http: try to avoid lowercasing incoming headers

PR-URL: nodejs#10558
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>

lib/_http_incoming.js

@@ -119,6 +119,146 @@ function _addHeaderLines(headers, n) {
 }
 
 
+// This function is used to help avoid the lowercasing of a field name if it
+// matches a 'traditional cased' version of a field name. It then returns the
+// lowercased name to both avoid calling toLowerCase() a second time and to
+// indicate whether the field was a 'no duplicates' field. If a field is not a
+// 'no duplicates' field, a `0` byte is prepended as a flag. The one exception
+// to this is the Set-Cookie header which is indicated by a `1` byte flag, since
+// it is an 'array' field and thus is treated differently in _addHeaderLines().
+// TODO: perhaps http_parser could be returning both raw and lowercased versions
+// of known header names to avoid us having to call toLowerCase() for those
+// headers.
+/* eslint-disable max-len */
+// 'array' header list is taken from:
+// https://mxr.mozilla.org/mozilla/source/netwerk/protocol/http/src/nsHttpHeaderArray.cpp
+/* eslint-enable max-len */
+function matchKnownFields(field) {
+  var low = false;
+  while (true) {
+    switch (field) {
+      case 'Content-Type':
+      case 'content-type':
+        return 'content-type';
+      case 'Content-Length':
+      case 'content-length':
+        return 'content-length';
+      case 'User-Agent':
+      case 'user-agent':
+        return 'user-agent';
+      case 'Referer':
+      case 'referer':
+        return 'referer';
+      case 'Host':
+      case 'host':
+        return 'host';
+      case 'Authorization':
+      case 'authorization':
+        return 'authorization';
+      case 'Proxy-Authorization':
+      case 'proxy-authorization':
+        return 'proxy-authorization';
+      case 'If-Modified-Since':
+      case 'if-modified-since':
+        return 'if-modified-since';
+      case 'If-Unmodified-Since':
+      case 'if-unmodified-since':
+        return 'if-unmodified-since';
+      case 'From':
+      case 'from':
+        return 'from';
+      case 'Location':
+      case 'location':
+        return 'location';
+      case 'Max-Forwards':
+      case 'max-forwards':
+        return 'max-forwards';
+      case 'Retry-After':
+      case 'retry-after':
+        return 'retry-after';
+      case 'ETag':
+      case 'etag':
+        return 'etag';
+      case 'Last-Modified':
+      case 'last-modified':
+        return 'last-modified';
+      case 'Server':
+      case 'server':
+        return 'server';
+      case 'Age':
+      case 'age':
+        return 'age';
+      case 'Expires':
+      case 'expires':
+        return 'expires';
+      case 'Set-Cookie':
+      case 'set-cookie':
+        return '\u0001';
+      // The fields below are not used in _addHeaderLine(), but they are common
+      // headers where we can avoid toLowerCase() if the mixed or lower case
+      // versions match the first time through.
+      case 'Transfer-Encoding':
+      case 'transfer-encoding':
+        return '\u0000transfer-encoding';
+      case 'Date':
+      case 'date':
+        return '\u0000date';
+      case 'Connection':
+      case 'connection':
+        return '\u0000connection';
+      case 'Cache-Control':
+      case 'cache-control':
+        return '\u0000cache-control';
+      case 'Vary':
+      case 'vary':
+        return '\u0000vary';
+      case 'Content-Encoding':
+      case 'content-encoding':
+        return '\u0000content-encoding';
+      case 'Cookie':
+      case 'cookie':
+        return '\u0000cookie';
+      case 'Origin':
+      case 'origin':
+        return '\u0000origin';
+      case 'Upgrade':
+      case 'upgrade':
+        return '\u0000upgrade';
+      case 'Expect':
+      case 'expect':
+        return '\u0000expect';
+      case 'If-Match':
+      case 'if-match':
+        return '\u0000if-match';
+      case 'If-None-Match':
+      case 'if-none-match':
+        return '\u0000if-none-match';
+      case 'Accept':
+      case 'accept':
+        return '\u0000accept';
+      case 'Accept-Encoding':
+      case 'accept-encoding':
+        return '\u0000accept-encoding';
+      case 'Accept-Language':
+      case 'accept-language':
+        return '\u0000accept-language';
+      case 'X-Forwarded-For':
+      case 'x-forwarded-for':
+        return '\u0000x-forwarded-for';
+      case 'X-Forwarded-Host':
+      case 'x-forwarded-host':
+        return '\u0000x-forwarded-host';
+      case 'X-Forwarded-Proto':
+      case 'x-forwarded-proto':
+        return '\u0000x-forwarded-proto';
+      default:
+        if (low)
+          return '\u0000' + field;
+        field = field.toLowerCase();
+        low = true;
+    }
+  }
+}
 // Add the given (field, value) pair to the message
 //
 // Per RFC2616, section 4.2 it is acceptable to join multiple instances of the
@@ -128,51 +268,27 @@ function _addHeaderLines(headers, n) {
 // always joined.
 IncomingMessage.prototype._addHeaderLine = _addHeaderLine;
 function _addHeaderLine(field, value, dest) {
-  field = field.toLowerCase();
-  switch (field) {
-    // Array headers:
-    case 'set-cookie':
-      if (dest[field] !== undefined) {
-        dest[field].push(value);
-      } else {
-        dest[field] = [value];
-      }
-      break;
-
-    /* eslint-disable max-len */
-    // list is taken from:
-    // https://mxr.mozilla.org/mozilla/source/netwerk/protocol/http/src/nsHttpHeaderArray.cpp
-    /* eslint-enable max-len */
-    case 'content-type':
-    case 'content-length':
-    case 'user-agent':
-    case 'referer':
-    case 'host':
-    case 'authorization':
-    case 'proxy-authorization':
-    case 'if-modified-since':
-    case 'if-unmodified-since':
-    case 'from':
-    case 'location':
-    case 'max-forwards':
-    case 'retry-after':
-    case 'etag':
-    case 'last-modified':
-    case 'server':
-    case 'age':
-    case 'expires':
-      // drop duplicates
-      if (dest[field] === undefined)
-        dest[field] = value;
-      break;
-
-    default:
-      // make comma-separated list
-      if (typeof dest[field] === 'string') {
-        dest[field] += ', ' + value;
-      } else {
-        dest[field] = value;
-      }
+  field = matchKnownFields(field);
+  var flag = field.charCodeAt(0);
+  if (flag === 0) {
+    field = field.slice(1);
+    // Make comma-separated list
+    if (typeof dest[field] === 'string') {
+      dest[field] += ', ' + value;
+    } else {
+      dest[field] = value;
+    }
+  } else if (flag === 1) {
+    // Array header -- only Set-Cookie at the moment
+    if (dest['set-cookie'] !== undefined) {
+      dest['set-cookie'].push(value);
+    } else {
+      dest['set-cookie'] = [value];
+    }
+  } else {
+    // Drop duplicates
+    if (dest[field] === undefined)
+      dest[field] = value;
   }
 }