content/mina-project/userguide/ch5-filters/ch5.1-blacklist-filter.mdtext

Title: 5.1 - Blacklist Filter
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# 5.1 - Blacklist Filter

This filter blocks connnections from blacklisted remote addresses. Onee can block _Addresses_ or _Subnets_. In any case, when an event happens on a blocked session, the session will simply be closed. Here are the events this filter handles :

* _event_ (MINA 2.1)
* _messageReceived_
* _messageSent_
* _sessionCreated_
* _sessionIdle_
* _sessionOpened_

There is no need to handle any other event.

## Blocking an address

Any address or subnet can be blocked live, ie it does not matter if a session is already active or not, this dynamicaly activated. 
It's enough to add the filter in the chain, and to set (or unset) the addresses to block:

    :::Java
    ...
    BlacklistFilter blackList = new BlacklistFilter();
    blackList.block(InetAddress.getByName("1.2.3.4"));
    acceptor.getFilterChain().addLast("blacklist", new BlacklistFilter());
    ...

Here, the "1.2.3.4" address will be blocked. 

## Unblocking an address

It's possible to unblock an address, it's just a matter of fetching the filter and remove a previously blocked addres:

    :::Java
    ...
    BlacklistFilter blackList = (BlacklistFilter)session.getFilterChain().get(BlacklistFilter.class);
    blackList.unblock(InetAddress.getByName("1.2.3.4"));
    ...

Here, the "1.2.3.4" address will be unblocked. 

## Performances

Currently, the implementation is not really optimal... We use a _List_ to store the blocked addresses/subnet, so the more of them you have in the list the longer it will take to process any event.