Fixed random bias.

spirelab · Feb 9, 2021 · 956fdd8 · 956fdd8
1 parent f7300b8
commit 956fdd8
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Showing 2 changed files with 10 additions and 3 deletions.
diff --git a/common.js b/common.js
@@ -95,8 +95,14 @@ module.exports.data2blob = function (data) {
     return blob;
 };
 
-// Generate random numbers
-module.exports.random = function (max) { (require('crypto').randomBytes(4).readUInt32BE(0) % max); };
+// Generate random numbers between 0 and max without bias.
+module.exports.random = function (max) {
+    const crypto = require('crypto');
+    var maxmask = 1, r;
+    while (maxmask < max) { maxmask = (maxmask << 1) + 1; }
+    do { r = (crypto.randomBytes(4).readUInt32BE(0) & maxmask); } while (r > max);
+    return r;
+};
 
 // Split a comma seperated string, ignoring commas in quotes.
 module.exports.quoteSplit = function (str) {

diff --git a/multiserver.js b/multiserver.js
@@ -178,7 +178,8 @@ module.exports.CreateMultiServer = function (parent, args) {
 
         // Get the next retry time in milliseconds
         function getConnectRetryTime() {
-            if (obj.retryBackoff < 30000) { obj.retryBackoff += ((require('crypto').randomBytes(4).readUInt32BE(0) % 3000) + 1000); }
+            // The (random & 0x1FFF) creates a random number between 0 and 4096.
+            if (obj.retryBackoff < 30000) { obj.retryBackoff += ((require('crypto').randomBytes(4).readUInt32BE(0) & 0x1FFF) + 1000); }
             return obj.retryBackoff;
         }