@Override
  public long getBlobBytesReceived() {
    return bytesReceived.get();
  }
{@inheritDoc}
<p/>
This function can only be called once the channel has been emptied.
@return the digest as computed by the digest algorithm set through {@link #setDigestAlgorithm(String)}. If none
was set, {@code null}.
@throws IllegalStateException if called before the channel has been emptied.
ambry-rest/src/main/java/com/github/ambry/rest/NettyRequest.java