[RFC] Automating "private cache" mode in Squid

[Amos Jeffries]

As the subject says I am looking at what is necessary to implement a 
"private cache" mode for Squid.

Goal:
  removing ignore-private option from refresh_pattern. It is completely 
unsafe in shared-cache traffic and real private caches should not need 
to specify it on every refresh_pattern line.


Background:
  HTTP splits the caching rules into shared cache and private cache. 
The intention here is that shared cache rules are followed by middleware 
proxies and private cache rules are followed by Browsers and other UA 
caches.
 However, in the last few years as end-users grow a number of devices 
and HTTP-enabled softwares all related to just themselves they have 
grown the need for a middleware proxy such as Squid to aggregate all of 
*that users* traffic through one gateway cache.


My previous thoughts around this have all revolved around the idea of 
adding the clients IP address to the cache key when private proxy mode 
is enabled. This has a major issue though in that it does not solve 
anything for users with multiple devices (and thus multiple IPs) or even 
devices using IPv4/IPv6 interchangeably (and thus multiple IPs even for 
localhost traffic).

The obvious alternative is a ON/OFF directive line offline_mode. But 
this is somewhat dangerous and it is likely that shared-cache admin will 
use it wrongly. I would _really_ like to avoid its existence if at all 
possible.

Does anyone have any ideas about what directions would be good to 
proceed for this project?


Amos