http: cleanup setHeader()

Several fields on OutgoingMessage were set after instantiation. These
have been included in the constructor to prevent mutation of the object
map after instantiation.

"name" is now explicitly checked to be a string. Where before if a
non-string was passed the following cryptic error was thrown:

    _http_outgoing.js:334
      var key = name.toLowerCase();
                     ^
    TypeError: undefined is not a function

Signed-off-by: Trevor Norris <trev.norris@gmail.com>

lib/_http_outgoing.js

@@ -82,9 +82,13 @@ function OutgoingMessage() {
 
   this.finished = false;
   this._hangupClose = false;
+  this._headerSent = false;
 
   this.socket = null;
   this.connection = null;
+  this._header = null;
+  this._headers = null;
+  this._headerNames = {};
 }
 util.inherits(OutgoingMessage, Stream);
 
@@ -323,23 +327,22 @@ function storeHeader(self, state, field, value) {
 
 
 OutgoingMessage.prototype.setHeader = function(name, value) {
-  if (arguments.length < 2) {
-    throw new Error('`name` and `value` are required for setHeader().');
-  }
-
-  if (this._header) {
+  if (typeof name !== 'string')
+    throw new TypeError('"name" should be a string');
+  if (value === undefined)
+    throw new Error('"name" and "value" are required for setHeader().');
+  if (this._header)
     throw new Error('Can\'t set headers after they are sent.');
-  }
+
+  if (this._headers === null)
+    this._headers = {};
 
   var key = name.toLowerCase();
-  this._headers = this._headers || {};
-  this._headerNames = this._headerNames || {};
   this._headers[key] = value;
   this._headerNames[key] = name;
 
-  if (automaticHeaders[key]) {
+  if (automaticHeaders[key])
     this._removedHeader[key] = false;
-  }
 };
 
 
@@ -387,6 +390,7 @@ OutgoingMessage.prototype._renderHeaders = function() {
 
   var headers = {};
   var keys = Object.keys(this._headers);
+
   for (var i = 0, l = keys.length; i < l; i++) {
     var key = keys[i];
     headers[this._headerNames[key]] = this._headers[key];

test/simple/test-http-write-head.js

@@ -28,6 +28,17 @@ var http = require('http');
 
 var s = http.createServer(function(req, res) {
   res.setHeader('test', '1');
+
+  // toLowerCase() is used on the name argument, so it must be a string.
+  var threw = false;
+  try {
+    res.setHeader(0xf00, 'bar');
+  } catch (e) {
+    assert.ok(e instanceof TypeError);
+    threw = true;
+  }
+  assert.ok(threw, 'Non-string names should throw');
+
   res.writeHead(200, { Test: '2' });
   res.end();
 });