SecureBPMN/GenericBreakGlass-XACML/src/com.sun.xacml/src/main/java/com/sun/xacml/combine/DenyOverridesPolicyAlg.java

/*
 * @(#)DenyOverridesPolicyAlg.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
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 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package com.sun.xacml.combine;

import com.sun.xacml.AbstractPolicy;
import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.MatchResult;
import com.sun.xacml.Obligation;

import com.sun.xacml.ctx.Result;

import java.net.URI;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;


/**
 * This is the standard Deny Overrides policy combining algorithm. It
 * allows a single evaluation of Deny to take precedence over any number
 * of permit, not applicable or indeterminate results. Note that since
 * this implementation does an ordered evaluation, this class also
 * supports the Ordered Deny Overrides algorithm.
 *
 * @since 1.0
 * @author Seth Proctor
 */
public class DenyOverridesPolicyAlg extends PolicyCombiningAlgorithm
{

    /**
     * The standard URN used to identify this algorithm
     */
    public static final String algId =
        "urn:oasis:names:tc:xacml:1.0:policy-combining-algorithm:" +
        "deny-overrides";

    // a URI form of the identifier
    private static URI identifierURI;
    // exception if the URI was invalid, which should never be a problem
    private static RuntimeException earlyException;

    static {
        try {
            identifierURI = URI.create(algId);
        } catch (IllegalArgumentException e) {
            earlyException = e;
        }
    }

    /**
     * Standard constructor.
     */
    public DenyOverridesPolicyAlg() {
        super(identifierURI);

        if (earlyException != null) {
            throw earlyException;
        }
    }

    /**
     * Protected constructor used by the ordered version of this algorithm.
     *
     * @param identifier the algorithm's identifier
     */
    protected DenyOverridesPolicyAlg(URI identifier) {
        super(identifier);
    }

    /**
     * Applies the combining rule to the set of policies based on the
     * evaluation context.
     *
     * @param context the context from the request
     * @param parameters a (possibly empty) non-null <code>List</code> of
     *                   <code>CombinerParameter<code>s
     * @param policyElements the policies to combine
     *
     * @return the result of running the combining algorithm
     */
    public Result combine(EvaluationCtx context, List<CombinerParameter> parameters,
    						List<CombinerElement> policyElements) {
        boolean atLeastOnePermit = false;
        Set<Obligation> permitObligations = new HashSet<Obligation>();
        Iterator<CombinerElement> it = policyElements.iterator();

        while (it.hasNext()) {
            AbstractPolicy policy = ((PolicyCombinerElement) it.next()).getPolicy();

            // make sure that the policy matches the context
            context.newEvent(policy);
            MatchResult match = policy.match(context);

            if (match.getResult() == MatchResult.INDETERMINATE) {
                Result result = new Result(Result.DECISION_DENY, context);
                context.closeCurrentEvent(result);
                return result;
            }
            
            if (match.getResult() == MatchResult.NO_MATCH) {
                context.closeCurrentEvent(
                        new Result(Result.DECISION_NOT_APPLICABLE));
            }

            if (match.getResult() == MatchResult.MATCH) {
                // evaluate the policy
                Result result = policy.evaluate(context);
                context.closeCurrentEvent(result);
                // do not treat the discarded values
                if (result != null) {
                    int effect = result.getDecision();
                
                    // unlike in the RuleCombining version of this alg, we
                    // always return DENY if any Policy returns DENY or
                    // INDETERMINATE
                    if ((effect == Result.DECISION_DENY) ||
                            (effect == Result.DECISION_INDETERMINATE)) {
                        return new Result(Result.DECISION_DENY,
                                          context,
                                          result.getObligations());
                    }
                
                    // remember if at least one Policy said PERMIT
                    if (effect == Result.DECISION_PERMIT) {
                        atLeastOnePermit = true;
                        permitObligations.addAll(result.getObligations());
                    }
                }
            }
        }
        
        // if we got a PERMIT, return it, otherwise it's NOT_APPLICABLE
        if (atLeastOnePermit) {
            return new Result(Result.DECISION_PERMIT,
                              context,
                              permitObligations);
        }
        return new Result(Result.DECISION_NOT_APPLICABLE,
                          context);
    }

}