xref: /external/protobuf/java/core/src/main/java/com/google/protobuf/UnsafeByteOperations.java

// Protocol Buffers - Google's data interchange format
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package com.google.protobuf;

import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * Provides a number of unsafe byte operations to be used by advanced applications with high
 * performance requirements. These methods are referred to as "unsafe" due to the fact that they
 * potentially expose the backing buffer of a {@link ByteString} to the application.
 *
 * <p><strong>DISCLAIMER:</strong> The methods in this class should only be called if it is
 * guaranteed that the buffer backing the {@link ByteString} will never change! Mutation of a
 * {@link ByteString} can lead to unexpected and undesirable consequences in your application,
 * and will likely be difficult to debug. Proceed with caution!
 */
@ExperimentalApi
public final class UnsafeByteOperations {
  private UnsafeByteOperations() {}

  /**
   * An unsafe operation that returns a {@link ByteString} that is backed by the provided buffer.
   *
   * @param buffer the Java NIO buffer to be wrapped
   * @return a {@link ByteString} backed by the provided buffer
   */
  public static ByteString unsafeWrap(ByteBuffer buffer) {
    if (buffer.hasArray()) {
      final int offset = buffer.arrayOffset();
      return ByteString.wrap(buffer.array(), offset + buffer.position(), buffer.remaining());
    } else {
      return new NioByteString(buffer);
    }
  }

  /**
   * Writes the given {@link ByteString} to the provided {@link ByteOutput}. Calling this method may
   * result in multiple operations on the target {@link ByteOutput}
   * (i.e. for roped {@link ByteString}s).
   *
   * <p>This method exposes the internal backing buffer(s) of the {@link ByteString} to the {@link
   * ByteOutput} in order to avoid additional copying overhead. It would be possible for a malicious
   * {@link ByteOutput} to corrupt the {@link ByteString}. Use with caution!
   *
   * <p> NOTE: The {@link ByteOutput} <strong>MUST NOT</strong> modify the provided buffers. Doing
   * so may result in corrupted data, which would be difficult to debug.
   *
   * @param bytes the {@link ByteString} to be written
   * @param  output  the output to receive the bytes
   * @throws IOException  if an I/O error occurs
   */
  public static void unsafeWriteTo(ByteString bytes, ByteOutput output) throws IOException {
    bytes.writeTo(output);
  }
}