validator function

Middleware validator(String target, FutureOr validate(dynamic value, Context c))

Generic validator middleware — Hono-style, use any validation logic.

target selects the input source:

Value	Source
'json'	Request body (application/json)
'query'	URL query parameters
'param'	Route path parameters (e.g. /:id)
'form'	Form body (application/x-www-form-urlencoded or multipart/form-data)
'header'	Request headers

validate receives the raw extracted value and the Context. Return:

• A Response to short-circuit the pipeline (e.g. error response).
• Any other value to store it; retrieve with c.req.valid<T>(target).

import 'package:darto/darto.dart';
import 'package:darto/validator.dart';

app.post('/posts', [
  validator('json', (value, c) {
    final body = value as Map<String, dynamic>;
    if (body['title'] == null) return c.badRequest({'error': 'title is required'});
    return body;
  }),
], (Context c) {
  final data = c.req.valid<Map<String, dynamic>>('json');
  return c.created({'post': data});
});

Works with any library — custom logic, zard, etc. To use zard schemas just add zard to your pubspec (you do not need the darto_validator package — that's only for zValidator):

import 'package:zard/zard.dart'; // add `zard` to pubspec — for z.*

final schema = z.map({'name': z.string().min(1)});

app.post('/users', [
  validator('json', (value, c) {
    final result = schema.safeParse(value);
    if (!result.success) return c.text('Invalid!', 401);
    return result.data;
  }),
], (Context c) {
  final data = c.req.valid<Map<String, dynamic>>('json');
  return c.created({'user': data});
});

Implementation

Middleware validator(
  String target,
  FutureOr<dynamic> Function(dynamic value, Context c) validate,
) {
  return (Context c, Next next) async {
    final input = await extractValidatorInput(target, c);
    final result = await validate(input, c);

    if (result is Response) {
      c.respond(result);
      return;
    }

    c.set(validatorKey(target), result);
    await next();
  };
}