feat: allow the RetryDelegatingHandler to be used with HttpClientFactory (#1030)

A default inner handler should not be created by the delegating handler as required by the client factory. This change moves the creation of `HttpClientHandler` to the base client.

Author: childish-sambino

src/SendGrid/BaseClient.cs

@@ -234,7 +234,7 @@ public async Task<Response> RequestAsync(
 
         private static HttpClient CreateHttpClientWithRetryHandler(BaseClientOptions options)
         {
-            return new HttpClient(new RetryDelegatingHandler(options.ReliabilitySettings));
+            return new HttpClient(new RetryDelegatingHandler(new HttpClientHandler(), options.ReliabilitySettings));
         }
 
         /// <summary>

src/SendGrid/Reliability/RetryDelegatingHandler.cs

@@ -33,8 +33,8 @@ public class RetryDelegatingHandler : DelegatingHandler
         /// </summary>
         /// <param name="settings">A ReliabilitySettings instance.</param>
         public RetryDelegatingHandler(ReliabilitySettings settings)
-            : this(new HttpClientHandler(), settings)
         {
+            this.settings = settings;
         }
 
         /// <summary>

tests/SendGrid.Tests/Integration.cs

@@ -5872,7 +5872,10 @@ public async Task TestRetryBehaviourThrowsTimeoutException()
                 ReliabilitySettings = new ReliabilitySettings(1, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(1))
             };
 
-            var retryHandler = new RetryDelegatingHandler(new HttpClientHandler(), options.ReliabilitySettings);
+            var retryHandler = new RetryDelegatingHandler(options.ReliabilitySettings);
+
+            // Verify we can set the inner handler after constrcution.
+            retryHandler.InnerHandler = new HttpClientHandler();
 
             HttpClient clientToInject = new HttpClient(retryHandler) { Timeout = TimeSpan.FromMilliseconds(1) };
             var sg = new SendGridClient(clientToInject, options.ApiKey);