test: actually check req.trailers null prototype in http-server-headers-null-proto

Author: mcollina

doc/api/http.md

@@ -2863,6 +2863,9 @@ The request/response headers object.
 
 Key-value pairs of header names and values. Header names are lower-cased.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 ```js
 // Prints something like:
 //
@@ -2900,6 +2903,9 @@ added:
 Similar to [`message.headers`][], but there is no join logic and the values are
 always arrays of strings, even for headers received just once.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 ```js
 // Prints something like:
 //
@@ -3086,6 +3092,9 @@ added: v0.3.0
 
 The request/response trailers object. Only populated at the `'end'` event.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 ### `message.trailersDistinct`
 
 <!-- YAML
@@ -3100,6 +3109,9 @@ Similar to [`message.trailers`][], but there is no join logic and the values are
 always arrays of strings, even for headers received just once.
 Only populated at the `'end'` event.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 ### `message.url`
 
 <!-- YAML

doc/api/http2.md

@@ -4120,6 +4120,9 @@ The request/response headers object.
 
 Key-value pairs of header names and values. Header names are lower-cased.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 ```js
 // Prints something like:
 //
@@ -4279,6 +4282,9 @@ added: v8.4.0
 
 The request/response trailers object. Only populated at the `'end'` event.
 
+The object has a null prototype and should not be accessed using the `in`
+operator.
+
 #### `request.url`
 
 <!-- YAML

test/parallel/test-http-server-headers-null-proto.js

@@ -35,7 +35,12 @@ const net = require('net');
 // Test 2: req.trailers has a null prototype
 {
   const server = http.createServer(common.mustCall((req, res) => {
+    req.on('end', common.mustCall(() => {
+      assert.strictEqual(Object.getPrototypeOf(req.trailers), null);
+      assert.strictEqual(req.trailers['x-client-trailer'], 'bar');
+    }));
     res.setHeader('Transfer-Encoding', 'chunked');
+    res.setHeader('Trailer', 'X-Trailer');
     res.write('Hello');
     res.addTrailers({
       'X-Trailer': 'test',
@@ -50,8 +55,12 @@ const net = require('net');
       client.write(
         'GET / HTTP/1.1\r\n' +
         'Host: localhost\r\n' +
-        'TE: trailers\r\n' +
+        'Transfer-Encoding: chunked\r\n' +
+        'Trailer: X-Client-Trailer\r\n' +
         'Connection: close\r\n' +
+        '\r\n' +
+        '0\r\n' +
+        'X-Client-Trailer: bar\r\n' +
         '\r\n',
       );
     }));