Add ResponseFormatException

- Improve error messaging when response body cannot be decoded/encoded

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## [2.4.1](https://github.com/Workiva/w_transport/compare/2.4.0...2.4.1)
+_TBD_
+
+- **Error Messaging:** When a response body cannot be properly decoded/encoded
+  using the `Encoding` dictated by the `content-type` header, a
+  `ResponseFormatException` will now be thrown with a much more descriptive
+  message. The content-type, encoding, and body will be included.
+
 ## [2.4.0](https://github.com/Workiva/w_transport/compare/2.3.2...2.4.0)
 _May 4, 2016_
 

lib/src/http/http_body.dart

@@ -20,6 +20,7 @@ import 'dart:typed_data';
 
 import 'package:http_parser/http_parser.dart' show MediaType;
 
+import 'package:w_transport/src/http/response_format_exception.dart';
 import 'package:w_transport/src/http/utils.dart' as http_utils;
 
 abstract class BaseHttpBody {
@@ -82,15 +83,25 @@ class HttpBody extends BaseHttpBody {
   /// Returns this request/response body as a list of bytes.
   Uint8List asBytes() {
     if (_bytes == null) {
-      _bytes = new Uint8List.fromList(encoding.encode(_body));
+      var encoded;
+      try {
+        encoded = encoding.encode(_body);
+      } catch (e) {
+        throw new ResponseFormatException(contentType, encoding, body: _body);
+      }
+      _bytes = new Uint8List.fromList(encoded);
     }
     return _bytes;
   }
 
   /// Returns this request/response body as a String.
   String asString() {
     if (_body == null) {
-      _body = encoding.decode(_bytes);
+      try {
+        _body = encoding.decode(_bytes);
+      } catch (e) {
+        throw new ResponseFormatException(contentType, encoding, bytes: _bytes);
+      }
     }
     return _body;
   }

lib/src/http/request_exception.dart

@@ -35,12 +35,13 @@ class RequestException implements Exception {
   /// URL of the attempted/unsuccessful request.
   final Uri uri;
 
-  /// Construct a new instance of [WHttpException] using information from
+  /// Construct a new instance of [RequestException] using information from
   /// an HTTP request and response.
   RequestException(this.method, this.uri, this.request, this.response,
       [this.error]);
 
-  /// Descriptive error message that includes the request method & URL and the response status.
+  /// Descriptive error message that includes the request method & URL and the
+  /// response status.
   String get message {
     String msg;
     if (request != null && request.autoRetry.numAttempts > 1) {

lib/src/http/response_format_exception.dart

@@ -0,0 +1,63 @@
+// Copyright 2015 Workiva Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+library w_transport.src.http.response_exception;
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:http_parser/http_parser.dart' show MediaType;
+
+/// An exception that is raised when a response to a request returns with a body
+/// that cannot successfully be encoded or decoded based on the expected
+/// content-type.
+class ResponseFormatException implements Exception {
+  final String body;
+
+  final Uint8List bytes;
+
+  final MediaType contentType;
+
+  final Encoding encoding;
+
+  /// Construct a new instance of [ResponseFormatException] using information
+  /// from the body of the response.
+  ResponseFormatException(this.contentType, this.encoding,
+      {this.body, this.bytes});
+
+  /// Descriptive error message that includes the content-type, encoding, as
+  /// well as the string or bytes that could not be encoded or decoded,
+  /// respectively.
+  String get message {
+    String description;
+    String bodyLine;
+    if (body != null) {
+      description = 'Body could not be encoded.';
+      bodyLine = 'Body: $body';
+    } else {
+      description = 'Bytes could not be decoded.';
+      bodyLine = 'Bytes: $bytes';
+    }
+
+    String msg = description;
+    msg += '\n\tContent-Type: $contentType';
+    msg += '\n\tEncoding: ${encoding.name}';
+    msg += '\n\t$bodyLine';
+
+    return msg;
+  }
+
+  @override
+  String toString() => 'ResponseFormatException: $message';
+}

lib/w_transport.dart

@@ -109,6 +109,8 @@ export 'package:w_transport/src/http/requests.dart'
     show FormRequest, JsonRequest, MultipartRequest, Request, StreamedRequest;
 export 'package:w_transport/src/http/response.dart'
     show BaseResponse, Response, StreamedResponse;
+export 'package:w_transport/src/http/response_format_exception.dart'
+    show ResponseFormatException;
 
 export 'package:w_transport/src/web_socket/w_socket.dart' show WSocket;
 export 'package:w_transport/src/web_socket/w_socket_close_event.dart'

test/unit/http/http_body_test.dart

@@ -136,6 +136,43 @@ void main() {
             new HttpBody.fromBytes(contentType, ASCII.encode('body'));
         expect(body.asString(), equals('body'));
       });
+
+      test('should throw ResponseFormatException if body cannot be encoded',
+          () {
+        MediaType contentType =
+            new MediaType('application', 'json', {'charset': ASCII.name});
+        HttpBody body = new HttpBody.fromString(contentType, 'bodyçå®');
+        var exception;
+        try {
+          body.asBytes();
+        } catch (e) {
+          exception = e;
+        }
+        expect(exception, isNotNull,
+            reason: 'should throw if body cannot be encoded');
+        expect(exception, new isInstanceOf<ResponseFormatException>(),
+            reason:
+                'should throw ResponseFormatException if body cannot be encoded');
+      });
+
+      test('should throw ResponseFormatException if bytes cannot be decoded',
+          () {
+        MediaType contentType =
+            new MediaType('application', 'json', {'charset': ASCII.name});
+        HttpBody body =
+            new HttpBody.fromBytes(contentType, UTF8.encode('bodyçå®'));
+        var exception;
+        try {
+          body.asString();
+        } catch (e) {
+          exception = e;
+        }
+        expect(exception, isNotNull,
+            reason: 'should throw if bytes cannot be decoded');
+        expect(exception, new isInstanceOf<ResponseFormatException>(),
+            reason:
+                'should throw ResponseFormatException if bytes cannot be decoded');
+      });
     });
 
     group('StreamedHttpBody', () {