Feature/expose http handlers (#224)

* temp commit

* trying to work out how to expose the http handlers in a decent way..

* pissing about at lunch

* changed to func so you can instanciate object or new it up each time

* docs for dele handlers

* upgraded to sdk 2.1.4

* some validation for consul services

docs/features/delegatinghandlers.rst

@@ -0,0 +1,43 @@
+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!

docs/index.rst

@@ -33,6 +33,8 @@ Thanks for taking a look at the Ocelot documentation. Please use the left hand n
    features/requestid
    features/middlewareinjection
    features/loadbalancer
+   features/delegatinghandlers
+
 
 .. toctree::
    :maxdepth: 2