sonbua / responsibilitychain Goto Github PK

CancellationTokens are essential to asynchronous operations. They should be part of any async method's parameters by default, even though as an optional one.

Current IAsyncHandler<TIn, TOut> definition:

public interface IAsyncHandler<TIn, TOut> : IHandler
{
    Task<TOut> HandleAsync(TIn input, Func<TIn, Task<TOut>> next);
}

HandleAsync(), once started, couldn't be cancelled.

It should look like this:

public interface IAsyncHandler<TIn, TOut> : IHandler
{
    Task<TOut> HandleAsync(TIn input, Func<TIn, CancellationToken, Task<TOut>> next, CancellationToken cancellationToken);
}

This is the current interface definition of IHandler<TIn, TOut> and IAsyncHandler<TIn, TOut>

public interface IHandler<TIn, TOut> : IHandler
{
    TOut Handle(TIn input, Func<TIn, TOut> next);
}

public interface IAsyncHandler<TIn, TOut> : IHandler
{
    Task<TOut> HandleAsync(TIn input, Func<TIn, Task<TOut>> next);
}

When client consumes this API via a composite handler, she often has to pass null as the next handler. This is inconvenient and adds noise to the code base. Having an additional Handle method on the abstract composite, which requires the input object only and no next delegate, improves readability.

Framework currently supports in resolving dependencies via an injected IServiceProvider instance in the composite handler's constructor like this

public class WorkLogParser : Handler<string, int>
    public WorkLogParser(IServiceProvider serviceProvider) : base(serviceProvider)
    {
        AddHandler<NestedHandler1>();
        AddHandler<NestedHandler2>();
    }
}

This makes SUT (WorkLogParser) hard to test in case one wants to mock out a nested handler (such as logging, database access,...) or a dependency of a nested handler.
So a handler (and composite handler) should expose all dependencies via constructor parameters instead of the service locator anti-pattern.

public class WorkLogParser : Handler<string, int>
    public WorkLogParser(NestedHandler1 nestedHandler1, NestedHandler2 nestedHandler2)
    {
        AddHandler(nestedHandler1);
        AddHandler(nestedHandler2);
    }
}

Currently child handler, which is added to an asynchronous composite, is not intercepted.