Add deprecation warning to "Referrer" special-casing

[rileyjshaw]

re: #3951

Test plan: npm test

[AhmadIbrahiim]

👌👌

[dougwilson]

Based on the linked issue, I think this message isn't happening in the correct life cycle. For example, it show be emitted when either req.get('referer') or req.get('referrer') is called when the value returned would be the value from this.headers.referrer.

The idea is that what is being deprecated is looking at req.headers.referrer, not just the req.get('referrer') (which would actually remain and be the way to access the former name.

[rileyjshaw]

@dougwilson thanks for the clarification, and sorry for the delay! I just updated the PR.

Now, if someone calls:

• req.get('referer') and receives this.headers.referrer, or
• req.get('referrer') and receives this.headers.referer

…the deprecation notice will print.

I hope that's what you meant re: lifecycles. As far as I can tell, the only other place this special-casing extends to is lib/response.js:750-753, but since that uses req.get() it should still flag correctly.

[rileyjshaw]

Also worth noting: tests all pass on this commit, but will need to be updated once the special-casing is removed.

[bjohansebas]

Hey @rileyjshaw, could you rebase this, please?

[rileyjshaw]

Happy to, @bjohansebas. Does that mean this is getting merged? 😄

[bjohansebas]

Happy to, @bjohansebas. Does that mean this is getting merged

I'm not sure if this will be included in this release, but it will most likely be in the next ones.

[bjohansebas]

This dependency is no longer in master, please add the dependency back.

[rileyjshaw]

Sorry for the delay, I just added it back in.

[wesleytodd]

I am not going to open a blocking review, but if we do decided to land this I think it will be very noisy. Most of the things sending this header in the wild are not things Express application owners can control and so they are highly unlikely to be able to fix. I am not opposed to trying, but I just want to call out that this may be difficult to follow through on removing support for.