Limiting retry behaviour to certain 50x errors (+1 squashed commits)

Squashed commits:

[2ef4f3e] Fixed type in test name

Author: dylan-asos

src/SendGrid/Reliability/RetryDelegatingHandler.cs

@@ -1,6 +1,7 @@
 namespace SendGrid.Helpers.Reliability
 {
     using System;
+    using System.Collections.Generic;
     using System.Net.Http;
     using System.Threading;
     using System.Threading.Tasks;
@@ -10,6 +11,8 @@
     /// </summary>
     public class RetryDelegatingHandler : DelegatingHandler
     {
+        private static List<int> retriableStatusCodes = new List<int>() { 500, 502, 503, 504 };
+
         private readonly ReliabilitySettings settings;
 
         /// <summary>
@@ -44,7 +47,7 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
                 {
                     responseMessage = await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
 
-                    ThrowHttpRequestExceptionIfResponseIsWithinTheServerErrorRange(responseMessage);
+                    ThrowHttpRequestExceptionIfResponseCodeIsRetriable(responseMessage);
 
                     sent = true;
                 }
@@ -76,11 +79,13 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
             return responseMessage;
         }
 
-        private static void ThrowHttpRequestExceptionIfResponseIsWithinTheServerErrorRange(HttpResponseMessage responseMessage)
+        private static void ThrowHttpRequestExceptionIfResponseCodeIsRetriable(HttpResponseMessage responseMessage)
         {
-            if ((int)responseMessage.StatusCode >= 500 && (int)responseMessage.StatusCode <= 504)
+            int statusCode = (int)responseMessage.StatusCode;
+
+            if (retriableStatusCodes.Contains(statusCode))
             {
-                throw new HttpRequestException(string.Format("Response Http Status code {0} indicates server error", responseMessage.StatusCode));
+                throw new HttpRequestException(string.Format("Http status code '{0}' indicates server error", statusCode));
             }
         }
     }

tests/SendGrid.Tests/Reliability/RetryDelegatingHandlerTests.cs

@@ -65,12 +65,23 @@ public async Task Invoke_ShouldReturnErrorWithoutRetryWhen500ErrorStatusIsNotTra
 
             var response = await client.SendAsync(new HttpRequestMessage());
 
-            Assert.Equal((HttpStatusCode)505, response.StatusCode);
+            Assert.Equal(HttpStatusCode.HttpVersionNotSupported, response.StatusCode);
             Assert.Equal(1, innerHandler.InvocationCount);
         }
 
         [Fact]
-        public async Task Invoke_ShoulddRetryOnceWhenFailedOnFirstAttemptThenSuccessful()
+        public async Task Invoke_ShouldReturnErrorWithoutRetryWhen501ErrorStatus()
+        {
+            innerHandler.AddBehaviour(innerHandler.NotImplemented);
+
+            var response = await client.SendAsync(new HttpRequestMessage());
+
+            Assert.Equal(HttpStatusCode.NotImplemented, response.StatusCode);
+            Assert.Equal(1, innerHandler.InvocationCount);
+        }
+
+        [Fact]
+        public async Task Invoke_ShouldRetryOnceWhenFailedOnFirstAttemptThenSuccessful()
         {
             innerHandler.AddBehaviour(innerHandler.TaskCancelled);
             innerHandler.AddBehaviour(innerHandler.OK);
@@ -96,7 +107,7 @@ public async Task Invoke_ShouldRetryTheExpectedAmountOfTimesAndReturnTimeoutExce
         public async Task Invoke_ShouldRetryTheExpectedAmountOfTimesAndReturnExceptionWhenInternalServerErrorsEncountered()
         {
             innerHandler.AddBehaviour(innerHandler.InternalServerError);
-            innerHandler.AddBehaviour(innerHandler.InternalServerError);
+            innerHandler.AddBehaviour(innerHandler.ServiceUnavailable);
 
             await Assert.ThrowsAsync<HttpRequestException>(() => client.SendAsync(new HttpRequestMessage()));
 

tests/SendGrid.Tests/Reliability/RetryTestBehaviourDelegatingHandler.cs

@@ -38,14 +38,22 @@ public Task<HttpResponseMessage> InternalServerError()
         {
             return CreateHttpResponse(HttpStatusCode.InternalServerError);
         }
+        public Task<HttpResponseMessage> ServiceUnavailable()
+        {
+            return CreateHttpResponse(HttpStatusCode.ServiceUnavailable);
+        }
 
         public Task<HttpResponseMessage> AuthenticationError()
         {
             return CreateHttpResponse(HttpStatusCode.Unauthorized);
         }
         public Task<HttpResponseMessage> HttpVersionNotSupported()
         {
-            return CreateHttpResponse((HttpStatusCode)505);
+            return CreateHttpResponse(HttpStatusCode.HttpVersionNotSupported);
+        }
+        public Task<HttpResponseMessage> NotImplemented()
+        {
+            return CreateHttpResponse(HttpStatusCode.NotImplemented);
         }
 
         public Task<HttpResponseMessage> CreateHttpResponse(HttpStatusCode statusCode)