SignedBlob.java

/**
 * Copyright (C) 2013-2017 Regents of the University of California.
 * @author: Jeff Thompson <jefft0@remap.ucla.edu>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * A copy of the GNU Lesser General Public License is in the file COPYING.
 */

package net.named_data.jndn.util;

import java.nio.ByteBuffer;

/**
 * A SignedBlob extends Blob to keep the offsets of a signed portion (e.g., the
 * bytes of Data packet).
 * This inherits from Blob, including Blob.size and Blob.buf.
 */
public class SignedBlob extends Blob {
  /**
   * Create a new SignedBlob with a null pointer and 0 for the offsets.
   */
  public
  SignedBlob()
  {
  }

  /**
   * Create a new SignedBlob as a copy of the given signedBlob.
   * @param signedBlob The SignedBlob to copy.
   */
  public
  SignedBlob(SignedBlob signedBlob)
  {
    super(signedBlob.buf(), false);
    signedPortionBeginOffset_ = signedBlob.signedPortionBeginOffset_;
    signedPortionEndOffset_ = signedBlob.signedPortionEndOffset_;
    setSignedBuffer();
  }

  /**
   * Create a new SignedBlob and take another pointer to the given blob's
   * buffer.
   * @param blob The Blob from which we take another pointer to the same buffer.
   * @param signedPortionBeginOffset The offset in the buffer of the beginning
   * of the signed portion.
   * @param signedPortionEndOffset The offset in the buffer of the end of the
   * signed portion.
   */
  public
  SignedBlob
    (Blob blob, int signedPortionBeginOffset, int signedPortionEndOffset)
  {
    super(blob);
    signedPortionBeginOffset_ = signedPortionBeginOffset;
    signedPortionEndOffset_ = signedPortionEndOffset;
    setSignedBuffer();
  }

  /**
   * Create a new SignedBlob from an existing ByteBuffer.  IMPORTANT: If copy
   * is false,
   * after calling this constructor, if you keep a pointer to the buffer then
   * you must treat it as immutable and promise not to change it.
   * @param buffer The existing ByteBuffer.  It is important that the buffer
   * position and limit are correct.
   * @param copy If true, copy the contents into a new byte array.  If false,
   * just take a slice which uses the existing byte array in buffer.
   * @param signedPortionBeginOffset The offset in the buffer of the beginning
   * of the signed portion.
   * @param signedPortionEndOffset The offset in the buffer of the end of the
   * signed portion.
   */
  public
  SignedBlob
    (ByteBuffer buffer, boolean copy, int signedPortionBeginOffset,
     int signedPortionEndOffset)
  {
    super(buffer, copy);
    signedPortionBeginOffset_ = signedPortionBeginOffset;
    signedPortionEndOffset_ = signedPortionEndOffset;
    setSignedBuffer();
  }

  /**
   * Create a new SignedBlob from the the byte array. IMPORTANT: If copy is false,
   * after calling this constructor, if you keep a pointer to the buffer then
   * you must treat it as immutable and promise not to change it.
   * @param value The byte array. If copy is true, this makes a copy.
   * @param copy If true, copy the contents into a new byte array.  If false,
   * just use ByteBuffer.wrap which uses the existing byte array.
   * @param signedPortionBeginOffset The offset in the buffer of the beginning
   * of the signed portion.
   * @param signedPortionEndOffset The offset in the buffer of the end of the
   * signed portion.
   */
  public
  SignedBlob
    (byte[] value, boolean copy, int signedPortionBeginOffset, int signedPortionEndOffset)
  {
    super(value, copy);
    signedPortionBeginOffset_ = signedPortionBeginOffset;
    signedPortionEndOffset_ = signedPortionEndOffset;
    setSignedBuffer();
  }

  /**
   * Get the length of the signed portion of the immutable byte buffer.
   * @return The length of the signed portion, or 0 if the pointer is null.
   */
  public final int
  signedSize()
  {
    if (signedBuffer_ != null)
      return signedBuffer_.limit();
    else
      return 0;
  }

  /**
   * Get a new read-only ByteBuffer for the signed portion of the byte buffer.
   * @return The new ByteBuffer, or null if the pointer is null.
   */
  public final ByteBuffer
  signedBuf()
  {
    if (signedBuffer_ != null)
      // We call asReadOnlyBuffer each time because it is still allowed to
      //   change the position and limit on a read-only buffer, and we don't
      //   want the caller to modify our buffer_.
      return signedBuffer_.asReadOnlyBuffer();
    else
      return null;
  }

  /**
   * Set up signedBuffer_ to a slice of buf() based on signedPortionBeginOffset_
   * and signedPortionEndOffset_.
   */
  private void
  setSignedBuffer()
  {
    if (!isNull()) {
      // Note that the result of buf() is already a separate ByteBuffer, so it
      //   is OK to change the position.
      ByteBuffer tempBuffer = buf();
      tempBuffer.position(signedPortionBeginOffset_);
      tempBuffer.limit(signedPortionEndOffset_);
      // Get a slice which is limited to the signed portion.
      signedBuffer_ = tempBuffer.slice();
    }
    else
      signedBuffer_ = null;
  }

  private ByteBuffer signedBuffer_;
  private int signedPortionBeginOffset_;
  private int signedPortionEndOffset_;
}