import 'package:content_length_validator/content_length_validator.dart';

  var handler = const Pipeline()
      .addMiddleware(
        maxContentLengthValidator(
          maxContentLength: YOUR_CONTENT_LENGTH,
        ),
      )
      .addMiddleware(logRequests())
      .addHandler(_echoRequest);

import 'package:content_length_validator/content_length_validator.dart';

Handler maxContentLengthValidator(Handler handler) {
    return handler.use(fromShelfMiddleware(maxContentLengthValidator(maxContentLength: YOUR_CONTENT_LENGTH,)));
}

.addMiddleware(
    maxContentLengthValidator(
      maxContentLength: YOUR_CONTENT_LENGTH,
      errorResponse: Response(
        413,
        body: 'Your body is too long',
        ),
      ),
    ),
  ),