private void handleResponseComplete(@Nullable Throwable cause) {
            if (cause == null || !req.isOpen()) {
                req.abort(ResponseCompleteException.get());
            } else {
                req.abort(cause);
            }
            handleRequestOrResponseComplete();
        }
Sets the 'content-length' header to the response.
core/src/main/java/com/linecorp/armeria/server/HttpServerHandler.java