fune/netwerk/dns/mdns/libmdns/fallback/DataWriter.jsm

/* -*- Mode: js; js-indent-level: 2; indent-tabs-mode: nil; tab-width: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */
/* jshint esnext: true, moz: true */

"use strict";

var EXPORTED_SYMBOLS = ["DataWriter"];

class DataWriter {
  constructor(data, maxBytes = 512) {
    if (typeof data === "number") {
      maxBytes = data;
      data = undefined;
    }

    this._buffer = new ArrayBuffer(maxBytes);
    this._data = new Uint8Array(this._buffer);
    this._cursor = 0;

    if (data) {
      this.putBytes(data);
    }
  }

  get buffer() {
    return this._buffer.slice(0, this._cursor);
  }

  get data() {
    return new Uint8Array(this.buffer);
  }

  // `data` is `Uint8Array`
  putBytes(data) {
    if (this._cursor + data.length > this._data.length) {
      throw new Error("DataWriter buffer is exceeded");
    }

    for (let i = 0, length = data.length; i < length; i++) {
      this._data[this._cursor] = data[i];
      this._cursor++;
    }
  }

  putByte(byte) {
    if (this._cursor + 1 > this._data.length) {
      throw new Error("DataWriter buffer is exceeded");
    }

    this._data[this._cursor] = byte;
    this._cursor++;
  }

  putValue(value, length) {
    length = length || 1;
    if (length == 1) {
      this.putByte(value);
    } else {
      this.putBytes(_valueToUint8Array(value, length));
    }
  }

  putLabel(label) {
    // Eliminate any trailing '.'s in the label (valid in text representation).
    label = label.replace(/\.$/, "");
    let parts = label.split(".");
    parts.forEach(part => {
      this.putLengthString(part);
    });
    this.putValue(0);
  }

  putLengthString(string) {
    if (string.length > 0xff) {
      throw new Error("String too long.");
    }
    this.putValue(string.length);
    for (let i = 0; i < string.length; i++) {
      this.putValue(string.charCodeAt(i));
    }
  }
}

/**
 * @private
 */
function _valueToUint8Array(value, length) {
  let arrayBuffer = new ArrayBuffer(length);
  let uint8Array = new Uint8Array(arrayBuffer);
  for (let i = length - 1; i >= 0; i--) {
    uint8Array[i] = value & 0xff;
    value = value >> 8;
  }

  return uint8Array;
}