Expose HttpConfig so retry behaviour is user-configurable

Analytics-CSharp/Segment/Analytics/Configuration.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Segment.Analytics.Policies;
+using Segment.Analytics.Retry;
 using Segment.Analytics.Utilities;
 using Segment.Concurrent;
 using Segment.Serialization;
@@ -47,6 +48,21 @@ private set
 
         public IEventPipelineProvider EventPipelineProvider { get; }
 
+        /// <summary>
+        /// HTTP retry configuration for rate limiting and exponential backoff. Defaults to
+        /// <c>null</c>. Set it before constructing <c>Analytics</c>, e.g.
+        /// <c>new Configuration("writeKey") { HttpConfig = new HttpConfig(...) }</c>.
+        /// Mirrors analytics-kotlin's mutable <c>Configuration.httpConfig</c>.
+        /// <para>
+        /// This sets the pipeline's starting configuration only. CDN settings take precedence:
+        /// any settings payload carrying an <c>httpConfig</c> key replaces this value, and a CDN
+        /// payload is treated as enabling a subsystem unless it says <c>"enabled": "false"</c>.
+        /// A payload with no <c>httpConfig</c> key leaves this value in effect. This matches the
+        /// behaviour of analytics-kotlin and analytics-swift.
+        /// </para>
+        /// </summary>
+        public HttpConfig HttpConfig { get; set; }
+
         /// <summary>
         /// Configuration that analytics can use
         /// </summary>

Analytics-CSharp/Segment/Analytics/Retry/RetryConfig.cs

@@ -3,7 +3,7 @@
 
 namespace Segment.Analytics.Retry
 {
-    internal class RateLimitConfig
+    public class RateLimitConfig
     {
         public bool Enabled { get; }
         public int MaxRetryCount { get; }
@@ -23,7 +23,7 @@ public RateLimitConfig(bool enabled = false, int maxRetryCount = 100, int maxRet
         );
     }
 
-    internal class BackoffConfig
+    public class BackoffConfig
     {
         public bool Enabled { get; }
         public int MaxRetryCount { get; }
@@ -57,7 +57,10 @@ public BackoffConfig(
             Default4xxBehavior = default4xxBehavior;
             Default5xxBehavior = default5xxBehavior;
             UnknownCodeBehavior = unknownCodeBehavior;
-            StatusCodeOverrides = statusCodeOverrides ?? DefaultStatusCodeOverrides;
+            // Copied because the property is public: sharing the static default would let
+            // one caller's mutation corrupt every BackoffConfig built afterwards.
+            StatusCodeOverrides = new Dictionary<int, RetryBehavior>(
+                statusCodeOverrides ?? DefaultStatusCodeOverrides);
         }
 
         public BackoffConfig Validated() => new BackoffConfig(
@@ -93,7 +96,11 @@ private static Dictionary<int, RetryBehavior> ValidateOverrides(
                 { 429, RetryBehavior.Retry },
                 { 460, RetryBehavior.Retry },
                 { 501, RetryBehavior.Drop },
-                { 505, RetryBehavior.Drop }
+                { 505, RetryBehavior.Drop },
+                // 511 is only retryable for an SDK that can re-authenticate via OAuth.
+                // This one cannot, so retrying would spend the budget on a request that
+                // can never succeed.
+                { 511, RetryBehavior.Drop }
             };
     }
 
@@ -109,7 +116,7 @@ public RetryConfig(RateLimitConfig rateLimitConfig = null, BackoffConfig backoff
         }
     }
 
-    internal class HttpConfig
+    public class HttpConfig
     {
         public RateLimitConfig RateLimitConfig { get; }
         public BackoffConfig BackoffConfig { get; }

Analytics-CSharp/Segment/Analytics/Retry/RetryStateMachine.cs

@@ -22,7 +22,7 @@ public RetryState HandleResponse(RetryState state, ResponseInfo response)
         {
             if (IsLegacyMode)
             {
-                if (response.StatusCode >= 200 && response.StatusCode <= 299)
+                if (response.StatusCode >= 200 && response.StatusCode < 400)
                     return state.RemoveBatch(response.BatchFile);
                 if (response.StatusCode == 429 || (response.StatusCode >= 500 && response.StatusCode <= 599))
                     return state; // Keep
@@ -31,7 +31,7 @@ public RetryState HandleResponse(RetryState state, ResponseInfo response)
 
             long currentTime = response.CurrentTime;
 
-            if (response.StatusCode >= 200 && response.StatusCode <= 299)
+            if (response.StatusCode >= 200 && response.StatusCode < 400)
             {
                 return state.With(
                     pipelineState: PipelineState.Ready,
@@ -41,15 +41,25 @@ public RetryState HandleResponse(RetryState state, ResponseInfo response)
                 );
             }
 
+            // Any retryable status with Retry-After → rate-limit path
+            if (response.RetryAfterSeconds.HasValue && response.RetryAfterSeconds.Value > 0)
+            {
+                RetryBehavior behavior = response.StatusCode == 429
+                    ? RetryBehavior.Retry  // 429 is always retryable
+                    : ResolveStatusCodeBehavior(response.StatusCode);
+                if (behavior == RetryBehavior.Retry && _config.RateLimitConfig.Enabled)
+                    return HandleRateLimitResponse(state, response, currentTime);
+            }
+
             if (response.StatusCode == 429)
             {
                 if (_config.RateLimitConfig.Enabled)
                     return HandleRateLimitResponse(state, response, currentTime);
                 return state.RemoveBatch(response.BatchFile);
             }
 
-            RetryBehavior behavior = ResolveStatusCodeBehavior(response.StatusCode);
-            if (behavior == RetryBehavior.Retry && _config.BackoffConfig.Enabled)
+            RetryBehavior statusBehavior = ResolveStatusCodeBehavior(response.StatusCode);
+            if (statusBehavior == RetryBehavior.Retry && _config.BackoffConfig.Enabled)
                 return HandleRetryableError(state, response, currentTime);
 
             return state.RemoveBatch(response.BatchFile);
@@ -131,20 +141,36 @@ public int GetRetryCount(RetryState state, string batchFile)
             return Math.Max(batchRetryCount, state.GlobalRetryCount);
         }
 
-        public bool ShouldDeleteBatch(int statusCode)
+        public bool ShouldDeleteBatch(int statusCode) => ShouldDeleteBatch(statusCode, null);
+
+        /// <summary>
+        /// Whether the batch file should be removed. <paramref name="retryAfterSeconds"/> must be
+        /// the same value handed to <see cref="HandleResponse"/>, so that the two agree on whether
+        /// this response took the rate-limit path.
+        /// </summary>
+        public bool ShouldDeleteBatch(int statusCode, int? retryAfterSeconds)
         {
             if (IsLegacyMode)
                 return statusCode >= 400 && statusCode <= 499 && statusCode != 429;
 
-            if (statusCode >= 200 && statusCode <= 299)
+            // Spec item 1: 2xx and 3xx are success.
+            if (statusCode >= 200 && statusCode < 400)
                 return true;
 
             if (statusCode == 429)
                 return !_config.RateLimitConfig.Enabled;
 
             RetryBehavior behavior = ResolveStatusCodeBehavior(statusCode);
-            if (behavior == RetryBehavior.Retry && !_config.BackoffConfig.Enabled)
-                return true;
+            if (behavior == RetryBehavior.Retry)
+            {
+                // A usable Retry-After sends this response down the rate-limit path, which has
+                // just scheduled the retry — keep the batch that retry will re-upload.
+                if (retryAfterSeconds.HasValue && retryAfterSeconds.Value > 0 && _config.RateLimitConfig.Enabled)
+                    return false;
+
+                // Otherwise only backoff can retry it; with backoff off, nothing will.
+                return !_config.BackoffConfig.Enabled;
+            }
 
             return behavior == RetryBehavior.Drop;
         }

Analytics-CSharp/Segment/Analytics/Retry/RetryTypes.cs

@@ -6,7 +6,7 @@ internal enum PipelineState
         RateLimited
     }
 
-    internal enum RetryBehavior
+    public enum RetryBehavior
     {
         Retry,
         Drop

Analytics-CSharp/Segment/Analytics/Utilities/EventPipeline.cs

@@ -48,7 +48,7 @@ public EventPipeline(
             string apiHost = HTTPClient.DefaultAPIHost)
             : this(analytics, logTag, apiKey, flushPolicies, apiHost, (HttpConfig)null) { }
 
-        internal EventPipeline(
+        public EventPipeline(
             Analytics analytics,
             string logTag,
             string apiKey,
@@ -69,7 +69,9 @@ internal EventPipeline(
             Running = false;
 
             var retryConfig = httpConfig != null
-                ? new RetryConfig(httpConfig.RateLimitConfig, httpConfig.BackoffConfig)
+                // User-supplied config arrives unclamped; the CDN path is already
+                // validated by HttpConfigParser.
+                ? new RetryConfig(httpConfig.RateLimitConfig.Validated(), httpConfig.BackoffConfig.Validated())
                 : new RetryConfig();
             _retryStateMachine = new RetryStateMachine(retryConfig);
             _retryState = RetryStateStorage.LoadRetryState(_storage);
@@ -78,7 +80,7 @@ internal EventPipeline(
         internal void UpdateHttpConfig(HttpConfig config)
         {
             var retryConfig = config != null
-                ? new RetryConfig(config.RateLimitConfig, config.BackoffConfig)
+                ? new RetryConfig(config.RateLimitConfig.Validated(), config.BackoffConfig.Validated())
                 : new RetryConfig();
             _retryStateMachine = new RetryStateMachine(retryConfig);
         }
@@ -209,11 +211,7 @@ await Scope.WithContext(_analytics.FileIODispatcher, () =>
                         HTTPClient.Response response = await _httpClient.UploadWithResponse(data, retryCount);
                         statusCode = response.StatusCode;
 
-                        if (!string.IsNullOrEmpty(response.RetryAfterHeader)
-                            && int.TryParse(response.RetryAfterHeader.Trim(), out int parsedRetryAfter))
-                        {
-                            retryAfterSeconds = parsedRetryAfter;
-                        }
+                        retryAfterSeconds = RetryAfterParser.Parse(response.RetryAfterHeader);
 
                         if (response.IsSuccessStatusCode)
                         {
@@ -223,7 +221,7 @@ await Scope.WithContext(_analytics.FileIODispatcher, () =>
                         else
                         {
                             Analytics.Logger.Log(LogLevel.Error, message: "Error " + statusCode + " uploading " + url);
-                            shouldCleanup = _retryStateMachine.ShouldDeleteBatch(statusCode);
+                            shouldCleanup = _retryStateMachine.ShouldDeleteBatch(statusCode, retryAfterSeconds);
                             if (shouldCleanup)
                             {
                                 _analytics.ReportInternalError(AnalyticsErrorType.NetworkServerRejected,

Analytics-CSharp/Segment/Analytics/Utilities/EventPipelineProvider.cs

@@ -11,7 +11,8 @@ public IEventPipeline Create(Analytics analytics, string key)
             return new EventPipeline(analytics, key, 
                     analytics.Configuration.WriteKey,
                     analytics.Configuration.FlushPolicies,
-                    analytics.Configuration.ApiHost);
+                    analytics.Configuration.ApiHost,
+                    analytics.Configuration.HttpConfig);
         }
     }
 }

Analytics-CSharp/Segment/Analytics/Utilities/HTTPClient.cs

@@ -5,6 +5,7 @@
 using System.Net;
 using System.Net.Http;
 using System.Net.Http.Headers;
+using System.Text;
 using System.Threading.Tasks;
 using Segment.Analytics.Retry;
 using Segment.Serialization;
@@ -25,6 +26,15 @@ public abstract class HTTPClient
 
         private readonly string _apiKey;
 
+        /// <summary>
+        /// Value for the Authorization header: the write key as HTTP Basic credentials with an
+        /// empty password, matching the other Segment SDKs. TAPI authenticates and routes on this
+        /// header rather than parsing the payload, so custom <see cref="HTTPClient"/>
+        /// implementations should send it on upload requests.
+        /// </summary>
+        protected string BasicAuthorization =>
+            "Basic " + Convert.ToBase64String(Encoding.UTF8.GetBytes(_apiKey + ":"));
+
         protected readonly string _apiHost;
 
         protected readonly string _cdnHost;
@@ -188,7 +198,8 @@ public class Response
             /// <summary>
             /// A convenient method to check if the http request is successful
             /// </summary>
-            public bool IsSuccessStatusCode => StatusCode >= 200 && StatusCode < 300;
+            // Spec item 1: 2xx and 3xx are success.
+            public bool IsSuccessStatusCode => StatusCode >= 200 && StatusCode < 400;
         }
     }
 
@@ -242,6 +253,7 @@ public override async Task<Response> DoPost(string url, byte[] data, int retryCo
 
                 var request = new HttpRequestMessage(HttpMethod.Post, url);
                 request.Headers.Add("Connection", "close");
+                request.Headers.Add("Authorization", BasicAuthorization);
                 request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/plain"));
                 if (retryCount > 0)
                     request.Headers.Add("X-Retry-Count", retryCount.ToString());

Analytics-CSharp/Segment/Analytics/Utilities/RetryAfterParser.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Globalization;
+
+namespace Segment.Analytics.Utilities
+{
+    internal static class RetryAfterParser
+    {
+        /// <summary>
+        /// Parses a Retry-After header value. Supports both integer seconds and HTTP-date (RFC 1123) format.
+        /// Returns the number of seconds to wait, or null if the header is empty/unparseable/in the past.
+        /// </summary>
+        internal static int? Parse(string headerValue, DateTimeOffset? now = null)
+        {
+            if (string.IsNullOrEmpty(headerValue))
+                return null;
+
+            string trimmed = headerValue.Trim();
+
+            if (int.TryParse(trimmed, out int parsedInt))
+            {
+                return parsedInt;
+            }
+
+            if (DateTimeOffset.TryParseExact(trimmed,
+                new[] { "r", "ddd, dd MMM yyyy HH:mm:ss 'GMT'" },
+                CultureInfo.InvariantCulture,
+                DateTimeStyles.AssumeUniversal,
+                out DateTimeOffset targetDate))
+            {
+                DateTimeOffset reference = now ?? DateTimeOffset.UtcNow;
+                int seconds = (int)(targetDate - reference).TotalSeconds;
+                return seconds > 0 ? seconds : (int?)null;
+            }
+
+            return null;
+        }
+    }
+}

Analytics-CSharp/Segment/Analytics/Utilities/SyncEventPipeline.cs

@@ -61,7 +61,7 @@ public SyncEventPipeline(
             CancellationToken? flushCancellationToken = null)
             : this(analytics, logTag, apiKey, flushPolicies, apiHost, flushTimeout, flushCancellationToken, null) { }
 
-        internal SyncEventPipeline(
+        public SyncEventPipeline(
             Analytics analytics,
             string logTag,
             string apiKey,
@@ -86,7 +86,9 @@ internal SyncEventPipeline(
             _flushCancellationToken = flushCancellationToken ?? CancellationToken.None;
 
             var retryConfig = httpConfig != null
-                ? new RetryConfig(httpConfig.RateLimitConfig, httpConfig.BackoffConfig)
+                // User-supplied config arrives unclamped; the CDN path is already
+                // validated by HttpConfigParser.
+                ? new RetryConfig(httpConfig.RateLimitConfig.Validated(), httpConfig.BackoffConfig.Validated())
                 : new RetryConfig();
             _retryStateMachine = new RetryStateMachine(retryConfig);
             _retryState = RetryStateStorage.LoadRetryState(_storage);
@@ -95,7 +97,7 @@ internal SyncEventPipeline(
         internal void UpdateHttpConfig(HttpConfig config)
         {
             var retryConfig = config != null
-                ? new RetryConfig(config.RateLimitConfig, config.BackoffConfig)
+                ? new RetryConfig(config.RateLimitConfig.Validated(), config.BackoffConfig.Validated())
                 : new RetryConfig();
             _retryStateMachine = new RetryStateMachine(retryConfig);
         }
@@ -234,11 +236,7 @@ await Scope.WithContext(_analytics.FileIODispatcher, () =>
                         HTTPClient.Response response = await _httpClient.UploadWithResponse(data, retryCount);
                         statusCode = response.StatusCode;
 
-                        if (!string.IsNullOrEmpty(response.RetryAfterHeader)
-                            && int.TryParse(response.RetryAfterHeader.Trim(), out int parsedRetryAfter))
-                        {
-                            retryAfterSeconds = parsedRetryAfter;
-                        }
+                        retryAfterSeconds = RetryAfterParser.Parse(response.RetryAfterHeader);
 
                         if (response.IsSuccessStatusCode)
                         {
@@ -248,7 +246,7 @@ await Scope.WithContext(_analytics.FileIODispatcher, () =>
                         else
                         {
                             Analytics.Logger.Log(LogLevel.Error, message: "Error " + statusCode + " uploading " + url);
-                            shouldCleanup = _retryStateMachine.ShouldDeleteBatch(statusCode);
+                            shouldCleanup = _retryStateMachine.ShouldDeleteBatch(statusCode, retryAfterSeconds);
                             if (shouldCleanup)
                             {
                                 _analytics.ReportInternalError(AnalyticsErrorType.NetworkServerRejected,

Analytics-CSharp/Segment/Analytics/Utilities/SyncEventPipelineProvider.cs

@@ -22,7 +22,8 @@ public IEventPipeline Create(Analytics analytics, string key)
                     analytics.Configuration.FlushPolicies,
                     analytics.Configuration.ApiHost,
                     _flushTimeout,
-                    _flushCancellationToken);
+                    _flushCancellationToken,
+                    analytics.Configuration.HttpConfig);
         }
     }
 }

Samples/UnitySample/UnityHTTPClient.cs

@@ -61,6 +61,7 @@ IEnumerator PostRequest(NetworkRequest networkRequest)
             using (var request = UnityWebRequest.Put(networkRequest.URL, networkRequest.Data))
             {
                 request.SetRequestHeader("Content-Type", "text/plain");
+                request.SetRequestHeader("Authorization", BasicAuthorization);
                 yield return request.SendWebRequest();
 
                 networkRequest.Response.StatusCode = (int)request.responseCode;