Free to filter software for linux

Compact Filter is a network packet filter for Linux. It features an easy-to-use compact filter representation and high performance.
The main features are: easy to use interface, compact filter representation (memory efficient), and very high performance.
A difference between CF and other firewalls, such as Netfilter, is its representation of the ruleset. In CF the user writes a filter which is then compiled and optimized in user-space. The optimized filter is then loaded into the kernel (using netlink). Consequently the in kernel packet filtering code only needs funtionality for setting up a filter and filtering packets, while the more complex code of optimizing the filter remains in user-space.
Because of the continuous increase of the bandwidth and the security threats, firewalls have to evolve towards more efficient filtering schemes. The truth is that the existing scheme does not scale so well with the combined growth of bandwidth and rulesets.
Our aim is to try another approach to perform packet filtering where we minimize the complexity of the filtering process. This result in, both, a reduction of the required CPU power to filter packets and a simpler (and smaller) kernel code. Of course, we are pushing all the smart and complex part out to the user-space, but, developing in user-space is much simpler and safer.
Enhancements:
- changed -d option to delete all filters
- added -D option to delete a specific filter
- changed default policy to permit rather than deny
- added -l option on flex to support --yylineno on older versions of flex
- new and improved install guide

mod_filter allows you to filter output from other modules inside of Apache. This allows you to implement filters (think Swedish Chef, jive, etc.).

You can also use it to retailer output for your locale. This works with HTML documents, mod_perl, PHP, JServ, CGIs, and for that matter just about any sort of custom handler you might have.

Hook::Filter is a runtime filtering layer on top of subroutine calls.

SYNOPSIS

Imagine you have a big program using a logging library that exports 3 functions called mydebug, myinfo and mywarn. Those functions generate far too much log, so you want to skip calling them except in some specific circumstances.

In your main program, write:

use Hook::Filter hook => ["mydebug","myinfo","mywarn"];

In all modules making use of the logging library, write:

use Hook::Filter;

Then create a file called ./hook_filter.rules. This file contains boolean expressions that specify when calls to the filtered subroutines should be allowed:

# allow calls to mydebug only inside package My::Filthy:Attempt
is_sub(mydebug) && from_pkg(My::Filthy::Attempt)

# allow all calls to myinfo except from inside packages under the namespace My::Test::
is_sub(myinfo) && !from_pkg(/^My::Test/)

# allow calls to mywarn from function do_stuff in package main
# whose third argument is a message that does not match the string invalid login name
is_sub(mywarn) && from_sub(do_stuff) && from_pkg(main) && !has_arg(3,/invalid login name/)

# all other calls to myinfo, mydebug or mywarn will be skipped

SYNOPSIS, Log::Dispatch

Your program uses Log::Dispatch. You want to enable Hook::Filter on top of the methods log and log_to from Log::Dispatch everywhere at once. And you want to use the filter rules located in /etc/myconf/filter_rules.conf. Easy: in main, write:

use Hook::Filter rules => /etc/myconf/filter_rules.conf, hook => [Log::Dispatch::log,Log::Dispatch::log_to];

IOLib-Filters is a filter package for IOLib. IOLib-Filters is mainly an example of how to write filters for IOLib.

IOLib is a portable universal data IO library. Implementations exist in C, C++ and Objective C and for many different platforms (including Linux, Win32, MacOS X and .NET).

IOLib provides a unified interface for accessing different types of data streams. It currently supports file IO, BSD sockets, memory buffers and SOCKS4/5 connections and can be extended with drivers easily.

It has support for different binary formats (Intel, Motorola, PDP) and it supports filters. You can write your own filters (e.g. for encryption or compression) and use them with IOLib.

bilateral filter is a denoising filter using the same technique as the selective gaussian blur, but with speedups and other enhancements.

The filter is slow when the blur radius is small but speeds up when the radius gets larger, which is the opposite behavior of the selective gaussian blur. Theres also an option for improved denoising of image gradients.

Constrictor is a Python module for parsing, filtering, and delivering mail as a Mail Delivery Agent (like Procmail). Constrictor provides the functionality to easily write a MDA in Python rather than reading some configuration file of its own syntax.
This has the advantages that configurations are readable and self-explanatory (at least, to anyone who knows Python) and that users have the full flexibility of the Python language at their disposal. Constrictor has the ability to deliver to maildir and Unix mbox format mailboxes, as well as bounce, forward, or reject messages.
Constrictor is currently beta software, at best. Im always very leery of software that messes with my mail, since one runs the risk of not only losing messages but, potentially, bouncing mail to great embarassment and chagrin. That said, I am currently using Constrictor on my own mailbox full-time, but, as always, your mileage may vary.
Installation
Constrictor is a single Python module that should be placed either in the directory you intend to invoke your MDA from, or in your Python library directory. The only non-standard module it relies on is the spamd module from the SpamAssassin distribution (available at http://spamassassin.apache.org/full/2.6x/dist/contrib/spamd.py), and only then if you intend to use the "spamassassin()" function to filter your mail (the module is loaded only when that function is called). Constrictor should work on all versions of Python greater than 2.3; it has been tested primarily on 2.3.4, 2.3.5, 2.4.1.
The spamassassin() function connects to a (optionally specified) spamd server (it defaults to localhost). If you do not have a spamd server, you cannot use this function.
For Postfix and Sendmail, edit your ~/.forward to include "|/path/to/filter.py". For more information on invoking this script as an MDA,see your MTAs manual or ask your administrator.
Enhancements:
- This release adds locking code to duplicate database (pickle file used to recognize duplicate messages) access.
- This release contains no known stability or delivery reliability issues, and thus is considered stable.

Filter::cpp is a cpp source filter.

SYNOPSIS

use Filter::cpp ;

This source filter pipes the current source file through the C pre-processor (cpp) if it is available.

As with all source filters its scope is limited to the current source file only. Every file you want to be processed by the filter must have a

use Filter::cpp ;

near the top.

Here is an example script which uses the filter:

use Filter::cpp ;

#define FRED 1
$a = 2 + FRED ;
print "a = $an" ;
#ifdef FRED
print "Hello FREDn" ;
#else
print "Where is FREDn" ;
#endif

And here is what it will output:

a = 3
Hello FRED

This example below, provided by Michael G Schwern, shows a clever way to get Perl to use a C pre-processor macro when the Filter::cpp module is available, or to use a Perl sub when it is not.

# use Filter::cpp if we can.
BEGIN { eval use Filter::cpp }

sub PRINT {
my($string) = shift;

#define PRINT($string)
(print $string."n")
}

PRINT("Mu");

Look at Michaels Tie::VecArray module for a practical use.