Invalid content type

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Filtering support for collections ([#97](https://github.com/f3ath/json-api-dart/pull/97))
 
+### Changed
+- The client will not attempt to decode the body of the HTTP response with error status if the correct Content-Type 
+is missing. Before in such cases a `FormatException` would be thrown.
+
 ## [4.1.0] - 2020-05-28
 ### Changed
 - `DartHttp` now defaults to utf8 if no encoding is specified in the response.

lib/src/client/json_api_client.dart

@@ -181,10 +181,14 @@ class JsonApiClient {
   Future<Response<D>> _call<D extends PrimaryData>(
       HttpRequest request, D Function(Object _) decodePrimaryData) async {
     final response = await _httpHandler(request);
-    final document = response.body.isEmpty ? null : jsonDecode(response.body);
-    if (document == null) {
+    final status = StatusCode(response.statusCode);
+    if (response.body.isEmpty ||
+        (status.isFailed &&
+            response.headers['content-type']?.contains(Document.contentType) !=
+                true)) {
       return Response(response.statusCode, response.headers);
     }
+    final document = response.body.isEmpty ? null : jsonDecode(response.body);
     if (StatusCode(response.statusCode).isPending) {
       return Response(response.statusCode, response.headers,
           asyncDocument: document == null

test/unit/client/non_json_response_test.dart

@@ -0,0 +1,23 @@
+import 'package:json_api/client.dart';
+import 'package:json_api/http.dart';
+import 'package:json_api/routing.dart';
+import 'package:test/test.dart';
+
+import '../../helper/test_http_handler.dart';
+
+void main() {
+  final handler = TestHttpHandler();
+  final client = RoutingClient(JsonApiClient(handler), StandardRouting());
+  test('Error status code with incorrect content-type is not decoded',
+      () async {
+    handler.nextResponse = HttpResponse(500, body: 'Something went wrong');
+
+    final r = await client.fetchCollection('books');
+    expect(r.isAsync, false);
+    expect(r.isSuccessful, false);
+    expect(r.isFailed, true);
+    expect(r.data, isNull);
+    expect(r.asyncData, isNull);
+    expect(r.statusCode, 500);
+  });
+}