[HttpKernel] Fix that the Store would not save responses with the X-Content-Digest header present
#36833
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fabpot
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…-Content-Digest header present
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Thank you @mpdude. |
This was referenced May 26, 2020
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…sponse body correctly (mpdude) This PR was squashed before being merged into the 3.4 branch. Discussion ---------- [HttpKernel] Fix regression where Store does not return response body correctly | Q | A | ------------- | --- | Branch? | 3.4 | Bug fix? | yes | New feature? | no | Deprecations? | no | Tickets | Fix #37174 | License | MIT | Doc PR | Since #36833, the `Store` no longer uses or trusts the `X-Content-Digest` header present on a response, since that may come (in the case of using `CachingHttpClient`) from upstream HTTP sources. Instead, the `X-Content-Digest` is re-computed every time a response is written by the `Store`. Additionally, the `Store` is implemented in a way that when restoring responses, it does _not_ actually load the response body, but just keeps the file path to the content on disk in another internal header called `X-Body-File`. It is up to others (`HttpCache`, for example) to actually load the content from there. For reasons I could not determine, the file path is also set as the response body. When the `HttpCache` performs revalidations, it may happen that it wants the `Store` to persist a previously restored response. In that case, the `Store` fails to honor its own `X-Body-File` header. Instead, it would compute (since #36833) the `X-Content-Digest`, which now is a hash of the cache file path. So, we end up with a response that still carries `X-Body-File` for the original, correct response. Since the `HttpCache` honors this value, we don't immediately notice that. But inside the `Store`, the request is now associated with the _new_ (bogus) content entry. It takes another round of looking up the content in the `Store` to now get a response where the `X-Body-File` _also_ points to the wrong content entry. Although I feel a bit uncomfortable with trusting headers that seemingly need to be evaluated in different classes and may come from elsewhere, my suggestion is to skip the write inside `Store` if `X-Body-File` and `X-Content-Digest` are both present and consistent with each other. Additionally, a `file_exists` check could be added to provide additional assertions, at the cost of accessing the filesystem. Commits ------- 176e769 [HttpKernel] Fix regression where Store does not return response body correctly
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Responses fetched from upstream sources might have a
X-Content-Digestheader, for example if the Symfony Cache is used upstream. This currently prevents theStorefrom saving such responses. In general, the value of this header should not be trusted.As I consider this header an implementation detail of the
Store, the fix tries to be local to that class; we should not rely on theHttpCacheor other classes to remove untrustworthy headers for us.This fixes the issue that when using the
HttpCachein combination with the Symfony HttpClient, responses that have also been cached upstream in an instance ofHttpCacheare not cached locally. It adds the overhead of re-computing the content digest every time theHttpCachesuccessfully re-validated a response.