PermitOverridesRuleAlg.java

/*
 * @(#)PermitOverridesRuleAlg.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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package com.sun.xacml.combine;

import java.net.URI;
import java.util.Iterator;
import java.util.List;

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

/**
 * This is the standard Permit Overrides rule combining algorithm. It allows a single evaluation of
 * Permit to take precedence over any number of deny, not applicable or indeterminate results. Note
 * that since this implementation does an ordered evaluation, this class also supports the Ordered
 * Permit Overrides algorithm.
 * 
 * @since 1.0
 * @author Seth Proctor
 */
public class PermitOverridesRuleAlg 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:"
            + "permit-overrides";

    // a URI form of the identifier
    private static final URI identifierURI = URI.create(algId);

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

    /**
     * Protected constructor used by the ordered version of this algorithm.
     * 
     * @param identifier
     *            the algorithm's identifier
     */
    protected PermitOverridesRuleAlg(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<? extends CombinerElement> ruleElements) {
        boolean atLeastOneError = false;
        boolean potentialPermit = false;
        boolean atLeastOneDeny = false;
        Result firstIndeterminateResult = null;
        Iterator<? extends 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 PERMIT, then regardless of what
            // else we've seen, we always return PERMIT
            if (value == Result.DECISION_PERMIT)
                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 PERMIT, then we can't let this
                // alg return DENY, since this Rule might have permitted
                // if it could do its stuff
                if (rule.getEffect() == Result.DECISION_PERMIT)
                    potentialPermit = true;
            } else {
                // keep track of whether we had at least one rule that
                // actually pertained to the request
                if (value == Result.DECISION_DENY)
                    atLeastOneDeny = true;
            }
        }

        // we didn't explicitly PERMIT, but we might have had some Rule
        // been evaluated, so we have to return INDETERMINATE
        if (potentialPermit)
            return firstIndeterminateResult;

        // some Rule said DENY, so since nothing could have permitted,
        // we return DENY
        if (atLeastOneDeny)
            return new Result(Result.DECISION_DENY, context.getResourceId().encode());

        // we didn't find anything that said DENY, 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.getResourceId().encode());
    }

}