c-icap is an implementation of an ICAP server

c-icap is an implementation of an ICAP server.
The implementation of c-icap was started from scratch. An alternative approach
would be implementing a module for the ICAP protocol (e.g., as an HTTP module
or an HTTP proxy module) on top of the Apache Web server. The latter approach
would have the advantage of using server modules that are extremely stable as
well as using other useful modules implemented on top of the Apache Web server,
for example, SSL, MIME, loggers and filters. However, writing the server from
scratch would result in a simple and more autonomous ICAP server.
c-icap can be used with HTTP proxies that support the ICAP protocol. Most of the
comercial HTTP proxies must support ICAP pcotocol. The open source Squid 3.0
proxy server supports the ICAP protocol too. Also you can use the Shweby proxy
server, which operates very well with the ICAP protocol.

c-icap supports request and response modification, "preview" functionality
(preview of requests) and "204 No Content"(No modification needed) responses.
It also supports the addition of services which are responsible for content
modifications. Currently, services can be implemented only in C/C++. In the future,
I am planning to implement Perl and Java service handlers which will allow services
written in Perl or Java.

c-icap allows the addition of modules, which can extend its functionality and
services. For instance, such modules can be loggers, authenticators and
authentication methods or access controlers.

Currently, only two services exist: the echo service and an antivirus service
based on ClamAV. Looking into the code of these services can help you understand
how services are created in a c-icap server. c-icap is reasonably stable. Tests
with several thousands of requests of echo and antivirus services were successfully
passed. However, c-icap is still under development and is subject to changes. For
example, function names and configuration parameters may be modified, include files
will be merged, and several new features will be added. In other words, you should
only use it for experimentation purposes.