code: // ASM: a very small and fast Java bytecode manipulation framework
  // Copyright (c) 2000-2011 INRIA, France Telecom
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  package clojure.asm;
  
  /**
   * A non standard class, field, method or code attribute, as defined in the Java Virtual Machine
   * Specification (JVMS).
   *
   * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7">JVMS
   *     4.7</a>
   * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.3">JVMS
   *     4.7.3</a>
   * @author Eric Bruneton
   * @author Eugene Kuleshov
   */
  public class Attribute {
  
    /** The type of this attribute, also called its name in the JVMS. */
    public final String type;
  
    /**
     * The raw content of this attribute, only used for unknown attributes (see {@link #isUnknown()}).
     * The 6 header bytes of the attribute (attribute_name_index and attribute_length) are <i>not</i>
     * included.
     */
    private byte[] content;
  
    /**
     * The next attribute in this attribute list (Attribute instances can be linked via this field to
     * store a list of class, field, method or code attributes). May be <tt>null</tt>.
     */
    Attribute nextAttribute;
  
    /**
     * 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. This means that the attribute
     * content can't be parsed to extract constant pool references, labels, etc. Instead, the
     * attribute content is read as an opaque byte array, and written back as is. This can lead to
     * invalid attributes, if the content actually contains constant pool references, labels, or other
     * symbolic references that need to be updated when there are changes to the constant pool, the
     * method bytecode, etc. 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 new Label[0];
    }
  
    /**
     * Reads a {@link #type} attribute. This method must return a <i>new</i> {@link Attribute} object,
     * of type {@link #type}, corresponding to the 'length' bytes starting at 'offset', in the given
     * ClassReader.
     *
     * @param classReader the class that contains the attribute to be read.
     * @param offset index of the first byte of the attribute's content in {@link ClassReader#b}. The
     *     6 attribute header bytes (attribute_name_index and attribute_length) are not taken into
     *     account here.
     * @param length the length of the attribute's content (excluding the 6 attribute header bytes).
     * @param charBuffer the buffer to be used to call the ClassReader methods requiring a
     *     'charBuffer' parameter.
     * @param codeAttributeOffset index of the first byte of content of the enclosing Code attribute
     *     in {@link ClassReader#b}, or -1 if the attribute to be read is not a code attribute. The 6
     *     attribute header bytes (attribute_name_index and attribute_length) 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 specified bytes.
     */
    protected Attribute read(
        final ClassReader classReader,
        final int offset,
        final int length,
        final char[] charBuffer,
        final int codeAttributeOffset,
        final Label[] labels) {
      Attribute attribute = new Attribute(type);
      attribute.content = new byte[length];
      System.arraycopy(classReader.b, offset, attribute.content, 0, length);
      return attribute;
    }
  
    /**
     * Returns the byte array form of the content of this attribute. The 6 header bytes
     * (attribute_name_index and attribute_length) must <i>not</i> be added in the returned
     * ByteVector.
     *
     * @param classWriter the class to which this attribute must be added. This parameter can be used
     *     to add the items that corresponds to this attribute to the constant pool of this class.
     * @param code the bytecode of the method corresponding to this code attribute, or <tt>null</tt>
     *     if this attribute is not a code attribute. Corresponds to the 'code' field of the Code
     *     attribute.
     * @param codeLength the length of the bytecode of the method corresponding to this code
     *     attribute, or 0 if this attribute is not a code attribute. Corresponds to the 'code_length'
     *     field of the 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 classWriter,
        final byte[] code,
        final int codeLength,
        final int maxStack,
        final int maxLocals) {
      return new ByteVector(content);
    }
  
    /**
     * Returns the number of attributes of the attribute list that begins with this attribute.
     *
     * @return the number of attributes of the attribute list that begins with this attribute.
     */
    final int getAttributeCount() {
      int count = 0;
      Attribute attribute = this;
      while (attribute != null) {
        count += 1;
        attribute = attribute.nextAttribute;
      }
      return count;
    }
  
    /**
     * Returns the total size in bytes of all the attributes in the attribute list that begins with
     * this attribute. This size includes the 6 header bytes (attribute_name_index and
     * attribute_length) per attribute. Also adds the attribute type names to the constant pool.
     *
     * @param symbolTable where the constants used in the attributes must be stored.
     * @return the size of all the attributes in this attribute list. This size includes the size of
     *     the attribute headers.
     */
    final int computeAttributesSize(final SymbolTable symbolTable) {
      final byte[] code = null;
      final int codeLength = 0;
      final int maxStack = -1;
      final int maxLocals = -1;
      return computeAttributesSize(symbolTable, code, codeLength, maxStack, maxLocals);
    }
  
    /**
     * Returns the total size in bytes of all the attributes in the attribute list that begins with
     * this attribute. This size includes the 6 header bytes (attribute_name_index and
     * attribute_length) per attribute. Also adds the attribute type names to the constant pool.
     *
     * @param symbolTable where the constants used in the attributes must be stored.
     * @param code the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
     *     if they are not code attributes. Corresponds to the 'code' field of the Code attribute.
     * @param codeLength the length of the bytecode of the method corresponding to these code
     *     attributes, or 0 if they are not code attributes. Corresponds to the 'code_length' field of
     *     the Code attribute.
     * @param maxStack the maximum stack size of the method corresponding to these code attributes, or
     *     -1 if they are not code attributes.
     * @param maxLocals the maximum number of local variables of the method corresponding to these
     *     code attributes, or -1 if they are not code attribute.
     * @return the size of all the attributes in this attribute list. This size includes the size of
     *     the attribute headers.
     */
    final int computeAttributesSize(
        final SymbolTable symbolTable,
        final byte[] code,
        final int codeLength,
        final int maxStack,
        final int maxLocals) {
      final ClassWriter classWriter = symbolTable.classWriter;
      int size = 0;
      Attribute attribute = this;
      while (attribute != null) {
        symbolTable.addConstantUtf8(attribute.type);
        size += 6 + attribute.write(classWriter, code, codeLength, maxStack, maxLocals).length;
        attribute = attribute.nextAttribute;
      }
      return size;
    }
  
    /**
     * Puts all the attributes of the attribute list that begins with this attribute, in the given
     * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per
     * attribute.
     *
     * @param symbolTable where the constants used in the attributes must be stored.
     * @param output where the attributes must be written.
     */
    final void putAttributes(final SymbolTable symbolTable, final ByteVector output) {
      final byte[] code = null;
      final int codeLength = 0;
      final int maxStack = -1;
      final int maxLocals = -1;
      putAttributes(symbolTable, code, codeLength, maxStack, maxLocals, output);
    }
  
    /**
     * Puts all the attributes of the attribute list that begins with this attribute, in the given
     * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per
     * attribute.
     *
     * @param symbolTable where the constants used in the attributes must be stored.
     * @param code the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
     *     if they are not code attributes. Corresponds to the 'code' field of the Code attribute.
     * @param codeLength the length of the bytecode of the method corresponding to these code
     *     attributes, or 0 if they are not code attributes. Corresponds to the 'code_length' field of
     *     the Code attribute.
     * @param maxStack the maximum stack size of the method corresponding to these code attributes, or
     *     -1 if they are not code attributes.
     * @param maxLocals the maximum number of local variables of the method corresponding to these
     *     code attributes, or -1 if they are not code attribute.
     * @param output where the attributes must be written.
     */
    final void putAttributes(
        final SymbolTable symbolTable,
        final byte[] code,
        final int codeLength,
        final int maxStack,
        final int maxLocals,
        final ByteVector output) {
      final ClassWriter classWriter = symbolTable.classWriter;
      Attribute attribute = this;
      while (attribute != null) {
        ByteVector attributeContent =
            attribute.write(classWriter, code, codeLength, maxStack, maxLocals);
        // Put attribute_name_index and attribute_length.
        output.putShort(symbolTable.addConstantUtf8(attribute.type)).putInt(attributeContent.length);
        output.putByteArray(attributeContent.data, 0, attributeContent.length);
        attribute = attribute.nextAttribute;
      }
    }
  
    /** A set of attribute prototypes (attributes with the same type are considered equal). */
    static final class Set {
  
      private static final int SIZE_INCREMENT = 6;
  
      private int size;
      private Attribute[] data = new Attribute[SIZE_INCREMENT];
  
      void addAttributes(final Attribute attributeList) {
        Attribute attribute = attributeList;
        while (attribute != null) {
          if (!contains(attribute)) {
            add(attribute);
          }
          attribute = attribute.nextAttribute;
        }
      }
  
      Attribute[] toArray() {
        Attribute[] result = new Attribute[size];
        System.arraycopy(data, 0, result, 0, size);
        return result;
      }
  
      private boolean contains(final Attribute attribute) {
        for (int i = 0; i < size; ++i) {
          if (data[i].type.equals(attribute.type)) {
            return true;
          }
        }
        return false;
      }
  
      private void add(final Attribute attribute) {
        if (size >= data.length) {
          Attribute[] newData = new Attribute[data.length + SIZE_INCREMENT];
          System.arraycopy(data, 0, newData, 0, size);
          data = newData;
        }
        data[size++] = attribute;
      }
    }
  }
  