zero copy large buffer random bytes

Author: calvinmetcalf

browser.js

@@ -1,5 +1,13 @@
 'use strict'
 
+// limit of Crypto.getRandomValues()
+// https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues
+var MAX_BYTES = 65536
+
+// Node supports requesting up to this number of bytes
+// https://github.com/nodejs/node/blob/master/lib/internal/crypto/random.js#L48
+var MAX_UINT32 = 4294967295
+
 function oldBrowser () {
   throw new Error('Secure random number generation is not supported by this browser.\nUse Chrome, Firefox or Internet Explorer 11')
 }
@@ -15,14 +23,21 @@ if (crypto && crypto.getRandomValues) {
 
 function randomBytes (size, cb) {
   // phantomjs needs to throw
-  if (size > 65536) throw new Error('requested too many random bytes')
+  if (size > MAX_UINT32) throw new Error('requested too many random bytes')
   // in case browserify  isn't using the Uint8Array version
   var bytes = Buffer.allocUnsafe(size)
 
   // This will not work in older browsers.
   // See https://developer.mozilla.org/en-US/docs/Web/API/window.crypto.getRandomValues
   if (size > 0) {  // getRandomValues fails on IE if size == 0
-    crypto.getRandomValues(bytes)
+    if (size > MAX_BYTES) {
+      for (var generated = 0; generated < size; generated += MAX_BYTES) {
+        var nextChunk = generated + MAX_BYTES > size ? size - generated : MAX_BYTES
+        crypto.getRandomValues(bytes.slice(generated, generated + nextChunk))
+      }
+    } else {
+      crypto.getRandomValues(bytes)
+    }
   }
 
   if (typeof cb === 'function') {

test.js

@@ -1,16 +1,29 @@
 var test = require('tape')
 var randomBytes = require('./')
+var MAX_BYTES = 65536
+var MAX_UINT32 = 4294967295
 
 test('sync', function (t) {
-  t.plan(4)
+  t.plan(9)
   t.equals(randomBytes(0).length, 0, 'len: ' + 0)
   t.equals(randomBytes(3).length, 3, 'len: ' + 3)
   t.equals(randomBytes(30).length, 30, 'len: ' + 30)
   t.equals(randomBytes(300).length, 300, 'len: ' + 300)
+  t.equals(randomBytes(17 + MAX_BYTES).length, 17 + MAX_BYTES, 'len: ' + 17 + MAX_BYTES)
+  t.equals(randomBytes(MAX_BYTES * 100).length, MAX_BYTES * 100, 'len: ' + MAX_BYTES * 100)
+  t.throws(function () {
+    randomBytes(MAX_UINT32 + 1)
+  })
+  t.throws(function () {
+    t.equals(randomBytes(-1))
+  })
+  t.throws(function () {
+    t.equals(randomBytes('hello'))
+  })
 })
 
 test('async', function (t) {
-  t.plan(4)
+  t.plan(9)
 
   randomBytes(0, function (err, resp) {
     if (err) throw err
@@ -35,22 +48,34 @@ test('async', function (t) {
 
     t.equals(resp.length, 300, 'len: ' + 300)
   })
-})
 
-if (process.browser) {
-  test('requesting to much throws', function (t) {
-    t.plan(1)
-    t.throws(function () {
-      randomBytes(65537)
+  randomBytes(17 + MAX_BYTES, function (err, resp) {
+    if (err) throw err
+
+    t.equals(resp.length, 17 + MAX_BYTES, 'len: ' + 17 + MAX_BYTES)
+  })
+
+  randomBytes(MAX_BYTES * 100, function (err, resp) {
+    if (err) throw err
+
+    t.equals(resp.length, MAX_BYTES * 100, 'len: ' + MAX_BYTES * 100)
+  })
+
+  t.throws(function () {
+    randomBytes(MAX_UINT32 + 1, function () {
+      t.ok(false, 'should not get here')
     })
   })
 
-  test('requesting to much throws async', function (t) {
-    t.plan(1)
-    t.throws(function () {
-      randomBytes(65537, function () {
-        t.ok(false, 'should not get here')
-      })
+  t.throws(function () {
+    randomBytes(-1, function () {
+      t.ok(false, 'should not get here')
     })
   })
-}
+
+  t.throws(function () {
+    randomBytes('hello', function () {
+      t.ok(false, 'should not get here')
+    })
+  })
+})