WebAPI return 404 on PUT/DELETE operations - asp.net-web-api

Question

This seems to be a fairly common issue, but none of the SO articles I have looked at have solved this for me.
I am working on a ASP.NET WebForms/MVC application running on IIS on Windows 10 (so not IIS Express) which is using jQuery AJAX to invoke a WebAPI application on a separate server. To get around CORS issues, and to add additional processing to all API calls, we implemented a server-side proxy using MVC controllers, so each call would end up somewhere like this:
[HttpPost]
public ActionResult Timesheets_Submit(Timesheet data)
{
var processedData = ProcessTheRequestInSomeWay(data);
var client = new SdkClient();
var results = client.Timesheets.Post(processedData);
return Json(results);
}
And this all worked quite successfully.
However, we are getting rather fed up of having to implement new server-side proxy methods each time we add a new API endpoint, so we decided to create a transparent server-side proxy using WebAPI, and have that do the real work.
The transparent server-side proxy is implemented like this:
public class TransparentProxyDelegatingHandler : DelegatingHandler
{
private static readonly Uri BaseUri = new Uri("https://my.apiserver.com");
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
request.Headers.Add("X-Forwarded-For", request.GetClientIpAddress());
request.RequestUri = new Uri(BaseUri, request.RequestUri.PathAndQuery.Replace("/Proxy", string.Empty));
ProcessRequestInSomeWay(request);
var response = await Client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
return response;
}
}
So a request to POST /Proxy/Timesheets will get translated into a call to POST https://my.apiserver.com/Timesheets and the response returned pretty much as-is.
The problem that I am having is that calls which use the PUT and DELETE verbs are being rejected as 404 Not Found by my UI (not by the API, I can still invoke that directly using e.g. Fiddler/Postman); the original proxy used those verbs, so it's not like they haven't been configured, it's just when I'm calling the delegating handler. The handler never gets invoked, so there's something happening in the routing engine that is causing MVC PUT/DELETE requests to work, but WebAPI PUT/DELETE requests to fail.

Answer 1

It turns out I was not registering the TransparentProxyDelegatingHandler correctly; I was registering it like this in my WebApiConfig:
configuration.MessageHandlers.Add(new TransparentProxyDelegatingHandler());
but as it turns out (thanks to https://blog.kloud.com.au/2013/11/24/do-it-yourself-web-api-proxy/), what I really wanted was:
configuration.Routes.MapHttpRoute(name: "proxy", routeTemplate: "proxy/{*path}",
handler: HttpClientFactory.CreatePipeline(
innerHandler: new HttpClientHandler(),
handlers: new DelegatingHandler[]
{
new TransparentProxyDelegatingHandler(),
}),
defaults: new { path = RouteParameter.Optional },
constraints: null);
I'm guessing that what was going on was that because I didn't have any actual ApiController implementations wired up to WebApi, it wasn't resolving correctly somehow in the early stages of the pipeline.