Delegating Handers
==================

Ocelot allows the user to add delegating handlers to the HttpClient transport. This feature was requested `GitHub #208 <https://github.com/TomPallister/Ocelot/issues/208>`_ and I decided that it was going to be useful in various ways.

Usage
^^^^^^

In order to add delegating handlers to the HttpClient transport you need to do the following.

.. code-block:: csharp

    services.AddOcelot()
            .AddDelegatingHandler(() => new FakeHandler())
            .AddDelegatingHandler(() => new FakeHandler());

Or for singleton like behaviour..

.. code-block:: csharp

    var handlerOne = new FakeHandler();
    var handlerTwo = new FakeHandler();

    services.AddOcelot()
            .AddDelegatingHandler(() => handlerOne)
            .AddDelegatingHandler(() => handlerTwo);

You can have as many DelegatingHandlers as you want and they are run in a first in first out order. If you are using Ocelot's QoS functionality then that will always be run after your last delegating handler.

In order to create a class that can be used a delegating handler it must look as follows

.. code-block:: csharp

    public class FakeHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            //do stuff and optionally call the base handler..
            return await base.SendAsync(request, cancellationToken);
        }
    }

Hopefully other people will find this feature useful!