Validation Guide - Flint Dart

Input Validation

Validate normalized request input right from the request. The same handler can accept JSON, URL-encoded forms, or multipart form data without branching on content type.

Validate Any Supported Request Body

CodeBlock dart

app.post('/register', (Context ctx) async {
  final data = await ctx.req.validate({
    'name': 'required|string|min:3',
    'email': 'required|email',
    'password': 'required|string|min:8',
    'avatar': 'required',
  }, messages: {
    'email.required': 'Email is required.',
    'email.email': 'Enter a valid email address.',
    'password.min': 'Password must be at least :min characters.',
  });

  final avatar = await ctx.req.input('avatar');
  return ctx.res.json({'ok': true, 'data': data, 'avatar': avatar != null});
});

Form Fields vs Files

CodeBlock dart

app.post('/profile', (Context ctx) async {
  final data = await ctx.req.validate({
    'bio': 'string|max:160',
    'website': 'string',
    'avatar': 'required',
  });
  final fields = await ctx.req.form();
  final avatar = await ctx.req.input('avatar');

  return ctx.res.json({
    'ok': true,
    'data': data,
    'field_count': fields.length,
    'has_avatar': avatar != null,
  });
});

Raw Body Access

CodeBlock dart

app.post('/webhooks/stripe', (Context ctx) async {
  final bytes = await ctx.req.rawBody();
  return ctx.res.json({'size': bytes.length});
});

Validation rules are pipe-separated (e.g. required|string|min:3). Supported rules include required, string, int, double, bool, email, regex:pattern, list, list:type, confirmed, date, in:a,b,c, not_in:a,b,c, min:n, and max:n.

By default, fields not present in your rules are treated as invalid. On failure, Flint throws a ValidationException with field errors. Custom messages can target field.rule, field, or rule keys and support :field, :min, :max, and :value placeholders.

validateForm() is still available for compatibility, but new code should use validate(), input(), and allInput().