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Byte Buddy is a Java library for creating Java classes at run time. This artifact is a build of Byte Buddy with all ASM dependencies repackaged into its own name space.
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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 net.bytebuddy.jar.asm.commons;

import java.util.ArrayList;
import java.util.List;
import net.bytebuddy.jar.asm.Attribute;
import net.bytebuddy.jar.asm.ByteVector;
import net.bytebuddy.jar.asm.ClassReader;
import net.bytebuddy.jar.asm.ClassWriter;
import net.bytebuddy.jar.asm.Label;

/**
 * A ModuleHashes attribute. This attribute is specific to the OpenJDK and may change in the future.
 *
 * @author Remi Forax
 */
public final class ModuleHashesAttribute extends Attribute {

  /** The name of the hashing algorithm. */
  public String algorithm;

  /** A list of module names. */
  public List modules;

  /** The hash of the modules in {@link #modules}. The two lists must have the same size. */
  public List hashes;

  /**
   * Constructs a new {@link ModuleHashesAttribute}.
   *
   * @param algorithm the name of the hashing algorithm.
   * @param modules a list of module names.
   * @param hashes the hash of the modules in 'modules'. The two lists must have the same size.
   */
  public ModuleHashesAttribute(
      final String algorithm, final List modules, final List hashes) {
    super("ModuleHashes");
    this.algorithm = algorithm;
    this.modules = modules;
    this.hashes = hashes;
  }

  /**
   * Constructs an empty {@link ModuleHashesAttribute}. This object can be passed as a prototype to
   * the {@link ClassReader#accept(net.bytebuddy.jar.asm.ClassVisitor, Attribute[], int)} method.
   */
  public ModuleHashesAttribute() {
    this(null, null, null);
  }

  @Override
  protected Attribute read(
      final ClassReader classReader,
      final int offset,
      final int length,
      final char[] charBuffer,
      final int codeAttributeOffset,
      final Label[] labels) {
    int currentOffset = offset;

    String hashAlgorithm = classReader.readUTF8(currentOffset, charBuffer);
    currentOffset += 2;

    int numModules = classReader.readUnsignedShort(currentOffset);
    currentOffset += 2;

    ArrayList moduleList = new ArrayList<>(numModules);
    ArrayList hashList = new ArrayList<>(numModules);

    for (int i = 0; i < numModules; ++i) {
      String module = classReader.readModule(currentOffset, charBuffer);
      currentOffset += 2;
      moduleList.add(module);

      int hashLength = classReader.readUnsignedShort(currentOffset);
      currentOffset += 2;
      byte[] hash = new byte[hashLength];
      for (int j = 0; j < hashLength; ++j) {
        hash[j] = (byte) classReader.readByte(currentOffset);
        currentOffset += 1;
      }
      hashList.add(hash);
    }
    return new ModuleHashesAttribute(hashAlgorithm, moduleList, hashList);
  }

  @Override
  protected ByteVector write(
      final ClassWriter classWriter,
      final byte[] code,
      final int codeLength,
      final int maxStack,
      final int maxLocals) {
    ByteVector byteVector = new ByteVector();
    byteVector.putShort(classWriter.newUTF8(algorithm));
    if (modules == null) {
      byteVector.putShort(0);
    } else {
      int numModules = modules.size();
      byteVector.putShort(numModules);
      for (int i = 0; i < numModules; ++i) {
        String module = modules.get(i);
        byte[] hash = hashes.get(i);
        byteVector
            .putShort(classWriter.newModule(module))
            .putShort(hash.length)
            .putByteArray(hash, 0, hash.length);
      }
    }
    return byteVector;
  }
}