001/***
002 * ASM: a very small and fast Java bytecode manipulation framework
003 * Copyright (c) 2000-2011 INRIA, France Telecom
004 * All rights reserved.
005 *
006 * Redistribution and use in source and binary forms, with or without
007 * modification, are permitted provided that the following conditions
008 * are met:
009 * 1. Redistributions of source code must retain the above copyright
010 *    notice, this list of conditions and the following disclaimer.
011 * 2. Redistributions in binary form must reproduce the above copyright
012 *    notice, this list of conditions and the following disclaimer in the
013 *    documentation and/or other materials provided with the distribution.
014 * 3. Neither the name of the copyright holders nor the names of its
015 *    contributors may be used to endorse or promote products derived from
016 *    this software without specific prior written permission.
017 *
018 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
019 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
020 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
021 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
022 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
023 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
024 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
025 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
026 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
027 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
028 * THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.springframework.asm;
031
032/**
033 * A non standard class, field, method or code attribute.
034 * 
035 * @author Eric Bruneton
036 * @author Eugene Kuleshov
037 */
038public class Attribute {
039
040    /**
041     * The type of this attribute.
042     */
043    public final String type;
044
045    /**
046     * The raw value of this attribute, used only for unknown attributes.
047     */
048    byte[] value;
049
050    /**
051     * The next attribute in this attribute list. May be <tt>null</tt>.
052     */
053    Attribute next;
054
055    /**
056     * Constructs a new empty attribute.
057     * 
058     * @param type
059     *            the type of the attribute.
060     */
061    protected Attribute(final String type) {
062        this.type = type;
063    }
064
065    /**
066     * Returns <tt>true</tt> if this type of attribute is unknown. The default
067     * implementation of this method always returns <tt>true</tt>.
068     * 
069     * @return <tt>true</tt> if this type of attribute is unknown.
070     */
071    public boolean isUnknown() {
072        return true;
073    }
074
075    /**
076     * Returns <tt>true</tt> if this type of attribute is a code attribute.
077     * 
078     * @return <tt>true</tt> if this type of attribute is a code attribute.
079     */
080    public boolean isCodeAttribute() {
081        return false;
082    }
083
084    /**
085     * Returns the labels corresponding to this attribute.
086     * 
087     * @return the labels corresponding to this attribute, or <tt>null</tt> if
088     *         this attribute is not a code attribute that contains labels.
089     */
090    protected Label[] getLabels() {
091        return null;
092    }
093
094    /**
095     * Reads a {@link #type type} attribute. This method must return a
096     * <i>new</i> {@link Attribute} object, of type {@link #type type},
097     * corresponding to the <tt>len</tt> bytes starting at the given offset, in
098     * the given class reader.
099     * 
100     * @param cr
101     *            the class that contains the attribute to be read.
102     * @param off
103     *            index of the first byte of the attribute's content in
104     *            {@link ClassReader#b cr.b}. The 6 attribute header bytes,
105     *            containing the type and the length of the attribute, are not
106     *            taken into account here.
107     * @param len
108     *            the length of the attribute's content.
109     * @param buf
110     *            buffer to be used to call {@link ClassReader#readUTF8
111     *            readUTF8}, {@link ClassReader#readClass(int,char[]) readClass}
112     *            or {@link ClassReader#readConst readConst}.
113     * @param codeOff
114     *            index of the first byte of code's attribute content in
115     *            {@link ClassReader#b cr.b}, or -1 if the attribute to be read
116     *            is not a code attribute. The 6 attribute header bytes,
117     *            containing the type and the length of the attribute, are not
118     *            taken into account here.
119     * @param labels
120     *            the labels of the method's code, or <tt>null</tt> if the
121     *            attribute to be read is not a code attribute.
122     * @return a <i>new</i> {@link Attribute} object corresponding to the given
123     *         bytes.
124     */
125    protected Attribute read(final ClassReader cr, final int off,
126            final int len, final char[] buf, final int codeOff,
127            final Label[] labels) {
128        Attribute attr = new Attribute(type);
129        attr.value = new byte[len];
130        System.arraycopy(cr.b, off, attr.value, 0, len);
131        return attr;
132    }
133
134    /**
135     * Returns the byte array form of this attribute.
136     * 
137     * @param cw
138     *            the class to which this attribute must be added. This
139     *            parameter can be used to add to the constant pool of this
140     *            class the items that corresponds to this attribute.
141     * @param code
142     *            the bytecode of the method corresponding to this code
143     *            attribute, or <tt>null</tt> if this attribute is not a code
144     *            attributes.
145     * @param len
146     *            the length of the bytecode of the method corresponding to this
147     *            code attribute, or <tt>null</tt> if this attribute is not a
148     *            code attribute.
149     * @param maxStack
150     *            the maximum stack size of the method corresponding to this
151     *            code attribute, or -1 if this attribute is not a code
152     *            attribute.
153     * @param maxLocals
154     *            the maximum number of local variables of the method
155     *            corresponding to this code attribute, or -1 if this attribute
156     *            is not a code attribute.
157     * @return the byte array form of this attribute.
158     */
159    protected ByteVector write(final ClassWriter cw, final byte[] code,
160            final int len, final int maxStack, final int maxLocals) {
161        ByteVector v = new ByteVector();
162        v.data = value;
163        v.length = value.length;
164        return v;
165    }
166
167    /**
168     * Returns the length of the attribute list that begins with this attribute.
169     * 
170     * @return the length of the attribute list that begins with this attribute.
171     */
172    final int getCount() {
173        int count = 0;
174        Attribute attr = this;
175        while (attr != null) {
176            count += 1;
177            attr = attr.next;
178        }
179        return count;
180    }
181
182    /**
183     * Returns the size of all the attributes in this attribute list.
184     * 
185     * @param cw
186     *            the class writer to be used to convert the attributes into
187     *            byte arrays, with the {@link #write write} method.
188     * @param code
189     *            the bytecode of the method corresponding to these code
190     *            attributes, or <tt>null</tt> if these attributes are not code
191     *            attributes.
192     * @param len
193     *            the length of the bytecode of the method corresponding to
194     *            these code attributes, or <tt>null</tt> if these attributes
195     *            are not code attributes.
196     * @param maxStack
197     *            the maximum stack size of the method corresponding to these
198     *            code attributes, or -1 if these attributes are not code
199     *            attributes.
200     * @param maxLocals
201     *            the maximum number of local variables of the method
202     *            corresponding to these code attributes, or -1 if these
203     *            attributes are not code attributes.
204     * @return the size of all the attributes in this attribute list. This size
205     *         includes the size of the attribute headers.
206     */
207    final int getSize(final ClassWriter cw, final byte[] code, final int len,
208            final int maxStack, final int maxLocals) {
209        Attribute attr = this;
210        int size = 0;
211        while (attr != null) {
212            cw.newUTF8(attr.type);
213            size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
214            attr = attr.next;
215        }
216        return size;
217    }
218
219    /**
220     * Writes all the attributes of this attribute list in the given byte
221     * vector.
222     * 
223     * @param cw
224     *            the class writer to be used to convert the attributes into
225     *            byte arrays, with the {@link #write write} method.
226     * @param code
227     *            the bytecode of the method corresponding to these code
228     *            attributes, or <tt>null</tt> if these attributes are not code
229     *            attributes.
230     * @param len
231     *            the length of the bytecode of the method corresponding to
232     *            these code attributes, or <tt>null</tt> if these attributes
233     *            are not code attributes.
234     * @param maxStack
235     *            the maximum stack size of the method corresponding to these
236     *            code attributes, or -1 if these attributes are not code
237     *            attributes.
238     * @param maxLocals
239     *            the maximum number of local variables of the method
240     *            corresponding to these code attributes, or -1 if these
241     *            attributes are not code attributes.
242     * @param out
243     *            where the attributes must be written.
244     */
245    final void put(final ClassWriter cw, final byte[] code, final int len,
246            final int maxStack, final int maxLocals, final ByteVector out) {
247        Attribute attr = this;
248        while (attr != null) {
249            ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
250            out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
251            out.putByteArray(b.data, 0, b.length);
252            attr = attr.next;
253        }
254    }
255}