test: clean up http-set-trailers

* remove shared state of request counting from each listener by using
  callbacks to report test finish. This also fixes slight race condition
  where one of the request could finish before the other was taken into
  account resulting in ECONNREFUSED due to premature server.close()
* slightly move code for better cohesion
* fix error comment in testHttp10 'Trailer ...' -> 'No trailer ...'

PR-URL: #30522
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

test/parallel/test-http-set-trailers.js

@@ -26,91 +26,77 @@ const http = require('http');
 const net = require('net');
 const util = require('util');
 
-let outstanding_reqs = 0;
-
-const server = http.createServer(function(req, res) {
-  res.writeHead(200, [['content-type', 'text/plain']]);
-  res.addTrailers({ 'x-foo': 'bar' });
-  res.end('stuff\n');
-});
-server.listen(0);
-
-
 // First, we test an HTTP/1.0 request.
-server.on('listening', function() {
-  const c = net.createConnection(this.address().port);
-  let res_buffer = '';
+function testHttp10(port, callback) {
+  const c = net.createConnection(port);
 
   c.setEncoding('utf8');
 
-  c.on('connect', function() {
-    outstanding_reqs++;
+  c.on('connect', () => {
     c.write('GET / HTTP/1.0\r\n\r\n');
   });
 
-  c.on('data', function(chunk) {
+  let res_buffer = '';
+  c.on('data', (chunk) => {
     res_buffer += chunk;
   });
 
   c.on('end', function() {
     c.end();
     assert.ok(
       !/x-foo/.test(res_buffer),
-      `Trailer in HTTP/1.0 response. Response buffer: ${res_buffer}`
+      `No trailer in HTTP/1.0 response. Response buffer: ${res_buffer}`
     );
-    outstanding_reqs--;
-    if (outstanding_reqs === 0) {
-      server.close();
-    }
+    callback();
   });
-});
+}
 
 // Now, we test an HTTP/1.1 request.
-server.on('listening', function() {
-  const c = net.createConnection(this.address().port);
-  let res_buffer = '';
-  let tid;
+function testHttp11(port, callback) {
+  const c = net.createConnection(port);
 
   c.setEncoding('utf8');
 
+  let tid;
   c.on('connect', function() {
-    outstanding_reqs++;
     c.write('GET / HTTP/1.1\r\n\r\n');
     tid = setTimeout(common.mustNotCall(), 2000, 'Couldn\'t find last chunk.');
   });
 
+  let res_buffer = '';
   c.on('data', function(chunk) {
     res_buffer += chunk;
     if (/0\r\n/.test(res_buffer)) { // got the end.
-      outstanding_reqs--;
       clearTimeout(tid);
       assert.ok(
         /0\r\nx-foo: bar\r\n\r\n$/.test(res_buffer),
         `No trailer in HTTP/1.1 response. Response buffer: ${res_buffer}`
       );
-      if (outstanding_reqs === 0) {
-        server.close();
-      }
+      callback();
     }
   });
-});
+}
 
 // Now, see if the client sees the trailers.
-server.on('listening', function() {
-  http.get({
-    port: this.address().port,
-    path: '/hello',
-    headers: {}
-  }, function(res) {
+function testClientTrailers(port, callback) {
+  http.get({ port, path: '/hello', headers: {} }, (res) => {
     res.on('end', function() {
       assert.ok('x-foo' in res.trailers,
                 `${util.inspect(res.trailers)} misses the 'x-foo' property`);
-      outstanding_reqs--;
-      if (outstanding_reqs === 0) {
-        server.close();
-      }
+      callback();
     });
     res.resume();
   });
-  outstanding_reqs++;
+}
+
+const server = http.createServer((req, res) => {
+  res.writeHead(200, [['content-type', 'text/plain']]);
+  res.addTrailers({ 'x-foo': 'bar' });
+  res.end('stuff\n');
+});
+server.listen(0, () => {
+  Promise.all([testHttp10, testHttp11, testClientTrailers]
+    .map(util.promisify)
+    .map((f) => f(server.address().port)))
+    .then(() => server.close());
 });