DNS Server Parse question section

[Roshan2115]

I’m stuck at this stage

import socket
import struct


known_domains = {
    "mail.reddit.com.i": "151.101.1.140", 
}

def build_dns_response(query):
    
    id = query[0:2]

  
    flags = struct.unpack("!H", query[2:4])[0]
    response_flags = (flags & 0x7FFF) | 0x8000  # Set QR to 1

    
    opcode = (flags >> 11) & 0x0F
    if opcode == 0: 
        rcode = 0 
    else:
        rcode = 4  

   
    question_start = 12
    question_name_end = query.find(b'\x00', question_start) + 1
    question_name = query[question_start:question_name_end].decode()

    
    ancount = 0
    answer = b''

    if rcode == 0 and question_name in known_domains:
        ip_address = known_domains[question_name]
        ancount = 1  
        
       
        answer_name = b'\x00\x00' 
        answer_type = struct.pack("!H", 1) 
        answer_class = struct.pack("!H", 1)  
        ttl = struct.pack("!I", 80)  
        rdata = socket.inet_aton(ip_address)  
        rdata_length = struct.pack("!H", len(rdata))

        answer = answer_name + answer_type + answer_class + ttl + rdata_length + rdata

   
    response_flags = (response_flags & 0xFFEF) | (rcode << 0)

    
    header = struct.pack("!HHHHHH", struct.unpack("!H", id)[0], response_flags, 1, ancount, 0, 0)

   
    response = header + query[12:] + answer
    return response

def start_udp_server():
    server_address = ('', 2053)
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.bind(server_address)

    print("UDP server is running on port 2053...")

    while True:
        data, address = sock.recvfrom(4096)
        print(f"Received packet from {address}: {data}")

        response_message = build_dns_response(data)

       
        sock.sendto(response_message, address)
        print(f"Sent response to {address}")

if __name__ == "__main__":
    start_udp_server()

Log:

 Running tests for Stage #HD8 (Parse question section)
remote: [tester::#HD8] Starting DNS server on 127.0.0.1:2053
remote: [tester::#HD8] Running program
remote: [tester::#HD8] DNS resolver listening on 127.0.0.1:5354
remote: [tester::#HD8] Connecting to 127.0.0.1:2053 using UDP
remote: [your_program] UDP server is running on port 2053...
remote: [your_program] Received packet from ('127.0.0.1', 48296): b'\x17\x08\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x0ccodecrafters\x02io\x00\x00\x01\x00\x01'
remote: [your_program] Sent response to ('127.0.0.1', 48296)
remote: [tester::#HD8] Querying: ;mail.reddit.com.i      IN       A
remote: [tester::#HD8] Sending Request: (Messages with >>> prefix are part of this log)
remote: [tester::#HD8] >>> ;; opcode: QUERY, status: NOERROR, id: 53510
remote: [tester::#HD8] >>> ;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
remote: [tester::#HD8] >>>
remote: [tester::#HD8] >>> ;; QUESTION SECTION:
remote: [tester::#HD8] >>> ;mail.reddit.com.i    IN       A
remote: [tester::#HD8] >>>
remote: [your_program] Received packet from ('127.0.0.1', 43502): b'\xd1\x06\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x04mail\x06reddit\x03com\x00\x00\x01\x00\x01'
remote: [tester::#HD8] Received Response: (Messages with >>> prefix are part of this log)
remote: [tester::#HD8] >>> ;; opcode: QUERY, status: NOERROR, id: 53510
remote: [tester::#HD8] >>> ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
remote: [tester::#HD8] >>>
remote: [tester::#HD8] >>> ;; QUESTION SECTION:
remote: [your_program] Sent response to ('127.0.0.1', 43502)
remote: [tester::#HD8] >>> ;mail.reddit.com.i   IN       A
remote: [tester::#HD8] >>>
remote: [tester::#HD8] Shutting down DNS resolver server...
remote: [tester::#HD8] Expected answer section to have at least one entry got 0
remote: [tester::#HD8] Test failed
remote: [tester::#HD8] Terminating program
remote: [tester::#HD8] Program terminated successfully

[andy1li]

I’ll take a look at your code and get back to you after the weekend.

[andy1li]

@Roshan2115 Please double-check that ANCOUNT is set correctly.