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Default draft protocol support: sessionless + handshake-less (SEP-2575 + SEP-2567) (#1610)

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Stephen Halter 2026-06-23 21:24:22 -07:00 • committed by GitHub
commit 6c323e783b
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1 changed files with 5704 additions and 712 deletions
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38
src/ModelContextProtocol.Core/Client/McpClient.Methods.cs
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@ -1174,7 +1174,10 @@ public abstract partial class McpClient : McpSession
{
Name = requestParams.Name,
Arguments = requestParams.Arguments,
Meta = GetMetaWithTaskCapability(requestParams.Meta),
// The SEP-2663 Tasks extension is draft-only. On a legacy session, send a plain tools/call
// (no task capability envelope) so the server returns a direct CallToolResult and never
// creates a task.
Meta = IsDraftProtocol() ? GetMetaWithTaskCapability(requestParams.Meta) : requestParams.Meta,
};
JsonRpcRequest jsonRpcRequest = new()
@ -1285,6 +1288,7 @@ public abstract partial class McpClient : McpSession
CancellationToken cancellationToken = default)
{
Throw.IfNull(requestParams);
ThrowIfTasksNotSupported(nameof(GetTaskAsync));
return SendRequestAsync(
RequestMethods.TasksGet,
@ -1307,6 +1311,7 @@ public abstract partial class McpClient : McpSession
CancellationToken cancellationToken = default)
{
Throw.IfNull(requestParams);
ThrowIfTasksNotSupported(nameof(UpdateTaskAsync));
return SendRequestAsync(
RequestMethods.TasksUpdate,
@ -1346,6 +1351,7 @@ public abstract partial class McpClient : McpSession
CancellationToken cancellationToken = default)
{
Throw.IfNull(requestParams);
ThrowIfTasksNotSupported(nameof(CancelTaskAsync));
return SendRequestAsync(
RequestMethods.TasksCancel,
@ -1376,30 +1382,42 @@ public abstract partial class McpClient : McpSession
// Per SEP-2663 §51, the per-request opt-in uses the SEP-2575 capabilities envelope:
// _meta/io.modelcontextprotocol/clientCapabilities/extensions/io.modelcontextprotocol/tasks = {}
// TODO: replace the literal with a shared NotificationMethods.ClientCapabilitiesMetaKey once
// the SEP-2575 plumbing lands and drop the local consts.
private const string ClientCapabilitiesMetaKey = "io.modelcontextprotocol/clientCapabilities";
private const string ExtensionsKey = "extensions";
private static JsonObject GetMetaWithTaskCapability(JsonObject? existingMeta)
{
JsonObject meta = existingMeta is not null
? (JsonObject)existingMeta.DeepClone()
: [];
if (meta[ClientCapabilitiesMetaKey] is not JsonObject capsRoot)
if (meta[MetaKeys.ClientCapabilities] is not JsonObject capsRoot)
{
capsRoot = [];
meta[ClientCapabilitiesMetaKey] = capsRoot;
meta[MetaKeys.ClientCapabilities] = capsRoot;
}
if (capsRoot[ExtensionsKey] is not JsonObject extensionsRoot)
if (capsRoot["extensions"] is not JsonObject extensionsRoot)
{
extensionsRoot = [];
capsRoot[ExtensionsKey] = extensionsRoot;
capsRoot["extensions"] = extensionsRoot;
}
extensionsRoot.TryAdd(McpExtensions.Tasks, new JsonObject());
return meta;
}
/// <summary>
/// Throws when the negotiated protocol version is not the draft revision. The SEP-2663 Tasks
/// extension is draft-only, and a task id only ever exists when the session negotiated draft, so
/// invoking <c>tasks/get</c>, <c>tasks/update</c>, or <c>tasks/cancel</c> on a legacy session is a
/// programming error rather than a recoverable protocol condition.
/// </summary>
private void ThrowIfTasksNotSupported(string operationName)
{
if (!IsDraftProtocol())
{
throw new InvalidOperationException(
$"'{operationName}' requires the draft protocol revision ('{DraftProtocolVersion}'). " +
$"The negotiated protocol version is '{NegotiatedProtocolVersion ?? "(none)"}'. " +
"The Tasks extension is only available under the draft revision.");
}
}
}