Added RetryHandler. (#80)

Author: nduijvelshoff

BunqSdk/BunqSdk.csproj

@@ -24,6 +24,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="10.0.3-*" />
+    <PackageReference Include="Polly" Version="6.0.*" />
     <PackageReference Include="System.Collections.Immutable" Version="1.4.0" />
   </ItemGroup>
   <ItemGroup>

BunqSdk/Http/ApiClient.cs

@@ -99,7 +99,7 @@ public ApiClient(ApiContext apiContext)
 
         private HttpClient CreateHttpClient()
         {
-            return new HttpClient(CreateHttpClientHandler())
+            return new HttpClient(new RetryHandler(CreateHttpClientHandler()))
             {
                 BaseAddress = new Uri(apiContext.GetBaseUri())
             };

BunqSdk/Http/RetryHandler.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using Polly;
+
+namespace Bunq.Sdk.Http
+{
+    public class RetryHandler : DelegatingHandler
+    {
+        public RetryHandler(HttpClientHandler handler) : base(handler) { }
+
+        protected override Task<HttpResponseMessage> SendAsync(
+            HttpRequestMessage request,
+            CancellationToken cancellationToken) =>
+            Policy
+                .Handle<HttpRequestException>()
+                .Or<TaskCanceledException>()
+                .OrResult<HttpResponseMessage>(x => !x.IsSuccessStatusCode)
+                .WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(3, retryAttempt)))
+                .ExecuteAsync(() => base.SendAsync(request, cancellationToken));
+    }
+}