ASM: a very small and fast Java bytecode manipulation framework
Copyright (c) 2000-2011 INRIA, France Telecom
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/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2011 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 org.objectweb.asm;

A non standard class, field, method or code attribute.
Author:
Eric Bruneton, Eugene Kuleshov/**
 * A non standard class, field, method or code attribute.
 * 
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

    
The type of this attribute.
/**
     * The type of this attribute.
     */
    public final String type;

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

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

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

    
Returns true if this type of attribute is unknown. The default
implementation of this method always returns true.
Returns:
true if this type of attribute is unknown./**
     * 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 true if this type of attribute is a code attribute.
Returns:
true if this type of attribute is a code attribute./**
     * 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.
Returns:
the labels corresponding to this attribute, or null if
        this attribute is not a code attribute that contains labels./**
     * 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 type attribute. This method must return a new Attribute object, of type type, corresponding to the len bytes starting at the given offset, in
the given class reader.
Params:
cr – 
           the class that contains the attribute to be read.
off –  index of the first byte of the attribute's content in cr.b. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.
len – 
           the length of the attribute's content.
buf –  buffer to be used to call 
           readUTF8, readClass or readConst.
codeOff –  index of the first byte of code's attribute content in cr.b, or -1 if the attribute to be read is not a code attribute. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.
labels – 
           the labels of the method's code, or null if the
           attribute to be read is not a code attribute.
Returns:
a new Attribute object corresponding to the given bytes./**
     * 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.
     * @param buf
     *            buffer to be used to call {@link ClassReader#readUTF8
     *            readUTF8}, {@link ClassReader#readClass(int,char[]) readClass}
     *            or {@link ClassReader#readConst readConst}.
     * @param codeOff
     *            index of the first byte of code's attribute content in
     *            {@link ClassReader#b cr.b}, or -1 if the attribute to be read
     *            is not a code attribute. The 6 attribute header bytes,
     *            containing the type and the length of the attribute, are not
     *            taken into account here.
     * @param labels
     *            the labels of the method's code, or <tt>null</tt> if the
     *            attribute to be read is not a code attribute.
     * @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 char[] buf, final int codeOff,
            final Label[] labels) {
        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.
Params:
cw – 
           the class to which this attribute must be added. This
           parameter can be used to add to the constant pool of this
           class the items that corresponds to this attribute.
code – 
           the bytecode of the method corresponding to this code
           attribute, or null if this attribute is not a code
           attributes.
len – 
           the length of the bytecode of the method corresponding to this
           code attribute, or null if this attribute is not a
           code attribute.
maxStack – 
           the maximum stack size of the method corresponding to this
           code attribute, or -1 if this attribute is not a code
           attribute.
maxLocals – 
           the maximum number of local variables of the method
           corresponding to this code attribute, or -1 if this attribute
           is not a code attribute.
Returns:
the byte array form of this attribute./**
     * Returns the byte array form of this attribute.
     * 
     * @param cw
     *            the class to which this attribute must be added. This
     *            parameter can be used to add to the constant pool of this
     *            class the items that corresponds to this attribute.
     * @param code
     *            the bytecode of the method corresponding to this code
     *            attribute, or <tt>null</tt> if this attribute is not a code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to this
     *            code attribute, or <tt>null</tt> if this attribute is not a
     *            code attribute.
     * @param maxStack
     *            the maximum stack size of the method corresponding to this
     *            code attribute, or -1 if this attribute is not a code
     *            attribute.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to this code attribute, or -1 if this attribute
     *            is not a code attribute.
     * @return the byte array form of this attribute.
     */
    protected ByteVector write(final ClassWriter cw, final byte[] code,
            final int len, final int maxStack, final int maxLocals) {
        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.
Returns:
the length of the attribute list that begins with this attribute./**
     * 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.
Params:
cw –  the class writer to be used to convert the attributes into byte arrays, with the write method.
code – 
           the bytecode of the method corresponding to these code
           attributes, or null if these attributes are not code
           attributes.
len – 
           the length of the bytecode of the method corresponding to
           these code attributes, or null if these attributes
           are not code attributes.
maxStack – 
           the maximum stack size of the method corresponding to these
           code attributes, or -1 if these attributes are not code
           attributes.
maxLocals – 
           the maximum number of local variables of the method
           corresponding to these code attributes, or -1 if these
           attributes are not code attributes.
Returns:
the size of all the attributes in this attribute list. This size
        includes the size of the attribute headers./**
     * 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.
     * @param code
     *            the bytecode of the method corresponding to these code
     *            attributes, or <tt>null</tt> if these attributes are not code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to
     *            these code attributes, or <tt>null</tt> if these attributes
     *            are not code attributes.
     * @param maxStack
     *            the maximum stack size of the method corresponding to these
     *            code attributes, or -1 if these attributes are not code
     *            attributes.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to these code attributes, or -1 if these
     *            attributes are not code attributes.
     * @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, final byte[] code, final int len,
            final int maxStack, final int maxLocals) {
        Attribute attr = this;
        int size = 0;
        while (attr != null) {
            cw.newUTF8(attr.type);
            size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
            attr = attr.next;
        }
        return size;
    }

    
Writes all the attributes of this attribute list in the given byte
vector.
Params:
cw –  the class writer to be used to convert the attributes into byte arrays, with the write method.
code – 
           the bytecode of the method corresponding to these code
           attributes, or null if these attributes are not code
           attributes.
len – 
           the length of the bytecode of the method corresponding to
           these code attributes, or null if these attributes
           are not code attributes.
maxStack – 
           the maximum stack size of the method corresponding to these
           code attributes, or -1 if these attributes are not code
           attributes.
maxLocals – 
           the maximum number of local variables of the method
           corresponding to these code attributes, or -1 if these
           attributes are not code attributes.
out – 
           where the attributes must be written./**
     * 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 code
     *            the bytecode of the method corresponding to these code
     *            attributes, or <tt>null</tt> if these attributes are not code
     *            attributes.
     * @param len
     *            the length of the bytecode of the method corresponding to
     *            these code attributes, or <tt>null</tt> if these attributes
     *            are not code attributes.
     * @param maxStack
     *            the maximum stack size of the method corresponding to these
     *            code attributes, or -1 if these attributes are not code
     *            attributes.
     * @param maxLocals
     *            the maximum number of local variables of the method
     *            corresponding to these code attributes, or -1 if these
     *            attributes are not code attributes.
     * @param out
     *            where the attributes must be written.
     */
    final void put(final ClassWriter cw, final byte[] code, final int len,
            final int maxStack, final int maxLocals, final ByteVector out) {
        Attribute attr = this;
        while (attr != null) {
            ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
            out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
            out.putByteArray(b.data, 0, b.length);
            attr = attr.next;
        }
    }
}