No HTML compression via custom server & app.render()

Bug report

Describe the bug

If you write custom server routes via app.render() there is no gzip compression for the HTML document. I looked at the source code: the handleCompression() fn is only called via the app.getRequestHandler(). I guess this is not intended.

https://github.com/vercel/next.js/blob/8efc8be3e911e9c1eeabaef9e8cca6fcef5189ba/packages/next/next-server/server/next-server.ts#L866-L872

To Reproduce

1. Clone the custom-server example (yarn create next-app --example custom-server custom-server-app)
2. yarn build && yarn start
3. Route to http://localhost:3000/a inspect HTML document response header via chrome dev tools or cURL
4. There is no Content-Encoding: gzip response header 👎
5. Route to index http://localhost:3000/ inspect HTML document response header via chrome dev tools or cURL
6. Content-Encoding: gzip response header available 👍

Expected behavior

• gzip compression of HTML documents rendered via app.render()
• Response Header: Content-Encoding: gzip

System information

• OS: macOS
• Version of Next.js: 9.5.2
• Version of Node.js: 12.18.2

[radoslawgrochowski]

I’ve added test cases, @timneutkens.

I have one question - should app.render with /static content also be compressed?

[bobaaaaa]

@YichiZ exactly