[http] Avoid boxing of status code tags

src/OpenTelemetry.Instrumentation.Http/CHANGELOG.md

@@ -3,8 +3,11 @@
 ## Unreleased
 
 * Fixed an issue of missing `http.client.duration` metric data in case of
-network failures (when response is not available).
-([#4098](https://github.com/open-telemetry/opentelemetry-dotnet/pull/4098))
+  network failures (when response is not available).
+  ([#4098](https://github.com/open-telemetry/opentelemetry-dotnet/pull/4098))
+
+* Improve perf by avoiding boxing of common status codes values.
+  ([#4361](https://github.com/open-telemetry/opentelemetry-dotnet/pull/4361))
 
 ## 1.0.0-rc9.14
 

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpHandlerDiagnosticListener.cs

@@ -209,7 +209,7 @@ public void OnStopActivity(Activity activity, object payload)
 
                 if (this.stopResponseFetcher.TryFetch(payload, out HttpResponseMessage response) && response != null)
                 {
-                    activity.SetTag(SemanticConventions.AttributeHttpStatusCode, (int)response.StatusCode);
+                    activity.SetTag(SemanticConventions.AttributeHttpStatusCode, TelemetryHelper.GetBoxedStatusCode(response.StatusCode));
 
                     if (currentStatusCode == ActivityStatusCode.Unset)
                     {

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpHandlerMetricsDiagnosticListener.cs

@@ -62,7 +62,7 @@ public override void OnEventWritten(string name, object payload)
 
                     if (this.stopResponseFetcher.TryFetch(payload, out HttpResponseMessage response) && response != null)
                     {
-                        tags.Add(new KeyValuePair<string, object>(SemanticConventions.AttributeHttpStatusCode, (int)response.StatusCode));
+                        tags.Add(new KeyValuePair<string, object>(SemanticConventions.AttributeHttpStatusCode, TelemetryHelper.GetBoxedStatusCode(response.StatusCode)));
                     }
 
                     // We are relying here on HttpClient library to set duration before writing the stop event.

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpWebRequestActivitySource.netfx.cs

@@ -123,7 +123,7 @@ private static void AddResponseTags(HttpWebResponse response, Activity activity)
         {
             if (activity.IsAllDataRequested)
             {
-                activity.SetTag(SemanticConventions.AttributeHttpStatusCode, (int)response.StatusCode);
+                activity.SetTag(SemanticConventions.AttributeHttpStatusCode, TelemetryHelper.GetBoxedStatusCode(response.StatusCode));
 
                 activity.SetStatus(SpanHelper.ResolveSpanStatusForHttpStatusCode(activity.Kind, (int)response.StatusCode));
 

src/OpenTelemetry.Instrumentation.Http/Implementation/TelemetryHelper.cs

@@ -0,0 +1,44 @@
+// <copyright file="TelemetryHelper.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System.Net;
+
+namespace OpenTelemetry.Instrumentation.Http.Implementation;
+
+internal static class TelemetryHelper
+{
+    private static readonly object[] BoxedStatusCodes;
+
+    static TelemetryHelper()
+    {
+        BoxedStatusCodes = new object[500];
+        for (int i = 0, c = 100; i < BoxedStatusCodes.Length; i++, c++)
+        {
+            BoxedStatusCodes[i] = c;
+        }
+    }
+
+    public static object GetBoxedStatusCode(HttpStatusCode statusCode)
+    {
+        int intStatusCode = (int)statusCode;
+        if (intStatusCode >= 100 && intStatusCode < 600)
+        {
+            return BoxedStatusCodes[intStatusCode - 100];
+        }
+
+        return intStatusCode;
+    }
+}