code: public final void handleMessageSent(HttpRequestContext context, long bytes) {
      checkNotNull(context, "context");
      context.sentMessageSize.addAndGet(bytes);
      if (context.span.getOptions().contains(Options.RECORD_EVENTS)) {
        // record compressed size
        recordMessageEvent(context.span, context.sentSeqId.addAndGet(1L), Type.SENT, bytes, 0L);
      }
    }
docs: Instrument an HTTP span after a message is sent. Typically called for every chunk of request or
  response is sent.
  
  @param context request specific {@link HttpRequestContext}
  @param bytes bytes sent.
  @since 0.19