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     * This method adds a (warning) message to the message pool of this PassVerifier. This method is normally only
051     * internally used by BCEL's class file verifier "JustIce" and should not be used from the outside.
052     *
053     * @param message message to be appended to the message list.
054     * @see #getMessages()
055     */
056    public void addMessage(final String message) {
057        messages.add(message);
058    }
059
060    /**
061     * Verifies, not cached.
062     *
063     * @return The VerificationResult.
064     */
065    public abstract VerificationResult do_verify();
066
067    /**
068     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
069     *
070     * @return the (warning) messages.
071     * @see #addMessage(String)
072     * @see #do_verify()
073     */
074    public String[] getMessages() {
075        return getMessagesList().toArray(ArrayUtils.EMPTY_STRING_ARRAY);
076    }
077
078    /**
079     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
080     *
081     * @see #addMessage(String)
082     * @see #do_verify()
083     */
084    public List<String> getMessagesList() {
085        verify(); // create messages if not already done (cached!)
086        return messages;
087    }
088
089    /**
090     * This method runs a verification pass conforming to the Java Virtual Machine Specification, 2nd edition, on a class
091     * file. PassVerifier instances perform caching; for example if the verify() method once determined a VerificationResult, then
092     * this result may be returned after every invocation of this method instead of running the verification pass anew;
093     * likewise with the result of getMessages().
094     *
095     * @return a VerificationResult.
096     * @see #getMessages()
097     * @see #addMessage(String)
098     */
099    public VerificationResult verify() {
100        if (verificationResult == null) {
101            verificationResult = do_verify();
102        }
103        return verificationResult;
104    }
105}