001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   https://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.bcel.verifier;
020
021import java.util.ArrayList;
022import java.util.List;
023
024import org.apache.commons.lang3.ArrayUtils;
025
026/**
027 * A PassVerifier actually verifies a class file; it is instantiated by a Verifier. The verification should conform with
028 * a certain pass as described in The Java Virtual Machine Specification, 2nd edition. This book describes four passes.
029 * Pass one means loading the class and verifying a few static constraints. Pass two actually verifies some other
030 * constraints that could enforce loading in referenced class files. Pass three is the first pass that actually checks
031 * constraints in the code array of a method in the class file; it has two parts with the first verifying static
032 * constraints and the second part verifying structural constraints (where a data flow analysis is used for). The fourth
033 * pass, finally, performs checks that can only be done at run-time. JustIce does not have a run-time pass, but certain
034 * constraints that are usually delayed until run-time for performance reasons are also checked during the second part
035 * of pass three. PassVerifier instances perform caching. That means, if you really want a new verification run of a
036 * certain pass you must use a new instance of a given PassVerifier.
037 *
038 * @see Verifier
039 * @see #verify()
040 */
041public abstract class PassVerifier {
042
043    /** The (warning) messages. */
044    private final List<String> messages = new ArrayList<>();
045
046    /** The VerificationResult cache. */
047    private VerificationResult verificationResult;
048
049    /**
050     * Constructs a PassVerifier.
051     */
052    public PassVerifier() {
053        // Default constructor for subclasses
054    }
055
056    /**
057     * This method adds a (warning) message to the message pool of this PassVerifier. This method is normally only
058     * internally used by BCEL's class file verifier "JustIce" and should not be used from the outside.
059     *
060     * @param message message to be appended to the message list.
061     * @see #getMessages()
062     */
063    public void addMessage(final String message) {
064        messages.add(message);
065    }
066
067    /**
068     * Verifies, not cached.
069     *
070     * @return The VerificationResult.
071     */
072    public abstract VerificationResult do_verify();
073
074    /**
075     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
076     *
077     * @return The (warning) messages.
078     * @see #addMessage(String)
079     * @see #do_verify()
080     */
081    public String[] getMessages() {
082        return getMessagesList().toArray(ArrayUtils.EMPTY_STRING_ARRAY);
083    }
084
085    /**
086     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
087     *
088     * @return The list of messages.
089     * @see #addMessage(String)
090     * @see #do_verify()
091     */
092    public List<String> getMessagesList() {
093        verify(); // create messages if not already done (cached!)
094        return messages;
095    }
096
097    /**
098     * This method runs a verification pass conforming to the Java Virtual Machine Specification, 2nd edition, on a class
099     * file. PassVerifier instances perform caching; for example if the verify() method once determined a VerificationResult, then
100     * this result may be returned after every invocation of this method instead of running the verification pass anew;
101     * likewise with the result of getMessages().
102     *
103     * @return A VerificationResult.
104     * @see #getMessages()
105     * @see #addMessage(String)
106     */
107    public VerificationResult verify() {
108        if (verificationResult == null) {
109            verificationResult = do_verify();
110        }
111        return verificationResult;
112    }
113}