tls: avoid calling Buffer.byteLength multiple times

There's no reason to be calling Buffer.byteLength() twice.
Small perf improvement

Run 1:
tls/convertprotocols.js n=1     v6.2.1 = 11852,  new = 12204 ......  -2.89%
tls/convertprotocols.js n=50000 v6.2.1 = 515660, new = 570610 .....  -9.63%

Run 2:
tls/convertprotocols.js n=1     v6.2.1 = 11729,  new = 12045 ......  -2.62%
tls/convertprotocols.js n=50000 v6.2.1 = 512080, new = 637730 ..... -19.70%

PR-URL: https://github.com/nodejs/node/pull/7236
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

1 files changed, 11 insertions, 9 deletions

diff --git a/lib/tls.js b/lib/tls.js
index 695edd8c5a6..849daeb07f3 100644
--- a/lib/tls.js
+++ b/lib/tls.js
@@ -29,17 +29,19 @@ exports.getCiphers = internalUtil.cachedResult(() => {
 // Convert protocols array into valid OpenSSL protocols list
 // ("\x06spdy/2\x08http/1.1\x08http/1.0")
 function convertProtocols(protocols) {
-  var buff = Buffer.allocUnsafe(protocols.reduce(function(p, c) {
-    return p + 1 + Buffer.byteLength(c);
+  const lens = Array(protocols.length);
+  const buff = Buffer.allocUnsafe(protocols.reduce((p, c, i) => {
+    var len = Buffer.byteLength(c);
+    lens[i] = len;
+    return p + 1 + len;
   }, 0));
 
-  protocols.reduce(function(offset, c) {
-    var clen = Buffer.byteLength(c);
-    buff[offset] = clen;
-    buff.write(c, offset + 1);
-
-    return offset + 1 + clen;
-  }, 0);
+  var offset = 0;
+  for (var i = 0, c = protocols.length; i < c; i++) {
+    buff[offset++] = lens[i];
+    buff.write(protocols[i], offset);
+    offset += lens[i];
+  }
 
   return buff;
 }