http: add http.ClientRequest.getRawHeaderNames()

Fixes: nodejs#37641

Author: simov

lib/_http_outgoing.js

@@ -35,6 +35,7 @@ const {
   ObjectCreate,
   ObjectDefineProperty,
   ObjectKeys,
+  ObjectValues,
   ObjectPrototypeHasOwnProperty,
   ObjectSetPrototypeOf,
   RegExpPrototypeTest,
@@ -602,6 +603,12 @@ OutgoingMessage.prototype.getHeaderNames = function getHeaderNames() {
 };
 
 
+// Returns an array of the names of the current outgoing raw headers.
+OutgoingMessage.prototype.getRawHeaderNames = function getRawHeaderNames() {
+  return this[kOutHeaders] !== null ? ObjectValues(this[kOutHeaders]) : [];
+};
+
+
 // Returns a shallow copy of the current outgoing headers.
 OutgoingMessage.prototype.getHeaders = function getHeaders() {
   const headers = this[kOutHeaders];

test/parallel/test-http-mutable-headers.js

@@ -171,7 +171,7 @@ function nextTest() {
 
   let bufferedResponse = '';
 
-  http.get({ port: s.address().port }, common.mustCall((response) => {
+  const req = http.get({ port: s.address().port, headers: {'X-foo': 'bar'} }, common.mustCall((response) => {
     switch (test) {
       case 'headers':
         assert.strictEqual(response.statusCode, 201);
@@ -214,4 +214,9 @@ function nextTest() {
       common.mustCall(nextTest)();
     }));
   }));
+
+  assert.deepStrictEqual(req.getHeaderNames(),
+                         ['x-foo', 'host']);
+  assert.deepStrictEqual(req.getRawHeaderNames(),
+                         ['X-foo', 'Host']);
 }