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After some research, the 'best' practice is to send only one raw with all value comma separated. But I found that Symfony handle some values of Vary by default.

Should I also open a PR to send only one row ?

Should I remove this part

This code is partially based on the Rack-Cache library by Ryan Tomayko,
 * which is released under the MIT license.

that break the CI ?

That's a false-positive, it should be ignored. Thanks for the follow up, I'll have a look ASAP.

I think we can remove the check part on headers.
The function requestMatch do it for use with this

$v1 = $env1[$key] ?? null;
            $v2 = $env2[$key] ?? null;
            if ($v1 !== $v2) {
                return false;
            }

• case 1:
  Two request with the header Foo: foo returning the same headers ( not specially the same body)

< HTTP/1.1 200 OK
< Content-Type: application/json
< Vary: Accept-Encoding
< Vary: Foo
< Content-Length: 1234
```
$v1 === $v2 : remove old response and keep last

- case 2: 
Two request with the header request1 `Foo: foo` and request2 `Foo:bar`

< HTTP/1.1 200 OK
< Content-Type: application/json
< Vary: Accept-Encoding
< Vary: Foo
< Content-Length: 1234

$v1 !== $v2 : remove old response and keep last


- case 3: 
Two requests with on first request `Foo:bar` and last `FooBar: fooBar` and  responses : 
1 : 

< HTTP/1.1 200 OK
< Content-Type: application/json
< Vary: Accept-Encoding
< Vary: Foo
< Content-Length: 1234

2 : 

< HTTP/1.1 200 OK
< Content-Type: application/json
< Vary: Accept-Encoding
< Vary: FooBar
< Content-Length: 1234

$v1 = null and $v2 = 'fooBar`
$v1 !== $v2 :keep previous response as Foobar don't exist. 

What do you think of this ? Am I missing something in my reflection ? 

Please update the patch as you see fit, I prefer reviewing patches :)

Thank you @philpichet.

Thank you @philpichet.

Thanks you for the review