Add helper getters for URIs and date/times to json_rpc_2.

pkg/json_rpc_2/lib/src/parameters.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library json_rpc_2.parameters;
 
 import 'dart:convert';
 
 import 'exception.dart';
 
@@ skipping 206 matching lines @@
   /// request if [value] doesn't exist.
   List get asList => _getTyped('an Array', (value) => value is List);
 
   /// Asserts that [value] is a [List] and returns it.
   ///
   /// If [value] doesn't exist, this returns [defaultValue].
   List asListOr(List defaultValue) => asList;
 
   /// Asserts that [value] exists and is a [Map] and returns it.
   ///
-  /// [asListOr] may be used to provide a default value instead of rejecting the
+  /// [asMapOr] may be used to provide a default value instead of rejecting the
   /// request if [value] doesn't exist.
   Map get asMap => _getTyped('an Object', (value) => value is Map);
 
   /// Asserts that [value] is a [Map] and returns it.
   ///
   /// If [value] doesn't exist, this returns [defaultValue].
   Map asMapOr(Map defaultValue) => asMap;
 
+  /// Asserts that [value] exists, is a string, and can be parsed as a
+  /// [DateTime] and returns it.
+  ///
+  /// [asDateTimeOr] may be used to provide a default value instead of rejecting
+  /// the request if [value] doesn't exist.
+  DateTime get asDateTime => _getParsed('date/time', DateTime.parse);
+
+  /// Asserts that [value] exists, is a string, and can be parsed as a
+  /// [DateTime] and returns it.
+  ///
+  /// If [value] doesn't exist, this returns [defaultValue].
+  DateTime asDateTimeOr(DateTime defaultValue) => asDateTime;
+
+  /// Asserts that [value] exists, is a string, and can be parsed as a
+  /// [Uri] and returns it.
+  ///
+  /// [asUriOr] may be used to provide a default value instead of rejecting the
+  /// request if [value] doesn't exist.
+  Uri get asUri => _getParsed('URI', Uri.parse);
+
+  /// Asserts that [value] exists, is a string, and can be parsed as a
+  /// [Uri] and returns it.
+  ///
+  /// If [value] doesn't exist, this returns [defaultValue].
+  Uri asUriOr(Uri defaultValue) => asUri;
+
   /// Get a parameter named [named] that matches [test], or the value of calling
   /// [orElse].
   ///
   /// [type] is used for the error message. It should begin with an indefinite
   /// article.
   _getTyped(String type, bool test(value)) {
     if (test(value)) return value;
     throw new RpcException.invalidParams('Parameter $_path for method '
         '"$method" must be $type, but was ${JSON.encode(value)}.');
   }
 
+  _getParsed(String description, parse(String value)) {
+    var string = asString;
+    try {
+      return parse(string);
+    } on FormatException catch (error) {
+      // DateTime.parse doesn't actually include any useful information in the
+      // FormatException, just the string that was being parsed. There's no use
+      // in including that in the RPC exception. See issue 17753.
+      var message = error.message;
+      if (message == string) {
+        message = '';
+      } else {
+        message = '\n$message';
+      }
+
+      throw new RpcException.invalidParams('Parameter $_path for method '
+          '"$method" must be a valid $description, but was '
+          '${JSON.encode(string)}.$message');
+    }
+  }
+
   void _assertPositional() {
     // Throw the standard exception for a mis-typed list.
     asList;
   }
 
   void _assertNamed() {
     // Throw the standard exception for a mis-typed map.
     asMap;
   }
 }
@@ skipping 16 matching lines @@
 
   int asIntOr(int defaultValue) => defaultValue;
 
   bool asBoolOr(bool defaultValue) => defaultValue;
 
   String asStringOr(String defaultValue) => defaultValue;
 
   List asListOr(List defaultValue) => defaultValue;
 
   Map asMapOr(Map defaultValue) => defaultValue;
+
+  DateTime asDateTimeOr(DateTime defaultValue) => defaultValue;
+
+  Uri asUriOr(Uri defaultValue) => defaultValue;
 }