http: optimize checkIsHttpToken()

This commit both makes checkIsHttpToken() inlinable and extracts
the character checking logic to a separate inlinable function so that
the main loop can be unrolled a bit.

PR-URL: https://github.com/nodejs/node/pull/6570
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

lib/_http_common.js

@@ -232,52 +232,65 @@ exports.httpSocketSetup = httpSocketSetup;
  * per the rules defined in RFC 7230
  * See https://tools.ietf.org/html/rfc7230#section-3.2.6
  *
+ * Allowed characters in an HTTP token:
+ * ^_`a-z  94-122
+ * A-Z     65-90
+ * -       45
+ * 0-9     48-57
+ * !       33
+ * #$%&'   35-39
+ * *+      42-43
+ * .       46
+ * |       124
+ * ~       126
+ *
  * This implementation of checkIsHttpToken() loops over the string instead of
  * using a regular expression since the former is up to 180% faster with v8 4.9
  * depending on the string length (the shorter the string, the larger the
  * performance difference)
+ *
+ * Additionally, checkIsHttpToken() is currently designed to be inlinable by v8,
+ * so take care when making changes to the implementation so that the source
+ * code size does not exceed v8's default max_inlined_source_size setting.
  **/
+function isValidTokenChar(ch) {
+  if (ch >= 94 && ch <= 122)
+    return true;
+  if (ch >= 65 && ch <= 90)
+    return true;
+  if (ch === 45)
+    return true;
+  if (ch >= 48 && ch <= 57)
+    return true;
+  if (ch === 34 || ch === 40 || ch === 41 || ch === 44)
+    return false;
+  if (ch >= 33 && ch <= 46)
+    return true;
+  if (ch === 124 || ch === 126)
+    return true;
+  return false;
+}
 function checkIsHttpToken(val) {
   if (typeof val !== 'string' || val.length === 0)
     return false;
-
-  for (var i = 0, len = val.length; i < len; i++) {
-    var ch = val.charCodeAt(i);
-
-    if (ch >= 65 && ch <= 90) // A-Z
-      continue;
-
-    if (ch >= 97 && ch <= 122) // a-z
-      continue;
-
-    // ^ => 94
-    // _ => 95
-    // ` => 96
-    // | => 124
-    // ~ => 126
-    if (ch === 94 || ch === 95 || ch === 96 || ch === 124 || ch === 126)
-      continue;
-
-    if (ch >= 48 && ch <= 57) // 0-9
-      continue;
-
-    // ! => 33
-    // # => 35
-    // $ => 36
-    // % => 37
-    // & => 38
-    // ' => 39
-    // * => 42
-    // + => 43
-    // - => 45
-    // . => 46
-    if (ch >= 33 && ch <= 46) {
-      if (ch === 34 || ch === 40 || ch === 41 || ch === 44)
+  if (!isValidTokenChar(val.charCodeAt(0)))
+    return false;
+  const len = val.length;
+  if (len > 1) {
+    if (!isValidTokenChar(val.charCodeAt(1)))
+      return false;
+    if (len > 2) {
+      if (!isValidTokenChar(val.charCodeAt(2)))
         return false;
-      continue;
+      if (len > 3) {
+        if (!isValidTokenChar(val.charCodeAt(3)))
+          return false;
+        for (var i = 4; i < len; i++) {
+          if (!isValidTokenChar(val.charCodeAt(i)))
+            return false;
+        }
+      }
     }
-
-    return false;
   }
   return true;
 }