Error handling and exceptions

Errors on the server reach your app as typed Dart exceptions. You define an exception once, throw it on the server, and catch it by type in your Flutter app. Failures carry structured data instead of strings.

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 throws a ServerpodClientException with status code 500 (specifically ServerpodClientInternalServerError). The error message and stack trace stay on the server, logged to the serverpod_session_log table.

info

Session logs live in serverpod_session_log, not serverpod_log; see logging for the difference. The Serverpod Insights app shows failed and slow calls.

Serializable exceptions

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

exception: MyException
fields:
  message: String
  errorType: MyEnum

Once the code is generated, 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 models: default sets the value when the field is omitted, and defaultModel sets it on the Dart side. See default values in Working with models.

info

Since exceptions are not persisted in the database, the defaultPersist keyword is not supported. If both default and defaultModel are specified, defaultModel takes precedence.

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

Handle errors in your app

A call from the client can fail in three ways, and you usually handle each one differently:

• A serializable exception you defined (MyException above): a known, app-level failure. Catch it by its type and show the user what happened. (On the wire, it travels as an HTTP 400 with a typed payload.)
• A ServerpodClientException: something went wrong in the communication or on the server. Its typed subclasses map to HTTP status codes: ServerpodClientBadRequest (400), ServerpodClientUnauthorized (401), ServerpodClientForbidden (403), ServerpodClientNotFound (404), and ServerpodClientInternalServerError (500).
• A connection failure: when the app cannot reach the server (offline, wrong URL, or a timeout), it throws a ServerpodClientException with a statusCode of -1. A call that exceeds the request size limit fails with a generic ServerpodClientException with status code 413.

Calls to streaming methods fail with their own connection-level exception family; see error handling in streams.

Catch the specific cases first, then fall back to the general one:

try {
  await client.example.doThingy();
} on MyException catch (e) {
  // A failure you defined and threw on the server.
  showError(e.message);
} on ServerpodClientUnauthorized catch (_) {
  // The call requires the user to sign in.
  redirectToSignIn();
} on ServerpodClientException catch (e) {
  if (e.statusCode == -1) {
    // Could not reach the server.
    showError('Cannot reach the server. Check your connection and try again.');
  } else {
    // The server returned an error, for example a 500.
    showError('Something went wrong. Please try again.');
  }
}

Don't leak sensitive data

Only the serializable exceptions you define reach the client, and every field on them is sent as-is. An uncaught exception becomes a generic 500 with no details, so internal errors never leak on their own. The risk is what you put on the exceptions you do send.

• Don't put stack traces, secrets, database IDs, or internal messages into serializable exception fields. Send only what the user should see.
• Write user-facing messages, and keep the diagnostic detail in your server logs where you can look it up later.
• Validate and sanitize input before acting on it, so a bad request fails cleanly instead of surfacing an internal error.