Missing Vary: Accept header causes incorrect caching in content-negotiation

[sanjana2505006]

The example uses res.format() to send different responses (HTML, JSON, text) depending on what the client asks for using the Accept header.
But the example does not include the Vary: Accept header.

Without this header, caches (like CDNs or proxies) may save one version of the page and give that same version to every user—even if they asked for a different format.
This means someone asking for JSON might accidentally get HTML from the cache.
Adding:
res.vary('Accept')

before calling res.format() tells caches that the response depends on the Accept header, so each format is cached correctly.

[yaxit24]

The "vary: Accept" header is correctly being sent. The advice to manually add "res.vary('Accept')" might be outdated or for a different version/context, but it is not needed here as the library handles it.

[krzysdz]

This was fixed in 12e0878 13 years ago, released in Express 3.0 and still exists today:

express/lib/response.js

Line 587 in 77bcd52

this.vary("Accept");

[sanjana2505006]

@yaxit24 @krzysdz Okay !