Skip Buffer encoding when not generating ETag for small response

History.md

@@ -2,6 +2,7 @@ unreleased
 ==========
 
   * Improve error message when autoloading invalid view engine
+  * Skip `Buffer` encoding when not generating ETag for small response
 
 4.15.5 / 2017-09-24
 ===================

lib/response.js

@@ -106,7 +106,6 @@ res.links = function(links){
 res.send = function send(body) {
   var chunk = body;
   var encoding;
-  var len;
   var req = this.req;
   var type;
 
@@ -171,23 +170,33 @@ res.send = function send(body) {
     }
   }
 
+  // determine if ETag should be generated
+  var etagFn = app.get('etag fn')
+  var generateETag = !this.get('ETag') && typeof etagFn === 'function'
+
   // populate Content-Length
+  var len
   if (chunk !== undefined) {
-    if (!Buffer.isBuffer(chunk)) {
-      // convert chunk to Buffer; saves later double conversions
+    if (!generateETag && chunk.length < 1000) {
+      // just calculate length when no ETag + small chunk
+      len = Buffer.byteLength(chunk, encoding)
+    } else if (!Buffer.isBuffer(chunk)) {
+      // convert chunk to Buffer and calculate
       chunk = new Buffer(chunk, encoding);
       encoding = undefined;
+      len = chunk.length
+    } else {
+      // get length of Buffer
+      len = chunk.length
     }
 
-    len = chunk.length;
     this.set('Content-Length', len);
   }
 
   // populate ETag
   var etag;
-  var generateETag = len !== undefined && app.get('etag fn');
-  if (typeof generateETag === 'function' && !this.get('ETag')) {
-    if ((etag = generateETag(chunk, encoding))) {
+  if (generateETag && len !== undefined) {
+    if ((etag = etagFn(chunk, encoding))) {
       this.set('ETag', etag);
     }
   }