/*
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* Filter.hh
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*
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* Copyright 2001, LifeLine Networks BV (www.lifeline.nl). All rights reserved.
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* Copyright 2001, Bastiaan Bakker. All rights reserved.
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*
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* See the COPYING file for the terms of usage and distribution.
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*/
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#ifndef _LOG4CPP_FILTER_HH
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#define _LOG4CPP_FILTER_HH
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#include <log4cpp/Portability.hh>
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#include <log4cpp/LoggingEvent.hh>
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namespace log4cpp {
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/**
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Users should extend this class to implement customized logging
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event filtering. Note that log4cpp::Category and
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lof4cpp::Appender have built-in filtering rules. It is suggested
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that you first use and understand the built-in rules before rushing
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to write your own custom filters.
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<p>This abstract class assumes and also imposes that filters be
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organized in a linear chain. The <code>decide(LoggingEvent)</code>
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method of each filter is called sequentially, in the order of their
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addition to the chain.
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<p>The <code>decide(LoggingEvent)</code> method must return a
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Decision value, either DENY, NEUTRAL or ACCCEPT.
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<p>If the value DENY is returned, then the log event is
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dropped immediately without consulting with the remaining
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filters.
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<p>If the value NEUTRAL is returned, then the next filter
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in the chain is consulted. If there are no more filters in the
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chain, then the log event is logged. Thus, in the presence of no
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filters, the default behaviour is to log all logging events.
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<p>If the value ACCEPT is returned, then the log
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event is logged without consulting the remaining filters.
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<p>The philosophy of log4cpp filters is largely inspired from the
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Linux ipchains.
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**/
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class LOG4CPP_EXPORT Filter {
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public:
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typedef enum { DENY = -1,
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NEUTRAL = 0,
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ACCEPT = 1
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} Decision;
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/**
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* Default Constructor for Filter
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**/
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Filter();
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/**
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* Destructor for Filter
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**/
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virtual ~Filter();
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/**
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* Set the next Filter in the Filter chain
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* @param filter The filter to chain
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**/
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virtual void setChainedFilter(Filter* filter);
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/**
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* Get the next Filter in the Filter chain
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* @return The next Filter or NULL if the current filter is the last
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* in the chain
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**/
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virtual Filter* getChainedFilter();
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/**
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* Get the last Filter in the Filter chain
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* @return The last Filter in the Filter chain
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**/
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virtual Filter* getEndOfChain();
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/**
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* Add a Filter to the end of the Filter chain. Convience method for
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* getEndOfChain()->setChainedFilter(filter).
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* @param filter The filter to add to the end of the chain.
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**/
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virtual void appendChainedFilter(Filter* filter);
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/**
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* Decide whether to accept or deny a LoggingEvent. This method will
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* walk the entire chain until a non neutral decision has been made
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* or the end of the chain has been reached.
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* @param event The LoggingEvent to decide on.
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* @return The Decision
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**/
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virtual Decision decide(const LoggingEvent& event);
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protected:
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/**
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* Decide whether <b>this</b> Filter accepts or denies the given
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* LoggingEvent. Actual implementation of Filter should override this
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* method and not <code>decide(LoggingEvent&)</code>.
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* @param event The LoggingEvent to decide on.
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* @return The Decision
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**/
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virtual Decision _decide(const LoggingEvent& event) = 0;
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private:
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Filter* _chainedFilter;
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};
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}
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#endif // _LOG4CPP_FILTER_HH
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