rochars / wavefile

 * Copyright (c) 2019 Rafael da Silva Rocha.

 * Copyright (c) 2017 Brett Zamir, 2012 Niklas von Hertzen

 *

 * 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.

 *

 */

const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

/**

 * Encode a byte buffer as a base64 string.

 * @param {!Uint8Array} bytes The buffer.

 * @return {string} A .wav file as a DataURI.

 */

/**

 * Decode a base64 string as a byte as buffer.

 * @param {string} base64 A .wav file as a DataURI.

 * @return {ArrayBuffer} A .wav file as a DataURI.

 */

export function decode(base64) {

  let lookup = new Uint8Array(256);

  for (let i = 0; i < chars.length; i++) {

    lookup[chars.charCodeAt(i)] = i;

  }

  let bufferLength = base64.length * 0.75;

  if (base64[base64.length - 1] === '=') {

    bufferLength--;

    if (base64[base64.length - 2] === '=') {

      bufferLength--;

    }

  }

  let buffer = new ArrayBuffer(bufferLength);

  let bytes = new Uint8Array(buffer);

  for (let i = 0, j = 0; i < base64.length; i += 4) {

    let encoded1 = lookup[base64.charCodeAt(i)];

    let encoded2 = lookup[base64.charCodeAt(i + 1)];

    let encoded3 = lookup[base64.charCodeAt(i + 2)];

    let encoded4 = lookup[base64.charCodeAt(i + 3)];

    bytes[j++] = encoded1 << 2 | encoded2 >> 4;

    bytes[j++] = (encoded2 & 15) << 4 | encoded3 >> 2;

    bytes[j++] = (encoded3 & 3) << 6 | encoded4 & 63;

  }

  return buffer;

}