Defer random initialization of node and clockseq. Fixes #189 (#220)

v1.js

@@ -6,17 +6,7 @@ var bytesToUuid = require('./lib/bytesToUuid');
 // Inspired by https://github.com/LiosK/UUID.js
 // and http://docs.python.org/library/uuid.html
 
-// random #'s we need to init node and clockseq
-var _seedBytes = rng();
-
-// Per 4.5, create and 48-bit node id, (47 random bits + multicast bit = 1)
-var _nodeId = [
-  _seedBytes[0] | 0x01,
-  _seedBytes[1], _seedBytes[2], _seedBytes[3], _seedBytes[4], _seedBytes[5]
-];
-
-// Per 4.2.2, randomize (14 bit) clockseq
-var _clockseq = (_seedBytes[6] << 8 | _seedBytes[7]) & 0x3fff;
+var _nodeId, _clockseq;
 
 // Previous uuid creation time
 var _lastMSecs = 0, _lastNSecs = 0;
@@ -27,9 +17,27 @@ function v1(options, buf, offset) {
   var b = buf || [];
 
   options = options || {};
-
+  var node = options.node || _nodeId;
   var clockseq = options.clockseq !== undefined ? options.clockseq : _clockseq;
 
+  // node and clockseq need to be initialized to random values if they're not
+  // specified.  We do this lazily to minimize issues related to insufficient
+  // system entropy.  See #189
+  if (node == null || clockseq == null) {
+    var seedBytes = rng();
+    if (node == null) {
+      // Per 4.5, create and 48-bit node id, (47 random bits + multicast bit = 1)
+      node = _nodeId = [
+        seedBytes[0] | 0x01,
+        seedBytes[1], seedBytes[2], seedBytes[3], seedBytes[4], seedBytes[5]
+      ];
+    }
+    if (clockseq == null) {
+      // Per 4.2.2, randomize (14 bit) clockseq
+      clockseq = _clockseq = (seedBytes[6] << 8 | seedBytes[7]) & 0x3fff;
+    }
+  }
+
   // UUID timestamps are 100 nano-second units since the Gregorian epoch,
   // (1582-10-15 00:00).  JSNumbers aren't precise enough for this, so
   // time is handled internally as 'msecs' (integer milliseconds) and 'nsecs'
@@ -89,7 +97,6 @@ function v1(options, buf, offset) {
   b[i++] = clockseq & 0xff;
 
   // `node`
-  var node = options.node || _nodeId;
   for (var n = 0; n < 6; ++n) {
     b[i + n] = node[n];
   }