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DelegatingHandlers not executing when routes not defined

I am working on a WebAPI 2 project which currently uses attribute-based routing exclusively, to the point that there are no routes defined in registration, and everything is working as expected.

However, I am now adding a DelegatingHandler to provide a heartbeat that I can ping with a HEAD request:

DelegatingHandler

public class HeartbeatMessagingHandler : DelegatingHandler
{
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
if (IsHeartbeat(request))
{
if (request.Method == HttpMethod.Head)
{
var response = new HttpResponseMessage(HttpStatusCode.NoContent) { Content = new StringContent(string.Empty) };
var task = new TaskCompletionSource<HttpResponseMessage>();
task.SetResult(response);
return task.Task;
}
}

return base.SendAsync(request, cancellationToken);
}

private static bool IsHeartbeat(HttpRequestMessage request)
{
return request.RequestUri.LocalPath.Equals("/Heartbeat", StringComparison.OrdinalIgnoreCase);
}
}


However, the handler is not being invoked if I make the expected HEAD http://localhost/heartbeat request; if I call any route that does exist then the handler is invoked; and if I add an old-school routing configuration then the handler is invoked on the expected /heartbeat endpoint.

HEAD http://localhost/heartbeat

/heartbeat

So, using attribute routing only, how can I handle a request to a "virtual" endpoint?

1 Answer
1

Most likely your handler is too late in the pipeline and a higher pipeline is short-circuiting the request before your handler has time to execute.

consider inserting your handler higher up so it has a better chance of intercepting the request

public static class WebApiConfig {
public static void Register(HttpConfiguration config) {
// Web API routes
config.MapHttpAttributeRoutes();

// add to the front of the pipeline
config.MessageHandlers.Insert(0, new HeartbeatMessagingHandler());
}
}


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