Returning Responses

[LadyNaggaga]

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[captainsafia]

Returning responses from minimal APIs

Minimal APIs takes care of setting content types from common response formats. For example, an endpoint that returns a text payload will automatically encode the response with the text/plain content type.

app.MapGet("/", () => "Hello World!");

$ http http://localhost:5075
HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Date: Sun, 29 Aug 2021 01:57:46 GMT
Server: Kestrel
Transfer-Encoding: chunked

Hello World!

Objects returns from an endpoint are automatically encoced as a JSON response object.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => new ToDo(1, "Take out the trash!"));

app.Run();
record ToDo(int Id, string Task);

$ http http://localhost:5075
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Date: Sun, 29 Aug 2021 02:03:23 GMT
Server: Kestrel
Transfer-Encoding: chunked

{
    "id": 1,
    "task": "Take out the trash!"
}

Returning Results from an endpoint

Minimal APIs also supports returning a standard IResult type from an endpoint. For example, to implement an endpoint that redirects to another endpoint.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/old-address", () => Results.Redirect("/new-address"));
app.MapGet("/new-address", () => "Welcome to the new space!");

app.Run();

Then when the user visits the "/old-address" they will receive a 302 redirect to the new location.

$ http http://localhost:5075/old-address
HTTP/1.1 302 Found
Content-Length: 0
Date: Sun, 29 Aug 2021 02:10:51 GMT
Location: /new-address
Server: Kestrel

A variety of extrension methods exist in the Http namespace for returning a wide variety of results, such as redirects, 404s, streams, and so forth.

We can also return streams and binary files from a minimal endpoint with these extension methods.

app.MapGet("/download/{name}", (string name) => {
    var file = GetFile(name);

    if (file is null)
    {
        return Results.NotFound();
    }

    return Results.File(file.Value);
});

Extending Results for library authors

As a library author, you might want to provide an API that allows users to return a custom Result from their endpoints. Minimal APIs provides support for a Results.Extensions static in the Microsoft.AspNetCore.Http namespace that can be used to expose extension methods that return a custom results type to the author. For example, suppose you wanted to provide an extension method that allowed developers to return a ToDoResult from their endpoints. In your library code, you can implement:

namespace MyLibraryNamespace;

public static class MyLibraryResults
{
  public static IResult MyLibraryResult(this IResultExtensions resultExtensions, string name)
    {
      return new MyLibraryType(name);
    }
  }
}

Then, users can invoke your custom results object in the endpoints within their application using the following:

using Microsoft.AspNetCore.Http;
app.MapGet("/view", () => Results.Extensions.MyLibraryResult("SomeText"));