fix(dart_frog): Response.json() overwrites content-type header (#596)

Author: easazade

.gitignore

@@ -1 +1,2 @@
-.idea
+.idea
+.vscode/settings.json

packages/dart_frog/lib/src/response.dart

@@ -55,7 +55,8 @@ class Response {
           body: body != null ? jsonEncode(body) : null,
           headers: {
             ...headers,
-            HttpHeaders.contentTypeHeader: ContentType.json.value,
+            if (!headers.containsKey(HttpHeaders.contentTypeHeader))
+              HttpHeaders.contentTypeHeader: ContentType.json.value,
           },
         );
 

packages/dart_frog/test/src/response_test.dart

@@ -184,6 +184,17 @@ void main() {
         final response = Response.json();
         expect(response.json(), completion(isEmpty));
       });
+
+      test('has correct content-type when overriden in headers', () {
+        final headers = <String, String>{
+          HttpHeaders.contentTypeHeader: ContentType.html.value,
+        };
+        final response = Response.json(headers: headers);
+        expect(
+          response.headers[HttpHeaders.contentTypeHeader],
+          equals(ContentType.html.value),
+        );
+      });
     });
   });
 }