the newest Mediatr and a handler with a synchronous method Handle: "not all code paths return a value"

Question

I have the newest MediatR (12.2.0) and I have a synchronous method which returns nothing. Do I really need to use "async Task" instead of "Task"? Because the following method gives me "not all code paths return a value":

public class UploadFileCommandHandler(IFileUploadingService fileUploadingService) 
    : IRequestHandler<UploadFileCommand>
{
    private readonly IFileUploadingService _fileUploadingService = fileUploadingService;

    public /* async */ Task Handle(UploadFileCommand request, CancellationToken cancellationToken)
    {
        _fileUploadingService.UploadFile(request.File); // <- this method returns VOID, not a task, see it below (the interface IFileUploadingService)
    }
}

public interface IFileUploadingService
{
    void UploadFile(File file);
}

I have to add "async" bur then I have the warning "async method lack of await". What is the correct solution?

Answer 1

Based on the name ideally you should refactor IFileUploadingService.UploadFile to be async ("truly" async), since it seems to be an IO-bound operation.

If the interface/implementation is outside of your control then usual approach would be to return Task.CompletedTask (though there can be edge cases):

public class UploadFileCommandHandler(IFileUploadingService fileUploadingService) 
    : IRequestHandler<UploadFileCommand>
{
    private readonly IFileUploadingService _fileUploadingService = fileUploadingService;

    public Task Handle(UploadFileCommand request, CancellationToken cancellationToken)
    {
        _fileUploadingService.UploadFile(request.File); // <- this method returns VOID, not a task, see it below (the interface IFileUploadingService)
        return Task.CompletedTask;
    }
}