base64-arraybuffer.ts

// original source: https://github.com/niklasvh/base64-arraybuffer/blob/master/src/index.ts

const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

// Use a lookup table to find the index.
const lookup = typeof Uint8Array === 'undefined' ? [] : new Uint8Array(256)
for (let i = 0; i < chars.length; i++) {
  lookup[chars.charCodeAt(i)] = i
}

export const encode = (arraybuffer: ArrayBuffer): string => {
  let bytes = new Uint8Array(arraybuffer),
    i,
    len = bytes.length,
    base64 = ''

  for (i = 0; i < len; i += 3) {
    base64 += chars[bytes[i] >> 2]
    base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)]
    base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)]
    base64 += chars[bytes[i + 2] & 63]
  }

  if (len % 3 === 2) {
    base64 = base64.substring(0, base64.length - 1) + '='
  } else if (len % 3 === 1) {
    base64 = base64.substring(0, base64.length - 2) + '=='
  }

  return base64
}

export const decode = (base64: string): ArrayBuffer => {
  let bufferLength = base64.length * 0.75,
    len = base64.length,
    i,
    p = 0,
    encoded1,
    encoded2,
    encoded3,
    encoded4

  if (base64[base64.length - 1] === '=') {
    bufferLength--
    if (base64[base64.length - 2] === '=') {
      bufferLength--
    }
  }

  const arraybuffer = new ArrayBuffer(bufferLength),
    bytes = new Uint8Array(arraybuffer)

  for (i = 0; i < len; i += 4) {
    encoded1 = lookup[base64.charCodeAt(i)]
    encoded2 = lookup[base64.charCodeAt(i + 1)]
    encoded3 = lookup[base64.charCodeAt(i + 2)]
    encoded4 = lookup[base64.charCodeAt(i + 3)]

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4)
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2)
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63)
  }

  return arraybuffer
}