Error handling and exceptions

Serverpod allows you to throw an exception on the server, serialize it, and catch it in your client app.

If you throw a normal exception that isn't caught by your code, it will be treated as an internal server error. The exception will be logged together with its stack trace, and a 500 HTTP status (internal server error) will be sent to the client. On the client side, this will throw a non-specific ServerpodException, which provides no more data than a session id number which can help identify the call in your logs.

tip

Use the Serverpod Insights app to view your logs. It will show any failed or slow calls and will make it easy to pinpoint any errors in your server.

info

Uncaught exceptions thrown in endpoints are logged in the serverpod_session_log table, not in the serverpod_log table. To understand more about the differences between these two tables, you can read more about logging in Serverpod.

Serializable exceptions

Serverpod allows adding data to an exception you throw on the server and extracting that data in the client. You use the same YAML files to define the serializable exceptions as you would with any serializable model (see serialization for details). The only difference is that you use the keyword exception instead of class.

exception: MyException
fields:
  message: String
  errorType: MyEnum

After you run serverpod generate, you can throw that exception when processing a call to the server.

class ExampleEndpoint extends Endpoint {
  Future<void> doThingy(Session session) {
    // ... do stuff ...
    if (failure) {
      throw MyException(
        message: 'Failed to do thingy',
        errorType: MyEnum.thingyError,
      );
    }
  }
}

In your app, catch the exception as you would catch any exception.

try {
  await client.example.doThingy();
}
on MyException catch(e) {
  print(e.message);
}
catch(e) {
  print('Something else went wrong.');
}

Custom serializable exception classes

If you already have a Dart exception class in a package shared by the server and client, the class must implement SerializableException for Serverpod to send it to the client. Otherwise, Serverpod treats the exception as an internal server error.

import 'package:serverpod_serialization/serverpod_serialization.dart';

class UserFacingException implements SerializableException {
  final String message;
  final String? code;

  UserFacingException({
    required this.message,
    this.code,
  });

  factory UserFacingException.fromJson(Map<String, dynamic> json) {
    return UserFacingException(
      message: json['message'] as String,
      code: json['code'] as String?,
    );
  }

  @override
  Map<String, dynamic> toJson() {
    return {
      'message': message,
      'code': code,
    };
  }

  @override
  String toString() => message;
}

The class must also be known to Serverpod's generated serialization manager. Register it in the server project's config/generator.yaml, then run serverpod generate:

extraClasses:
  - package:my_project_shared/my_project_shared.dart:UserFacingException

The SerializableException interface marks the exception as safe to serialize to the client. See Custom serializable classes for how the extraClasses entry registers the type for code generation.

Default values in exceptions

Serverpod allows you to specify default values for fields in exceptions, similar to how it's done in models using the default and defaultModel keywords. If you're unfamiliar with how these keywords work, you can refer to the Default Values section in the Working with Models documentation.

info

Since exceptions are not persisted in the database, the defaultPersist keyword is not supported. If both default and defaultModel are specified, defaultModel will always take precedence, making it unnecessary to use both.

exception: MyException
fields:
  message: String, default="An error occurred"
  errorCode: int, default=1001