ASP.NET Core 6 - Use URI's extension to get Accept header value - rest

Question

I'm migrating an application from NancyFx to Kestrel in ASP.NET Core 6.
In Nancy, you could specify the Accept value in the URI. For example, these Uris:
http://localhost:5000/my/resource.json
http://localhost:5000/my/resource.protobuf
http://localhost:5000/my/resource.xml
Would be the equivalent of setting the Accepts header to application/json, application/protobuf or application/xml respectively.
Does this exist in Kestrel? I remember finding one example, long ago, of regex-ing the route and doing it somewhat manually. But
I can't find that post again, and
If I have to do that, I'm not sure I want to :)
Is there a way to configure this behavior in ASP.NET Core 6?
The object returned from my handler in the controller is already capable of being serialized to json/xml/whatever. I just need to check the URI to set the content-type of the response so the correct formatter will be invoked.
At the moment, I have a client that will speak to both Nancy and Kestrel and it was written to use the URI to get the type. I'm fine to rewrite/update the client so it will use the Accept header. But getting the URI method to work will make the initial integration easier and a refactor to use the headers can come next.

Answer 1

I created a very simple middleware that reads the accept value from the query string and sets the Accept header to the request:
public class AcceptHeaderFromQueryString
{
private readonly RequestDelegate _next;
public AcceptHeaderFromQueryString(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
var accept = context.Request.Query["accept"];
if (!string.IsNullOrEmpty(accept))
{
context.Request.Headers.Accept = accept;
}
await _next(context);
}
}
Register the middleware:
app.UseMiddleware<AcceptHeaderFromQueryString>();
I added [Produces(MediaTypeNames.Application.Json, MediaTypeNames.Application.Xml)] attribute to my api controller action (this step is not required):
[HttpGet]
[Produces(MediaTypeNames.Application.Json, MediaTypeNames.Application.Xml)]
public IEnumerable<WeatherForecast> Get()
{
return Enumerable.Range(1, 5).Select(index => new WeatherForecast
{
Date = DateTime.Now.AddDays(index),
TemperatureC = Random.Shared.Next(-20, 55),
Summary = Summaries[Random.Shared.Next(Summaries.Length)]
})
.ToArray();
}
Finally I added support for xml serialization in Program.cs:
builder.Services.AddControllers()
.AddXmlDataContractSerializerFormatters();
Then I tried these urls and they both gave appropriate response:
https://localhost:7258/weatherforecast?accept=application/json
https://localhost:7258/weatherforecast?accept=application/xml

Answer 2

You possibly want the [Consumes] attribute. This allows you to specify a controller action that only gets called from a route of the specified content type.
Obviously this is not using the Accepts header but the content type of the request.