Use new error response format to parse errors (#309)

* Fix parsing errors

* Another test for recovering from header

* Another one on parsing details

Author: simolus3

packages/powersync_core/lib/src/exceptions.dart

@@ -61,7 +61,12 @@ class SyncResponseException implements Exception {
   static SyncResponseException _fromResponseBody(
       http.BaseResponse response, String body) {
     final decoded = convert.jsonDecode(body);
-    final details = _stringOrFirst(decoded['error']?['details']) ?? body;
+    final details = switch (decoded['error']) {
+          final Map<String, Object?> details => _errorDescription(details),
+          _ => null,
+        } ??
+        body;
+
     final message = '${response.reasonPhrase ?? "Request failed"}: $details';
     return SyncResponseException(response.statusCode, message);
   }
@@ -73,6 +78,37 @@ class SyncResponseException implements Exception {
     );
   }
 
+  /// Extracts an error description from an error resonse looking like
+  /// `{"code":"PSYNC_S2106","status":401,"description":"Authentication required","name":"AuthorizationError"}`.
+  static String? _errorDescription(Map<String, Object?> raw) {
+    final code = raw['code']; // Required, string
+    final description = raw['description']; // Required, string
+
+    final name = raw['name']; // Optional, string
+    final details = raw['details']; // Optional, string
+
+    if (code is! String || description is! String) {
+      return null;
+    }
+
+    final fullDescription = StringBuffer(code);
+    if (name is String) {
+      fullDescription.write('($name)');
+    }
+
+    fullDescription
+      ..write(': ')
+      ..write(description);
+
+    if (details is String) {
+      fullDescription
+        ..write(', ')
+        ..write(details);
+    }
+
+    return fullDescription.toString();
+  }
+
   int statusCode;
   String description;
 
@@ -84,18 +120,6 @@ class SyncResponseException implements Exception {
   }
 }
 
-String? _stringOrFirst(Object? details) {
-  if (details == null) {
-    return null;
-  } else if (details is String) {
-    return details;
-  } else if (details case [final String first, ...]) {
-    return first;
-  } else {
-    return null;
-  }
-}
-
 class PowersyncNotReadyException implements Exception {
   /// @nodoc
   PowersyncNotReadyException(this.message);

packages/powersync_core/test/exceptions_test.dart

@@ -0,0 +1,56 @@
+import 'dart:convert';
+
+import 'package:http/http.dart';
+import 'package:powersync_core/src/exceptions.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('SyncResponseException', () {
+    const errorResponse =
+        '{"error":{"code":"PSYNC_S2106","status":401,"description":"Authentication required","name":"AuthorizationError"}}';
+
+    test('fromStreamedResponse', () async {
+      final exc = await SyncResponseException.fromStreamedResponse(
+          StreamedResponse(Stream.value(utf8.encode(errorResponse)), 401));
+
+      expect(exc.statusCode, 401);
+      expect(exc.description,
+          'Request failed: PSYNC_S2106(AuthorizationError): Authentication required');
+    });
+
+    test('fromResponse', () {
+      final exc =
+          SyncResponseException.fromResponse(Response(errorResponse, 401));
+      expect(exc.statusCode, 401);
+      expect(exc.description,
+          'Request failed: PSYNC_S2106(AuthorizationError): Authentication required');
+    });
+
+    test('with description', () {
+      const errorResponse =
+          '{"error":{"code":"PSYNC_S2106","status":401,"description":"Authentication required","name":"AuthorizationError", "details": "Missing authorization header"}}';
+
+      final exc =
+          SyncResponseException.fromResponse(Response(errorResponse, 401));
+      expect(exc.statusCode, 401);
+      expect(exc.description,
+          'Request failed: PSYNC_S2106(AuthorizationError): Authentication required, Missing authorization header');
+    });
+
+    test('malformed', () {
+      const malformed =
+          '{"message":"Route GET:/foo/bar not found","error":"Not Found","statusCode":404}';
+
+      final exc = SyncResponseException.fromResponse(Response(malformed, 401));
+      expect(exc.statusCode, 401);
+      expect(exc.description,
+          'Request failed: {"message":"Route GET:/foo/bar not found","error":"Not Found","statusCode":404}');
+
+      final exc2 = SyncResponseException.fromResponse(Response(
+          'not even json', 500,
+          reasonPhrase: 'Internal server error'));
+      expect(exc2.statusCode, 500);
+      expect(exc2.description, 'Internal server error');
+    });
+  });
+}