Page Cache caches all safe HTTP methods (GET+HEAD), but generates the same cache ID for either: add test coverage to prove this is correct

+1 for this fix

Urgs, we hardcode the cache ID in there :( \Drupal\system\Tests\Cache\PageCacheTagsTestBase::verifyPageCache

Back in D7 the page cache expected that a full response is always generated. The response body was removed upon delivery. This is a bit like gzip encoding works: Always store the response encoded but if a client does not understand that, then unzip upon delivery.

If I'm not completely mistaken, this is also how the Symfony HttpCache works regarding HEAD requests. So I'm not completely convinced that this is a problem.

In fact HttpFoundation\Response::prepare() completely takes care of that.

I checked what Varnish does in this case. Upon a cache-miss, Varnish fetches from the backend using GET, even if the client did a HEAD request.

I think that application code (such as REST resources) should not care at all about whether a request was GET or HEAD, but instead always deliver the whole response. Symfony will take care of removing the body upon prepare() if necessary. Also if the site is behind a reverse proxy, we can assume that HEAD requests will not reach to the backend at all. Therefore there is no point in differentiate between GET and HEAD on controller level.

I'm tempted to close this as won't fix. What do you think @Wim?

Symfony will take care of removing the body upon prepare() if necessary.

Does it? I tried it on the command line and saw an actual response body, do we miss something by bypassing HTTP kernel?

I think it'd then be valuable to convert this issue to a test-only issue to encode what you wrote in a test, to ensure that expectation is never broken.

+1

I'm still confused about what I've seen, but well, we have a test which proves the opposite.

It works for me... not sure what @dawehner is seeing...

curl --head -i http://drupal8alt.dev

HTTP/1.1 200 OK
Date: Fri, 14 Oct 2016 00:00:30 GMT
Server: Apache/2.4.18 (Unix) PHP/7.0.7 LibreSSL/2.2.7
X-Content-Type-Options: nosniff
X-Powered-By: PHP/7.0.7
Cache-Control: must-revalidate, no-cache, private
X-Drupal-Dynamic-Cache: HIT
X-UA-Compatible: IE=edge
Content-language: en
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Drupal-Cache-Tags: block_view config:block.block.stark_admin config:block.block.stark_branding config:block.block.stark_local_actions config:block.block.stark_local_tasks config:block.block.stark_login config:block.block.stark_messages config:block.block.stark_page_title config:block.block.stark_tools config:block_list config:system.menu.admin config:system.menu.tools config:system.site config:user.role.anonymous config:user.settings rendered
X-Drupal-Cache-Contexts: languages:language_interface route theme url.path url.query_args user.permissions user.roles:authenticated
Expires: Sun, 19 Nov 1978 05:00:00 GMT
X-Generator: Drupal 8 (https://www.drupal.org)
X-Drupal-Cache: MISS
Content-Type: text/html; charset=UTF-8

curl -i http://drupal8alt.dev

HTTP/1.1 200 OK
Date: Fri, 14 Oct 2016 00:00:34 GMT
Server: Apache/2.4.18 (Unix) PHP/7.0.7 LibreSSL/2.2.7
X-Content-Type-Options: nosniff
X-Powered-By: PHP/7.0.7
Cache-Control: must-revalidate, no-cache, private
X-Drupal-Dynamic-Cache: HIT
X-UA-Compatible: IE=edge
Content-language: en
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Drupal-Cache-Tags: block_view config:block.block.stark_admin config:block.block.stark_branding config:block.block.stark_local_actions config:block.block.stark_local_tasks config:block.block.stark_login config:block.block.stark_messages config:block.block.stark_page_title config:block.block.stark_tools config:block_list config:system.menu.admin config:system.menu.tools config:system.site config:user.role.anonymous config:user.settings rendered
X-Drupal-Cache-Contexts: languages:language_interface route theme url.path url.query_args user.permissions user.roles:authenticated
Expires: Sun, 19 Nov 1978 05:00:00 GMT
X-Generator: Drupal 8 (https://www.drupal.org)
X-Drupal-Cache: MISS
Vary: Accept-Encoding
Content-Length: 5866
Content-Type: text/html; charset=UTF-8

Committed and pushed cae82ac to 8.3.x and 781e927 to 8.2.x. Thanks!