1629202 - Storage estimate does not return the correct cache storage usage

Status: RESOLVED INVALID

(Core :: Storage: Cache API, defect)

Description

[Xiyuan Liu]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.92 Safari/537.36

Steps to reproduce:

1. Check the current storage usage with navigator.storage.estimate()
2. Add a sized string to cache.
   const str = new Array(1024*1024/4+1).join('abcd');
   const response = new Response(str);
   const cache = await caches.open('test');
   cache.put('foo', response);
3. Check storage usage again

Actual results:

Usage increased by 164795 bytes

Expected results:

Usage should increase by 1MB. Chrome works as expected.

Comment 1

[Xiyuan Liu]

UA: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:75.0) Gecko/20100101 Firefox/75.0

Comment 2

[BugBot [:suhaib / :marco]]

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Comment 3

[Ben Kelly [:bkelly, not reviewing]]

This is most likely because cache API in firefox compresses body data.

Comment 4

[Tom Tung [:tt, :ttung]]

(In reply to Xiyuan Liu from comment #0)

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.92 Safari/537.36

Steps to reproduce:

1. Check the current storage usage with navigator.storage.estimate()
2. Add a sized string to cache.
   const str = new Array(1024*1024/4+1).join('abcd');
   const response = new Response(str);
   const cache = await caches.open('test');
   cache.put('foo', response);
3. Check storage usage again

Actual results:

Usage increased by 164795 bytes

Expected results:

Usage should increase by 1MB. Chrome works as expected.

It's not clear to me why you expect Cache API should store 1 MB in this case. My understanding is that browsers can have their own implementations unless the spec specifies the behavior.

And, I think Ben's comment in comment 3 is correct. It's because Cache API compresses body data.

Please feel free to reopen this if you don't think so.