ndn-js/js/util/dynamic-buffer.js

A JavaScript client library for Named Data Networking

/**
 * Encapsulate a Buffer and support dynamic reallocation.
 * Copyright (C) 2013-2019 Regents of the University of California.
 * @author: Jeff Thompson <jefft0@remap.ucla.edu>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * A copy of the GNU Lesser General Public License is in the file COPYING.
 */

/**
 * Create a DynamicBuffer where this.array is a Buffer of size length.
 * To access the array, use this.array or call slice.
 * @constructor
 * @param {number} length the initial length of the array.  If null, use a default.
 */
var DynamicBuffer = function DynamicBuffer(length)
{
  if (!length)
    length = 16;

  this.array = new Buffer(length);
};

exports.DynamicBuffer = DynamicBuffer;

/**
 * Ensure that this.array has the length, reallocate and copy if necessary.
 * Update the length of this.array which may be greater than length.
 * @param {number} length The minimum length for the array.
 */
DynamicBuffer.prototype.ensureLength = function(length)
{
  if (this.array.length >= length)
    return;

  // See if double is enough.
  var newLength = this.array.length * 2;
  if (length > newLength)
    // The needed length is much greater, so use it.
    newLength = length;

  var newArray = new Buffer(newLength);
  this.array.copy(newArray);
  this.array = newArray;
};

/**
 * Copy the value to this.array at offset, reallocating if necessary.
 * @param {Buffer} value The buffer to copy.
 * @param {number} offset The offset in the buffer to start copying into.
 * @return {number} The new offset which is offset + value.length.
 */
DynamicBuffer.prototype.copy = function(value, offset)
{
  this.ensureLength(value.length + offset);

  if (Buffer.isBuffer(value))
    value.copy(this.array, offset);
  else
    // Need to make value a Buffer to copy.
    new Buffer(value).copy(this.array, offset);

  return offset + value.length;
};

/**
 * Ensure that this.array has the length. If necessary, reallocate the array
 *   and shift existing data to the back of the new array.
 * Update the length of this.array which may be greater than length.
 * @param {number} length The minimum length for the array.
 */
DynamicBuffer.prototype.ensureLengthFromBack = function(length)
{
  if (this.array.length >= length)
    return;

  // See if double is enough.
  var newLength = this.array.length * 2;
  if (length > newLength)
    // The needed length is much greater, so use it.
    newLength = length;

  var newArray = new Buffer(newLength);
  // Copy to the back of newArray.
  this.array.copy(newArray, newArray.length - this.array.length);
  this.array = newArray;
};

/**
 * First call ensureLengthFromBack to make sure the bytearray has
 * offsetFromBack bytes, then copy value into the array starting
 * offsetFromBack bytes from the back of the array.
 * @param {Buffer} value The buffer to copy.
 * @param {number} offsetFromBack The offset from the back of the array to start
 * copying.
 */
DynamicBuffer.prototype.copyFromBack = function(value, offsetFromBack)
{
  this.ensureLengthFromBack(offsetFromBack);

  if (Buffer.isBuffer(value))
    value.copy(this.array, this.array.length - offsetFromBack);
  else
    // Need to make value a Buffer to copy.
    new Buffer(value).copy(this.array, this.array.length - offsetFromBack);
};

/**
 * Return this.array.slice(begin, end);
 * @param {number} begin The begin index for the slice.
 * @param {number} end (optional) The end index for the slice.
 * @return {Buffer} The buffer slice.
 */
DynamicBuffer.prototype.slice = function(begin, end)
{
  if (end == undefined)
    return this.array.slice(begin);
  else
    return this.array.slice(begin, end);
};