default long getBlobBytesReceived() {
    return 0;
  }
Gets the number of bytes read as part of the blob data at this point in time. After the request has been fully read,
this can be used to determine the full blob size in bytes. The result of this method is only valid for requests
that have blob data in them.
@return the current number of blob bytes read from the request body.
ambry-api/src/main/java/com/github/ambry/rest/RestRequest.java