perf: improve If-None-Match token parsing

Author: dougwilson

HISTORY.md

@@ -2,6 +2,7 @@ unreleased
 ==========
 
   * Fix regression matching multiple ETags in `If-None-Match`
+  * perf: improve `If-None-Match` token parsing
 
 0.5.1 / 2017-09-11
 ==================

index.js

@@ -14,13 +14,6 @@
 
 var CACHE_CONTROL_NO_CACHE_REGEXP = /(?:^|,)\s*?no-cache\s*?(?:,|$)/
 
-/**
- * Simple expression to split token list.
- * @private
- */
-
-var TOKEN_LIST_REGEXP = / *, */
-
 /**
  * Module exports.
  * @public
@@ -64,7 +57,7 @@ function fresh (reqHeaders, resHeaders) {
     }
 
     var etagStale = true
-    var matches = noneMatch.split(TOKEN_LIST_REGEXP)
+    var matches = parseTokenList(noneMatch)
     for (var i = 0; i < matches.length; i++) {
       var match = matches[i]
       if (match === etag || match === 'W/' + etag || 'W/' + match === etag) {
@@ -106,3 +99,39 @@ function parseHttpDate (date) {
     ? timestamp
     : NaN
 }
+
+/**
+ * Parse a HTTP token list.
+ *
+ * @param {string} str
+ * @private
+ */
+
+function parseTokenList (str) {
+  var end = 0
+  var list = []
+  var start = 0
+
+  // gather tokens
+  for (var i = 0, len = str.length; i < len; i++) {
+    switch (str.charCodeAt(i)) {
+      case 0x20: /*   */
+        if (start === end) {
+          start = end = i + 1
+        }
+        break
+      case 0x2c: /* , */
+        list.push(str.substring(start, end))
+        start = end = i + 1
+        break
+      default:
+        end = i + 1
+        break
+    }
+  }
+
+  // final token
+  list.push(str.substring(start, end))
+
+  return list
+}