BUG: "Vary: Cookie" is not sent for the first time

Summary:
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For Page cache (page_enhanced); “Vary: Accept-Encoding, Cookie” is never sent for the first time (cache creation).

Only “Vary: Accept-Encoding” is sent when there is no file cache; afterwards “Vary: Accept-Encoding, Cookie” is sent correctly when reply comes from the cache.

(w3tc 0.9.4)

Reproduction steps:
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1) Activate w3tc page cache with page_enhanced mode.

2) log out wordpress

3) Clear you browser’s cache.

4) request a page http://your-site.com/

5) There is a problem here. You will not see “Vary: Accept-Encoding, Cookie”. Only “Vary: Accept-Encoding” is sent.

This is the first time file cache is created and wordpress will read the cache out.

6) Refrest (F5) to request the same page again http://your-site.com/

7) Now, you will see “Vary: Accept-Encoding, Cookie”.

This is your server directly responding from cache, not wordpress. There is no problem here.

For the first time a page’s cache created, wordpress reads out the cached file. WordPress just returns “Vary: Accept-Encoding”.

It must return “Vary: Accept-Encoding, Cookie”

Waiting for the developer to fix it.

To view http headers while reproducing the bug, you can use “Live HTTP Headers” Firefox plugin.
https://addons.mozilla.org/en-us/firefox/addon/live-http-headers/

BTW, this bug is not server dependent IMHO, please read my previous bug fix (about nginx page cache) if you will use nginx while reproducing the bug.

Thanks

https://wordpress.org/plugins/w3-total-cache/