Module header 

DNS header parsing (RFC 1035 Section 4.1.1).

The DNS header is 12 bytes:

+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                      ID                         |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR|   Opcode  |AA|TC|RD|RA| Z|AD|CD|   RCODE    |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    QDCOUNT                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ANCOUNT                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    NSCOUNT                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|                    ARCOUNT                       |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Constants

DNS_HEADER_LEN

DNS header size in bytes.

Functions

build_flags

Build a raw 16-bit flags value from individual components.

read_aa

AA flag: Authoritative Answer.

read_ad

AD flag: Authenticated Data (DNSSEC).

read_ancount

Answer count.

read_arcount

Additional count.

read_cd

CD flag: Checking Disabled (DNSSEC).

read_id

Read the DNS transaction ID.

read_nscount

Authority count.

read_opcode

Opcode (4 bits).

read_qdcount

Question count.

read_qr

QR flag: 0 = query, 1 = response.

read_ra

RA flag: Recursion Available.

read_rcode

RCODE (4 bits): Response code.

read_rd

RD flag: Recursion Desired.

read_tc

TC flag: Truncation.

read_z

Z flag (reserved).

write_aa

write_ad

write_ancount

write_arcount

write_cd

write_id

Write the DNS transaction ID.

write_nscount

write_opcode

write_qdcount

write_qr

write_ra

write_rcode

write_rd

write_tc

write_z