Handling Exceptions and status codes

MagicOnion allows you to return the result of server processing as a status code separately from the return value. This is similar to HTTP status codes or gRPC status codes. You can also include application-specific status codes in these status codes.

Notifying the client of the status code from the server

If you want to return a custom status code from the server to the client, you can use ReturnStatusException.

public Task SendMessageAsync(string message)
{
    if (message.Contains("foo"))
    {
        //
        throw new ReturnStatusException((Grpc.Core.StatusCode)MyStatusCode.SomethingWentWrong, "invalid");
    }

    // ....

The ReturnStatusException has an Grpc.Core.StatusCode enumeration type as the status code, and this value is notified to the client. To return a custom status code for the application, cast your own int value or enumeration type to the Grpc.Core.StatusCode enumeration type.

If you are performance-centric and want to avoid throwing exceptions, you can use CallContext.Status (ServiceContext.CallContext.Status) to set the status directly.

Exception handling on the client

All exceptions that occur when a method is called on the client are received as a RpcException of gRPC.

var client = MagicOnionClient.Create<IGreeterService>(channel);
try
{
    var result = await client.SayHelloAsync("Alice", 18);
}
catch (RpcException ex)
{
    // handle exception ...
    if (((MyStatusCode)ex.Status.StatusCode) == MyStatusCode.SomethingWentWrong)
    {
        // ...
    }
}

If there is a problem with the network, RpcException is thrown with StatusCode.Unavailable. You can investigate the detailed error content with the InnerException property.

Unhandled exceptions on the server

If an unhandled exception is thrown during a method call on the server, except for ReturnStatusException, the client treats it as an RpcException with StatusCode.Unknown.

If MagicOnionOption.IsReturnExceptionStackTraceInErrorDetail is true, the client can receive the stack trace of the server exception. This is very useful for debugging, but it has a critical security issue, so it should only be enabled in debug builds.