HttpClientHandler request metrics

src/libraries/System.Net.Http/ref/System.Net.Http.cs

@@ -135,6 +135,8 @@ public HttpClientHandler() { }
         public long MaxRequestContentBufferSize { get { throw null; } set { } }
         [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("browser")]
         public int MaxResponseHeadersLength { get { throw null; } set { } }
+        [System.CLSCompliantAttribute(false)]
+        public System.Diagnostics.Metrics.IMeterFactory? MeterFactory { get { throw null; } set { } }
         [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("browser")]
         public bool PreAuthenticate { get { throw null; } set { } }
         public System.Collections.Generic.IDictionary<string, object?> Properties { get { throw null; } }
@@ -397,6 +399,8 @@ public SocketsHttpHandler() { }
         public int MaxConnectionsPerServer { get { throw null; } set { } }
         public int MaxResponseDrainSize { get { throw null; } set { } }
         public int MaxResponseHeadersLength { get { throw null; } set { } }
+        [System.CLSCompliantAttribute(false)]
+        public System.Diagnostics.Metrics.IMeterFactory? MeterFactory { get { throw null; } set { } }
         public System.TimeSpan PooledConnectionIdleTimeout { get { throw null; } set { } }
         public System.TimeSpan PooledConnectionLifetime { get { throw null; } set { } }
         public bool PreAuthenticate { get { throw null; } set { } }
@@ -901,3 +905,15 @@ public WarningHeaderValue(int code, string agent, string text, System.DateTimeOf
         public static bool TryParse([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] string? input, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Net.Http.Headers.WarningHeaderValue? parsedValue) { throw null; }
     }
 }
+namespace System.Net.Http.Metrics
+{
+    public sealed class HttpMetricsEnrichmentContext
+    {
+        internal HttpMetricsEnrichmentContext() { }
+        public System.Net.Http.HttpRequestMessage Request { get { throw null; } }
+        public System.Net.Http.HttpResponseMessage? Response { get { throw null; } }
+        public System.Exception? Exception { get { throw null; } }
+        public void AddCustomTag(string name, object? value) { throw null; }
+        public static void AddCallback(System.Net.Http.HttpRequestMessage request, System.Action<System.Net.Http.Metrics.HttpMetricsEnrichmentContext> callback) { throw null; }
+    }
+}

src/libraries/System.Net.Http/src/System.Net.Http.csproj

@@ -122,6 +122,8 @@
     <Compile Include="System\Net\Http\Headers\UriHeaderParser.cs" />
     <Compile Include="System\Net\Http\Headers\ViaHeaderValue.cs" />
     <Compile Include="System\Net\Http\Headers\WarningHeaderValue.cs" />
+    <Compile Include="System\Net\Http\Metrics\HttpMetricsEnrichmentContext.cs" />
+    <Compile Include="System\Net\Http\Metrics\MetricsHandler.cs" />
     <Compile Include="System\Net\Http\SocketsHttpHandler\SocketsHttpPlaintextStreamFilterContext.cs" />
     <Compile Include="$(CommonPath)DisableRuntimeMarshalling.cs"
              Link="Common\DisableRuntimeMarshalling.cs" />
@@ -227,7 +229,7 @@
              Link="Common\System\Net\DebugSafeHandleZeroOrMinusOneIsInvalid.cs" />
     <Compile Include="$(CommonPath)System\Threading\Tasks\TaskCompletionSourceWithCancellation.cs"
              Link="Common\System\Threading\Tasks\TaskCompletionSourceWithCancellation.cs" />
-  <!-- Header support -->
+    <!-- Header support -->
     <Compile Include="$(CommonPath)System\Net\Http\aspnetcore\IHttpStreamHeadersHandler.cs">
       <Link>Common\System\Net\Http\aspnetcore\IHttpStreamHeadersHandler.cs</Link>
     </Compile>
@@ -471,4 +473,4 @@
   <ItemGroup>
     <None Include="Resources\SR.resx" />
   </ItemGroup>
-</Project>
+</Project>

src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/BrowserHttpHandler.cs

@@ -289,7 +289,6 @@ private static HttpResponseMessage ConvertResponse(HttpRequestMessage request, W
 
         protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
         {
-            ArgumentNullException.ThrowIfNull(request);
             bool? allowAutoRedirect = _isAllowAutoRedirectTouched ? AllowAutoRedirect : null;
 #if FEATURE_WASM_THREADS
             return JSHost.CurrentOrMainJSSynchronizationContext.Send(() =>

src/libraries/System.Net.Http/src/System/Net/Http/BrowserHttpHandler/SocketsHttpHandler.cs

@@ -9,6 +9,7 @@
 using System.Threading.Tasks;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics;
+using System.Diagnostics.Metrics;
 
 namespace System.Net.Http
 {
@@ -91,6 +92,13 @@ public int MaxResponseDrainSize
             set => throw new PlatformNotSupportedException();
         }
 
+        [CLSCompliant(false)]
+        public IMeterFactory? MeterFactory
+        {
+            get => throw new PlatformNotSupportedException();
+            set => throw new PlatformNotSupportedException();
+        }
+
         public TimeSpan ResponseDrainTimeout
         {
             get => throw new PlatformNotSupportedException();

src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs

@@ -78,7 +78,6 @@ internal override ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage re
         {
             if (IsEnabled())
             {
-                ArgumentNullException.ThrowIfNull(request);
                 return SendAsyncCore(request, async, cancellationToken);
             }
             else

src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.AnyMobile.cs

@@ -1,12 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Metrics;
 using System.Globalization;
+using System.Net.Http.Metrics;
 using System.Net.Security;
 using System.Reflection;
 using System.Runtime.ExceptionServices;
@@ -21,37 +21,28 @@ namespace System.Net.Http
     public partial class HttpClientHandler : HttpMessageHandler
     {
         private readonly SocketsHttpHandler? _socketHandler;
-        private readonly DiagnosticsHandler? _diagnosticsHandler;
-
         private readonly HttpMessageHandler? _nativeHandler;
+        private MetricsHandler? _metricsHandler;
 
         private static readonly ConcurrentDictionary<string, MethodInfo?> s_cachedMethods =
             new ConcurrentDictionary<string, MethodInfo?>();
 
+        private IMeterFactory? _meterFactory;
         private ClientCertificateOption _clientCertificateOptions;
 
         private volatile bool _disposed;
 
         public HttpClientHandler()
         {
-            HttpMessageHandler handler;
-
             if (IsNativeHandlerEnabled)
             {
                 _nativeHandler = CreateNativeHandler();
-                handler = _nativeHandler;
             }
             else
             {
                 _socketHandler = new SocketsHttpHandler();
-                handler = _socketHandler;
                 ClientCertificateOptions = ClientCertificateOption.Manual;
             }
-
-            if (DiagnosticsHandler.IsGloballyEnabled())
-            {
-                _diagnosticsHandler = new DiagnosticsHandler(handler, DistributedContextPropagator.Current);
-            }
         }
 
         protected override void Dispose(bool disposing)
@@ -73,6 +64,21 @@ protected override void Dispose(bool disposing)
             base.Dispose(disposing);
         }
 
+        [CLSCompliant(false)]
+        public IMeterFactory? MeterFactory
+        {
+            get => _meterFactory;
+            set
+            {
+                ObjectDisposedException.ThrowIf(_disposed, this);
+                if (_metricsHandler != null)
+                {
+                    throw new InvalidOperationException(SR.net_http_operation_started);
+                }
+                _meterFactory = value;
+            }
+        }
+
         [UnsupportedOSPlatform("browser")]
         public bool UseCookies
         {
@@ -713,19 +719,9 @@ protected internal override HttpResponseMessage Send(HttpRequestMessage request,
         protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
             CancellationToken cancellationToken)
         {
-            if (DiagnosticsHandler.IsGloballyEnabled() && _diagnosticsHandler != null)
-            {
-                return _diagnosticsHandler!.SendAsync(request, cancellationToken);
-            }
-
-            if (IsNativeHandlerEnabled)
-            {
-                return _nativeHandler!.SendAsync(request, cancellationToken);
-            }
-            else
-            {
-                return _socketHandler!.SendAsync(request, cancellationToken);
-            }
+            ArgumentNullException.ThrowIfNull(request);
+            MetricsHandler handler = _metricsHandler ?? SetupHandlerChain();
+            return handler.SendAsync(request, cancellationToken);
         }
 
         // lazy-load the validator func so it can be trimmed by the ILLinker if it isn't used.
@@ -741,6 +737,23 @@ protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessa
             }
         }
 
+        private MetricsHandler SetupHandlerChain()
+        {
+            HttpMessageHandler handler = IsNativeHandlerEnabled ? _nativeHandler! : _socketHandler!;
+            if (DiagnosticsHandler.IsGloballyEnabled())
+            {
+                handler = new DiagnosticsHandler(handler, DistributedContextPropagator.Current);
+            }
+            MetricsHandler metricsHandler = new MetricsHandler(handler, _meterFactory);
+
+            // Ensure a single handler is used for all requests.
+            if (Interlocked.CompareExchange(ref _metricsHandler, metricsHandler, null) != null)
+            {
+                handler.Dispose();
+            }
+            return _metricsHandler;
+        }
+
         private void ThrowForModifiedManagedSslOptionsIfStarted()
         {
             // Hack to trigger an InvalidOperationException if a property that's stored on

src/libraries/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs

@@ -9,8 +9,10 @@
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Diagnostics;
+using System.Diagnostics.Metrics;
 #if TARGET_BROWSER
+using System.Diagnostics;
+using System.Net.Http.Metrics;
 using HttpHandlerType = System.Net.Http.BrowserHttpHandler;
 #else
 using HttpHandlerType = System.Net.Http.SocketsHttpHandler;
@@ -23,7 +25,33 @@ public partial class HttpClientHandler : HttpMessageHandler
         private readonly HttpHandlerType _underlyingHandler;
 
 #if TARGET_BROWSER
-        private HttpMessageHandler Handler { get; }
+        private IMeterFactory? _meterFactory;
+        private MetricsHandler? _metricsHandler;
+
+        private MetricsHandler Handler
+        {
+            get
+            {
+                if (_metricsHandler != null)
+                {
+                    return _metricsHandler;
+                }
+
+                HttpMessageHandler handler = _underlyingHandler;
+                if (DiagnosticsHandler.IsGloballyEnabled())
+                {
+                    handler = new DiagnosticsHandler(handler, DistributedContextPropagator.Current);
+                }
+                MetricsHandler metricsHandler = new MetricsHandler(handler, _meterFactory);
+
+                // Ensure a single handler is used for all requests.
+                if (Interlocked.CompareExchange(ref _metricsHandler, metricsHandler, null) != null)
+                {
+                    metricsHandler.Dispose();
+                }
+                return _metricsHandler;
+            }
+        }
 #else
         private HttpHandlerType Handler => _underlyingHandler;
 #endif
@@ -34,14 +62,6 @@ public HttpClientHandler()
         {
             _underlyingHandler = new HttpHandlerType();
 
-#if TARGET_BROWSER
-            Handler = _underlyingHandler;
-            if (DiagnosticsHandler.IsGloballyEnabled())
-            {
-                Handler = new DiagnosticsHandler(Handler, DistributedContextPropagator.Current);
-            }
-#endif
-
             ClientCertificateOptions = ClientCertificateOption.Manual;
         }
 
@@ -60,6 +80,33 @@ protected override void Dispose(bool disposing)
         public virtual bool SupportsProxy => HttpHandlerType.SupportsProxy;
         public virtual bool SupportsRedirectConfiguration => HttpHandlerType.SupportsRedirectConfiguration;
 
+        /// <summary>
+        /// Gets or sets the <see cref="IMeterFactory"/> to create a custom <see cref="Meter"/> for the <see cref="HttpClientHandler"/> instance.
+        /// </summary>
+        /// <remarks>
+        /// When <see cref="MeterFactory"/> is set to a non-<see langword="null"/> value, all metrics emitted by the <see cref="HttpClientHandler"/> instance
+        /// will be recorded using the <see cref="Meter"/> provided by the <see cref="IMeterFactory"/>.
+        /// </remarks>
+        [CLSCompliant(false)]
+        public IMeterFactory? MeterFactory
+        {
+#if TARGET_BROWSER
+            get => _meterFactory;
+            set
+            {
+                ObjectDisposedException.ThrowIf(_disposed, this);
+                if (_metricsHandler != null)
+                {
+                    throw new InvalidOperationException(SR.net_http_operation_started);
+                }
+                _meterFactory = value;
+            }
+#else
+            get => _underlyingHandler.MeterFactory;
+            set => _underlyingHandler.MeterFactory = value;
+#endif
+        }
+
         [UnsupportedOSPlatform("browser")]
         public bool UseCookies
         {
@@ -296,11 +343,21 @@ public SslProtocols SslProtocols
         [UnsupportedOSPlatform("browser")]
         //[UnsupportedOSPlatform("ios")]
         //[UnsupportedOSPlatform("tvos")]
-        protected internal override HttpResponseMessage Send(HttpRequestMessage request, CancellationToken cancellationToken) =>
-            Handler.Send(request, cancellationToken);
+        protected internal override HttpResponseMessage Send(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+#if TARGET_BROWSER
+            throw new PlatformNotSupportedException();
+#else
+            ArgumentNullException.ThrowIfNull(request);
+            return Handler.Send(request, cancellationToken);
+#endif
+        }
 
-        protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) =>
-            Handler.SendAsync(request, cancellationToken);
+        protected internal override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            ArgumentNullException.ThrowIfNull(request);
+            return Handler.SendAsync(request, cancellationToken);
+        }
 
         // lazy-load the validator func so it can be trimmed by the ILLinker if it isn't used.
         private static Func<HttpRequestMessage, X509Certificate2?, X509Chain?, SslPolicyErrors, bool>? s_dangerousAcceptAnyServerCertificateValidator;

src/libraries/System.Net.Http/src/System/Net/Http/HttpMessageInvoker.cs

@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.IO;
-using System.Net.Http.Headers;
 using System.Runtime.Versioning;
 using System.Threading;
 using System.Threading.Tasks;
@@ -124,7 +122,6 @@ protected virtual void Dispose(bool disposing)
             if (disposing && !_disposed)
             {
                 _disposed = true;
-
                 if (_disposeHandler)
                 {
                     _handler.Dispose();

src/libraries/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs

@@ -30,7 +30,7 @@ public class HttpRequestMessage : IDisposable
         private Version _version;
         private HttpVersionPolicy _versionPolicy;
         private HttpContent? _content;
-        private HttpRequestOptions? _options;
+        internal HttpRequestOptions? _options;
 
         public Version Version
         {