http_parser: use pushValueToArray for headers

For performance add headers to the headers Array by pushing them on from
JS. Benchmark added to demonstrate this case.

PR-URL: #3780
Reviewed-By: Fedor Indutny <fedor@indutny.com>

benchmark/http/bench-parser.js

@@ -0,0 +1,55 @@
+'use strict';
+
+const common = require('../common');
+const HTTPParser = process.binding('http_parser').HTTPParser;
+const REQUEST = HTTPParser.REQUEST;
+const kOnHeaders = HTTPParser.kOnHeaders | 0;
+const kOnHeadersComplete = HTTPParser.kOnHeadersComplete | 0;
+const kOnBody = HTTPParser.kOnBody | 0;
+const kOnMessageComplete = HTTPParser.kOnMessageComplete | 0;
+const CRLF = '\r\n';
+
+const bench = common.createBenchmark(main, {
+  fields: [4, 8, 16, 32],
+  n: [1e5],
+});
+
+
+function main(conf) {
+  const fields = conf.fields >>> 0;
+  const n = conf.n >>> 0;
+  var header = `GET /hello HTTP/1.1${CRLF}Content-Type: text/plain${CRLF}`;
+
+  for (var i = 0; i < fields; i++) {
+    header += `X-Filler${i}: ${Math.random().toString(36).substr(2)}${CRLF}`;
+  }
+  header += CRLF;
+
+  processHeader(new Buffer(header), n);
+}
+
+
+function processHeader(header, n) {
+  const parser = newParser(REQUEST);
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    parser.execute(header, 0, header.length);
+    parser.reinitialize(REQUEST);
+  }
+  bench.end(n);
+}
+
+
+function newParser(type) {
+  const parser = new HTTPParser(type);
+
+  parser.headers = [];
+
+  parser[kOnHeaders] = function() { };
+  parser[kOnHeadersComplete] = function() { };
+  parser[kOnBody] = function() { };
+  parser[kOnMessageComplete] = function() { };
+
+  return parser;
+}

src/node_http_parser.cc

@@ -632,12 +632,23 @@ class Parser : public BaseObject {
   Local<Array> CreateHeaders() {
     // num_values_ is either -1 or the entry # of the last header
     // so num_values_ == 0 means there's a single header
-    Local<Array> headers = Array::New(env()->isolate(), 2 * num_values_);
-
-    for (int i = 0; i < num_values_; ++i) {
-      headers->Set(2 * i, fields_[i].ToString(env()));
-      headers->Set(2 * i + 1, values_[i].ToString(env()));
-    }
+    Local<Array> headers = Array::New(env()->isolate());
+    Local<Function> fn = env()->push_values_to_array_function();
+    Local<Value> argv[NODE_PUSH_VAL_TO_ARRAY_MAX * 2];
+    int i = 0;
+
+    do {
+      size_t j = 0;
+      while (i < num_values_ && j < ARRAY_SIZE(argv) / 2) {
+        argv[j * 2] = fields_[i].ToString(env());
+        argv[j * 2 + 1] = values_[i].ToString(env());
+        i++;
+        j++;
+      }
+      if (j > 0) {
+        fn->Call(env()->context(), headers, j * 2, argv).ToLocalChecked();
+      }
+    } while (i < num_values_);
 
     return headers;
   }