Packet Structure

// Complete DNS packet structure
interface DNSPacket {
  type: 'query' | 'response'; // Packet type
  id?: number; // Transaction ID (0-65535)
  flags?: number; // DNS flags bitfield
  questions?: Question[]; // Question section
  answers?: Answer[]; // Answer section
  authorities?: Answer[]; // Authority section
  additionals?: Answer[]; // Additional section
}

// Question structure
interface Question {
  type: string; // DNS record type ('A', 'AAAA', 'MX', etc.)
  class?: string; // DNS class (default: 'IN')
  name: string; // Domain name to query
}

// Answer/Authority/Additional structure
interface Answer {
  type: string; // DNS record type
  class?: string; // DNS class (default: 'IN')
  name: string; // Domain name
  ttl?: number; // Time to live in seconds
  // Record-specific data properties
}

const dnsPacket = require('dns-packet');

// DNS flag constants
const AUTHORITATIVE_ANSWER = dnsPacket.AUTHORITATIVE_ANSWER; // 1 << 10 (0x0400)
const TRUNCATED_RESPONSE = dnsPacket.TRUNCATED_RESPONSE;     // 1 << 9  (0x0200)
const RECURSION_DESIRED = dnsPacket.RECURSION_DESIRED;       // 1 << 8  (0x0100)
const RECURSION_AVAILABLE = dnsPacket.RECURSION_AVAILABLE;   // 1 << 7  (0x0080)
const AUTHENTIC_DATA = dnsPacket.AUTHENTIC_DATA;             // 1 << 5  (0x0020)
const CHECKING_DISABLED = dnsPacket.CHECKING_DISABLED;       // 1 << 4  (0x0010)
const DNSSEC_OK = dnsPacket.DNSSEC_OK;                       // 1 << 15 (0x8000)

// Extended flag properties in decoded headers
interface DecodedHeader {
  id: number;
  type: 'query' | 'response';
  flags: number;         // Raw flags value
  flag_qr: boolean;      // Query/Response flag
  opcode: string;        // Operation code name
  flag_aa: boolean;      // Authoritative Answer
  flag_tc: boolean;      // Truncated Response
  flag_rd: boolean;      // Recursion Desired
  flag_ra: boolean;      // Recursion Available
  flag_z: boolean;       // Zero flag (reserved)
  flag_ad: boolean;      // Authentic Data
  flag_cd: boolean;      // Checking Disabled
  rcode: string;         // Response code name
  questions: Array;      // Question section array
  answers: Array;        // Answer section array
  authorities: Array;    // Authority section array
  additionals: Array;    // Additional section array
}

const dnsPacket = require('dns-packet');

// Single flag
const queryPacket = {
  type: 'query',
  flags: dnsPacket.RECURSION_DESIRED,
  questions: [{ type: 'A', name: 'example.com' }]
};

// Multiple flags using bitwise OR
const flags = dnsPacket.RECURSION_DESIRED | dnsPacket.DNSSEC_OK;
const secureQuery = {
  type: 'query',
  flags: flags,
  questions: [{ type: 'A', name: 'example.com' }]
};

// Check for flags using bitwise AND
const hasRecursion = packet.flags & dnsPacket.RECURSION_DESIRED;
const isAuthoritative = packet.flags & dnsPacket.AUTHORITATIVE_ANSWER;

const { question } = require('dns-packet');

// Question encoding/decoding
question.encode(q, buf, offset);
question.decode(buf, offset);
question.encodingLength(q);

// Question structure
interface Question {
  type: string; // Record type ('A', 'AAAA', 'MX', etc.)
  class?: string; // DNS class (defaults to 'IN')
  name: string; // Domain name to query
}

const q = {
  type: 'A',
  class: 'IN', // Optional, defaults to 'IN'
  name: 'example.com'
};

const encodedQuestion = question.encode(q);

const { answer } = require('dns-packet');

// Answer encoding/decoding (also used for authorities and additionals)
answer.encode(a, buf, offset);
answer.decode(buf, offset);
answer.encodingLength(a);

// Answer structure (same for authorities and additionals)
interface Answer {
  type: string; // Record type
  class?: string; // DNS class (defaults to 'IN')
  name: string; // Domain name
  ttl?: number; // Time to live in seconds
  // Additional properties based on record type
}

// A record answer
const aRecord = {
  type: 'A',
  name: 'example.com',
  ttl: 300,
  data: '192.168.1.1'
};

// MX record answer
const mxRecord = {
  type: 'MX',
  name: 'example.com',
  ttl: 3600,
  preference: 10,
  exchange: 'mail.example.com'
};

// TXT record answer
const txtRecord = {
  type: 'TXT',
  name: 'example.com',
  ttl: 300,
  data: ['v=spf1 include:_spf.google.com ~all']
};

const { name } = require('dns-packet');

// Name encoding/decoding
name.encode(str, buf, offset, options);
name.decode(buf, offset, options);
name.encodingLength(str, options);

// Options for name encoding/decoding
interface NameOptions {
  mail?: boolean; // Handle mail address format (@ as .)
}

// Standard domain name
const domain = 'example.com';
const encoded = name.encode(domain);
const decoded = name.decode(encoded, 0);

// Mail address format (for SOA RNAME field)
const mailAddr = 'admin@example.com';
const encodedMail = name.encode('admin.example.com', buf, offset, { mail: true });

const queryPacket = {
  type: 'query',
  id: Math.floor(Math.random() * 65536),
  flags: dnsPacket.RECURSION_DESIRED,
  questions: [{
    type: 'A',
    name: 'example.com'
  }]
};

const responsePacket = {
  type: 'response',
  id: 1234, // Must match query ID
  flags: dnsPacket.RECURSION_AVAILABLE | dnsPacket.AUTHORITATIVE_ANSWER,
  questions: [/* original questions */],
  answers: [{
    type: 'A',
    name: 'example.com',
    ttl: 300,
    data: '192.168.1.1'
  }]
};

try {
  const packet = dnsPacket.decode(buffer);
  
  // Validate packet structure
  if (!packet.questions || packet.questions.length === 0) {
    throw new Error('No questions in packet');
  }
  
  // Check for truncation
  if (packet.flags & dnsPacket.TRUNCATED_RESPONSE) {
    console.warn('Response was truncated, consider using TCP');
  }
  
} catch (error) {
  if (error.message.includes('buffer overflow')) {
    console.error('Malformed DNS packet');
  } else if (error.message.includes('name too long')) {
    console.error('Domain name exceeds maximum length');
  } else {
    console.error('DNS parsing error:', error.message);
  }
}

const encoded = question.encode(q);
console.log('Question bytes:', question.encode.bytes);

const decoded = answer.decode(buf, offset);
console.log('Answer bytes consumed:', answer.decode.bytes);