[squid-users] refresh_pattern and same objects

[Amos Jeffries]

On 3/09/2015 2:58 a.m., Yuri Voinov wrote:
> 
> Here is an example.
> 
> Look at this three screenshots.
> 
> First. Two images requested by one client at the same time.
> 
> http://i.imgur.com/JbMhTQ4.png
> 
> This is the same image:
> http://i.imgur.com/4khcCOT.png
> http://i.imgur.com/Ya58kfG.png
> 
> Agree?
> 
> And - image is too small to contains any functional payload. Agree? So,

Size does not enter into it. You are applying the pattern on all
websites. The image sizes *will* be different on each of those websites.
A tracking icon here, a visible icon there, a feature-length movie .gif
somewhere else.


> argument is simple random value to suppress caching. Right?

On *this* website. Maybe.

Could still be a 2x2 pixel background pattern generated on the fly by a
server script based on the parameter.

Or just that you are getting 2x2 pixels and others might be getting more.


> 
> So, will cache or remains uncached?

Better to be un-cached actually. If its clearly and purely a tracker you
can save yourself and users trouble by 451'ing it.

Create yourself a ERR_BLANK empty file in the Squid templates directory
and deny_info 451:ERR_BLANK. 300 more bytes savings.


(451 being "Blocked For Legal Reasons" since its policy not technical
error, you can choose another if you wish).


> 
> Will cache with store-ID:
> 
> http://i.imgur.com/ZZmOMKz.png
> 
> What I'm doing wrong?

You are assuming that what you found out about rs.mail.ru applies to
every other website ever created now or in future.

It *probably* applies for images from other domains sharing the same
webmail or CMS system used by that domain.

But there is nearly zero chance of it always applying everywhere.


Amos