fix: Generates invalid UUIDs

Fixes #56

src/crypto.ts

@@ -25,11 +25,18 @@ export abstract class Crypto implements globalThis.Crypto {
    * @returns UUID v4 string
    */
   public randomUUID(): string {
+    // Generate a random Uint8Array with 16 elements
     const b = this.getRandomValues(new Uint8Array(16));
+
+    // Bitwise AND operation followed by OR operator to modify 6th and 8th elements of the array
     b[6] = (b[6] & 0x0f) | 0x40;
     b[8] = (b[8] & 0x3f) | 0x80;
+
+    // Lowercasing the result after converting each element in hexadecimal format
     const uuid = Convert.ToHex(b).toLowerCase();
 
-    return `${uuid.substring(0, 8)}-${uuid.substring(8, 12)}-${uuid.substring(12, 16)}-${uuid.substring(16)}`;
+    // Return the string created by extracting substrings from the given result
+    return `${uuid.substring(0, 8)}-${uuid.substring(8, 12)}-${uuid.substring(12, 16)}-${uuid.substring(16, 20)}-${uuid.substring(20)}`;
+
   }
 }

test/crypto.ts

@@ -1,20 +1,37 @@
-import * as assert from "assert";
+import * as assert from "node:assert";
+import * as nodeCrypto from "node:crypto";
 import { Crypto, SubtleCrypto } from "../src";
 
 context("Crypto", () => {
 
-  it("Crypto matches to globalThis.Crypto", () => {
-    class MyCrypto extends Crypto {
-      public subtle = new SubtleCrypto();
-      public getRandomValues<T extends ArrayBufferView | null>(array: T): T {
-        throw new Error("Method not implemented.");
+  class MyCrypto extends Crypto {
+    public subtle = new SubtleCrypto();
+    public getRandomValues<T extends ArrayBufferView | null>(array: T): T {
+      if (ArrayBuffer.isView(array)) {
+        const buffer = Buffer.from(array.buffer, array.byteOffset, array.byteLength);
+        nodeCrypto.randomFillSync(buffer);
       }
 
+      return array;
     }
+  }
 
+  it("Crypto matches to globalThis.Crypto", () => {
+    // tslint:disable-next-line: no-shadowed-variable
     let crypto: globalThis.Crypto;
     crypto = new MyCrypto();
     assert.ok(crypto);
   });
 
+  it("randomUUID", () => {
+    const crypto = new MyCrypto();
+
+    let counter = 1000;
+    const regex = /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+    while (counter--) {
+      const uuid = crypto.randomUUID();
+      assert.ok(new RegExp(regex).test(uuid), `UUID ${uuid} is incorrect`);
+    }
+  });
+
 });