src/main/java/org/apache/bcel/classfile/Unknown.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.bcel.classfile;

import java.io.DataInput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.Arrays;

import org.apache.bcel.Const;
import org.apache.commons.lang3.SystemProperties;

/**
 * This class represents a reference to an unknown (that is, application-specific) attribute of a class. It is instantiated
 * from the {@link Attribute#readAttribute(java.io.DataInput, ConstantPool)} method. Applications that need to read in
 * application-specific attributes should create an {@link UnknownAttributeReader} implementation and attach it via
 * {@link Attribute#addAttributeReader(String, UnknownAttributeReader)}.
 *
 * @see Attribute
 * @see UnknownAttributeReader
 */
public final class Unknown extends Attribute {

    /**
     * Arbitrary to limit the maximum length of unknown attributes to avoid OOM errors.
     */
    static final int MAX_LEN = 1_000_000;

    private static final String MAX_LEN_PROP = "BCEL.Attribute.Unknown.max_attribute_length";

    private byte[] bytes;

    private final String name;

    /**
     * Constructs a new instance for a non-standard attribute.
     *
     * @param nameIndex Index in constant pool.
     * @param length Content length in bytes.
     * @param bytes Attribute contents.
     * @param constantPool Array of constants.
     */
    public Unknown(final int nameIndex, final int length, final byte[] bytes, final ConstantPool constantPool) {
        super(Const.ATTR_UNKNOWN, nameIndex, length, constantPool);
        this.bytes = bytes;
        this.name = constantPool.getConstantUtf8(nameIndex).getBytes();
    }

    /**
     * Constructs a new instance from a DataInput.
     * <p>
     * The size of an <a href="https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-4.html#jvms-4.7">Attribute</a> unknown to the JVM specification is
     * limited to 1 MB and is overridden with the system property {@code BCEL.Attribute.Unknown.max_attribute_length}.
     * </p>
     *
     * @param nameIndex    Index in constant pool.
     * @param length       Content length in bytes.
     * @param input        Input stream.
     * @param constantPool Array of constants.
     * @throws IOException if an I/O error occurs.
     * @see <a href="https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-4.html#jvms-4.7">Attribute</a>
     */
    Unknown(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
        this(nameIndex, length, (byte[]) null, constantPool);
        if (length > 0) {
            if (length > SystemProperties.getInt(MAX_LEN_PROP, () -> MAX_LEN)) {
                throw new IOException(
                        String.format("Unknown attribute length %,d > %,d; use the %s system property to increase the limit.", length, MAX_LEN, MAX_LEN_PROP));
            }
            bytes = new byte[length];
            input.readFully(bytes);
        }
    }

    /**
     * Constructs a new instance from another instance. Note that both objects use the same references (shallow copy). Use clone() for a physical copy.
     *
     * @param unknown Source.
     */
    public Unknown(final Unknown unknown) {
        this(unknown.getNameIndex(), unknown.getLength(), unknown.getBytes(), unknown.getConstantPool());
    }

    /**
     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
     *
     * @param v Visitor object.
     */
    @Override
    public void accept(final Visitor v) {
        v.visitUnknown(this);
    }

    /**
     * @return deep copy of this attribute.
     */
    @Override
    public Attribute copy(final ConstantPool constantPool) {
        final Unknown c = (Unknown) clone();
        if (bytes != null) {
            c.bytes = bytes.clone();
        }
        c.setConstantPool(constantPool);
        return c;
    }

    /**
     * Dumps unknown bytes to file stream.
     *
     * @param file Output file stream.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void dump(final DataOutputStream file) throws IOException {
        super.dump(file);
        if (super.getLength() > 0) {
            file.write(bytes, 0, super.getLength());
        }
    }

    /**
     * @return data bytes.
     */
    public byte[] getBytes() {
        return bytes;
    }

    /**
     * @return name of attribute.
     */
    @Override
    public String getName() {
        return name;
    }

    /**
     * @param bytes the bytes to set.
     */
    public void setBytes(final byte[] bytes) {
        this.bytes = bytes;
    }

    /**
     * @return String representation.
     */
    @Override
    public String toString() {
        if (super.getLength() == 0 || bytes == null) {
            return "(Unknown attribute " + name + ")";
        }
        final String hex;
        final int limit = 10;
        if (super.getLength() > limit) {
            final byte[] tmp = Arrays.copyOf(bytes, limit);
            hex = Utility.toHexString(tmp) + "... (truncated)";
        } else {
            hex = Utility.toHexString(bytes);
        }
        return "(Unknown attribute " + name + ": " + hex + ")";
    }
}