ASP.NET Web API–The inner handler has not been assigned

I created the following messagehandler to add the correlation id to an outgoing HTTP request:

	public class AddCorrelationIdToRequestHandler : DelegatingHandler
	{
	private const string CorrelationIdHeaderName = "X-Correlation-Id";
	protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
	{
	request.Headers.Add(CorrelationIdHeaderName, CorrelationContainer.GetCorrelationId().ToString());
	return base.SendAsync(request, cancellationToken);
	}
	}

view raw AddCorrelationIdToRequestHandler.cs hosted with ❤ by GitHub

and used the following code to link it to the HttpClient:

	var addCorrelationIdhandler = new AddCorrelationIdToRequestHandler();
	var client = new HttpClient(addCorrelationIdhandler);

view raw httpClientConfig.cs hosted with ❤ by GitHub

Looked OK to me until I tried to execute this code. This failed horribly with the following error message:

  "message": "An error has occurred.",

  "exceptionMessage": "The inner handler has not been assigned.",

  "exceptionType": "System.InvalidOperationException",

  "stackTrace": "   at System.Net.Http.DelegatingHandler.SetOperationStarted()
   at System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at CorrelationId.AddCorrelationIdToRequestHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)

What was not obvious to me is that you have to specify the next handler in the request pipeline. As I only had one handler added, I had to specify the HttpClientHandler as the next (and final) handler:

	var addCorrelationIdhandler = new AddCorrelationIdToRequestHandler()
	{
	InnerHandler = new HttpClientHandler()
	};
	var client = new HttpClient(addCorrelationIdhandler);

view raw httpClientConfigFixed.cs hosted with ❤ by GitHub