independent csprng solution

src/util.ts

@@ -8,7 +8,6 @@
 
 import * as _dayjs from "dayjs";
 const dayjs = _dayjs;
-const crypto = require("crypto").webcrypto;
 
 export const isDev = process.env.NODE_ENV === "development";
 export const appName = "Uptime Kuma";
@@ -115,13 +114,64 @@ export function getRandomInt(min: number, max: number) {
     return Math.floor(Math.random() * (max - min + 1)) + min;
 }
 
-export function getCryptoRandomInt(min: number, max: number) {
-    const randomBuffer = new Uint32Array(1);
-    crypto.getRandomValues(randomBuffer);
-    const randomNumber = randomBuffer[0] / (0xffffffff + 1);
-    min = Math.ceil(min);
-    max = Math.floor(max);
-    return Math.floor(randomNumber * (max - min + 1)) + min;
+/**
+ * Returns either the NodeJS crypto.randomBytes() function or its
+ * browser equivalent implemented via window.crypto.getRandomValues()
+ */
+let getRandomBytes = (
+    (typeof window !== 'undefined' && window.crypto)
+
+        // Browsers
+        ? function () {
+            return (numBytes: number) => {
+                let randomBytes = new Uint8Array(numBytes);
+                for (let i = 0; i < numBytes; i += 65536) {
+                    window.crypto.getRandomValues(randomBytes.subarray(i, i + Math.min(numBytes - i, 65536)));
+                }
+                return randomBytes;
+            };
+        }
+
+         // Node
+        : function() {
+            return require("crypto").randomBytes;
+        }
+)();
+
+export function getCryptoRandomInt(min: number, max: number):number {
+
+    // synchronous version of: https://github.com/joepie91/node-random-number-csprng
+
+    const range = max - min
+    if (range >= Math.pow(2, 32))
+        console.log("Warning! Range is too large.")
+
+    let tmpRange = range
+    let bitsNeeded = 0
+    let bytesNeeded = 0
+    let mask = 1
+
+    while (tmpRange > 0) {
+        if (bitsNeeded % 8 === 0) bytesNeeded += 1
+        bitsNeeded += 1
+        mask = mask << 1 | 1
+        tmpRange = tmpRange >>> 1
+    }
+
+    const randomBytes = getRandomBytes(bytesNeeded)
+    let randomValue = 0
+
+    for (let i = 0; i < bytesNeeded; i++) {
+	    randomValue |= randomBytes[i] << 8 * i
+    }
+
+    randomValue = randomValue & mask;
+
+    if (randomValue <= range) {
+        return min + randomValue
+    } else {
+        return getCryptoRandomInt(min, max)
+    }
 }
 
 export function genSecret(length = 64) {