refactor: add inferContentType parameter to SturdyHttp constructor (#4)

* refactor: add inferContentType parameter to SturdyHttp constructor

* run format

* add trailing comma

* clarify test names

lib/src/network_request.dart

@@ -169,17 +169,25 @@ class RawRequest extends NetworkRequest {
         );
 }
 
-/// The body of a [NetworkRequest].
+/// The body of a [NetworkRequest]. Note that this type is aimed at providing
+/// readability and type safety and does not dictate behavior of [SturdyHttp]
+/// with regards to the content-type header. If you want [SturdyHttp] to infer
+/// the content-type header, configure this via the `inferContentType` parameter
+/// when constructing the instance.
 @Freezed(copyWith: false)
 class NetworkRequestBody with _$NetworkRequestBody {
   /// An empty body. Results in `null` being passed to `data` of the request.
   const factory NetworkRequestBody.empty() = _Empty;
 
-  /// A JSON body. Passed directly to `data` of the request.
+  /// A JSON body. Passed directly to `data` of the request. If `inferContentType`
+  /// has been provided as `true` to the [SturdyHttp] instance, will result in
+  /// an `application-json` `content-type`.
   const factory NetworkRequestBody.json(Json data) = _Json;
 
   /// A raw body. Allows for nullable untyped data that is passed directly
   /// to `data` of the request, useful for instances where the data type
-  /// is not known until runtime.
+  /// is not known until runtime. If `inferContentType` has been provided as
+  /// `true` to the [SturdyHttp] instance *and* the [data] can be used to infer
+  /// the `content-type` header, it will be inferred.
   const factory NetworkRequestBody.raw(Object? data) = _Raw;
 }

lib/src/sturdy_http.dart

@@ -47,13 +47,15 @@ class SturdyHttp {
     SturdyHttpEventListener? eventListener,
     HttpClientAdapter? customAdapter,
     Map<String, String>? proxy,
+    bool inferContentType = true,
   }) : this._(
           dio: _configureDio(
             baseUrl: baseUrl,
             deserializer: deserializer,
             interceptors: interceptors,
             customAdapter: customAdapter,
             proxy: proxy,
+            inferContentType: inferContentType,
           ),
           deserializer: deserializer,
           eventListener: eventListener,
@@ -227,6 +229,7 @@ Dio _configureDio({
   required Deserializer deserializer,
   required HttpClientAdapter? customAdapter,
   required Map<String, String>? proxy,
+  required bool inferContentType,
 }) {
   return Dio()
     // Instruct Dio to use the same Isolate approach as requested of SturdyHttp
@@ -236,10 +239,12 @@ Dio _configureDio({
     ..options.baseUrl = baseUrl
     ..options.listFormat = ListFormat.multiCompatible
     ..interceptors.addAll(interceptors)
-    ..interceptors.removeImplyContentTypeInterceptor()
     ..map((dio) {
       if (customAdapter != null) {
-        return dio..httpClientAdapter = customAdapter;
+        dio.httpClientAdapter = customAdapter;
+      }
+      if (!inferContentType) {
+        dio.interceptors.removeImplyContentTypeInterceptor();
       }
       return dio;
     });

test/src/sturdy_http_test.dart

@@ -39,25 +39,80 @@ void main() {
       String baseUrl = 'http://example.com',
       List<Interceptor> interceptors = const [],
       Map<String, String>? proxy,
+      bool inferContentType = false,
     }) {
       return SturdyHttp(
         baseUrl: baseUrl,
         customAdapter: charlatan.toFakeHttpClientAdapter(),
         eventListener: eventListener,
         interceptors: interceptors,
         proxy: proxy,
+        inferContentType: inferContentType,
       );
     }
 
     group('interceptors', () {
-      test('it returns the correct interceptors', () {
+      test('it returns the provided interceptors', () {
         final interceptors = [_FakeInterceptor()];
-        final subject = buildSubject(interceptors: interceptors);
+        final subject = buildSubject(
+          interceptors: interceptors,
+          inferContentType: false,
+        );
 
         expect(subject.interceptors, interceptors);
       });
     });
 
+    group('inferContentType', () {
+      test('it does not infer content-type when false', () async {
+        String? contentType;
+        final subject = buildSubject(
+          inferContentType: false,
+          interceptors: [
+            _FakeInterceptor(
+              onRequestInvoked: (options) {
+                contentType =
+                    options.headers[Headers.contentTypeHeader] as String?;
+              },
+            )
+          ],
+        );
+
+        charlatan.whenPost('/infer', (request) => null);
+
+        await subject.execute(
+          PostRequest('/infer', data: NetworkRequestBody.json({'foo': 'bar'})),
+          onResponse: (r) {},
+        );
+
+        expect(contentType, isNull);
+      });
+
+      test('it infers content-type when true', () async {
+        String? contentType;
+        final subject = buildSubject(
+          inferContentType: true,
+          interceptors: [
+            _FakeInterceptor(
+              onRequestInvoked: (options) {
+                contentType =
+                    options.headers[Headers.contentTypeHeader] as String?;
+              },
+            )
+          ],
+        );
+
+        charlatan.whenPost('/infer', (request) => null);
+
+        await subject.execute(
+          PostRequest('/infer', data: NetworkRequestBody.json({'foo': 'bar'})),
+          onResponse: (r) {},
+        );
+
+        expect(contentType, 'application/json');
+      });
+    });
+
     group('baseUrl', () {
       test('it returns the correct baseUrl', () {
         const baseUrl = 'https://foo.com';
@@ -756,7 +811,17 @@ class Result<S, F> with _$Result<S, F> {
   const factory Result.failure(F failure) = _Failure;
 }
 
-class _FakeInterceptor extends Interceptor {}
+class _FakeInterceptor extends Interceptor {
+  final Function(RequestOptions options)? onRequestInvoked;
+
+  _FakeInterceptor({this.onRequestInvoked});
+
+  @override
+  void onRequest(RequestOptions options, RequestInterceptorHandler handler) {
+    onRequestInvoked?.call(options);
+    super.onRequest(options, handler);
+  }
+}
 
 class _SturdyHttpEventListener extends SturdyHttpEventListener {
   final void Function(RequestOptions) onAuthFailure;