Re: RFC: ETag support for zope.browserresource

On Mon, Aug 09, 2010 at 07:37:30PM -0300, Sidnei da Silva wrote:
> On Mon, Aug 9, 2010 at 3:25 PM, Marius Gedminas <[email protected]> wrote:
> > I've added ETag support for zope.browserresource in a branch:
> > http://zope3.pov.lt/trac/changeset/115596
> >
> > Does anybody have any comments/objections?  If not, I'd like to merge
> > this to trunk and release zope.browserresource 3.11.0.
> 
> +1 as long as there's a way to disable or configure how it's computed.

How would you like that to be configured?

Option #1:

  <browser:resource/resourceDirectory etags="off" /> ?

Option #2:

  getMultiAdapter((resource, request), IETag).computeETag() ?

  This is maybe a bit problematic, because the actual File object that
  contains all the data--such as filename--doesn't implement any
  interfaces.  And neither does FileResource.

> There's some information about issues with ETags here:
> 
>   http://developer.yahoo.com/performance/rules.html#etags
> 
> I see that your implementation uses last-modified + size, which should
> generally be fine. However if you're load-balancing across two
> different servers and the timestamps don't match then the ETag is
> useless.

Would you prefer a sha1 checksum?

> On a completely different note, I see that the File object reads the
> whole file into memory.

And it does that twice for every request that results in a 200 response:
once to auto-detect the content-type, the second time to return the
actual data.

> Hum. Maybe RAM is cheaper than Disk these days
> and it doesn't matter, but reading whole files into memory generally
> raises a red flag for me.
> 
> hoping-no-one-is-serving-iso-files-through-zope.browserresource-ly yours,

Marius Gedminas
-- 
http://pov.lt/ -- Zope 3/BlueBream consulting and development

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