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: #7236
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

Author: jasnell

benchmark/tls/convertprotocols.js

@@ -0,0 +1,20 @@
+'use strict';
+
+constcommon=require('../common.js');
+consttls=require('tls');
+
+constbench=common.createBenchmark(main,{
+n: [1,50000]
+});
+
+functionmain(conf){
+constn=+conf.n;
+
+vari=0;
+varm={};
+common.v8ForceOptimization(
+tls.convertNPNProtocols,['ABC','XYZ123','FOO'],m);
+bench.start();
+for(;i<n;i++)tls.convertNPNProtocols(['ABC','XYZ123','FOO'],m);
+bench.end(n);
+}

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")
 functionconvertProtocols(protocols){
-varbuff=Buffer.allocUnsafe(protocols.reduce(function(p,c){
-returnp+1+Buffer.byteLength(c);
+constlens=Array(protocols.length);
+constbuff=Buffer.allocUnsafe(protocols.reduce((p,c,i)=>{
+varlen=Buffer.byteLength(c);
+lens[i]=len;
+returnp+1+len;
 },0));
 
-protocols.reduce(function(offset,c){
-varclen=Buffer.byteLength(c);
-buff[offset]=clen;
-buff.write(c,offset+1);
-
-returnoffset+1+clen;
-},0);
+varoffset=0;
+for(vari=0,c=protocols.length;i<c;i++){
+buff[offset++]=lens[i];
+buff.write(protocols[i],offset);
+offset+=lens[i];
+}
 
 returnbuff;
 }