dns_message.ts

import { randomBytes } from 'crypto';
import { IDnsHeader, IDnsMessage, IQuestion, IResourceRecord } from './types';
import {
  convertHeaderToByteString,
  convertQuestionsToByteString,
  convertResourceRecordToByteString
} from './utils';

/**
 * This interface is used with the DnsMessage class to accept the args.
 * All the arguments are optional.
 * The header argument has Partial capabilities.
 */
interface DnsMessageArgs {
  header?: Partial<IDnsHeader>;
  questions?: IQuestion[];
  answers?: IResourceRecord[];
  authority?: IResourceRecord[];
  additional?: IResourceRecord[];
}

class DnsMessage implements IDnsMessage {
  header: IDnsHeader;
  questions: IQuestion[];
  answers: IResourceRecord[];
  authority: IResourceRecord[];
  additional: IResourceRecord[];

  /**
   * Default header with following values
   * - id: random integer
   * - flags (hex): 0100
   * - anCount, arCount, nsCount: 0
   * - qrCount: 1
   *
   * @type {IDnsHeader}
   */
  #_defaultHeader: IDnsHeader = {
    id: parseInt(randomBytes(2).toString('hex'), 16),
    qr: 0b0,
    opcode: 0b0000,
    aa: 0b0,
    tc: 0b0,
    rd: 0b1,
    ra: 0b0,
    z: 0b000,
    rCode: 0b0000,
    anCount: 0x0000,
    arCount: 0x0000,
    nsCount: 0x0000,
    qdCount: 0x0001
  };

  constructor({
    header = undefined,
    questions = [],
    answers = [],
    authority = [],
    additional = []
  }: DnsMessageArgs) {
    if (header === undefined) {
      this.header = this.#_defaultHeader;
    } else {
      this.header = { ...this.#_defaultHeader, ...header };
    }

    this.questions = questions;
    this.answers = answers;
    this.authority = authority;
    this.additional = additional;
  }

  toByteString(): string {
    return (
      convertHeaderToByteString(this.header) +
      convertQuestionsToByteString(this.questions) +
      convertResourceRecordToByteString(this.answers) +
      convertResourceRecordToByteString(this.authority) +
      convertResourceRecordToByteString(this.additional)
    );
  }
}

export { DnsMessage };