Make compact encoding of UUIDs

src/common/coding/base64.js

@@ -31,7 +31,7 @@ export function encode(u8Arr) {
 }
 
 export function decode(string, start = 0) {
-  const buffer = new ArrayBuffer(Math.floor(((string.length - start) * 3) / 4));
+  const buffer = new ArrayBuffer(Math.ceil(((string.length - start) * 3) / 4));
   const view = new DataView(buffer);
 
   for (let i = start; i < string.length; i += 4) {

src/common/coding/id.js

@@ -1,5 +1,39 @@
-import { customAlphabet } from 'nanoid/non-secure';
-import alpha from './alphabet.js';
+import { v4 } from 'uuid';
+import { encode as b64encode, decode as b64decode } from './base64.js';
 
-// The ID is 20 digits for a similar collision probability as UUID v4
-export default customAlphabet(alpha, 20);
+function doEncode(u8arr) {
+  const { buffer, byteOffset, byteLength } = u8arr;
+  const view = new DataView(buffer, byteOffset, byteLength);
+  const int3 = view.getUint32(8);
+  const int4 = view.getUint32(12);
+  if (int3 >>> 30 !== 2) throw Error('encode_uuid.not_variant_1');
+
+  view.setUint32(8, ((int3 & 0x3fffffff) << 2) | (int4 >>> 30));
+  view.setUint32(12, (int4 & 0x3fffffff) << 2);
+
+  return b64encode(u8arr).substr(0, 21);
+}
+
+export function id() {
+  const u8arr = new Uint8Array(16);
+  v4({}, u8arr);
+  return doEncode(u8arr);
+}
+
+export function encode(u8arr) {
+  // Make a copy so we aren't modifying the original
+  return doEncode(new Uint8Array(u8arr));
+}
+
+export function decode(id) {
+  const u8arr = b64decode(id);
+  const { buffer, byteOffset, byteLength } = u8arr;
+  const view = new DataView(buffer, byteOffset, byteLength);
+  const int3 = view.getUint32(8);
+  const int4 = view.getUint32(12);
+
+  view.setUint32(8, (int3 >>> 2) | 0x80000000);
+  view.setUint32(12, (int4 >>> 2) | (int3 << 30));
+
+  return u8arr;
+}

src/common/coding/index.js

@@ -11,7 +11,7 @@ export {
   splitRef,
 } from './path.js';
 
-export { default as makeId } from './id.js';
+export { id as makeId, encode as encodeId, decode as decodeId } from './id.js';
 export { default as decorate } from './decorate.js';
 export * from './serialize.js';
 export * from './encodeTree.js';

src/common/coding/test/id.test.js

@@ -0,0 +1,10 @@
+import { encode, decode } from '../id.js';
+import { v4 } from 'uuid';
+
+test('roundtrip', () => {
+  const bytes = new Uint8Array(16);
+  v4({}, bytes);
+  const str = encode(bytes);
+  const bytes2 = decode(str);
+  expect(bytes2).toEqual(bytes);
+});