fix(server): address Node v10.x req close event firing order

lib/server.js

@@ -1143,19 +1143,37 @@ Server.prototype._setupRequest = function _setupRequest(req, res) {
     // the connection (or we lose the connection).
     // we consider a closed request as flushed from metrics point of view
     function onClose() {
-        res._flushed = true;
-        req._timeFlushed = process.hrtime();
-
         res.removeListener('finish', onFinish);
         res.removeListener('error', onError);
+
         req._connectionState = 'close';
 
+        // Do no handle close if request is already flushed
+        // In Node >= 10 res's close event is always emitted
+        // Introduced in: https://github.com/nodejs/node/pull/20611
+        if (res._flushed) {
+            return;
+        }
+
+        // Handle close and return error if request is not flushed yet
+        res._flushed = true;
+        req._timeFlushed = process.hrtime();
+
         // Request was aborted or closed. Override the status code
         res.statusCode = 444;
-
-        self._finishReqResCycle(req, res, new errors.RequestCloseError());
+        self._finishReqResCycle(
+            req,
+            res,
+            res.err || new errors.RequestCloseError()
+        );
     }
-    req.once('close', onClose);
+
+    // Handle res's close on to the next cycle
+    // Required in Node >= 10:
+    // introduced in: https://github.com/nodejs/node/pull/20941
+    req.once('close', function onReqClose() {
+        setImmediate(onClose);
+    });
 
     // Response lifecycle events
     function onFinish() {

test/plugins/audit.test.js

@@ -676,16 +676,23 @@ describe('audit logger', function() {
             assert.ok(data);
             assert.ok(data.req_id);
             assert.isNumber(data.latency);
-            assert.equal(444, data.res.statusCode);
+            assert.equal(data.res.statusCode, 444);
             done();
         });
 
         SERVER.get('/audit', function(req, res, next) {
-            req.emit('close');
-            res.send();
-            next();
+            setTimeout(function() {
+                res.send();
+                next();
+            }, 100);
         });
 
-        CLIENT.get('/audit', function(err, req, res) {});
+        CLIENT.get(
+            {
+                path: '/audit',
+                requestTimeout: 50
+            },
+            function(err, req, res) {}
+        );
     });
 });

test/server.test.js

@@ -1924,8 +1924,12 @@ test("should emit 'after' on successful request", function(t) {
     });
 
     SERVER.get('/foobar', function(req, res, next) {
-        res.send('hello world');
-        next();
+        setTimeout(function() {
+            res.send('hello world');
+            setTimeout(function() {
+                next();
+            }, 500);
+        }, 500);
     });
 
     CLIENT.get('/foobar', function(err, _, res) {