@CanIgnoreReturnValue
  @Override
  public synchronized SeekableByteChannel position(long newPosition) {
    plaintextPosition = newPosition;
    return this;
  }
Sets the position in the plaintext. Setting the position to a value greater than the plaintext
size is legal. A later attempt to read byte will throw an IOException.
java_src/src/main/java/com/google/crypto/tink/subtle/StreamingAeadSeekableDecryptingChannel.java