Fix empty location redirects and add separate test

plugins/http2_adapter/lib/src/http2_adapter.dart

@@ -6,6 +6,7 @@ import 'dart:typed_data';
 import 'package:dio/dio.dart';
 import 'package:dio/io.dart';
 import 'package:http2/http2.dart';
+import 'package:meta/meta.dart';
 
 part 'client_setting.dart';
 
@@ -219,30 +220,24 @@ class Http2Adapter implements HttpClientAdapter {
 
     // Handle redirection.
     if (needRedirect) {
-      final url = responseHeaders.value('location');
-      if (url == null) {
+      if (responseHeaders['location'] == null) {
+        // Redirect without location is illegal.
         throw DioException.connectionError(
           requestOptions: options,
           reason: 'Received redirect without location header.',
         );
       }
-      final uri = Uri.parse(url);
+      final url = responseHeaders.value('location');
+      // An empty `location` header is considered a self redirect.
+      final uri = Uri.parse(url ?? '');
       redirects.add(
         RedirectRecord(
           statusCode,
           options.method,
           uri,
         ),
       );
-      final String path;
-      if (uri.hasScheme) {
-        /// This is a full URL which has to be redirected to as is.
-        path = uri.toString();
-      } else {
-        /// This is relative with or without leading slash and is
-        /// resolved against the URL of the original request.
-        path = options.uri.resolveUri(uri).path;
-      }
+      final String path = resolveRedirectUri(options.uri, uri);
       return _fetch(
         options.copyWith(
           path: path,
@@ -274,6 +269,18 @@ class Http2Adapter implements HttpClientAdapter {
         statusCodes.contains(status);
   }
 
+  @visibleForTesting
+  static String resolveRedirectUri(Uri currentUri, Uri redirectUri) {
+    if (redirectUri.hasScheme) {
+      /// This is a full URL which has to be redirected to as is.
+      return redirectUri.toString();
+    }
+
+    /// This is relative with or without leading slash and is
+    /// resolved against the URL of the original request.
+    return currentUri.resolveUri(redirectUri).toString();
+  }
+
   @override
   void close({bool force = false}) {
     connectionManager.close(force: force);

plugins/http2_adapter/pubspec.yaml

@@ -16,6 +16,7 @@ environment:
 
 dependencies:
   http2: ^2.1.0
+  meta: ^1.9.1
   dio: ^5.2.0
 
 dev_dependencies:

plugins/http2_adapter/test/http2_test.dart

@@ -182,30 +182,40 @@ void main() {
       final response = await dio.get(
         '/redirect',
         queryParameters: {'url': 'https://httpbun.com/get'},
-        onReceiveProgress: (received, total) {
-          // ignore progress
-        },
       );
       expect(response.isRedirect, isTrue);
-
-      // Redirects are not supported in web.
-      // Rhe browser will follow the redirects automatically.
       expect(response.redirects.length, 1);
+
       final ri = response.redirects.first;
       expect(ri.statusCode, 302);
       expect(ri.location.path, '/get');
       expect(ri.method, 'GET');
     });
 
+    test(
+      'empty location',
+      () async {
+        final response = await dio.get(
+          '/redirect',
+        );
+        expect(response.isRedirect, isTrue);
+        expect(response.redirects.length, 1);
+
+        final ri = response.redirects.first;
+        expect(ri.statusCode, 302);
+        expect(ri.location.path, '/get');
+        expect(ri.method, 'GET');
+      },
+      skip: 'Httpbun does not support empty location redirects',
+    );
+
     test('multiple', () async {
       final response = await dio.get(
         '/redirect/3',
       );
       expect(response.isRedirect, isTrue);
-
-      // Redirects are not supported in web.
-      // The browser will follow the redirects automatically.
       expect(response.redirects.length, 3);
+
       final ri = response.redirects.first;
       expect(ri.statusCode, 302);
       expect(ri.method, 'GET');

plugins/http2_adapter/test/redirect_test.dart

@@ -0,0 +1,45 @@
+import 'package:dio_http2_adapter/dio_http2_adapter.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(Http2Adapter.resolveRedirectUri, () {
+    test('empty location', () async {
+      final current = Uri.parse('https://example.com');
+      final result = Http2Adapter.resolveRedirectUri(
+        current,
+        Uri.parse(''),
+      );
+
+      expect(result, current.toString());
+    });
+
+    test('relative location 1', () async {
+      final result = Http2Adapter.resolveRedirectUri(
+        Uri.parse('https://example.com/foo'),
+        Uri.parse('/bar'),
+      );
+
+      expect(result, 'https://example.com/bar');
+    });
+
+    test('relative location 2', () async {
+      final result = Http2Adapter.resolveRedirectUri(
+        Uri.parse('https://example.com/foo'),
+        Uri.parse('../bar'),
+      );
+
+      expect(result, 'https://example.com/bar');
+    });
+
+    test('different location', () async {
+      final current = Uri.parse('https://example.com/foo');
+      final target = 'https://somewhere.com/bar';
+      final result = Http2Adapter.resolveRedirectUri(
+        current,
+        Uri.parse(target),
+      );
+
+      expect(result, target);
+    });
+  });
+}