Attribute.java

/***
 * ASM: a very small and fast Java bytecode manipulation framework Copyright (c)
 * 2000-2007 INRIA, France Telecom All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer. 2. Redistributions in
 * binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other
 * materials provided with the distribution. 3. Neither the name of the
 * copyright holders nor the names of its contributors may be used to endorse or
 * promote products derived from this software without specific prior written
 * permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package jdave.org.objectweb.asm;

/**
 * A non standard class, field, method or code attribute.
 * 
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {
    /**
     * The type of this attribute.
     */
    public final String type;

    /**
     * The raw value of this attribute, used only for unknown attributes.
     */
    byte[] value;

    /**
     * The next attribute in this attribute list. May be <tt>null</tt>.
     */
    Attribute next;

    /**
     * Constructs a new empty attribute.
     * 
     * @param type
     *            the type of the attribute.
     */
    protected Attribute(final String type) {
        this.type = type;
    }

    /**
     * Returns <tt>true</tt> if this type of attribute is unknown. The default
     * implementation of this method always returns <tt>true</tt>.
     * 
     * @return <tt>true</tt> if this type of attribute is unknown.
     */
    public boolean isUnknown() {
        return true;
    }

    /**
     * Returns <tt>true</tt> if this type of attribute is a code attribute.
     * 
     * @return <tt>true</tt> if this type of attribute is a code attribute.
     */
    public boolean isCodeAttribute() {
        return false;
    }

    /**
     * Returns the labels corresponding to this attribute.
     * 
     * @return the labels corresponding to this attribute, or <tt>null</tt> if
     *         this attribute is not a code attribute that contains labels.
     */
    protected Label[] getLabels() {
        return null;
    }

    /**
     * Reads a {@link #type type} attribute. This method must return a
     * <i>new</i> {@link Attribute} object, of type {@link #type type},
     * corresponding to the <tt>len</tt> bytes starting at the given offset, in
     * the given class reader.
     * 
     * @param cr
     *            the class that contains the attribute to be read.
     * @param off
     *            index of the first byte of the attribute's content in
     *            {@link ClassReader#b cr.b}. The 6 attribute header bytes,
     *            containing the type and the length of the attribute, are not
     *            taken into account here.
     * @param len
     *            the length of the attribute's content.
     * @return a <i>new</i> {@link Attribute} object corresponding to the given
     *         bytes.
     */
    protected Attribute read(final ClassReader cr, final int off, final int len) {
        final Attribute attr = new Attribute(type);
        attr.value = new byte[len];
        System.arraycopy(cr.b, off, attr.value, 0, len);
        return attr;
    }

    /**
     * Returns the byte array form of this attribute.
     * 
     * @return the byte array form of this attribute.
     */
    protected ByteVector write() {
        final ByteVector v = new ByteVector();
        v.data = value;
        v.length = value.length;
        return v;
    }

    /**
     * Returns the length of the attribute list that begins with this attribute.
     * 
     * @return the length of the attribute list that begins with this attribute.
     */
    final int getCount() {
        int count = 0;
        Attribute attr = this;
        while (attr != null) {
            count += 1;
            attr = attr.next;
        }
        return count;
    }

    /**
     * Returns the size of all the attributes in this attribute list.
     * 
     * @param cw
     *            the class writer to be used to convert the attributes into
     *            byte arrays, with the {@link #write write} method.
     * @return the size of all the attributes in this attribute list. This size
     *         includes the size of the attribute headers.
     */
    final int getSize(final ClassWriter cw) {
        Attribute attr = this;
        int size = 0;
        while (attr != null) {
            cw.newUTF8(attr.type);
            size += attr.write().length + 6;
            attr = attr.next;
        }
        return size;
    }

    /**
     * Writes all the attributes of this attribute list in the given byte
     * vector.
     * 
     * @param cw
     *            the class writer to be used to convert the attributes into
     *            byte arrays, with the {@link #write write} method.
     * @param out
     *            where the attributes must be written.
     */
    final void put(final ClassWriter cw, final ByteVector out) {
        Attribute attr = this;
        while (attr != null) {
            final ByteVector b = attr.write();
            out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
            out.putByteArray(b.data, 0, b.length);
            attr = attr.next;
        }
    }
}