    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 *
    017 */
    018package org.apache.bcel.verifier;
    019
    020import java.util.ArrayList;
    021import java.util.List;
    022
    023import org.apache.commons.lang3.ArrayUtils;
    024
    025/**
    026 * A PassVerifier actually verifies a class file; it is instantiated by a Verifier. The verification should conform with
    027 * a certain pass as described in The Java Virtual Machine Specification, 2nd edition. This book describes four passes.
    028 * Pass one means loading the class and verifying a few static constraints. Pass two actually verifies some other
    029 * constraints that could enforce loading in referenced class files. Pass three is the first pass that actually checks
    030 * constraints in the code array of a method in the class file; it has two parts with the first verifying static
    031 * constraints and the second part verifying structural constraints (where a data flow analysis is used for). The fourth
    032 * pass, finally, performs checks that can only be done at run-time. JustIce does not have a run-time pass, but certain
    033 * constraints that are usually delayed until run-time for performance reasons are also checked during the second part
    034 * of pass three. PassVerifier instances perform caching. That means, if you really want a new verification run of a
    035 * certain pass you must use a new instance of a given PassVerifier.
    036 *
    037 * @see Verifier
    038 * @see #verify()
    039 */
    040public abstract class PassVerifier {
    041
    042    /** The (warning) messages. */
    043    private final List<String> messages = new ArrayList<>();
    044    /** The VerificationResult cache. */
    045    private VerificationResult verificationResult;
    046
    047    /**
    048     * This method adds a (warning) message to the message pool of this PassVerifier. This method is normally only
    049     * internally used by BCEL's class file verifier "JustIce" and should not be used from the outside.
    050     *
    051     * @see #getMessages()
    052     */
    053    public void addMessage(final String message) {
    054        messages.add(message);
    055    }
    056
    057    /** Does the real verification work, uncached. */
    058    public abstract VerificationResult do_verify();
    059
    060    /**
    061     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
    062     *
    063     * @see #addMessage(String)
    064     * @see #do_verify()
    065     */
    066    public String[] getMessages() {
    067        verify(); // create messages if not already done (cached!)
    068        return messages.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
    069    }
    070
    071    /**
    072     * This method runs a verification pass conforming to the Java Virtual Machine Specification, 2nd edition, on a class
    073     * file. PassVerifier instances perform caching; i.e. if the verify() method once determined a VerificationResult, then
    074     * this result may be returned after every invocation of this method instead of running the verification pass anew;
    075     * likewise with the result of getMessages().
    076     *
    077     * @see #getMessages()
    078     * @see #addMessage(String)
    079     */
    080    public VerificationResult verify() {
    081        if (verificationResult == null) {
    082            verificationResult = do_verify();
    083        }
    084        return verificationResult;
    085    }
    086}