Properly set connection lease timeout regardless of .NET target framework

iothub/device/src/Transport/Http/HttpClientHelper.cs

@@ -75,9 +75,6 @@ public HttpClientHelper(
             _authenticationHeaderProvider = authenticationHeaderProvider;
             _defaultErrorMapping = new ReadOnlyDictionary<HttpStatusCode, Func<HttpResponseMessage, Task<Exception>>>(defaultErrorMapping);
 
-            ServicePoint servicePoint = ServicePointManager.FindServicePoint(_baseAddress);
-            servicePoint.ConnectionLeaseTimeout = s_defaultConnectionLeaseTimeout.Milliseconds;
-
 #if NET451
             TlsVersions.Instance.SetLegacyAcceptableVersions();
 
@@ -104,8 +101,6 @@ public HttpClientHelper(
                 _httpClientHandler.UseProxy = (proxy != null);
                 _httpClientHandler.Proxy = proxy;
             }
-
-            _httpClientObj = _httpClientHandler != null ? new HttpClient(_httpClientHandler) : new HttpClient();
 #else
 
             _httpClientHandler = httpClientHandler ?? new HttpClientHandler();
@@ -123,11 +118,11 @@ public HttpClientHelper(
                 _httpClientHandler.UseProxy = proxy != null;
                 _httpClientHandler.Proxy = proxy;
             }
+#endif
 
-            _httpClientHandler.MaxConnectionsPerServer = DefaultMaxConnectionsPerServer;
+            ServicePointHelpers.SetLimits(_httpClientHandler, _baseAddress);
 
-            _httpClientObj = new HttpClient(_httpClientHandler);
-#endif
+            _httpClientObj = _httpClientHandler != null ? new HttpClient(_httpClientHandler) : new HttpClient();
 
             _httpClientObj.BaseAddress = _baseAddress;
             _httpClientObj.Timeout = timeout;

iothub/device/src/Transport/Http/ServicePointHelpers.cs

@@ -0,0 +1,48 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Net;
+using System.Net.Http;
+
+namespace Microsoft.Azure.Devices.Client
+{
+    // This type manages changing HttpClient defaults to more appropriate values
+    // There are two limits we target:
+    // - Per Server Connection Limit
+    // - Keep Alive Connection Timeout
+    // On .NET Core 2.1+ the HttpClient defaults to using the HttpSocketHandler so we adjust both limits on the client handler
+    //
+    // On .NET Standard & NET 4.51+ the HttpClient defaults to using the HttpClientHandler
+    //   and there is no easy way to set Keep Alive Connection Timeout but it's mitigated by setting the service point's connection lease timeout
+    internal static class ServicePointHelpers
+    {
+        // These default values are consistent with Azure.Core default values:
+        // https://github.com/Azure/azure-sdk-for-net/blob/7e3cf643977591e9041f4c628fd4d28237398e0b/sdk/core/Azure.Core/src/Pipeline/ServicePointHelpers.cs#L28
+        internal const int DefaultMaxConnectionsPerServer = 50;
+
+        internal const int DefaultConnectionLeaseTimeout = 300 * 1000; // 5 minutes
+
+        // messageHandler passed in is an HttpClientHandler for .NET Framework and .NET standard, and a SocketsHttpHandler for .NET core
+        public static void SetLimits(HttpMessageHandler messageHandler, Uri baseUri, int connectionLeaseTimeoutMilliseconds = DefaultConnectionLeaseTimeout)
+        {
+            switch (messageHandler)
+            {
+                case HttpClientHandler httpClientHandler:
+#if !NET451
+                    httpClientHandler.MaxConnectionsPerServer = DefaultMaxConnectionsPerServer;
+#endif
+                    ServicePoint servicePoint = ServicePointManager.FindServicePoint(baseUri);
+                    servicePoint.ConnectionLeaseTimeout = connectionLeaseTimeoutMilliseconds;
+                    break;
+#if NETCOREAPP2_1_OR_GREATER || NET5_0_OR_GREATER
+                // SocketsHttpHandler is only available in netcore2.1 and onwards
+                case SocketsHttpHandler socketsHttpHandler:
+                    socketsHttpHandler.MaxConnectionsPerServer = DefaultMaxConnectionsPerServer;
+                    socketsHttpHandler.PooledConnectionLifetime = TimeSpan.FromMilliseconds(connectionLeaseTimeoutMilliseconds);
+                    break;
+#endif
+            }
+        }
+    }
+}