char(v)
    end
    return ret
end

--A table of known IP addresses.
responses = {
    ["localhost"]                       = "127.0.0.1",
    ["google-public-dns-a.google.com"]  = "8.8.8.8"
}

--Read the query.
transaction_id  = io.stdin:read(2)
flags           = io.stdin:read(2)
questions       = io.stdin:read(2)
answer_rrs      = io.stdin:read(2)
authority_rrs   = io.stdin:read(2)
additional_rrs  = io.stdin:read(2)

query = ""
raw_query = ""
while true do
    --Read a byte, then as many bytes as the hex value of the first one.
    byte = io.stdin:read(1)
    raw_query = raw_query .. byte
    if byte:byte(1)==0x00 then --NULL marks end of the string.
        break
    end
    for i=1,byte:byte(1) do
        byte = io.stdin:read(1)
        raw_query = raw_query .. byte
        query = query .. byte
    end
    query = query .. '.'
end
query=query:sub(1,query:len()-1) --strip the trailing dot.

ip = responses[query]
-- 1... .... .... .... = Response: Message is a response
-- .000 0... .... .... = Opcode: Standard query (0)
-- .... .0.. .... .... = Authoritative: Server is not an authority for domain
-- .... ..0. .... .... = Truncated: Message is not truncated
-- .... ...1 .... .... = Recursion desired: Do query recursively
flags = unhex('81')
if ip ~= nil then
    ip = ipv4_to_hex(ip)
    answers = unhex("00 01")
    -- .... .... 1... .... = Recursion available: Server can do recursive queries
    -- .... .... .0.. .... = Z: reserved (0)
    -- .... .... ..0. .... = Answer authenticated: Answer/authority portion was
    --                       not authenticated by the server
    -- .... .... ...0 .... = Non-authenticated data: Unacceptable
    -- .... .... .... 0000 = Reply code: No error (0)
    flags = unhex("81 80")
else
    answers = unhex("00 00")
    --.... .... 1... .... = Recursion available: Server can do recursive queries
    --.... .... ..1. .... = Answer authenticated: Answer/authority portion was
    --                      authenticated by the server
    --.... .... ...0 .... = Non-authenticated data: Unacceptable
    --.... .... .... 0011 = Reply code: No such name (3)
    flags = unhex("81 a3")
end

q_type = io.stdin:read(2)
class = io.stdin:read(2)
aditional_records = io.stdin:read(11) --hardcoded for "dig".

io.stderr:write("Got a query '"..query.."'.\n")
io.stderr:flush()

io.stdout:write(transaction_id)

io.stdout:write(flags) --flags, hardcoded.

io.stdout:write(questions)
io.stdout:write(answers)
io.stdout:write(unhex("00 00"))
io.stdout:write(unhex("00 00"))

--question section
io.stdout:write(raw_query)
io.stdout:write(q_type)
io.stdout:write(class)

if ip ~= nil then
    --answer section
    io.stdout:write(unhex("c0 0c")) --hostname offset?
    io.stdout:write(q_type)
    io.stdout:write(class)
    io.stdout:write(unhex("00 00 00 da")) --TTL = 3min38s
    io.stdout:write(unhex("00 04")) --data length
    io.stdout:write(ip)
end

io.stdout:flush()