SecureBPMN/designer/src/com.sun.xacml/src/main/java/com/sun/xacml/combine/DenyOverridesRuleAlg.java

/*
 * @(#)DenyOverridesRuleAlg.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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 * This software is provided "AS IS," without a warranty of any kind. ALL
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package com.sun.xacml.combine;

import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.Rule;

import com.sun.xacml.ctx.Result;

import java.net.URI;

import java.util.Iterator;
import java.util.List;


/**
 * This is the standard Deny Overrides rule 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 DenyOverridesRuleAlg extends RuleCombiningAlgorithm
{

    /**
     * The standard URN used to identify this algorithm
     */
    public static final String algId =
        "urn:oasis:names:tc:xacml:1.0:rule-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 DenyOverridesRuleAlg() {
        super(identifierURI);

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

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

    /**
     * Applies the combining rule to the set of rules 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 ruleElements the rules to combine
     *
     * @return the result of running the combining algorithm
     */
    public Result combine(EvaluationCtx context, List<CombinerParameter> parameters,
                          List<CombinerElement> ruleElements) {
        boolean atLeastOneError = false;
        boolean potentialDeny = false;
        boolean atLeastOnePermit = false;
        Result firstIndeterminateResult = null;
        Iterator<CombinerElement> it = ruleElements.iterator();

        while (it.hasNext()) {
            Rule rule = ((RuleCombinerElement)(it.next())).getRule();
            Result result = rule.evaluate(context);
            int value = result.getDecision();
            
            // if there was a value of DENY, then regardless of what else
            // we've seen, we always return DENY
            if (value == Result.DECISION_DENY) {
                return result;
            }
            
            // if it was INDETERMINATE, then we couldn't figure something
            // out, so we keep track of these cases...
            if (value == Result.DECISION_INDETERMINATE) {
                atLeastOneError = true;

                // there are no rules about what to do if multiple cases
                // cause errors, so we'll just return the first one
                if (firstIndeterminateResult == null) {
                    firstIndeterminateResult = result;
                }

                // if the Rule's effect is DENY, then we can't let this
                // alg return PERMIT, since this Rule might have denied
                // if it could do its stuff
                if (rule.getEffect() == Result.DECISION_DENY) {
                    potentialDeny = true;
                }
            } else {
                // keep track of whether we had at least one rule that
                // actually pertained to the request
                if (value == Result.DECISION_PERMIT) {
                    atLeastOnePermit = true;
                }
            }
        }
        
        // we didn't explicitly DENY, but we might have had some Rule
        // been evaluated, so we have to return INDETERMINATE
        if (potentialDeny) {
            return firstIndeterminateResult;
        }
        
        // some Rule said PERMIT, so since nothing could have denied,
        // we return PERMIT
        if (atLeastOnePermit) {
            return new Result(Result.DECISION_PERMIT,
                              context);
        }
        
        // we didn't find anything that said PERMIT, but if we had a
        // problem with one of the Rules, then we're INDETERMINATE
        if (atLeastOneError) {
            return firstIndeterminateResult;
        }
        
        // if we hit this point, then none of the rules actually applied
        // to us, so we return NOT_APPLICABLE
        return new Result(Result.DECISION_NOT_APPLICABLE,
                          context);
    }

}