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Send MCP-Protocol-Version header in Streamable HTTP client transport (#500)

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Stephen Halter 2025-06-17 14:27:26 -07:00 • committed by GitHub
commit befa31d5c9
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10 changed files with 69 additions and 24 deletions
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2
Directory.Build.props
View file

@ -1,6 +1,6 @@
<Project>
<PropertyGroup>
<LangVersion>13</LangVersion>
<LangVersion>preview</LangVersion>
<TreatWarningsAsErrors>true</TreatWarningsAsErrors>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>

2
src/ModelContextProtocol.AspNetCore/HttpServerTransportOptions.cs
View file

@ -28,7 +28,7 @@ public class HttpServerTransportOptions
/// </summary>
/// <remarks>
/// If <see langword="true"/>, the "/sse" endpoint will be disabled, and client information will be round-tripped as part
/// of the "mcp-session-id" header instead of stored in memory. Unsolicited server-to-client messages and all server-to-client
/// of the "MCP-Session-Id" header instead of stored in memory. Unsolicited server-to-client messages and all server-to-client
/// requests are also unsupported, because any responses may arrive at another ASP.NET Core application process.
/// Client sampling and roots capabilities are also disabled in stateless mode, because the server cannot make requests.
/// Defaults to <see langword="false"/>.

21
src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs
View file

@ -26,6 +26,7 @@ internal sealed class StreamableHttpHandler(
ILoggerFactory loggerFactory,
IServiceProvider applicationServices)
{
private const string McpSessionIdHeaderName = "Mcp-Session-Id";
private static readonly JsonTypeInfo<JsonRpcError> s_errorTypeInfo = GetRequiredJsonTypeInfo<JsonRpcError>();
public ConcurrentDictionary<string, HttpMcpSession<StreamableHttpServerTransport>> Sessions { get; } = new(StringComparer.Ordinal);
@ -70,8 +71,8 @@ internal sealed class StreamableHttpHandler(
}
finally
{
// Stateless sessions are 1:1 with HTTP requests and are outlived by the MCP session tracked by the mcp-session-id.
// Non-stateless sessions are 1:1 with the mcp-session-id and outlive the POST request.
// Stateless sessions are 1:1 with HTTP requests and are outlived by the MCP session tracked by the Mcp-Session-Id.
// Non-stateless sessions are 1:1 with the Mcp-Session-Id and outlive the POST request.
// Non-stateless sessions get disposed by a DELETE request or the IdleTrackingBackgroundService.
if (HttpServerTransportOptions.Stateless)
{
@ -90,7 +91,7 @@ internal sealed class StreamableHttpHandler(
return;
}
var sessionId = context.Request.Headers["mcp-session-id"].ToString();
var sessionId = context.Request.Headers[McpSessionIdHeaderName].ToString();
var session = await GetSessionAsync(context, sessionId);
if (session is null)
{
@ -117,7 +118,7 @@ internal sealed class StreamableHttpHandler(
public async Task HandleDeleteRequestAsync(HttpContext context)
{
var sessionId = context.Request.Headers["mcp-session-id"].ToString();
var sessionId = context.Request.Headers[McpSessionIdHeaderName].ToString();
if (Sessions.TryRemove(sessionId, out var session))
{
await session.DisposeAsync();
@ -157,14 +158,14 @@ internal sealed class StreamableHttpHandler(
return null;
}
context.Response.Headers["mcp-session-id"] = session.Id;
context.Response.Headers[McpSessionIdHeaderName] = session.Id;
context.Features.Set(session.Server);
return session;
}
private async ValueTask<HttpMcpSession<StreamableHttpServerTransport>?> GetOrCreateSessionAsync(HttpContext context)
{
var sessionId = context.Request.Headers["mcp-session-id"].ToString();
var sessionId = context.Request.Headers[McpSessionIdHeaderName].ToString();
if (string.IsNullOrEmpty(sessionId))
{
@ -188,11 +189,11 @@ internal sealed class StreamableHttpHandler(
{
SessionId = sessionId,
};
context.Response.Headers["mcp-session-id"] = sessionId;
context.Response.Headers[McpSessionIdHeaderName] = sessionId;
}
else
{
// "(uninitialized stateless id)" is not written anywhere. We delay writing the mcp-session-id
// "(uninitialized stateless id)" is not written anywhere. We delay writing the MCP-Session-Id
// until after we receive the initialize request with the client info we need to serialize.
sessionId = "(uninitialized stateless id)";
transport = new()
@ -204,7 +205,7 @@ internal sealed class StreamableHttpHandler(
var session = await CreateSessionAsync(context, transport, sessionId);
// The HttpMcpSession is not stored between requests in stateless mode. Instead, the session is recreated from the mcp-session-id.
// The HttpMcpSession is not stored between requests in stateless mode. Instead, the session is recreated from the MCP-Session-Id.
if (!HttpServerTransportOptions.Stateless)
{
if (!Sessions.TryAdd(sessionId, session))
@ -299,7 +300,7 @@ internal sealed class StreamableHttpHandler(
var sessionJson = JsonSerializer.Serialize(statelessId, StatelessSessionIdJsonContext.Default.StatelessSessionId);
transport.SessionId = Protector.Protect(sessionJson);
context.Response.Headers["mcp-session-id"] = transport.SessionId;
context.Response.Headers[McpSessionIdHeaderName] = transport.SessionId;
return ValueTask.CompletedTask;
};
}

27
src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs
View file

@ -27,6 +27,7 @@ internal sealed partial class StreamableHttpClientSessionTransport : TransportBa
private readonly CancellationTokenSource _connectionCts;
private readonly ILogger _logger;
private string? _negotiatedProtocolVersion;
private Task? _getReceiveTask;
public StreamableHttpClientSessionTransport(
@ -84,7 +85,7 @@ internal sealed partial class StreamableHttpClientSessionTransport : TransportBa
},
};
CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders, SessionId);
CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders, SessionId, _negotiatedProtocolVersion);
var response = await _httpClient.SendAsync(httpRequestMessage, HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
@ -118,14 +119,17 @@ internal sealed partial class StreamableHttpClientSessionTransport : TransportBa
throw new McpException($"Streamable HTTP POST response completed without a reply to request with ID: {rpcRequest.Id}");
}
if (rpcRequest.Method == RequestMethods.Initialize && rpcResponseOrError is JsonRpcResponse)
if (rpcRequest.Method == RequestMethods.Initialize && rpcResponseOrError is JsonRpcResponse initResponse)
{
// We've successfully initialized! Copy session-id and start GET request if any.
if (response.Headers.TryGetValues("mcp-session-id", out var sessionIdValues))
// We've successfully initialized! Copy session-id and protocol version, then start GET request if any.
if (response.Headers.TryGetValues("Mcp-Session-Id", out var sessionIdValues))
{
SessionId = sessionIdValues.FirstOrDefault();
}
var initializeResult = JsonSerializer.Deserialize(initResponse.Result, McpJsonUtilities.JsonContext.Default.InitializeResult);
_negotiatedProtocolVersion = initializeResult?.ProtocolVersion;
_getReceiveTask = ReceiveUnsolicitedMessagesAsync();
}
@ -169,7 +173,7 @@ internal sealed partial class StreamableHttpClientSessionTransport : TransportBa
// Send a GET request to handle any unsolicited messages not sent over a POST response.
using var request = new HttpRequestMessage(HttpMethod.Get, _options.Endpoint);
request.Headers.Accept.Add(s_textEventStreamMediaType);
CopyAdditionalHeaders(request.Headers, _options.AdditionalHeaders, SessionId);
CopyAdditionalHeaders(request.Headers, _options.AdditionalHeaders, SessionId, _negotiatedProtocolVersion);
using var response = await _httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, _connectionCts.Token).ConfigureAwait(false);
@ -244,11 +248,20 @@ internal sealed partial class StreamableHttpClientSessionTransport : TransportBa
}
}
internal static void CopyAdditionalHeaders(HttpRequestHeaders headers, IDictionary<string, string>? additionalHeaders, string? sessionId = null)
internal static void CopyAdditionalHeaders(
HttpRequestHeaders headers,
IDictionary<string, string>? additionalHeaders,
string? sessionId = null,
string? protocolVersion = null)
{
if (sessionId is not null)
{
headers.Add("mcp-session-id", sessionId);
headers.Add("Mcp-Session-Id", sessionId);
}
if (protocolVersion is not null)
{
headers.Add("MCP-Protocol-Version", protocolVersion);
}
if (additionalHeaders is null)

1
src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj
View file

@ -7,7 +7,6 @@
<PackageId>ModelContextProtocol.Core</PackageId>
<Description>Core .NET SDK for the Model Context Protocol (MCP)</Description>
<PackageReadmeFile>README.md</PackageReadmeFile>
<LangVersion>preview</LangVersion>
</PropertyGroup>
<PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">

1
src/ModelContextProtocol/ModelContextProtocol.csproj
View file

@ -7,7 +7,6 @@
<PackageId>ModelContextProtocol</PackageId>
<Description>.NET SDK for the Model Context Protocol (MCP) with hosting and dependency injection extensions.</Description>
<PackageReadmeFile>README.md</PackageReadmeFile>
<LangVersion>preview</LangVersion>
</PropertyGroup>
<PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">

35
tests/ModelContextProtocol.AspNetCore.Tests/MapMcpStreamableHttpTests.cs
View file

@ -1,5 +1,6 @@
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Primitives;
using ModelContextProtocol.Client;
namespace ModelContextProtocol.AspNetCore.Tests;
@ -143,4 +144,38 @@ public class MapMcpStreamableHttpTests(ITestOutputHelper outputHelper) : MapMcpT
Assert.Equal("SseTestServer", mcpClient.ServerInfo.Name);
}
[Fact]
public async Task StreamableHttpClient_SendsMcpProtocolVersionHeader_AfterInitialization()
{
var protocolVersionHeaderValues = new List<string?>();
Builder.Services.AddMcpServer().WithHttpTransport(ConfigureStateless).WithTools<EchoHttpContextUserTools>();
await using var app = Builder.Build();
app.Use(next =>
{
return async context =>
{
if (!StringValues.IsNullOrEmpty(context.Request.Headers["mcp-session-id"]))
{
protocolVersionHeaderValues.Add(context.Request.Headers["mcp-protocol-version"]);
}
await next(context);
};
});
app.MapMcp();
await app.StartAsync(TestContext.Current.CancellationToken);
await using var mcpClient = await ConnectAsync();
await mcpClient.ListToolsAsync(cancellationToken: TestContext.Current.CancellationToken);
// The header should be included in the GET request, the initialized notification, and the tools/list call.
Assert.Equal(3, protocolVersionHeaderValues.Count);
Assert.All(protocolVersionHeaderValues, v => Assert.Equal("2025-03-26", v));
}
}

2
tests/ModelContextProtocol.AspNetCore.Tests/MapMcpTests.cs
View file

@ -195,7 +195,7 @@ public abstract class MapMcpTests(ITestOutputHelper testOutputHelper) : KestrelI
"TestAuthType", "name", "role"));
[McpServerToolType]
private class EchoHttpContextUserTools(IHttpContextAccessor contextAccessor)
protected class EchoHttpContextUserTools(IHttpContextAccessor contextAccessor)
{
[McpServerTool, Description("Echoes the input back to the client with their user name.")]
public string EchoWithUserName(string message)

1
tests/ModelContextProtocol.AspNetCore.Tests/ModelContextProtocol.AspNetCore.Tests.csproj
View file

@ -4,7 +4,6 @@
<TargetFrameworks>net9.0;net8.0</TargetFrameworks>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<LangVersion>Latest</LangVersion>
<IsPackable>false</IsPackable>
<IsTestProject>true</IsTestProject>
<RootNamespace>ModelContextProtocol.AspNetCore.Tests</RootNamespace>

1
tests/ModelContextProtocol.Tests/ModelContextProtocol.Tests.csproj
View file

@ -5,7 +5,6 @@
<TargetFrameworks>net9.0;net8.0</TargetFrameworks>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<LangVersion>Latest</LangVersion>
<IsPackable>false</IsPackable>
<IsTestProject>true</IsTestProject>