http: lazy create IncomingMessage.headers

When rawHeaders is enough don't create the headers object.

PR-URL: #35281
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_incoming.js

@@ -24,10 +24,16 @@
 const {
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
+  Symbol
 } = primordials;
 
 const Stream = require('stream');
 
+const kHeaders = Symbol('kHeaders');
+const kHeadersCount = Symbol('kHeadersCount');
+const kTrailers = Symbol('kTrailers');
+const kTrailersCount = Symbol('kTrailersCount');
+
 function readStart(socket) {
   if (socket && !socket._paused && socket.readable)
     socket.resume();
@@ -58,9 +64,11 @@ function IncomingMessage(socket) {
   this.httpVersionMinor = null;
   this.httpVersion = null;
   this.complete = false;
-  this.headers = {};
+  this[kHeaders] = null;
+  this[kHeadersCount] = 0;
   this.rawHeaders = [];
-  this.trailers = {};
+  this[kTrailers] = null;
+  this[kTrailersCount] = 0;
   this.rawTrailers = [];
 
   this.aborted = false;
@@ -93,6 +101,44 @@ ObjectDefineProperty(IncomingMessage.prototype, 'connection', {
   }
 });
 
+ObjectDefineProperty(IncomingMessage.prototype, 'headers', {
+  get: function() {
+    if (!this[kHeaders]) {
+      this[kHeaders] = {};
+
+      const src = this.rawHeaders;
+      const dst = this[kHeaders];
+
+      for (let n = 0; n < this[kHeadersCount]; n += 2) {
+        this._addHeaderLine(src[n + 0], src[n + 1], dst);
+      }
+    }
+    return this[kHeaders];
+  },
+  set: function(val) {
+    this[kHeaders] = val;
+  }
+});
+
+ObjectDefineProperty(IncomingMessage.prototype, 'trailers', {
+  get: function() {
+    if (!this[kTrailers]) {
+      this[kTrailers] = {};
+
+      const src = this.rawTrailers;
+      const dst = this[kTrailers];
+
+      for (let n = 0; n < this[kTrailersCount]; n += 2) {
+        this._addHeaderLine(src[n + 0], src[n + 1], dst);
+      }
+    }
+    return this[kTrailers];
+  },
+  set: function(val) {
+    this[kTrailers] = val;
+  }
+});
+
 IncomingMessage.prototype.setTimeout = function setTimeout(msecs, callback) {
   if (callback)
     this.on('timeout', callback);
@@ -133,14 +179,18 @@ function _addHeaderLines(headers, n) {
     let dest;
     if (this.complete) {
       this.rawTrailers = headers;
-      dest = this.trailers;
+      this[kTrailersCount] = n;
+      dest = this[kTrailers];
     } else {
       this.rawHeaders = headers;
-      dest = this.headers;
+      this[kHeadersCount] = n;
+      dest = this[kHeaders];
     }
 
-    for (let i = 0; i < n; i += 2) {
-      this._addHeaderLine(headers[i], headers[i + 1], dest);
+    if (dest) {
+      for (let i = 0; i < n; i += 2) {
+        this._addHeaderLine(headers[i], headers[i + 1], dest);
+      }
     }
   }
 }