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Filter extensibility

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This feature and document is applies to the server-side only.

Implementing filters by inheriting from MagicOnionFilterAttribute or StreamingHubFilterAttribute is not the only way to implement filters. You can also implement filters using filter interfaces. These interfaces provide a programming model similar to ASP.NET Core MVC filters.

You can use the following interfaces to implement filters:

  • IMagicOnionFilterFactory<T>: Factory interface to generate filter instances
  • IMagicOnionOrderedFilter: Interface to specify the order of filters
  • IMagicOnionServiceFilter: Interface for Unary service filters
  • IStreamingHubFilter: Interface for StreamingHub filters

Implementing filter using filter interfaces​

You can implement filters by implementing the IMagicOnionServiceFilter and IStreamingHubFilter interfaces. MagicOnionFilterAttribute and StreamingHubFilterAttribute provide implementations to make it easier to use these interfaces.

For example, by implementing these two interfaces, you can implement filters that support both Unary services and StreamingHub.

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false)]
class SampleFilterAttribute : IMagicOnionServiceFilter, IStreamingHubFilter, Attribute
{
    public async ValueTask Invoke(ServiceContext context, Func<ServiceContext, ValueTask> next)
    {
        ...
    }

    public async ValueTask Invoke(StreamingHubContext context, Func<StreamingHubContext, ValueTask> next)
    {
        ...
    }
}

Implementing filter using filter factory​

IMagicOnionFilterFactory<T> interface provides a factory method to generate filters. By using this factory, you can flexibly generate filter instances using DI while using the arguments of the filter attribute.

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false)]
class SampleFilterAttribute : Attrubute, IMagicOnionFilterFactory<IMagicOnionServiceFilter>
{
    public string Name { get; set; }

    public SampleFilterAttribute(string name)
    {
        Name = name;
    }

    public IMagicOnionServiceFilter CreateInstance(IServiceProvider serviceProvider)
    {
        return new FilterImpl(serviceProvider.GetRequiredService<ILogger<SampleFilterAttribute>>());
    }

    class FilterImpl : IMagicOnionServiceFilter, IMagicOnionOrderedFilter
    {
        readonly string name;
        readonly ILogger logger;

        public int Order { get; set; } = int.MaxValue;

        public FilterImpl(string name, ILogger logger)
        {
            this.name = name;
            this.logger = logger;
        }

        public async ValueTask Invoke(ServiceContext context, Func<ServiceContext, ValueTask> next)
        {
            logger.LogInformation($"SampleFilter[{name}] Begin: {context.Path}");
            await next(context);
            logger.LogInformation($"SampleFilter[{name}] End: {context.Path}");
        }
    }
}

[SampleFilter("MyService")]
class MyService : ServiceBase<IMyService>
{
    ...
}