[squid-users] confused about ICAP and who's downloading what

[Antony Stone]

On Sunday 21 June 2015 at 00:31:45 (EU time), Jason Haar wrote:

> When a web page is requested by a client, what component does what? Does
> squid do the download, pass the content to ICAP, or does it (like with
> parent proxies), just tell the ICAP software to do the download itself?

The former - squid does the download and passes the content to ICAP.

ICAP is simply a means for modifying, or providing information about, HTTP 
requests and responses which are fed to the ICAP server.  The ICAP server 
itself doesn't perform any HTTP requests.

See https://tools.ietf.org/html/rfc3507 for more details (the diagrams in 3.1 
and 3.2 show how the dataflow works).

As that RFC says, "ICAP is, in essence, a lightweight protocol for executing a 
'remote procedure call' on HTTP messages.  It allows ICAP clients to pass HTTP 
messages to ICAP servers for some sort of transformation or other processing".

Squid is the ICAP client in your setup.


Regards,


Antony.

-- 
"I estimate there's a world market for about five computers."

 - Thomas J Watson, Chairman of IBM

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