.net core中实现服务自动发现

.net core中自带了依赖注入框架，asp.net core或worker框架下可以直接使用， 控制台程序可以通过加入Microsoft.Extensions.DependencyInjection程序包来支持。自带的di框架功能还行， 但是一个不方便的地方是没有提供服务自动发现、注册的接口，稍微大的程序都是需要通过反射自己写一个发现程序的。

今天网上找到了一个第三方实现的服务发现的库Scrutor，还比较好用， 示例如下：

var collection = new ServiceCollection();

collection.Scan(scan => scan
     // We start out with all types in the assembly of ITransientService
    .FromAssemblyOf<ITransientService>()
        // AddClasses starts out with all public, non-abstract types in this assembly.
        // These types are then filtered by the delegate passed to the method.
        // In this case, we filter out only the classes that are assignable to ITransientService.
        .AddClasses(classes => classes.AssignableTo<ITransientService>())
            // We then specify what type we want to register these classes as.
            // In this case, we want to register the types as all of its implemented interfaces.
            // So if a type implements 3 interfaces; A, B, C, we'd end up with three separate registrations.
            .AsImplementedInterfaces()
            // And lastly, we specify the lifetime of these registrations.
            .WithTransientLifetime()
        // Here we start again, with a new full set of classes from the assembly above.
        // This time, filtering out only the classes assignable to IScopedService.
        .AddClasses(classes => classes.AssignableTo<IScopedService>())
            // Now, we just want to register these types as a single interface, IScopedService.
            .As<IScopedService>()
            // And again, just specify the lifetime.
            .WithScopedLifetime()
        // Generic interfaces are also supported too, e.g. public interface IOpenGeneric<T> 
        .AddClasses(classes => classes.AssignableTo(typeof(IOpenGeneric<>)))
            .AsImplementedInterfaces()
        // And you scan generics with multiple type parameters too
        // e.g. public interface IQueryHandler<TQuery, TResult>
        .AddClasses(classes => classes.AssignableTo(typeof(IQueryHandler<,>)))
            .AsImplementedInterfaces());

这个类本身是比较好用的，但是它仍需要手工制定程序集作为扫描范围。 这个程序集的范围并不是所有程序集，往往只有用户代码程序集， asp.net core程序内部是有这个功能的，例如它内部就能扫描所有用户程序集，生成ApiController，网上搜了一下，发现还是一个内部接口，不过可以通过反射来调用：

	public static Assembly[] GetAssemblies()
	{
		var manager = new ApplicationPartManager();

		var method = manager.GetType()
		                    .GetMethod("PopulateDefaultParts",
			                     BindingFlags.NonPublic | BindingFlags.Instance);


		//加载入口程序集的依赖项树中的所有非官方包的依赖程序集
		var assembly = Assembly.GetEntryAssembly().FullName;
		method.Invoke(manager, new object[] { assembly });

		return manager.ApplicationParts.OfType<AssemblyPart>().Select(i => i.Assembly).ToArray();
	}