Default FPC Accepts non text/html, Serves Cache Hit as text/html

[astorm]

The default full page cache (FPC) implementation will cache content with non html Content-Type headers (text/css, application/javascript, etc), and then re-serve the content as text/html. This can cause unstable and unacceptable application behavior. For example, Google Chrome will not render CSS files served with a text/html header.

This is not a theoretical problem. It was encountered when converting an business critical feature for a popular Magento 1 theme to a Magento 2 theme. While suggestions for better coding practices are appreciated, the shipping full page cache engine should not ship with functionality that's broken.

Possible fixes include ensuring the FPC engine skips caching non text/html content, or ensuring the FPC engine preserves header. This is a decision that needs to be made by the Magento core engineering team as it has long term implications for the behavior of the platform.

Steps to reproduce

1. Install Magento from develop branch.
2. Ensure Full Page Cache is Enabled at System -> Cache Management
3. Install Attached Module (Pulsestorm_BugFullPageCacheHeader.tar.gz
   )
4. Load URL: http://magento.example.com/pulsestorm_bugfullpagecacheheader/
5. Reload URL: http://magento.example.com/pulsestorm_bugfullpagecacheheader/

Expected result

1. Both results return a text/css Content-Type: header

Actual result

1. Second Result returns a text/html header

Curl output below

$ curl '-I' 'http://magento-2-with-keys.dev/pulsestorm_bugfullpagecacheheader/'
HTTP/1.1 200 OK
Date: Sun, 20 Mar 2016 18:41:07 GMT
Server: Apache/2.4.16 (Unix) PHP/5.6.19
X-Powered-By: PHP/5.6.19
Expires: Fri, 20 Mar 2015 18:41:08 GMT
Cache-Control: max-age=0, must-revalidate, no-cache, no-store
Pragma: no-cache
X-Magento-Cache-Control: max-age=86400, public, s-maxage=86400
X-Magento-Cache-Debug: MISS
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Content-Type: text/css;charset=UTF-8

Alans-MacBook-Pro:magento2 alanstorm$ curl '-I' 'http://magento-2-with-keys.dev/pulsestorm_bugfullpagecacheheader/'
HTTP/1.1 200 OK
Date: Sun, 20 Mar 2016 18:41:09 GMT
Server: Apache/2.4.16 (Unix) PHP/5.6.19
X-Powered-By: PHP/5.6.19
X-Magento-Cache-Debug: HIT
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Content-Type: text/html; charset=UTF-8

[alankent]

That's a pretty clear bug.

[choukalos]

Created bug MAGETWO-50710 for internal tracking

[astorm]

Any update/ETA on this? It's causing a real world problem for an extension/theme developer who's migrating their theme to Magento 2.

[astorm]

Any update/ETA on this? It's causing a real world problem for an extension/theme developer who's migrating their theme to Magento 2.

/cc @piotrekkaminski

[pboisvert]

@choukalos Can you update this issue? Jira shows as closed now but unsure when that ticket will be released (2.1 or earlier in a patch).

[piotrekkaminski]

The issue looks fixed in internal repository and should be available already in 2.1rc versions.