Request headers that influenced a response should be listed in a Vary response header.
This tells Unpoly to partition its cache for that URL so that each
request header value gets a separate cache entries.
You can set a Vary header manually from your server-side code. You may also be using
a library like unpoly-rails that sets the Vary header automatically.
Tip
Server-side Unpoly apps may inspect request headers to customize or shorten responses,
e.g. by omitting content that isn't targeted.
When a response is optimized in that fasion, a Vary header should be sent.
Example
The user makes a request to /sitemap in order to updates a fragment .menu.
Unpoly makes a request like this:
GET /sitemap HTTP/1.1
X-Up-Target: .menu
The server may choose to optimize its response by only render only the HTML for
the .menu fragment. It responds with the HTTP seen below. Note that it includes a Vary header
indicating that the X-Up-Target header has influenced the response body:
Vary: X-Up-Target
<div class="menu">...</div>
After observing the Vary: X-Up-Target header, Unpoly will partition cache entries to /sitemap by X-Up-Target value.
That means a request targeting .menu is no longer a cache hit for a request targeting a different selector.
See How cache entries are matched for more examples.
Resources
