All files / helpers generate-fid.ts

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/**
 * @license
 * Copyright 2019 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
import { bufferToBase64UrlSafe } from './buffer-to-base64-url-safe';
 
/** Generates a new FID using random values from Web Crypto API. */
export function generateFid(): string {
  // A valid FID has exactly 22 base64 characters, which is 132 bits, or 16.5
  // bytes. our implementation generates a 17 byte array instead.
  const fidByteArray = new Uint8Array(17);
  crypto.getRandomValues(fidByteArray);
 
  // Replace the first 4 random bits with the constant FID header of 0b0111.
  fidByteArray[0] = 0b01110000 + (fidByteArray[0] % 0b00010000);
 
  return encode(fidByteArray);
}
 
/** Converts a FID Uint8Array to a base64 string representation. */
function encode(fidByteArray: Uint8Array): string {
  const b64String = bufferToBase64UrlSafe(fidByteArray);
 
  // Remove the 23rd character that was added because of the extra 4 bits at the
  // end of our 17 byte array, and the '=' padding.
  return b64String.substr(0, 22);
}