[gql_dio_link] Add extra from context

links/gql_dio_link/lib/src/dio_link.dart

@@ -39,6 +39,22 @@ class DioLinkResponseContext extends ContextEntry {
       ];
 }
 
+/// Dio link extra context
+@immutable
+class DioExtraContext extends ContextEntry {
+  /// Custom field that will be passed to Dio request options and response
+  final Map<String, dynamic> extra;
+
+  const DioExtraContext({
+    this.extra = const {},
+  });
+
+  @override
+  List<Object> get fieldsForEquality => [
+        extra,
+      ];
+}
+
 extension _CastDioResponse on dio.Response {
   dio.Response<T> castData<T>() => dio.Response<T>(
         data: data as T?,
@@ -91,6 +107,7 @@ class DioLink extends Link {
         ...defaultHeaders,
         ..._getHttpLinkHeaders(request),
       },
+      extra: _getRequestExtra(request),
     );
 
     if (dioResponse.statusCode! >= 300 ||
@@ -130,6 +147,7 @@ class DioLink extends Link {
   Future<dio.Response<Map<String, dynamic>>> _executeDioRequest({
     required Map<String, dynamic> body,
     required Map<String, String> headers,
+    required Map<String, dynamic>? extra,
   }) async {
     try {
       final res = await client.post<dynamic>(
@@ -138,6 +156,7 @@ class DioLink extends Link {
         options: dio.Options(
           responseType: dio.ResponseType.json,
           headers: headers,
+          extra: extra,
         ),
       );
       if (res.data is Map<String, dynamic> == false) {
@@ -215,6 +234,17 @@ class DioLink extends Link {
     }
   }
 
+  Map<String, dynamic>? _getRequestExtra(Request request) {
+    try {
+      final DioExtraContext? extraContext = request.context.entry();
+      return extraContext?.extra;
+    } catch (e) {
+      throw ContextReadException(
+        originalException: e,
+      );
+    }
+  }
+
   /// Closes the underlining Dio client
   void close({bool force = false}) {
     client.close(force: force);

links/gql_dio_link/test/gql_dio_link_test.dart

@@ -249,6 +249,73 @@ void main() {
       ).called(1);
     });
 
+    test("adds extra from context", () async {
+      when(
+        client.post<dynamic>(
+          any,
+          data: anyNamed("data"),
+          options: anyNamed("options"),
+        ),
+      ).thenAnswer(
+            (invocation) {
+          final options = invocation.namedArguments.entries
+              .firstWhere((element) => element.key == Symbol("options"))
+              .value as dio.Options;
+          return Future.value(
+            dio.Response<Map<String, dynamic>>(
+              data: <String, dynamic>{
+                "data": <String, dynamic>{},
+              },
+              statusCode: 200,
+              requestOptions: dio.RequestOptions(
+                path: path,
+                headers: options.headers,
+                extra: options.extra,
+              ),
+            ),
+          );
+        },
+      );
+
+      await execute(
+        Request(
+          operation: Operation(
+            document: parseString("query MyQuery {}"),
+          ),
+          variables: const <String, dynamic>{"i": 12},
+          context: Context.fromList(
+            const [
+              DioExtraContext(
+                extra: {
+                  "foo": "bar",
+                },
+              ),
+            ],
+          ),
+        ),
+      ).first;
+
+      verify(
+        client.post<dynamic>(
+          any,
+          data: anyNamed("data"),
+          options: argThat(
+            predicate((dio.Options o) => o.extEqual(dio.Options(
+              responseType: dio.ResponseType.json,
+              headers: <String, dynamic>{
+                dio.Headers.contentTypeHeader: dio.Headers.jsonContentType,
+                dio.Headers.acceptHeader: "*/*",
+              },
+              extra: <String, dynamic>{
+                "foo": "bar",
+              },
+            ))),
+            named: "options",
+          ),
+        ),
+      ).called(1);
+    });
+
     test("adds default headers", () async {
       final client = MockDio();
       final link = DioLink(