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Fix request-scoped draft client capabilities (#1685)

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Tarek Mahmoud Sayed <tarekms@ntdev.microsoft.com>
This commit is contained in:
Pranav Senthilnathan 2026-07-12 13:56:10 -04:00 • committed by GitHub
commit a8d374b280
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1 changed files with 306 additions and 40 deletions
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54
src/ModelContextProtocol.Core/Server/DestinationBoundMcpServer.cs
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@ -5,18 +5,66 @@ using System.Text.Json.Nodes;
namespace ModelContextProtocol.Server;
#pragma warning disable MCPEXP002
internal sealed class DestinationBoundMcpServer(McpServerImpl server, ITransport? transport) : McpServer
internal sealed class DestinationBoundMcpServer(McpServerImpl server, ITransport? transport, JsonRpcMessageContext? requestContext = null) : McpServer
#pragma warning restore MCPEXP002
{
private readonly bool _isJuly2026OrLaterRequest = server.IsJuly2026OrLaterProtocolRequest(requestContext);
private readonly ClientCapabilities? _requestClientCapabilities = requestContext?.ClientCapabilities;
private readonly Implementation? _requestClientInfo = requestContext?.ClientInfo;
public override string? SessionId => transport?.SessionId ?? server.SessionId;
public override string? NegotiatedProtocolVersion => server.NegotiatedProtocolVersion;
public override ClientCapabilities? ClientCapabilities => server.ClientCapabilities;
public override Implementation? ClientInfo => server.ClientInfo;
public override McpServerOptions ServerOptions => server.ServerOptions;
public override IServiceProvider? Services => server.Services;
[Obsolete(Obsoletions.DeprecatedLogging_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
public override LoggingLevel? LoggingLevel => server.LoggingLevel;
public override ClientCapabilities? ClientCapabilities
{
get
{
// In stateless transport mode, a single request does not have a persistent bidirectional channel.
// Server-to-client requests (sampling, roots, elicitation) are unsupported in this mode and the
// capability gates rely on a null ClientCapabilities value to report that unsupported-state path.
if (!server.HasStatefulTransport())
{
return null;
}
// On protocol revision 2026-07-28+, client capabilities are request-scoped (_meta on each request)
// and must not be inferred from prior requests. Missing per-request capabilities therefore means
// "no declared capabilities for this request", represented by an empty object. A fresh instance is
// returned deliberately: ClientCapabilities is a mutable DTO handed to user handlers, so a shared
// static empty instance could be mutated and leak across requests.
if (_isJuly2026OrLaterRequest)
{
return _requestClientCapabilities ?? new ClientCapabilities();
}
// Legacy protocol behavior uses session-scoped capabilities established during initialize (or
// pre-populated migration data), so ignore per-request values and return the server session state.
return server.ClientCapabilities;
}
}
public override Implementation? ClientInfo
{
get
{
// On protocol revision 2026-07-28+, client info is request-scoped (carried in each request's _meta),
// mirroring how ClientCapabilities is resolved above. Return only this request's declared value and
// do not fall back to shared session state, which under a stateful transport could belong to a
// different concurrent request.
if (_isJuly2026OrLaterRequest)
{
return _requestClientInfo;
}
// Legacy protocol behavior uses session-scoped client info established during initialize.
return server.ClientInfo;
}
}
/// <summary>
/// Gets or sets the MRTR context for the current request, if any.
/// Set by <see cref="McpServerImpl.CreateDestinationBoundServer"/> when an MRTR-aware handler invocation is in progress.