Attribute.java

// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package io.ebean.enhance.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, as returned by {@link
   * #write(ClassWriter,byte[],int,int,int)}. The 6 header bytes of the attribute
   * (attribute_name_index and attribute_length) are <i>not</i> included.
   */
  private ByteVector cachedContent;

  /**
   * 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 {@literal null}.
   */
  Attribute nextAttribute;

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

  /**
   * Returns {@literal true} 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 {@literal true}.
   *
   * @return {@literal true} if this type of attribute is unknown.
   */
  public boolean isUnknown() {
    return true;
  }

  /**
   * Returns {@literal true} if this type of attribute is a Code attribute.
   *
   * @return {@literal true} 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 {@literal null} if this attribute is not
   *     a Code attribute that contains labels.
   * @deprecated no longer used by ASM.
   */
  @Deprecated(forRemoval = false)
  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}. 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}, 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 {@literal null} if the attribute to be read
   *     is not a Code attribute. Labels defined in the attribute must be created and added to this
   *     array, if not already present, by calling the {@link #readLabel} method (do not create
   *     {@link Label} instances directly).
   * @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.cachedContent = new ByteVector(classReader.readBytes(offset, length));
    return attribute;
  }

  /**
   * Reads an attribute with the same {@link #type} as the given attribute. This method returns a
   * new {@link Attribute} object, corresponding to the 'length' bytes starting at 'offset', in the
   * given ClassReader.
   *
   * @param attribute The attribute prototype that is used for reading.
   * @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}. 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}, 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 {@literal null} if the attribute to be read
   *     is not a Code attribute. Labels defined in the attribute are added to this array, if not
   *     already present.
   * @return a new {@link Attribute} object corresponding to the specified bytes.
   */
  public static Attribute read(
      final Attribute attribute,
      final ClassReader classReader,
      final int offset,
      final int length,
      final char[] charBuffer,
      final int codeAttributeOffset,
      final Label[] labels) {
    return attribute.read(classReader, offset, length, charBuffer, codeAttributeOffset, labels);
  }

  /**
   * Returns the label corresponding to the given bytecode offset by calling {@link
   * ClassReader#readLabel}. This creates and adds the label to the given array if it is not already
   * present. Note that this created label may be a {@link Label} subclass instance, if the given
   * ClassReader overrides {@link ClassReader#readLabel}. Hence {@link #read(ClassReader, int, int,
   * char[], int, Label[])} must not manually create {@link Label} instances.
   *
   * @param classReader the class that contains the attribute to be read.
   * @param bytecodeOffset a bytecode offset in a method.
   * @param labels the already created labels, indexed by their offset. If a label already exists
   *     for bytecodeOffset this method does not create a new one. Otherwise it stores the new label
   *     in this array.
   * @return a label for the given bytecode offset.
   */
  public static Label readLabel(
      final ClassReader classReader, final int bytecodeOffset, final Label[] labels) {
    return classReader.readLabel(bytecodeOffset, labels);
  }

  /**
   * Calls {@link #write(ClassWriter,byte[],int,int,int)} if it has not already been called and
   * returns its result or its (cached) previous result.
   *
   * @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 {@literal null}
   *     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.
   */
  private ByteVector maybeWrite(
      final ClassWriter classWriter,
      final byte[] code,
      final int codeLength,
      final int maxStack,
      final int maxLocals) {
    if (cachedContent == null) {
      cachedContent = write(classWriter, code, codeLength, maxStack, maxLocals);
    }
    return cachedContent;
  }

  /**
   * 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.
   *
   * <p>This method is only invoked once to compute the binary form of this attribute. Subsequent
   * changes to the attribute after it was written for the first time will not be considered.
   *
   * @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 {@literal null}
   *     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 cachedContent;
  }

  /**
   * Returns the byte array form of the content of the given attribute. The 6 header bytes
   * (attribute_name_index and attribute_length) are <i>not</i> added in the returned byte array.
   *
   * @param attribute The attribute that should be written.
   * @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 {@literal null}
   *     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.
   */
  public static byte[] write(
      final Attribute attribute,
      final ClassWriter classWriter,
      final byte[] code,
      final int codeLength,
      final int maxStack,
      final int maxLocals) {
    ByteVector content = attribute.maybeWrite(classWriter, code, codeLength, maxStack, maxLocals);
    byte[] result = new byte[content.length];
    System.arraycopy(content.data, 0, result, 0, content.length);
    return result;
  }

  /**
   * 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 {@literal
   *     null} 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.maybeWrite(classWriter, code, codeLength, maxStack, maxLocals).length;
      attribute = attribute.nextAttribute;
    }
    return size;
  }

  /**
   * Returns the total size in bytes of all the attributes that correspond to the given field,
   * method or class access flags and signature. 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 accessFlags some field, method or class access flags.
   * @param signatureIndex the constant pool index of a field, method of class signature.
   * @return the size of all the attributes in bytes. This size includes the size of the attribute
   *     headers.
   */
  static int computeAttributesSize(
      final SymbolTable symbolTable, final int accessFlags, final int signatureIndex) {
    int size = 0;
    // Before Java 1.5, synthetic fields are represented with a Synthetic attribute.
    if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0
        && symbolTable.getMajorVersion() < Opcodes.V1_5) {
      // Synthetic attributes always use 6 bytes.
      symbolTable.addConstantUtf8(Constants.SYNTHETIC);
      size += 6;
    }
    if (signatureIndex != 0) {
      // Signature attributes always use 8 bytes.
      symbolTable.addConstantUtf8(Constants.SIGNATURE);
      size += 8;
    }
    // ACC_DEPRECATED is ASM specific, the ClassFile format uses a Deprecated attribute instead.
    if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
      // Deprecated attributes always use 6 bytes.
      symbolTable.addConstantUtf8(Constants.DEPRECATED);
      size += 6;
    }
    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 {@literal
   *     null} 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.maybeWrite(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;
    }
  }

  /**
   * Puts all the attributes that correspond to the given field, method or class access flags and
   * signature, 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 accessFlags some field, method or class access flags.
   * @param signatureIndex the constant pool index of a field, method of class signature.
   * @param output where the attributes must be written.
   */
  static void putAttributes(
      final SymbolTable symbolTable,
      final int accessFlags,
      final int signatureIndex,
      final ByteVector output) {
    // Before Java 1.5, synthetic fields are represented with a Synthetic attribute.
    if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0
        && symbolTable.getMajorVersion() < Opcodes.V1_5) {
      output.putShort(symbolTable.addConstantUtf8(Constants.SYNTHETIC)).putInt(0);
    }
    if (signatureIndex != 0) {
      output
          .putShort(symbolTable.addConstantUtf8(Constants.SIGNATURE))
          .putInt(2)
          .putShort(signatureIndex);
    }
    if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
      output.putShort(symbolTable.addConstantUtf8(Constants.DEPRECATED)).putInt(0);
    }
  }

  /** 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;
    }
  }
}