The Internet Content Adaption Protocol (ICAP) is today's status quo if you like to link an Internet proxy, cache or gateway with a filtering service on a callout server.
Current version is 1.0 (ICAP/1.0). ICAP is a typical client-server protocol similar to HTTP and it has been developed to vector HTTP content from proxies to filter services. We at webwasher extended ICAP usage to also encapsulate FTP and SMTP data.
There are several interesting products available from well-known vendors that include either an ICAP client or an ICAP server.
WebWasher is the only product that includes both, an ICAP client and server, and uses this protocol not only for talking to 3rd party products but also for its internal communication.
Finally in April 2003, the ICAP protocol became RFC 3507.

ICAP links

ICAP specification RFC 3507 (local copy)
ICAP errata page (local copy) published as RFC errata
Documented ICAP extensions in this Internet-Draft expired(local copy)
Organisation of ICAP vendors: The ICAP Forum
Mailing list: ICAP newsgroup
Info about open proxy Squid ICAP project


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Last Change: 2007-04-19