public long updateBytesRead(long delta) {
      return totalBytesRead.addAndGet(delta);
    }
Updates the number of bytes that have been successfully read into the given {@link AsyncWritableChannel}.
@param delta the number of bytes read in the current invocation.
@return the total number of bytes read until now.
ambry-test-utils/src/main/java/com/github/ambry/rest/MockRestRequest.java