[squid-users] Caching ChromeOS update files

[Kevin Byers]

Hi there,

I am trying to setup squid to specifically cache ChromeOS updates for
Chromebooks but I am currently stuck and lacking the proper knowledge
to solve the issue.
Issue #1: The update files are not being cached by squid.
TCP_MISS_ABORTED/206 messages occur in the squid access.log. I haven't
seen a HIT yet.
Issue #2: The update process on the Chromebooks seems to stall when
they are using squid as the proxy. The Chromebook will show the update
progress as a percentage increasing in number, and eventually it stops
changing. After waiting a while with no changes, the Chromebook will
stop the update process.

Here's the Chromebook update download logic that squid needs to adapt to:
A) Chromebooks update by fetching a single file from dl.google.com.
B) The update files can be up to about 500 megabytes.
C) Chromebooks always request a partial download (HTTP 206) even if
they are downloading the full file from the beginning.
D) Chromebooks will resume downloading the file from a prior partial download.
E) The HTTP response headers for the files have age:0 and
cache-control: public,max-age=86400. There is no "partial" attribute.

Do any of these above things make it impossible to cache the update files?

Here's the squid configuration that I am using:  https://pastebin.com/m15g84xv
Essentially, I increased the cache file size limits to 1 GB and
allowed only Chromebook IP traffic to squid.
I am only caching the files in RAM so there is no hard disk cache.
I created a refresh pattern to keep the update files cached for 7 days.
The Chromebooks are using a PAC file which only sends dl.google.com
traffic to squid, so squid is only dealing with dl.google.com traffic.

I am using squid 3.5.27 on ubuntu 18.04 LTS server edition VM with 2
vCPUs and 8 GB RAM.

Kevin Byers