Retry http 429 responses

src/NuGet.Core/NuGet.Protocol/EnhancedHttpRetryHelper.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using NuGet.Common;
 
@@ -26,6 +28,11 @@ internal class EnhancedHttpRetryHelper
         /// </summary>
         public const int DefaultRetryCount = 6;
 
+        /// <summary>
+        /// The default value indicating whether or not to retry HTTP 429 responses.
+        /// </summary>
+        public const bool DefaultRetry429 = true;
+
         /// <summary>
         /// The environment variable used to change the delay value.
         /// </summary>
@@ -41,6 +48,11 @@ internal class EnhancedHttpRetryHelper
         /// </summary>
         public const string RetryCountEnvironmentVariableName = "NUGET_ENHANCED_MAX_NETWORK_TRY_COUNT";
 
+        /// <summary>
+        /// The environment variabled to to disable retrying HTTP 429 responses.
+        /// </summary>
+        public const string Retry429EnvironmentVariableName = "NUGET_RETRY_HTTP_429";
+
         private readonly IEnvironmentVariableReader _environmentVariableReader;
 
         private bool? _isEnabled = null;
@@ -49,6 +61,8 @@ internal class EnhancedHttpRetryHelper
 
         private int? _delayInMilliseconds = null;
 
+        private bool? _retry429 = null;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="EnhancedHttpRetryHelper" /> class.
         /// </summary>
@@ -74,6 +88,11 @@ public EnhancedHttpRetryHelper(IEnvironmentVariableReader environmentVariableRea
         /// </summary>
         internal int DelayInMilliseconds => _delayInMilliseconds ??= GetIntFromEnvironmentVariable(DelayInMillisecondsEnvironmentVariableName, defaultValue: DefaultDelayMilliseconds, _environmentVariableReader);
 
+        /// <summary>
+        /// Gets a value indicating whether or not retryable HTTP 4xx responses should be retried.
+        /// </summary>
+        internal bool Retry429 => _retry429 ??= GetBoolFromEnvironmentVariable(Retry429EnvironmentVariableName, defaultValue: true, _environmentVariableReader);
+
         /// <summary>
         /// Gets a <see cref="bool" /> value from the specified environment variable.
         /// </summary>
@@ -106,7 +125,7 @@ private static int GetIntFromEnvironmentVariable(string variableName, int defaul
         {
             try
             {
-                if (int.TryParse(environmentVariableReader.GetEnvironmentVariable(variableName), out int parsedValue))
+                if (int.TryParse(environmentVariableReader.GetEnvironmentVariable(variableName), out int parsedValue) && parsedValue >= 0)
                 {
                     return parsedValue;
                 }

src/NuGet.Core/NuGet.Protocol/HttpSource/HttpRetryHandler.cs

@@ -204,7 +204,11 @@ public async Task<HttpResponseMessage> SendAsync(
                             requestUri,
                             bodyStopwatch.ElapsedMilliseconds));
 
-                        if ((int)response.StatusCode >= 500)
+                        int statusCode = (int)response.StatusCode;
+                        // 5xx == server side failure
+                        // 408 == request timeout
+                        // 429 == too many requests
+                        if (statusCode >= 500 || ((statusCode == 408 || statusCode == 429) && _enhancedHttpRetryHelper.Retry429))
                         {
                             success = false;
                         }

test/NuGet.Core.Tests/NuGet.Protocol.Tests/EnhancedHttpRetryHelperTests.cs

@@ -0,0 +1,111 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+#nullable enable
+
+using System.Collections.Generic;
+using Test.Utility;
+using Xunit;
+
+namespace NuGet.Protocol.Tests
+{
+    public class EnhancedHttpRetryHelperTests
+    {
+        [Fact]
+        public void NoEnvionrmentVaraiblesSet_UsesDefaultValues()
+        {
+            // Arrange
+            TestEnvironmentVariableReader testEnvironmentVariableReader = new TestEnvironmentVariableReader(new Dictionary<string, string>());
+
+            // Act
+            EnhancedHttpRetryHelper helper = new(testEnvironmentVariableReader);
+
+            // Assert
+            Assert.Equal(helper.IsEnabled, EnhancedHttpRetryHelper.DefaultEnabled);
+            Assert.Equal(helper.RetryCount, EnhancedHttpRetryHelper.DefaultRetryCount);
+            Assert.Equal(helper.DelayInMilliseconds, EnhancedHttpRetryHelper.DefaultDelayMilliseconds);
+            Assert.Equal(helper.Retry429, EnhancedHttpRetryHelper.DefaultRetry429);
+        }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData("5")]
+        [InlineData("something")]
+        public void InvalidBoolValue_UsesDefault(string value)
+        {
+            // Arrange
+            var dict = new Dictionary<string, string>()
+            {
+                [EnhancedHttpRetryHelper.IsEnabledEnvironmentVariableName] = value
+            };
+            var environmentReader = new TestEnvironmentVariableReader(dict);
+
+            // Act
+            EnhancedHttpRetryHelper helper = new(environmentReader);
+
+            // Assert
+            Assert.Equal(helper.IsEnabled, EnhancedHttpRetryHelper.DefaultEnabled);
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void ValidBoolValue_UsesValue(bool value)
+        {
+            // Arrange
+            var dict = new Dictionary<string, string>()
+            {
+                [EnhancedHttpRetryHelper.IsEnabledEnvironmentVariableName] = value.ToString().ToLowerInvariant()
+            };
+            var environmentReader = new TestEnvironmentVariableReader(dict);
+
+            // Act
+            EnhancedHttpRetryHelper helper = new(environmentReader);
+
+            // Assert
+            Assert.Equal(helper.IsEnabled, value);
+        }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData("true")]
+        [InlineData("something")]
+        [InlineData("-5")]
+        public void InvalidIntValue_UsesDefault(string value)
+        {
+            // Arrange
+            var dict = new Dictionary<string, string>()
+            {
+                [EnhancedHttpRetryHelper.RetryCountEnvironmentVariableName] = value
+            };
+            var environmentReader = new TestEnvironmentVariableReader(dict);
+
+            // Act
+            EnhancedHttpRetryHelper helper = new(environmentReader);
+
+            // Assert
+            Assert.Equal(helper.RetryCount, EnhancedHttpRetryHelper.DefaultRetryCount);
+        }
+
+        [Theory]
+        [InlineData(5)]
+        [InlineData(10)]
+        [InlineData(100)]
+        public void ValidIntValue_UsesValue(int value)
+        {
+            // Arrange
+            var dict = new Dictionary<string, string>()
+            {
+                [EnhancedHttpRetryHelper.RetryCountEnvironmentVariableName] = value.ToString().ToLowerInvariant()
+            };
+            var environmentReader = new TestEnvironmentVariableReader(dict);
+
+            // Act
+            EnhancedHttpRetryHelper helper = new(environmentReader);
+
+            // Assert
+            Assert.Equal(helper.RetryCount, value);
+        }
+
+    }
+}