DNS answer section promblem

Challenges
1

I stuck on this stage(header answer section).
I tried so far :

import socket
import struct

class DomainLabel:
    def __init__(self, name):
        self.name = name
        self.len = len(name)

    def bytes(self):
        return bytes([self.len]) + self.name.encode()

class LabelSequence:
    def __init__(self, labels):
        self.labels = labels

    def bytes(self):
        qName = bytearray()
        for label in self.labels:
            qName.extend(label.bytes())
        qName.append(0)  
        return bytes(qName)

class DNSAnswer:
    def __init__(self, name, qtype, qclass, ttl, data):
        self.name = name
        self.type = qtype
        self.class_ = qclass
        self.ttl = ttl
        self.len = len(data)
        self.data = data

    def bytes(self):
        ansName = self.name.bytes()

        ansType = struct.pack('!H', self.type)
        ansClass = struct.pack('!H', self.class_)
        ansTTL = struct.pack('!I', self.ttl)
        ansLen = struct.pack('!H', self.len)

        return ansName + ansType + ansClass + ansTTL + ansLen + self.data


domain_to_ip = {
    "example.com": "192.0.2.1",
    "www.example.com": "192.0.2.1",
    "google.com": "142.250.64.14",
    "github.com": "140.82.112.3",
}

def main():
    udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    udp_socket.bind(("127.0.0.1", 2053))
    print("DNS server listening on 127.0.0.1:2053")
    
    while True:
        try:
            buf, source = udp_socket.recvfrom(512)
            print(f"Received data from: {source}")
            response = build_dns_response(buf)
            udp_socket.sendto(response, source)
            print(f"Sent response to: {source}")
        except Exception as e:
            print(f"Error receiving data: {e}")
            continue 

def build_dns_response(query):
    id, flags, qdcount, _, _, _ = struct.unpack("!HHHHHH", query[:12])
    question_name, qtype, qclass = parse_question_section(query[12:])

    ip_address = domain_to_ip.get(question_name)
    if ip_address is None:
        print(f"No record found for {question_name}")
        return build_error_response(id, 3) 

    answer_section = build_answer_section(question_name, qtype, ip_address)

   
    qr = 1  
    opcode = (flags >> 11) & 0b1111
    aa = 1 
    tc = 0 
    rd = (flags >> 8) & 0b1
    ra = 0 
    z = 0  
    rcode = 0  

    response_flags = (qr << 15) | (opcode << 11) | (aa << 10) | (tc << 9) | (rd << 8) | (ra << 7) | rcode

    header = struct.pack("!HHHHHH",
                         id, 
                         response_flags,
                         qdcount, 
                         1, 
                         0,  
                         0)  

    response = header + query[12:] + answer_section
    print(f"Built DNS Response:\n{response.hex()}")
    return response

def parse_question_section(question):
    labels = []
    idx = 0
    while question[idx] != 0:
        length = question[idx]
        labels.append(question[idx + 1: idx + 1 + length])
        idx += length + 1
    question_name = b".".join(labels).decode('utf-8')
    qtype, qclass = struct.unpack("!HH", question[idx + 1: idx + 5])
    return question_name, qtype, qclass

def build_answer_section(domain_name, qtype, ip_address):
    if qtype == 1: 
        packed_ip = socket.inet_aton(ip_address)
        answer = DNSAnswer(
            name=LabelSequence([DomainLabel(domain_name)]),
            qtype=1,  
            qclass=1, 
            ttl=60, 
            data=packed_ip
        )
    else:
        print(f"Unsupported query type: {qtype}")
        return b''

    return answer.bytes()

def build_error_response(query_id, rcode):
    response_flags = 0b10000000 | rcode  
    header = struct.pack("!HHHHHH", query_id, response_flags, 1, 0, 0, 0)  
    return header

if __name__ == "__main__":
    main()

Error:

remote: [your_program] Received data from: ('127.0.0.1', 42373)
remote: [your_program] No record found for codecrafters.io
remote: [your_program] Sent response to: ('127.0.0.1', 42373)
remote: [tester::#HD8] Querying: ;reddit.com.   IN       A
remote: [tester::#HD8] Sending Request: (Messages with >>> prefix are part of this log)
remote: [tester::#HD8] >>> ;; opcode: QUERY, status: NOERROR, id: 13890
remote: [tester::#HD8] >>> ;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
remote: [tester::#HD8] >>>
remote: [tester::#HD8] >>> ;; QUESTION SECTION:
remote: [tester::#HD8] >>> ;reddit.com. IN       A
remote: [tester::#HD8] >>>
remote: [your_program] Received data from: ('127.0.0.1', 40356)
remote: [your_program] No record found for reddit.com
remote: [your_program] Sent response to: ('127.0.0.1', 40356)
remote: [tester::#HD8] Shutting down DNS resolver server...
remote: [tester::#HD8] Expected QR field to be set to 1. 1 indicates that it is a response. Got 0
remote: [tester::#HD8] Test failed
remote: [tester::#HD8] Terminating program
remote: [tester::#HD8] Program terminated successfully
2

This is the reason, the header you send in your response indicates it is a query and not a response, your response is sending 0 indicating you are querying and not answering a query.

QR - Query Response - 1 bit - 0 for queries, 1 for responses.

I’m bad with bitwise operations so I can’t say if you’re doing something wrong with:

But it seems like the problem is there at least.

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