Chapter 26. Packet Filtering in Component
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# Chapter 26. Packet Filtering in Component

Artur Hefczyc <artur.hefczyc@tigase.net> v2.0, June 2014: Reformatted for AsciiDoc. :toc: :numbered: :website: http://tigase.net/ :Date: 2010-04-06 21:22

## The Packet Filter API

The Tigase server offers an API to filter packets traffic inside every component. You can separately filter incoming and outgoing packets.

By filtering we understand intercepting a packet and possibly making some changes to the packet or just blocking the packet completely. By blocking we understand stopping from any further processing and just dropping the packet.

The packet filtering is based on the PacketFilterIfc interface. Please have a look in the JavaDoc documentation to this interface for all the details. The main filtering method is `Packet filter(Packet packet);` which takes packets as an input, processes it, possibly alerting the packet content (may add or remove some payloads) and returns a Packet for further processing. If it returns null it means the packet is blocked and no further processing is permitted otherwise it returns a Packet object which is either the same object it received as a parameter or a modified copy of the original object.

Please note, although Packet object is not unmodifiable instance it is recommended to not make any changes on the existing object. The same Packet might be processed at the same time by other components or threads, therefore modification of the Packet may lead to unpredictable results.

Please refer to an example code in PacketCounter which is a very simple filter counting different types of packets. This filter is by default loaded to all components which might be very helpful for assessing traffic shapes on newly deployed installation. You can get counters for all types of packets, where they are generated, where they flow, what component they put the most load on.

This is because packet filter can also generate and present own statistics which are accessible via normal statistics monitoring mechanisms. To take advantage of the statistics functionality the packet filter has to implement `void getStatistics(StatisticsList list);` method. Normally the method can be empty but you can generate and add to the list own statistics from the filter. Please refer to PacketCounter for an example implementation code.

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