Duplicated accept-encoding vary header in response

[Marco Reni]

🐛 Bug Report

If the vary header has already been set as a string with multiple concatenated values, one of which is "accept-encoding", the plugin adds a second vary header with the "accept-encoding" value.

To Reproduce

Steps to reproduce the behavior:

1- register the plugin, then set the following into a route

reply.header('vary', 'accept-encoding,accept-version');

2- Check the response

Expected behavior

The value should not be added if already set inside the vary header.

NOTE: the plugin works correctly if the vary header is set as an array, ie. reply.header('vary', ['accept-encoding','accept-version']);, but I think the string version should also be handled.

Your Environment

• node version: 14.15.1
• fastify version: 3.12.0
• os: Mac

[Matteo Collina]

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

[Marco Reni]

Will do!