rochars / minibuffer

 * Copyright (c) 2018 Rafael da Silva Rocha.

 *

 * Permission is hereby granted, free of charge, to any person obtaining

 * a copy of this software and associated documentation files (the

 * "Software"), to deal in the Software without restriction, including

 * without limitation the rights to use, copy, modify, merge, publish,

 * distribute, sublicense, and/or sell copies of the Software, and to

 * permit persons to whom the Software is furnished to do so, subject to

 * the following conditions:

 *

 * The above copyright notice and this permission notice shall be

 * included in all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE

 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION

 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION

 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

 *

 */

/**

 * @fileoverview A minimalist buffer reader and writer.

 * @see https://github.com/rochars/minibuffer

 */

/** @module minibuffer */

import {unpack, packTo, unpackString, packStringTo} from 'byte-data';

/**

 * @type {string}

 * @private

 */

const RANGE_EROR = "Range error";

/**

 * A class to read and write to buffers.

 */

export default class MiniBuffer {

  constructor() {

    /**

     * @type {number}

     */

    this.head = 0;

  }

  /**

   * Set the MiniBuffer head to zero.

   */

  clear() {

    this.head = 0;

  }

  /**

   * Read a number from a buffer.

   * @param {!Uint8Array} buffer The buffer.

   * @param {!Object} typeDefinition The type definition.

   * @param {?number=} index The index to read.

   * @return {number|undefined} The number.

   * @throws {Error} If word size + index > buffer.length

   */

  read(buffer, typeDefinition, index=null) {

    index = index === null ? this.head : index;

    /** @type {number} */

    let size = typeDefinition.bits / 8;

    if (index + size > buffer.length) {

      throw new Error(RANGE_EROR);

    }

    /** @type {number|undefined} */

    let num = unpack(buffer, typeDefinition, index);

    this.head = size + index;

    return num;

  }

  /**

   * Write a number to a buffer.

   * @param {!Uint8Array} buffer The buffer.

   * @param {!Object} typeDefinition The type definition.

   * @param {number} num The number to write.

   * @param {?number=} index The buffer index to write.

   * @throws {Error} If word size + index > buffer.length

   */

  write(buffer, typeDefinition, num, index=null) {

    index = index === null ? this.head : index;

    /** @type {number} */

    let size = typeDefinition.bits / 8;

    if (index + size > buffer.length) {

      throw new Error(RANGE_EROR);

    }

    this.head = packTo(num, typeDefinition, buffer, index);

  }

  /**

   * Read a UTF-8 string from a buffer.

   * @param {!Uint8Array} buffer The buffer.

   * @param {number} size the max size of the string.

   * @param {?number=} index The buffer index to read.

   * @return {string} The string.

   * @throws {Error} If size + index > buffer.length

   */

  /**

   * Write a UTF-8 string to a buffer. If the string is smaller

   * than the max size the output buffer is filled with 0s.

   * @param {!Uint8Array} buffer The buffer.

   * @param {string} str The string to be written as bytes.

   * @param {number=} size The size of the string.

   * @param {?number=} index The buffer index to write.

   * @throws {Error} If size + index > buffer.length

   */

  writeStr(buffer, str, size=str.length, index=null) {

    index = index === null ? this.head : index;

    /** @type {number} */

    let limit = index + size;

    if (limit > buffer.length) {

      throw new Error(RANGE_EROR);

    }

    this.head = packStringTo(str, buffer, index);

    if (this.head < index + size) {

      for (; this.head<limit; this.head++) {

        buffer[this.head] = 0;

      }

    }

  }

}