refactor: defer detection Web Crypto API until creation of Scru128Gen…

…erator

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## v3.0.3 - unreleased
+
+### Maintenance
+
+- Refactored default random number generator to defer detection Web Crypto API
+  until creation of `Scru128Generator`
+- Fixed wrong test case
+
 ## v3.0.2 - 2023-07-17
 
 Most notably, v3 switches the letter case of generated IDs from uppercase (e.g.,

src/index.ts

@@ -471,7 +471,7 @@ export class Scru128Generator {
     /** Returns a 32-bit random unsigned integer. */
     nextUint32(): number;
   }) {
-    this.rng = randomNumberGenerator || new DefaultRandom();
+    this.rng = randomNumberGenerator || getDefaultRandom();
   }
 
   /**
@@ -620,37 +620,38 @@ export class Scru128Generator {
 /** A global flag to force use of cryptographically strong RNG. */
 declare const SCRU128_DENY_WEAK_RNG: boolean;
 
-/** Stores `crypto.getRandomValues()` available in the environment. */
-let getRandomValues: (buffer: Uint32Array) => Uint32Array = (buffer) => {
-  // fall back on Math.random() unless the flag is set to true
-  if (typeof SCRU128_DENY_WEAK_RNG !== "undefined" && SCRU128_DENY_WEAK_RNG) {
-    throw new Error("no cryptographically strong RNG available");
-  }
-
-  for (let i = 0; i < buffer.length; i++) {
-    buffer[i] =
-      Math.trunc(Math.random() * 0x1_0000) * 0x1_0000 +
-      Math.trunc(Math.random() * 0x1_0000);
+/** Returns the default random number generator available in the environment. */
+const getDefaultRandom = (): { nextUint32(): number } => {
+  // detect Web Crypto API
+  if (
+    typeof crypto !== "undefined" &&
+    typeof crypto.getRandomValues !== "undefined"
+  ) {
+    return new BufferedCryptoRandom();
+  } else {
+    // fall back on Math.random() unless the flag is set to true
+    if (typeof SCRU128_DENY_WEAK_RNG !== "undefined" && SCRU128_DENY_WEAK_RNG) {
+      throw new Error("no cryptographically strong RNG available");
+    }
+    return {
+      nextUint32: (): number =>
+        Math.trunc(Math.random() * 0x1_0000) * 0x1_0000 +
+        Math.trunc(Math.random() * 0x1_0000),
+    };
   }
-  return buffer;
 };
 
-// detect Web Crypto API
-if (typeof crypto !== "undefined" && crypto.getRandomValues) {
-  getRandomValues = (buffer) => crypto.getRandomValues(buffer);
-}
-
 /**
- * Wraps `crypto.getRandomValues()` and compatibles to enable buffering; this
- * uses a small buffer by default to avoid unbearable throughput decline in some
- * environments as well as the waste of time and space for unused values.
+ * Wraps `crypto.getRandomValues()` to enable buffering; this uses a small
+ * buffer by default to avoid both unbearable throughput decline in some
+ * environments and the waste of time and space for unused values.
  */
-class DefaultRandom {
+class BufferedCryptoRandom {
   private readonly buffer = new Uint32Array(8);
-  private cursor = Infinity;
+  private cursor = 0xffff;
   nextUint32(): number {
     if (this.cursor >= this.buffer.length) {
-      getRandomValues(this.buffer);
+      crypto.getRandomValues(this.buffer);
       this.cursor = 0;
     }
     return this.buffer[this.cursor++];