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}