Fixing connection error (cfug#1912)

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### New Pull Request Checklist

- [x] I have read the
[Documentation](https://pub.dev/documentation/dio/latest/)
- [x] I have searched for a similar pull request in the
[project](https://github.com/cfug/dio/pulls) and found none
- [x] I have updated this branch with the latest `main` branch to avoid
conflicts (via merge from master or rebase)
- [x] I have added the required tests to prove the fix/feature I'm
adding
- [x] I have updated the documentation (if necessary)
- [x] I have run the tests without failures
- [x] I have updated the `CHANGELOG.md` in the corresponding package

### Additional context and info (if any)

fixing cfug#1911

<!-- Provide more context and info about the PR. -->

dio/CHANGELOG.md

@@ -5,7 +5,7 @@ See the [Migration Guide][] for the complete breaking changes list.**
 
 ## Unreleased
 
-*None.*
+- Fix failing requests throw `DioException`s with `.unknown` instead of `.connectionError` on `SocketException`.
 
 ## 5.3.2
 

dio/lib/src/adapters/io_adapter.dart

@@ -115,14 +115,18 @@ class IOHttpClientAdapter implements HttpClientAdapter {
         if (v != null) request.headers.set(k, v);
       });
     } on SocketException catch (e) {
-      if (!e.message.contains('timed out')) {
-        rethrow;
+      if (e.message.contains('timed out')) {
+        throw DioException.connectionTimeout(
+          requestOptions: options,
+          timeout: options.connectTimeout ??
+              httpClient.connectionTimeout ??
+              Duration.zero,
+          error: e,
+        );
       }
-      throw DioException.connectionTimeout(
+      throw DioException.connectionError(
         requestOptions: options,
-        timeout: options.connectTimeout ??
-            httpClient.connectionTimeout ??
-            Duration.zero,
+        reason: e.message,
         error: e,
       );
     }

dio/lib/src/dio_exception.dart

@@ -151,13 +151,14 @@ class DioException implements Exception {
   factory DioException.connectionError({
     required RequestOptions requestOptions,
     required String reason,
+    Object? error,
   }) =>
       DioException(
         type: DioExceptionType.connectionError,
         message: 'The connection errored: $reason',
         requestOptions: requestOptions,
         response: null,
-        error: null,
+        error: error,
       );
 
   /// The request info for the request that throws exception.

dio/test/basic_test.dart

@@ -44,11 +44,7 @@ void main() {
       throwsA(
         allOf([
           isA<DioException>(),
-          (DioException e) =>
-              e.type ==
-              (isWeb
-                  ? DioExceptionType.connectionError
-                  : DioExceptionType.unknown),
+          (DioException e) => e.type == (DioExceptionType.connectionError),
           if (!isWeb) (DioException e) => e.error is SocketException,
         ]),
       ),

dio/test/stacktrace_test.dart

@@ -205,64 +205,58 @@ void main() async {
       },
       testOn: '!browser',
     );
-
-    group('DioExceptionType.unknown', () {
+    group('DioExceptionType.connectionError', () {
       test(
-        JsonUnsupportedObjectError,
+        'SocketException on request',
         () async {
-          final dio = Dio()..options.baseUrl = 'https://does.not.exist';
-
+          final dio = Dio()
+            ..options.baseUrl = 'https://does.not.exist'
+            ..httpClientAdapter = IOHttpClientAdapter();
           await expectLater(
-            dio.get(
-              '/test',
-              options: Options(contentType: Headers.jsonContentType),
-              data: Object(),
-            ),
+            dio.get('/test', data: 'test'),
             throwsA(
               allOf([
                 isA<DioException>(),
-                (DioException e) => e.type == DioExceptionType.unknown,
-                (DioException e) => e.error is JsonUnsupportedObjectError,
-                (DioException e) => e.stackTrace
+                (e) => e.type == DioExceptionType.connectionError,
+                (e) => e.error is SocketException,
+                (e) => (e.error as SocketException)
+                    .message
+                    .contains("Failed host lookup: 'does.not.exist'"),
+                (e) => e.stackTrace
                     .toString()
                     .contains('test/stacktrace_test.dart'),
               ]),
             ),
           );
         },
-        testOn: '!browser',
+        testOn: 'vm',
       );
-
+    });
+    group('DioExceptionType.unknown', () {
       test(
-        'SocketException on request',
+        JsonUnsupportedObjectError,
         () async {
-          final dio = Dio()
-            ..options.baseUrl = 'https://does.not.exist'
-            ..httpClientAdapter = IOHttpClientAdapter(
-              createHttpClient: () {
-                final client = MockHttpClient();
-                when(client.openUrl(any, any)).thenThrow(
-                  SocketException('test'),
-                );
-                return client;
-              },
-            );
+          final dio = Dio()..options.baseUrl = 'https://does.not.exist';
 
           await expectLater(
-            dio.get('/test', data: 'test'),
+            dio.get(
+              '/test',
+              options: Options(contentType: Headers.jsonContentType),
+              data: Object(),
+            ),
             throwsA(
               allOf([
                 isA<DioException>(),
-                (e) => e.type == DioExceptionType.unknown,
-                (e) => e.error is SocketException,
-                (e) => e.stackTrace
+                (DioException e) => e.type == DioExceptionType.unknown,
+                (DioException e) => e.error is JsonUnsupportedObjectError,
+                (DioException e) => e.stackTrace
                     .toString()
                     .contains('test/stacktrace_test.dart'),
               ]),
             ),
           );
         },
-        testOn: 'vm',
+        testOn: '!browser',
       );
 
       test(