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 */
017package org.apache.bcel.verifier;
018
019import java.util.ArrayList;
020import java.util.List;
021
022import org.apache.commons.lang3.ArrayUtils;
023
024/**
025 * A PassVerifier actually verifies a class file; it is instantiated by a Verifier. The verification should conform with
026 * a certain pass as described in The Java Virtual Machine Specification, 2nd edition. This book describes four passes.
027 * Pass one means loading the class and verifying a few static constraints. Pass two actually verifies some other
028 * constraints that could enforce loading in referenced class files. Pass three is the first pass that actually checks
029 * constraints in the code array of a method in the class file; it has two parts with the first verifying static
030 * constraints and the second part verifying structural constraints (where a data flow analysis is used for). The fourth
031 * pass, finally, performs checks that can only be done at run-time. JustIce does not have a run-time pass, but certain
032 * constraints that are usually delayed until run-time for performance reasons are also checked during the second part
033 * of pass three. PassVerifier instances perform caching. That means, if you really want a new verification run of a
034 * certain pass you must use a new instance of a given PassVerifier.
035 *
036 * @see Verifier
037 * @see #verify()
038 */
039public abstract class PassVerifier {
040
041    /** The (warning) messages. */
042    private final List<String> messages = new ArrayList<>();
043    /** The VerificationResult cache. */
044    private VerificationResult verificationResult;
045
046    /**
047     * This method adds a (warning) message to the message pool of this PassVerifier. This method is normally only
048     * internally used by BCEL's class file verifier "JustIce" and should not be used from the outside.
049     *
050     * @param message message to be appended to the message list.
051     * @see #getMessages()
052     */
053    public void addMessage(final String message) {
054        messages.add(message);
055    }
056
057    /**
058     * Verifies, not cached.
059     *
060     * @return The VerificationResult
061     */
062    public abstract VerificationResult do_verify();
063
064    /**
065     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
066     *
067     * @return the (warning) messages.
068     * @see #addMessage(String)
069     * @see #do_verify()
070     */
071    public String[] getMessages() {
072        return getMessagesList().toArray(ArrayUtils.EMPTY_STRING_ARRAY);
073    }
074
075    /**
076     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
077     *
078     * @see #addMessage(String)
079     * @see #do_verify()
080     */
081    public List<String> getMessagesList() {
082        verify(); // create messages if not already done (cached!)
083        return messages;
084    }
085
086    /**
087     * This method runs a verification pass conforming to the Java Virtual Machine Specification, 2nd edition, on a class
088     * file. PassVerifier instances perform caching; i.e. if the verify() method once determined a VerificationResult, then
089     * this result may be returned after every invocation of this method instead of running the verification pass anew;
090     * likewise with the result of getMessages().
091     *
092     * @return a VerificationResult.
093     * @see #getMessages()
094     * @see #addMessage(String)
095     */
096    public VerificationResult verify() {
097        if (verificationResult == null) {
098            verificationResult = do_verify();
099        }
100        return verificationResult;
101    }
102}