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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
There is a newer version: 9.1.6
/*
 * ProGuardCORE -- library to process Java bytecode.
 *
 * Copyright (c) 2002-2020 Guardsquare NV
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package proguard.classfile.editor;

import proguard.classfile.*;
import proguard.classfile.attribute.*;

/**
 * This class can add and delete attributes to and from classes, fields, methods, and code
 * attributes. Attributes to be added must be filled out beforehand, including their references to
 * the constant pool. Existing attributes of the same type are always replaced.
 *
 * @author Eric Lafortune
 */
public class AttributesEditor {
  private final ProgramClass targetClass;
  private final ProgramMember targetMember;
  private final CodeAttribute targetAttribute;
  private final boolean replaceAttributes;

  /** Creates a new AttributeAdder that will edit attributes in the given target class. */
  public AttributesEditor(ProgramClass targetClass, boolean replaceAttributes) {
    this(targetClass, null, null, replaceAttributes);
  }

  /** Creates a new AttributeAdder that will edit attributes in the given target class member. */
  public AttributesEditor(
      ProgramClass targetClass, ProgramMember targetMember, boolean replaceAttributes) {
    this(targetClass, targetMember, null, replaceAttributes);
  }

  /** Creates a new AttributeAdder that will edit attributes in the given target code attribute. */
  public AttributesEditor(
      ProgramClass targetClass,
      ProgramMember targetMember,
      CodeAttribute targetAttribute,
      boolean replaceAttributes) {
    this.targetClass = targetClass;
    this.targetMember = targetMember;
    this.targetAttribute = targetAttribute;
    this.replaceAttributes = replaceAttributes;
  }

  /** Finds the specified attribute in the target. */
  public Attribute findAttribute(String attributeName) {
    // What's the target?
    return targetAttribute != null
        ? findAttribute(
            targetAttribute.u2attributesCount, targetAttribute.attributes, attributeName)
        : targetMember != null
            ? findAttribute(targetMember.u2attributesCount, targetMember.attributes, attributeName)
            : findAttribute(targetClass.u2attributesCount, targetClass.attributes, attributeName);
  }

  /** Adds the given attribute to the target. */
  public void addAttribute(Attribute attribute) {
    // What's the target?
    if (targetAttribute != null) {
      // Try to replace an existing attribute.
      if (!replaceAttributes
          || !replaceAttribute(
              targetAttribute.u2attributesCount, targetAttribute.attributes, attribute)) {
        // Otherwise append the attribute.
        targetAttribute.attributes =
            addAttribute(targetAttribute.u2attributesCount, targetAttribute.attributes, attribute);

        targetAttribute.u2attributesCount++;
      }
    } else if (targetMember != null) {
      // Try to replace an existing attribute.
      if (!replaceAttributes
          || !replaceAttribute(
              targetMember.u2attributesCount, targetMember.attributes, attribute)) {
        // Otherwise append the attribute.
        targetMember.attributes =
            addAttribute(targetMember.u2attributesCount, targetMember.attributes, attribute);

        targetMember.u2attributesCount++;
      }
    } else {
      // Try to replace an existing attribute.
      if (!replaceAttributes
          || !replaceAttribute(targetClass.u2attributesCount, targetClass.attributes, attribute)) {
        // Otherwise append the attribute.
        targetClass.attributes =
            addAttribute(targetClass.u2attributesCount, targetClass.attributes, attribute);

        targetClass.u2attributesCount++;
      }
    }
  }

  /** Deletes the specified attribute from the target. */
  public void deleteAttribute(String attributeName) {
    // What's the target?
    if (targetAttribute != null) {
      targetAttribute.u2attributesCount =
          deleteAttribute(
              targetAttribute.u2attributesCount, targetAttribute.attributes, attributeName);
    } else if (targetMember != null) {
      targetMember.u2attributesCount =
          deleteAttribute(targetMember.u2attributesCount, targetMember.attributes, attributeName);
    } else {
      targetClass.u2attributesCount =
          deleteAttribute(targetClass.u2attributesCount, targetClass.attributes, attributeName);
    }
  }

  // Small utility methods.

  /**
   * Tries to put the given attribute in place of an existing attribute of the same name, returning
   * whether it was present.
   */
  private boolean replaceAttribute(
      int attributesCount, Attribute[] attributes, Attribute attribute) {
    // Find the attribute with the same name.
    int index =
        findAttributeIndex(attributesCount, attributes, attribute.getAttributeName(targetClass));
    if (index < 0) {
      return false;
    }

    attributes[index] = attribute;

    return true;
  }

  /**
   * Appends the given attribute to the given array of attributes, creating a new array if
   * necessary.
   */
  private Attribute[] addAttribute(
      int attributesCount, Attribute[] attributes, Attribute attribute) {
    // Is the array too small to contain the additional attribute?
    if (attributes.length <= attributesCount) {
      // Create a new array and copy the attributes into it.
      Attribute[] newAttributes = new Attribute[attributesCount + 1];
      System.arraycopy(attributes, 0, newAttributes, 0, attributesCount);
      attributes = newAttributes;
    }

    // Append the attribute.
    attributes[attributesCount] = attribute;

    return attributes;
  }

  /**
   * Deletes the attributes with the given name from the given array of attributes, returning the
   * new number of attributes.
   */
  private int deleteAttribute(int attributesCount, Attribute[] attributes, String attributeName) {
    // Find the attribute.
    int index = findAttributeIndex(attributesCount, attributes, attributeName);
    if (index < 0) {
      return attributesCount;
    }

    // Shift the other attributes in the array.
    System.arraycopy(attributes, index + 1, attributes, index, attributesCount - index - 1);

    // Clear the last entry in the array.
    attributes[--attributesCount] = null;

    return attributesCount;
  }

  /** Finds the index of the attribute with the given name in the given array of attributes. */
  private int findAttributeIndex(
      int attributesCount, Attribute[] attributes, String attributeName) {
    for (int index = 0; index < attributesCount; index++) {
      Attribute attribute = attributes[index];

      if (attribute.getAttributeName(targetClass).equals(attributeName)) {
        return index;
      }
    }

    return -1;
  }

  /** Finds the attribute with the given name in the given array of attributes. */
  private Attribute findAttribute(
      int attributesCount, Attribute[] attributes, String attributeName) {
    for (int index = 0; index < attributesCount; index++) {
      Attribute attribute = attributes[index];

      if (attribute.getAttributeName(targetClass).equals(attributeName)) {
        return attribute;
      }
    }

    return null;
  }
}