validate: Add MapField, Field.deserialize, Field.decode

packages/validate/example/main.dart

@@ -73,6 +73,14 @@ Future<void> main() async {
     ''');
   });
   
+  app.post('/b', (req, res) async {
+    var form = Form(fields: [
+      MapField('todo', todoForm),
+    ]);
+    var data = await form.read(req);
+    return data;
+  });
+
   app.fallback((req, res) => throw AngelHttpException.notFound());
 
   app.errorHandler = (e, req, res) {
@@ -82,7 +90,7 @@ Future<void> main() async {
     }
   };
 
-  await http.startServer('127.0.0.1', 3000);
+  await http.startServer('127.0.0.1', 3011);
   print('Listening at ${http.uri}');
 }
 

packages/validate/lib/src/common_fields.dart

@@ -353,12 +353,12 @@ class ImageField extends Field<Image> {
   }
 }
 
+/// A [Field] implementation that reads structured data by decoding it with a [Form].
 class MapField extends Field<Map<String, dynamic>> {
-  @override
-  final String name;
+  /// The underlying [Form] that specifies the types of data this object must contained.
   final Form form;
 
-  MapField(this.name, this.form, {String label, bool isRequired = true})
+  MapField(String name, this.form, {String label, bool isRequired = true})
       : super(name, 'text', label: label, isRequired: isRequired);
 
   @override
@@ -369,17 +369,17 @@ class MapField extends Field<Map<String, dynamic>> {
   FutureOr<FieldReadResult<Map<String, dynamic>>> read(
       Map<String, dynamic> fields, Iterable<UploadedFile> files) {
     var value = fields[name];
-    Map mapValue;
+    Map<String, dynamic> mapValue;
 
     // Value can be either a Map, or a JSON-encoded Map.
     if (value == null) {
       return null;
     } else if (value is Map) {
-      mapValue = value;
+      mapValue = value.cast();
     } else if (value is String) {
       var decoded = json.decode(value);
       if (decoded is Map) {
-        mapValue = decoded;
+        mapValue = decoded.cast();
       } else {
         return FieldReadResult.failure([
           'If "$name" is given as a string, then it must produce a map/dict/object when decoded as JSON.'
@@ -390,6 +390,6 @@ class MapField extends Field<Map<String, dynamic>> {
           ['"$name" must be either a map/dict/object, or a string.']);
     }
 
-
+    return form.readFromMap(mapValue);
   }
 }

packages/validate/lib/src/field.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:convert';
 import 'package:angel_framework/angel_framework.dart';
 import 'package:matcher/matcher.dart';
 import 'form.dart';
@@ -57,6 +58,14 @@ abstract class Field<T> {
   /// [matchers] fails.
   Field<T> match(Iterable<Matcher> matchers) => _MatchedField(this, matchers);
 
+  /// Wraps this instance in one that calls the [converter] to deserialize
+  /// the value into another type.
+  Field<U> deserialize<U>(FutureOr<U> Function(T) converter) =>
+      _DeserializeField(this, converter);
+
+  /// Same as [deserialize], but uses a [codec] to deserialize data.
+  Field<U> decode<U>(Codec<U, T> codec) => deserialize(codec.decode);
+
   /// Calls [read], and returns the retrieve value from the body.
   ///
   /// If [query] is `true` (default: `false`), then the value will
@@ -124,3 +133,26 @@ class _MatchedField<T> extends Field<T> {
     }
   }
 }
+
+class _DeserializeField<T, U> extends Field<U> {
+  final Field<T> inner;
+  final FutureOr<U> Function(T) converter;
+
+  _DeserializeField(this.inner, this.converter)
+      : super(inner.name, inner.type,
+            label: inner.label, isRequired: inner.isRequired);
+
+  @override
+  FutureOr<X> accept<X>(FormRenderer<X> renderer) => inner.accept(renderer);
+
+  @override
+  FutureOr<FieldReadResult<U>> read(
+      Map<String, dynamic> fields, Iterable<UploadedFile> files) async {
+    var result = await inner.read(fields, files);
+    if (!result.isSuccess) {
+      return FieldReadResult.failure(result.errors);
+    } else {
+      return FieldReadResult.success(await converter(result.value));
+    }
+  }
+}