Reduce dependencies to 8.x versions of packages

Directory.Packages.props

@@ -1,36 +1,59 @@
 <Project>
   <PropertyGroup>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
-    <SystemVersion>9.0.3</SystemVersion>
     <System10Version>10.0.0-preview.2.25163.2</System10Version>
-    <MicrosoftExtensionsVersion>9.0.3</MicrosoftExtensionsVersion>
     <MicrosoftExtensionsAIVersion>9.3.0-preview.1.25161.3</MicrosoftExtensionsAIVersion>
   </PropertyGroup>
+
+  <!-- Product dependencies netstandard -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <PackageVersion Include="Microsoft.Bcl.Memory" Version="9.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="8.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.0" />
+    <PackageVersion Include="System.IO.Pipelines" Version="8.0.0" />
+    <PackageVersion Include="System.Text.Json" Version="8.0.5" />
+    <PackageVersion Include="System.Threading.Channels" Version="8.0.0" />
+  </ItemGroup>
+
+  <!-- Product dependencies LTS -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
+    <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="8.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.0" />
+    <PackageVersion Include="System.IO.Pipelines" Version="8.0.0" />
+  </ItemGroup>
+
+  <!-- Product dependencies .NET 9 -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'net9.0'">
+    <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="9.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="9.0.0" />
+    <PackageVersion Include="System.IO.Pipelines" Version="9.0.0" />
+  </ItemGroup>
+
+  <!-- Product dependencies shared -->
   <ItemGroup>
-    <!-- Product dependencies -->
-    <PackageVersion Include="coverlet.collector" Version="6.0.4">
-      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-      <PrivateAssets>all</PrivateAssets>
-    </PackageVersion>
-    <PackageVersion Include="Microsoft.Bcl.Memory" Version="$(SystemVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.AI" Version="$(MicrosoftExtensionsAIVersion)" />
     <PackageVersion Include="Microsoft.Extensions.AI.Abstractions" Version="$(MicrosoftExtensionsAIVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="$(MicrosoftExtensionsVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="$(MicrosoftExtensionsVersion)" />
+    <PackageVersion Include="Microsoft.Extensions.AI" Version="$(MicrosoftExtensionsAIVersion)" />
     <PackageVersion Include="System.Net.ServerSentEvents" Version="$(System10Version)" />
-    <PackageVersion Include="System.Text.Json" Version="$(SystemVersion)" />
-    <PackageVersion Include="System.Threading.Channels" Version="$(SystemVersion)" />
+  </ItemGroup>
+
+  <ItemGroup>
 
     <!-- Build Infra & Packaging -->
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
 
     <!-- Testing dependencies -->
     <PackageVersion Include="Anthropic.SDK" Version="5.0.0" />
+    <PackageVersion Include="coverlet.collector" Version="6.0.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageVersion>
     <PackageVersion Include="GitHubActionsTestLogger" Version="2.4.1" />
     <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="$(MicrosoftExtensionsAIVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="$(MicrosoftExtensionsVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.Logging" Version="$(MicrosoftExtensionsVersion)" />
-    <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="$(MicrosoftExtensionsVersion)" />
+    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="9.0.3" />
+    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="9.0.3" />
+    <PackageVersion Include="Microsoft.Extensions.Logging" Version="9.0.3" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="9.0.3" />
+    <PackageVersion Include="Microsoft.Extensions.Options" Version="9.0.3" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="Moq" Version="4.20.72" />
     <PackageVersion Include="OpenTelemetry" Version="1.11.2" />

samples/QuickstartClient/QuickstartClient.csproj

@@ -15,6 +15,7 @@
     <ItemGroup>
         <PackageReference Include="Anthropic.SDK" />
         <PackageReference Include="Microsoft.Extensions.Hosting" />
+        <PackageReference Include="Microsoft.Extensions.AI" />
     </ItemGroup>
 
 </Project>

src/Common/Polyfills/System/Threading/Channels/ChannelExtensions.cs

@@ -0,0 +1,17 @@
+using System.Runtime.CompilerServices;
+
+namespace System.Threading.Channels;
+
+internal static class ChannelExtensions
+{
+    public static async IAsyncEnumerable<T> ReadAllAsync<T>(this ChannelReader<T> reader, [EnumeratorCancellation] CancellationToken cancellationToken)
+    {
+        while (await reader.WaitToReadAsync(cancellationToken).ConfigureAwait(false))
+        {
+            while (reader.TryRead(out var item))
+            {
+                yield return item;
+            }
+        }
+    }
+}

src/ModelContextProtocol.AspNetCore/ModelContextProtocol.AspNetCore.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>net9.0;net8.0</TargetFrameworks>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>

src/ModelContextProtocol/Client/McpClientExtensions.cs

@@ -24,7 +24,7 @@ public static Task PingAsync(this IMcpClient client, CancellationToken cancellat
         return client.SendRequestAsync(
             RequestMethods.Ping, 
             parameters: null,
-            McpJsonUtilities.JsonContext.Default.Object,
+            McpJsonUtilities.JsonContext.Default.Object!,
             McpJsonUtilities.JsonContext.Default.Object,
             cancellationToken: cancellationToken);
     }
@@ -52,7 +52,7 @@ public static async Task<IList<McpClientTool>> ListToolsAsync(
         {
             var toolResults = await client.SendRequestAsync(
                 RequestMethods.ToolsList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListToolsResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -96,7 +96,7 @@ public static async IAsyncEnumerable<McpClientTool> EnumerateToolsAsync(
         {
             var toolResults = await client.SendRequestAsync(
                 RequestMethods.ToolsList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListToolsResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -128,7 +128,7 @@ public static async Task<IList<McpClientPrompt>> ListPromptsAsync(
         {
             var promptResults = await client.SendRequestAsync(
                 RequestMethods.PromptsList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListPromptsResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -166,7 +166,7 @@ public static async IAsyncEnumerable<Prompt> EnumeratePromptsAsync(
         {
             var promptResults = await client.SendRequestAsync(
                 RequestMethods.PromptsList,
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListPromptsResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -230,7 +230,7 @@ public static async Task<IList<ResourceTemplate>> ListResourceTemplatesAsync(
         {
             var templateResults = await client.SendRequestAsync(
                 RequestMethods.ResourcesTemplatesList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListResourceTemplatesResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -271,7 +271,7 @@ public static async IAsyncEnumerable<ResourceTemplate> EnumerateResourceTemplate
         {
             var templateResults = await client.SendRequestAsync(
                 RequestMethods.ResourcesTemplatesList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListResourceTemplatesResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -304,7 +304,7 @@ public static async Task<IList<Resource>> ListResourcesAsync(
         {
             var resourceResults = await client.SendRequestAsync(
                 RequestMethods.ResourcesList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListResourcesResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -345,7 +345,7 @@ public static async IAsyncEnumerable<Resource> EnumerateResourcesAsync(
         {
             var resourceResults = await client.SendRequestAsync(
                 RequestMethods.ResourcesList, 
-                CreateCursorDictionary(cursor),
+                CreateCursorDictionary(cursor)!,
                 McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
                 McpJsonUtilities.JsonContext.Default.ListResourcesResult,
                 cancellationToken: cancellationToken).ConfigureAwait(false);
@@ -374,7 +374,7 @@ public static Task<ReadResourceResult> ReadResourceAsync(
 
         return client.SendRequestAsync(
             RequestMethods.ResourcesRead, 
-            new Dictionary<string, object?> { ["uri"] = uri },
+            new Dictionary<string, object> { ["uri"] = uri },
             McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
             McpJsonUtilities.JsonContext.Default.ReadResourceResult,
             cancellationToken: cancellationToken);
@@ -401,7 +401,7 @@ public static Task<CompleteResult> GetCompletionAsync(this IMcpClient client, Re
 
         return client.SendRequestAsync(
             RequestMethods.CompletionComplete, 
-            new Dictionary<string, object?>
+            new Dictionary<string, object>
             {
                 ["ref"] = reference,
                 ["argument"] = new Argument { Name = argumentName, Value = argumentValue }
@@ -424,7 +424,7 @@ public static Task SubscribeToResourceAsync(this IMcpClient client, string uri,
 
         return client.SendRequestAsync(
             RequestMethods.ResourcesSubscribe, 
-            new Dictionary<string, object?> { ["uri"] = uri },
+            new Dictionary<string, object> { ["uri"] = uri },
             McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
             McpJsonUtilities.JsonContext.Default.EmptyResult,
             cancellationToken: cancellationToken);
@@ -443,7 +443,7 @@ public static Task UnsubscribeFromResourceAsync(this IMcpClient client, string u
 
         return client.SendRequestAsync(
             RequestMethods.ResourcesUnsubscribe,
-            new Dictionary<string, object?> { ["uri"] = uri },
+            new Dictionary<string, object> { ["uri"] = uri },
             McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
             McpJsonUtilities.JsonContext.Default.EmptyResult,
             cancellationToken: cancellationToken);
@@ -629,7 +629,7 @@ public static Task SetLoggingLevel(this IMcpClient client, LoggingLevel level, C
 
         return client.SendRequestAsync(
             RequestMethods.LoggingSetLevel,
-            new Dictionary<string, object?> { ["level"] = level },
+            new Dictionary<string, object> { ["level"] = level },
             McpJsonUtilities.JsonContext.Default.DictionaryStringObject,
             McpJsonUtilities.JsonContext.Default.EmptyResult,
             cancellationToken: cancellationToken);

src/ModelContextProtocol/Diagnostics.cs

@@ -7,10 +7,20 @@ internal static class Diagnostics
 {
     internal static ActivitySource ActivitySource { get; } = new("Experimental.ModelContextProtocol");
 
+    internal static Meter Meter { get; } = new("Experimental.ModelContextProtocol");
+
+    internal static Histogram<double> CreateDurationHistogram(string name, string description, bool longBuckets) =>
+        Diagnostics.Meter.CreateHistogram<double>(name, "s", description
+#if NET9_0_OR_GREATER
+        , advice: longBuckets ? LongSecondsBucketBoundaries : ShortSecondsBucketBoundaries
+#endif
+        );
+
+#if NET9_0_OR_GREATER
     /// <summary>
     /// Follows boundaries from http.server.request.duration/http.client.request.duration
     /// </summary>
-    internal static InstrumentAdvice<double> ShortSecondsBucketBoundaries { get; } = new()
+    private static InstrumentAdvice<double> ShortSecondsBucketBoundaries { get; } = new()
     {
         HistogramBucketBoundaries = [0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10],
     };
@@ -19,11 +29,9 @@ internal static class Diagnostics
     /// Not based on a standard. Larger bucket sizes for longer lasting operations, e.g. HTTP connection duration.
     /// See https://github.com/open-telemetry/semantic-conventions/issues/336
     /// </summary>
-    internal static InstrumentAdvice<double> LongSecondsBucketBoundaries { get; } = new()
+    private static InstrumentAdvice<double> LongSecondsBucketBoundaries { get; } = new()
     {
         HistogramBucketBoundaries = [0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300],
     };
-
-    internal static Meter Meter { get; } = new("Experimental.ModelContextProtocol");
-
+#endif
 }

src/ModelContextProtocol/ModelContextProtocol.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net8.0;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net9.0;net8.0;netstandard2.0</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <IsPackable>true</IsPackable>
     <PackageId>ModelContextProtocol</PackageId>
@@ -12,22 +12,33 @@
   <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">
     <IsAotCompatible>true</IsAotCompatible>
   </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.AI.Abstractions" />
-    <PackageReference Include="Microsoft.Extensions.AI" />
-    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" />
-    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
-    <PackageReference Include="System.Net.ServerSentEvents" />
-  </ItemGroup>
 
+  <!-- Dependencies only needed by netstandard2.0 -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="..\Common\Polyfills\**\*.cs" />
     <PackageReference Include="Microsoft.Bcl.Memory" />
     <PackageReference Include="System.Text.Json" />
     <PackageReference Include="System.Threading.Channels" />
   </ItemGroup>
 
+  <!-- Dependencies only needed by netstandard2.0 or net8.0 -->
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net8.0'">
+    <PackageReference Include="System.IO.Pipelines" />
+  </ItemGroup>
+
+  <!-- Dependencies needed by all -->
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.AI.Abstractions" />
+    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
+    <PackageReference Include="System.Net.ServerSentEvents" />
+
+    <!-- Temporarily removed until new version can be picked up that
+         has reduced dependencies:
+         <PackageReference Include="Microsoft.Extensions.AI" />
+    -->
+  </ItemGroup>
+
   <ItemGroup>
     <None Include="..\..\README.md" pack="true" PackagePath="\" />
   </ItemGroup>

src/ModelContextProtocol/Protocol/Transport/SseResponseStreamTransport.cs

@@ -53,7 +53,7 @@ private void WriteJsonRpcMessageToBuffer(SseItem<IJsonRpcMessage?> item, IBuffer
             return;
         }
 
-        JsonSerializer.Serialize(GetUtf8JsonWriter(writer), item.Data, McpJsonUtilities.JsonContext.Default.IJsonRpcMessage);
+        JsonSerializer.Serialize(GetUtf8JsonWriter(writer), item.Data, McpJsonUtilities.JsonContext.Default.IJsonRpcMessage!);
     }
 
     /// <inheritdoc/>

src/ModelContextProtocol/Protocol/Transport/StreamClientSessionTransport.cs

@@ -29,9 +29,16 @@ public StreamClientSessionTransport(
         _serverInput = serverInput;
         EndpointName = endpointName;
 
-        // Start reading messages in the background
+        // Start reading messages in the background. We use the rarer pattern of new Task + Start
+        // in order to ensure that the body of the task will always see _readTask initialized.
+        // It is then able to reliably null it out on completion.
         Logger.TransportReadingMessages(endpointName);
-        _readTask = Task.Run(() => ReadMessagesAsync(_shutdownCts.Token), CancellationToken.None);
+        var readTask = new Task<Task>(
+            thisRef => ((StreamClientSessionTransport)thisRef!).ReadMessagesAsync(_shutdownCts.Token), 
+            this,
+            TaskCreationOptions.DenyChildAttach);
+        _readTask = readTask.Unwrap();
+        readTask.Start();
 
         SetConnected(true);
     }
@@ -117,6 +124,7 @@ private async Task ReadMessagesAsync(CancellationToken cancellationToken)
         }
         finally
         {
+            _readTask = null;
             await CleanupAsync(cancellationToken).ConfigureAwait(false);
         }
     }

src/ModelContextProtocol/Protocol/Types/ContextInclusion.cs

@@ -6,7 +6,7 @@ namespace ModelContextProtocol.Protocol.Types;
 /// A request to include context from one or more MCP servers (including the caller), to be attached to the prompt.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
 /// </summary>
-[JsonConverter(typeof(JsonStringEnumConverter<ContextInclusion>))]
+[JsonConverter(typeof(CustomizableJsonStringEnumConverter<ContextInclusion>))]
 public enum ContextInclusion
 {
     /// <summary>

src/ModelContextProtocol/Protocol/Types/LoggingLevel.cs

@@ -7,7 +7,7 @@ namespace ModelContextProtocol.Protocol.Types;
 /// These map to syslog message severities, as specified in RFC-5424:
 /// https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1
 /// </summary>
-[JsonConverter(typeof(JsonStringEnumConverter<LoggingLevel>))]
+[JsonConverter(typeof(CustomizableJsonStringEnumConverter<LoggingLevel>))]
 public enum LoggingLevel
 {
     /// <summary>Detailed debug information, typically only valuable to developers.</summary>

src/ModelContextProtocol/Protocol/Types/Role.cs

@@ -6,7 +6,7 @@ namespace ModelContextProtocol.Protocol.Types;
 /// Represents the type of role in the conversation.
 /// <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">See the schema for details</see>
 /// </summary>
-[JsonConverter(typeof(JsonStringEnumConverter<Role>))]
+[JsonConverter(typeof(CustomizableJsonStringEnumConverter<Role>))]
 public enum Role
 {
     /// <summary>