missing vary header for preCompressed files

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure it has not already been reported

Fastify version

3.19.0

Plugin version

4.2.0

Node.js version

14.x

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

11.15.1

Description

The Vary Header is not included when serving preCompressed assets. This can cause issues with caches serving the incorrect version of pages to browsers.

Steps to Reproduce

Serve preCompressed assets and check the header response in devtools and you’ll see no vary: content-encoding header present.

Expected Behavior

I’d expect the vary: content-encoding header to be served with all assets. This applies whether or not they werepreCompressed and whether or not the compressed version is served. The MDN article for vary also notes some other times it should be included, like with 304 responses.

related

#158

[mcollina]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[Uzlopak]

Probably connected with #300