issue 114/improvement: move creation of httpclient instance to virtua…

…l property (#119)

* improvement: move creation of httpclient instance to virtual

* update readme

README.md

@@ -234,6 +234,33 @@ var settings = new UnleashSettings()
 };
 ```
 
+### HttpMessageHandlers/Custom HttpClient initialization
+If you need to specify HttpMessageHandlers or to control the instantiation of the HttpClient, you can create a custom
+HttpClientFactory that inherits from DefaultHttpClientFactory, and override the method CreateHttpClientInstance.
+Then configure UnleashSettings to use your custom HttpClientFactory. 
+
+```csharp
+internal class CustomHttpClientFactory : DefaultHttpClientFactory
+{
+    protected override HttpClient CreateHttpClientInstance(Uri unleashApiUri)
+    {
+        var messageHandler = new CustomHttpMessageHandler();
+        var httpClient = new HttpClient(messageHandler)
+        {
+            BaseAddress = apiUri,
+            Timeout = TimeSpan.FromSeconds(5)
+        };
+    }
+}
+
+var settings = new UnleashSettings
+{
+    AppName = "dotnet-test",
+    //...
+    HttpClientFactory = new CustomHttpClientFactory()
+};
+```
+
 ### Dynamic custom HTTP headers
 If you need custom http headers that change during the lifetime of the client, a provider can be defined via the `UnleashSettings`. 
 

src/Unleash/DefaultHttpClientFactory.cs

@@ -36,11 +36,7 @@ public HttpClient Create(Uri unleashApiUri)
 
             return _httpClientCache.GetOrAdd(key, k =>
             {
-                var client = new HttpClient
-                {
-                    BaseAddress = unleashApiUri,
-                    Timeout = Timeout
-                };
+                var client = CreateHttpClientInstance(unleashApiUri);
                 // Refresh DNS cache each 60 seconds
                 var servicePoint = ServicePointManager.FindServicePoint(unleashApiUri);
                 ConfigureServicePoint(servicePoint);
@@ -51,6 +47,17 @@ public HttpClient Create(Uri unleashApiUri)
             });
         }
 
+        protected virtual HttpClient CreateHttpClientInstance(Uri unleashApiUri)
+        {
+            var client = new HttpClient
+            {
+                BaseAddress = unleashApiUri,
+                Timeout = Timeout
+            };
+
+            return client;
+        }
+
         protected virtual void ConfigureHttpClient(HttpClient httpClient)
         {
         }

tests/Unleash.Tests/DefaultUnleashTests.cs

@@ -1,6 +1,7 @@
 using FluentAssertions;
 using NUnit.Framework;
 using System;
+using Unleash.Tests.Mock;
 
 namespace Unleash.Tests
 {
@@ -27,5 +28,19 @@ public void ConfigureEvents_should_invoke_callback()
             // Assert
             callbackCalled.Should().BeTrue();
         }
+
+        [Test]
+        public void Configure_Http_Client_Factory()
+        {
+            // Arrange
+            var factory = new HttpClientFactoryMock();
+            var apiUri = new Uri("http://localhost:8080/");
+
+            // Act
+            var client = factory.Create(apiUri);
+
+            // Assert
+            factory.CreateHttpClientInstanceCalled.Should().BeTrue();
+        }
     }
 }

tests/Unleash.Tests/Mock/HttpClientFactoryMock.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Unleash.Tests.Mock
+{
+    internal class HttpClientFactoryMock : DefaultHttpClientFactory
+    {
+        public bool CreateHttpClientInstanceCalled { get; private set; }
+
+        protected override HttpClient CreateHttpClientInstance(Uri unleashApiUri)
+        {
+            CreateHttpClientInstanceCalled = true;
+
+            return base.CreateHttpClientInstance(unleashApiUri);
+        }
+
+    }
+}

tests/Unleash.Tests/Unleash.Tests.csproj

@@ -88,6 +88,7 @@
     <Compile Include="IOTests.cs" />
     <Compile Include="Metrics\MetricsBucketTests.cs" />
     <Compile Include="Mock\ConfigurableMessageHandlerMock.cs" />
+    <Compile Include="Mock\HttpClientFactoryMock.cs" />
     <Compile Include="Mock\MockApiClient.cs" />
     <Compile Include="Mock\MockHttpMessageHandler.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />