buffer: convert offset & length to int properly

As per ecma-262 2015's #sec-%typedarray%-buffer-byteoffset-length,
`offset` would be an integer, not a 32 bit unsigned integer. Also,
`length` would be an integer with the maximum value of 2^53 - 1, not a
32 bit unsigned integer.

This would be a problem because, if we create a buffer from an
arraybuffer, from an offset which is greater than 2^32, it would be
actually pointing to a different location in arraybuffer. For example,
if we use 2^40 as offset, then the actual value used will be 0,
because `byteOffset >>>= 0` will convert `byteOffset` to a 32 bit
unsigned int, which is based on 2^32 modulo.

PR-URL: https://github.com/nodejs/node/pull/9492

Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/internal/util.js b/lib/internal/util.js
index 4ada8dd0cc..ae8b1e0b64 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -161,3 +161,21 @@ exports.cachedResult = function cachedResult(fn) {
     return result;
   };
 };
+
+/*
+ * Implementation of ToInteger as per ECMAScript Specification
+ * Refer: http://www.ecma-international.org/ecma-262/6.0/#sec-tointeger
+ */
+const toInteger = exports.toInteger = function toInteger(argument) {
+  const number = +argument;
+  return Number.isNaN(number) ? 0 : Math.trunc(number);
+};
+
+/*
+ * Implementation of ToLength as per ECMAScript Specification
+ * Refer: http://www.ecma-international.org/ecma-262/6.0/#sec-tolength
+ */
+exports.toLength = function toLength(argument) {
+  const len = toInteger(argument);
+  return len <= 0 ? 0 : Math.min(len, Number.MAX_SAFE_INTEGER);
+};