fix `Resource with the 304 status code and the 'content-length: x' he…

…ader does not load` (close DevExpress#1602) (DevExpress#1638)

* fix `Resource with the 304 status code and the 'content-length: x' header does not load` (close DevExpress#1602)

* fix tests

* fix review issue

src/request-pipeline/index.js

@@ -96,7 +96,11 @@ const stages = {
                         ctx.onResponseEventDataWithoutBody.push({ rule, opts: configureResponseEvent.opts });
                 });
 
-                ctx.destRes.pipe(ctx.res);
+                if (ctx.contentInfo.isNotModified)
+                    ctx.res.end();
+                else
+                    ctx.destRes.pipe(ctx.res);
+
                 if (ctx.onResponseEventDataWithoutBody.length) {
                     ctx.res.on('finish', () => {
                         const responseInfo = requestEventInfo.createResponseInfo(ctx);
@@ -117,7 +121,7 @@ const stages = {
                 }
             }
             else
-                ctx.res.end('');
+                ctx.res.end();
 
             return;
         }

test/server/proxy-test.js

@@ -3338,5 +3338,45 @@ describe('Proxy', () => {
                 testRedirectRequestStatusCode(202, false)
             ]);
         });
+
+        it('Should not pipe the request with the 304 status code (Not Modified) (GH-1602)', () => {
+            const server = net.createServer(socket => {
+                socket.on('data', () => {
+                    socket.write([
+                        'HTTP/1.1 304 Not Modified',
+                        'Content-Length: 5',
+                        '',
+                        ''
+                    ].join('\r\n'));
+                });
+            });
+
+            return getFreePort()
+                .then(port => new Promise(resolve => server.listen(port, () => resolve(port))))
+                .then(port => new Promise((resolve, reject) => {
+                    const proxyUrl   = proxy.openSession(`http://127.0.0.1:${port}/`, session);
+                    const reqOptions = Object.assign(urlLib.parse(proxyUrl), {
+                        method:  'GET',
+                        headers: { 'if-none-match': 'NQQ6Iyi1ttEATRNQs+U9yQ==' }
+                    });
+
+                    const req = http.request(reqOptions, res => {
+                        const chunks = [];
+
+                        res.on('data', chunk => chunks.push(chunk));
+                        res.on('end', () => resolve({ res, body: Buffer.concat(chunks).toString() }));
+                    });
+
+                    req.on('error', reject);
+                    req.setTimeout(1500, () => reject('timeout'));
+                    req.end();
+                }))
+                .then(({ res, body }) => {
+                    expect(res.statusCode).eql(304);
+                    expect(res.headers['content-length']).eql('5');
+                    expect(body).eql('');
+                    server.close();
+                });
+        });
     });
 });