fix: when WebVPN token is expired, the webvpn_proxy is stuck in the FormatException state

Author: w568w

lib/util/io/dio_utils.dart

@@ -104,4 +104,39 @@ class DioUtils {
     setProxy(dio, SettingsProvider.getInstance().proxy);
     return dio;
   }
+
+  /// Fetch with the [options], but when T is JSON-like and the response is not,
+  /// throw a [DioException] WITH the response data.
+  /// (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 {
+    Response<String> response = await dio.fetch(options);
+    if (T == String) {
+      return response as Response<T>;
+    } else {
+      try {
+        dynamic transformedResponseData = await dio.transformer
+            .transformResponse(
+                options.copyWith(responseType: ResponseType.json),
+                ResponseBody.fromString(response.data!, response.statusCode!,
+                    headers: response.headers.map,
+                    statusMessage: response.statusMessage));
+        return Response<T>(
+          data: transformedResponseData,
+          requestOptions: response.requestOptions,
+          statusCode: response.statusCode,
+          statusMessage: response.statusMessage,
+          isRedirect: response.isRedirect,
+          redirects: response.redirects,
+          headers: response.headers,
+        );
+      } catch (e) {
+        throw DioException(
+          requestOptions: options,
+          response: response,
+          error: e,
+        );
+      }
+    }
+  }
 }

lib/util/webvpn_proxy.dart

@@ -79,21 +79,21 @@ class WebvpnProxy {
     }
   }
 
-  // Check if we have logged in to WebVPN, returns false if we haven't
-  static bool checkResponse(Response<dynamic> response) {
+  // Check if we should login to WebVPN. Return `true` if we should login now.
+  static bool isResponseRequiringLogin(Response<dynamic> response) {
     // When 302 is raised when the method is `POST`, it means that we haven't logged in
     if (response.requestOptions.method == "POST" &&
         response.statusCode == 302 &&
         response.headers['location'] != null &&
         response.headers['location']!.isNotEmpty) {
-      return false;
+      return true;
     }
 
     if (response.realUri.toString().startsWith(WEBVPN_LOGIN_URL)) {
-      return false;
+      return true;
     }
 
-    return true;
+    return false;
   }
 
   /// Bind WebVPN proxy to a person info so that it updates automatically when [personInfo] changes.
@@ -284,19 +284,37 @@ class WebvpnProxy {
     await loginWebvpn(dio);
 
     // First attempt
-    Response<T> response = await dio.fetch<T>(options);
-    if (checkResponse(response)) {
-      return response;
+    try {
+      Response<T> response = await DioUtils.fetchWithJsonError(dio, options);
+      if (!isResponseRequiringLogin(response)) {
+        return response;
+      }
+    } on DioException catch (e) {
+      if (e.response == null) {
+        rethrow;
+      }
+      if (!isResponseRequiringLogin(e.response!)) {
+        rethrow;
+      }
     }
 
     // Re-login
     isLoggedIn = false;
     await loginWebvpn(dio);
 
     // Second attempt
-    response = await dio.fetch<T>(options);
-    if (checkResponse(response)) {
-      return response;
+    try {
+      Response<T> response = await DioUtils.fetchWithJsonError(dio, options);
+      if (!isResponseRequiringLogin(response)) {
+        return response;
+      }
+    } on DioException catch (e) {
+      if (e.response == null) {
+        rethrow;
+      }
+      if (!isResponseRequiringLogin(e.response!)) {
+        rethrow;
+      }
     }
 
     // All attempts failed