Merge pull request #503 from DanXi-Dev/fix-webvpn-again

fix: expand redirect code handling for WebVPN login

Author: w568w

lib/util/io/dio_utils.dart

@@ -45,6 +45,30 @@ class DioUtils {
             return status! < 400;
           });
 
+  /// Get the location to which the [response] is redirected.
+  ///
+  /// If the response is not a valid redirect response, return null.
+  ///
+  /// It doesn't check whether the "location" is empty, relative, etc.
+  /// You should do it yourself.
+  ///
+  /// ## Formality
+  /// This method is a bit different from the original one (see [HttpClientResponse.isRedirect] in `http_impl.dart`),
+  /// which considers the request HTTP method and excludes some invalid combinations (e.g., POST can only be redirected by 303).
+  /// But in practice, we don't need to (and cannot) be so strict. Some badly designed servers may return 302 for POST requests.
+  static String? getRedirectLocation(Response<dynamic> response) {
+    final statusCode = response.statusCode;
+    bool isRedirect = statusCode == HttpStatus.movedPermanently ||
+        statusCode == HttpStatus.permanentRedirect ||
+        statusCode == HttpStatus.found ||
+        statusCode == HttpStatus.seeOther ||
+        statusCode == HttpStatus.temporaryRedirect;
+    if (isRedirect) {
+      return response.headers['location']?[0];
+    }
+    return null;
+  }
+
   /// Process the redirect response manually and return the final response.
   ///
   /// What makes this method necessary is that the default behavior of [Dio] is
@@ -54,10 +78,8 @@ class DioUtils {
   static Future<Response<dynamic>> processRedirect(
       Dio dio, Response<dynamic> response) async {
     // Prevent the redirect being processed by HttpClient, with the 302 response caught manually.
-    if (response.statusCode == 302 &&
-        response.headers['location'] != null &&
-        response.headers['location']!.isNotEmpty) {
-      String location = response.headers['location']![0];
+    String? location = getRedirectLocation(response);
+    if (location != null) {
       if (location.isEmpty) return response;
       if (!Uri.parse(location).isAbsolute) {
         location = '${response.requestOptions.uri.origin}/$location';
@@ -110,7 +132,9 @@ class DioUtils {
   /// (The original [fetch] will throw a [DioException] WITHOUT the response data when [FormatException] occurs.)
   static Future<Response<T>> fetchWithJsonError<T>(
       Dio dio, RequestOptions options) async {
-    if (T == dynamic || options.responseType == ResponseType.bytes || options.responseType == ResponseType.stream) {
+    if (T == dynamic ||
+        options.responseType == ResponseType.bytes ||
+        options.responseType == ResponseType.stream) {
       // If T is dynamic, or the caller wants bytes or stream, just call the original fetch.
       // Because we are going to parse the response data as [String] below!
       return await dio.fetch(options) as Response<T>;

lib/util/webvpn_proxy.dart

@@ -158,7 +158,8 @@ class WebvpnProxy {
       Dio dio, IndependentCookieJar jar, PersonInfo? info) async {
     Response<dynamic>? res = await dio.get(WEBVPN_ID_REQUEST_URL,
         options: DioUtils.NON_REDIRECT_OPTION_WITH_FORM_TYPE);
-    if (res.statusCode == 302) {
+    if (DioUtils.getRedirectLocation(res) != null) {
+      // if we are redirected to UIS, we need to login to UIS first
       await DioUtils.processRedirect(dio, res);
       res = await UISLoginTool.loginUIS(dio, WEBVPN_UIS_LOGIN_URL, jar, info);
       if (res == null) {