How create a middleware with api endpoints in .NET Core - api

Question

I have created the web application with the web api. The application contains some Controllers for example TodoController:
namespace TodoApi.Controllers
{
[Route("api/[controller]")]
public class TodoController : Controller
{
private readonly TodoContext _context;
public TodoController(TodoContext context)
{
_context = context;
}
[HttpGet]
public IEnumerable<TodoItem> GetAll()
{
return _context.TodoItems.ToList();
}
}
}
If I create the GET request - /api/todo - I get the list of Todos from database.
I have a list of controllers and api endpoints like above.
I would like distribute this api to another application ideally like middleware - my idea is register in Startup.cs like this:
public void ConfigureServices(IServiceCollection services)
{
services.AddTodoApi();
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
app.UseTodoApi();
}
This will be awesome use case for my api but I don't know how this controllers api endpoints rewrite like middleware and return same JSON data same approache like using classic Controllers.
How can I write the middleware in .NET Core for creating API endpoints?

Answer 1

Instead of the separate middleware, you may configure the MVC middleware to discovery controllers from another assembly:
// using System.Reflection;
public void ConfigureServices(IServiceCollection services)
{
...
services
.AddMvc()
.AddApplicationPart(typeof(TodoController).GetTypeInfo().Assembly);
Controllers are part of MVC middleware, they are not a separate part of request pipeline (but this is what middlewares are). When you register the custom middleware, it by default invokes on each request and you have HttpContext context as an input parameter to work with/edit
Request/Response data. But ASP.NET Core provides Map* extensions that are used as a convention for branching the pipeline.
Map branches the request pipeline based on matches of the given request path. If the request path starts with the given path, the branch is executed.
Example:
private static void HandleMapTodo(IApplicationBuilder app)
{
app.Run(async context =>
{
await context.Response.WriteAsync("/api/todo was handled");
});
}
public void Configure(IApplicationBuilder app)
{
app.Map("/api/todo", HandleMapTodo);
}
Note, that as middleware knows nothing about MVC middleware, you have only access to "raw" request and do not have features like model binding or MVC action filters.

Answer 2

Because it looks like the perfect microservices approach (similar than what my team is doing right now) I'd create a client assembly that can consume your API, the one that contains your TodoController, if you define a contract, and interface, for that API you can register it in your other assembly as it was a midleware and also you could mock that behaviour in your unit tests.
So, as I said, you could inject your client in ConfigureServices method, you can create:
public static IServiceCollection AddTodoRestClient(this IServiceCollection services)
{
services.AddSingleton<ITodoRestClient, TodoRestClient>();
return services;
}
Also consider that you will need to provide the enpoint so, it might looks like:
public static IServiceCollection AddConfiguredTodoClient(this IServiceCollection services, string todoEndpoint)
{
AddTodoClient(services);
ITodoRestClient todoRestClient = services.BuildServiceProvider().GetService<ITodoRestClient>();
// Imagine you have a configure method...
todoRestClient.Configure(services, todoEndpoint);
return services;
}
You can create those methods in a TodoRestClientInjector class and use them in Configure method on your startup.
I hope it helps
--- MORE DETAILS TO ANSWER COMMENTS ---
For me TodoClient is a Rest client library that implements calls to the ToDo API, (I've edited previous code to be TodoRestClient) methos like, i.e., CreateTodoItem(TodoDto todoItem) which implementation would call to the TodoController.Post([FromBody] item) or GetTodos() which wuold call TodoController.Get() and so on and so forth....
Regarding the enpoints... This approach implies to have (at least) two different applications (.NET Core apps), on the one hand the ASP NET Core app that has your TodoController and on the other hand a console application or another ASP NET Core API on which startup class you'll do the inyection adn the Rest client (the Todo Rest client) configuration ...
In a microservices approach using docker, in a dev environment, you'll use docker-compose-yml, but in a traditional approach you'll use concrete ports to define the endpoints...
So, imagine that you have in the second service a controller that need to use TodoController, to achieve so I'll use the above aproach and the "SecondController" would look like:
public class SecondController : Controller
{
private readonly SecondContext _context;
private readonly TodoRestClient _todoRestClient;
public TodoController(SecondContext context, ITodoRestClient todoRestClient)
{
_context = context;
_todoRestClient= todoRestClient;
}
// Whatever logic in this second controller... but the usage would be like:
_todoRestClient.GetTodos()
}
Just few final hints: it's key to minimize calls between services because it increases latency, and more and more if this happens on cascade. Also consider Docker usage, looks challenging but it is quite easy to start and, indeed, is thought to be used in scenarios that the one you presented and solutions like mine.
Again, I hope it helps.
Juan