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
023/**
024 * A PassVerifier actually verifies a class file; it is instantiated
025 * by a Verifier.
026 * The verification should conform with a certain pass as described
027 * in The Java Virtual Machine Specification, 2nd edition.
028 * This book describes four passes. Pass one means loading the
029 * class and verifying a few static constraints. Pass two actually
030 * verifies some other constraints that could enforce loading in
031 * referenced class files. Pass three is the first pass that actually
032 * checks constraints in the code array of a method in the class file;
033 * it has two parts with the first verifying static constraints and
034 * the second part verifying structural constraints (where a data flow
035 * analysis is used for). The fourth pass, finally, performs checks
036 * that can only be done at run-time.
037 * JustIce does not have a run-time pass, but certain constraints that
038 * are usually delayed until run-time for performance reasons are also
039 * checked during the second part of pass three.
040 * PassVerifier instances perform caching.
041 * That means, if you really want a new verification run of a certain
042 * pass you must use a new instance of a given PassVerifier.
043 *
044 * @see Verifier
045 * @see #verify()
046 */
047public abstract class PassVerifier {
048
049    /** The (warning) messages. */
050    private final List<String> messages = new ArrayList<>();
051    /** The VerificationResult cache. */
052    private VerificationResult verificationResult = null;
053
054
055    /**
056     * This method runs a verification pass conforming to the
057     * Java Virtual Machine Specification, 2nd edition, on a
058     * class file.
059     * PassVerifier instances perform caching;
060     * i.e. if the verify() method once determined a VerificationResult,
061     * then this result may be returned after every invocation of this
062     * method instead of running the verification pass anew; likewise with
063     * the result of getMessages().
064     *
065     * @see #getMessages()
066     * @see #addMessage(String)
067     */
068    public VerificationResult verify() {
069        if (verificationResult == null) {
070            verificationResult = do_verify();
071        }
072        return verificationResult;
073    }
074
075
076    /** Does the real verification work, uncached. */
077    public abstract VerificationResult do_verify();
078
079
080    /**
081     * This method adds a (warning) message to the message pool of this
082     * PassVerifier. This method is normally only internally used by
083     * BCEL's class file verifier "JustIce" and should not be used from
084     * the outside.
085     *
086     * @see #getMessages()
087     */
088    public void addMessage( final String message ) {
089        messages.add(message);
090    }
091
092
093    /**
094     * Returns the (warning) messages that this PassVerifier accumulated
095     * during its do_verify()ing work.
096     *
097     * @see #addMessage(String)
098     * @see #do_verify()
099     */
100    public String[] getMessages() {
101        verify(); // create messages if not already done (cached!)
102        return messages.toArray(new String[messages.size()]);
103    }
104}