http: attach request as res.req

This change makes it possible for userland http-related modules
to pave over edge cases that require referencing the original request
when handling a response--making a "Lodash for HTTP" library possible.
More information and research in #28673

Fixes: #28673

doc/api/http.md

@@ -1589,6 +1589,15 @@ Removes a header that's queued for implicit sending.
 response.removeHeader('Content-Encoding');
 ```
 
+### `response.req`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {http.IncomingMessage}
+
+A reference to the original HTTP `request` object.
+
 ### `response.sendDate`
 <!-- YAML
 added: v0.7.5

doc/api/http2.md

@@ -3418,6 +3418,15 @@ Removes a header that has been queued for implicit sending.
 response.removeHeader('Content-Encoding');
 ```
 
+### `response.req`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {http2.Http2ServerRequest}
+
+A reference to the original HTTP2 `request` object.
+
 #### `response.sendDate`
 <!-- YAML
 added: v8.4.0

lib/_http_server.js

@@ -173,6 +173,7 @@ function ServerResponse(req) {
 
   if (req.method === 'HEAD') this._hasBody = false;
 
+  this.req = req;
   this.sendDate = true;
   this._sent100 = false;
   this._expect_continue = false;

lib/internal/http2/compat.js

@@ -522,6 +522,10 @@ class Http2ServerResponse extends Stream {
     return this[kStream].headersSent;
   }
 
+  get req() {
+    return this[kStream][kRequest];
+  }
+
   get sendDate() {
     return this[kState].sendDate;
   }

test/parallel/test-http-server.js

@@ -49,6 +49,8 @@ const server = http.createServer(function(req, res) {
   res.id = request_number;
   req.id = request_number++;
 
+  assert.strictEqual(res.req, req);
+
   if (req.id === 0) {
     assert.strictEqual(req.method, 'GET');
     assert.strictEqual(url.parse(req.url).pathname, '/hello');

test/parallel/test-http2-compat-serverresponse.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const assert = require('assert');
+const h2 = require('http2');
+
+// Http2ServerResponse should expose convenience properties
+
+const server = h2.createServer();
+server.listen(0, common.mustCall(function() {
+  const port = server.address().port;
+  server.once('request', common.mustCall(function(request, response) {
+    assert.strictEqual(response.req, request);
+
+    response.on('finish', common.mustCall(function() {
+      process.nextTick(() => {
+        server.close();
+      });
+    }));
+    response.end();
+  }));
+
+  const url = `http://localhost:${port}`;
+  const client = h2.connect(url, common.mustCall(function() {
+    const headers = {
+      ':path': '/foobar',
+      ':method': 'GET',
+      ':scheme': 'http',
+      ':authority': `localhost:${port}`
+    };
+    const request = client.request(headers);
+    request.on('end', common.mustCall(function() {
+      client.close();
+    }));
+    request.end();
+    request.resume();
+  }));
+}));