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Add ISessionMigrationHandler (#1270)

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Mackinnon Buck 2026-02-19 15:31:34 -08:00 • committed by GitHub
commit 27a3196c7f
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1 changed files with 589 additions and 26 deletions
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30
src/ModelContextProtocol.Core/Server/StreamableHttpServerTransport.cs
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@ -42,6 +42,7 @@ public sealed partial class StreamableHttpServerTransport : ITransport
private SseEventWriter? _httpSseWriter;
private ISseEventStreamWriter? _storeSseWriter;
private TaskCompletionSource<bool>? _httpResponseTcs;
private string? _negotiatedProtocolVersion;
private bool _getHttpRequestStarted;
private bool _getHttpResponseCompleted;
@ -82,9 +83,13 @@ public sealed partial class StreamableHttpServerTransport : ITransport
public ISseEventStreamStore? EventStreamStore { get; init; }
/// <summary>
/// Gets or sets the negotiated protocol version for this session.
/// Gets or sets an optional callback invoked after the initialization handshake completes.
/// </summary>
internal string? NegotiatedProtocolVersion { get; private set; }
/// <remarks>
/// When set, this callback is invoked with the <see cref="InitializeRequestParams"/> after a successful
/// initialization handshake. This can be used to persist session data for cross-instance migration.
/// </remarks>
public Func<InitializeRequestParams, CancellationToken, ValueTask>? OnSessionInitialized { get; init; }
/// <inheritdoc/>
public ChannelReader<JsonRpcMessage> MessageReader => _incomingChannel.Reader;
@ -92,12 +97,23 @@ public sealed partial class StreamableHttpServerTransport : ITransport
internal ChannelWriter<JsonRpcMessage> MessageWriter => _incomingChannel.Writer;
/// <summary>
/// Handles the initialize request by capturing the protocol version and invoking the user callback.
/// Handles initialization by capturing the negotiated protocol version and optionally invoking
/// <see cref="OnSessionInitialized"/> so session data can be persisted.
/// </summary>
internal async ValueTask HandleInitRequestAsync(InitializeRequestParams? initParams)
/// <remarks>
/// This is called automatically when an <c>initialize</c> request is processed via
/// <see cref="HandlePostRequestAsync(JsonRpcMessage, Stream, CancellationToken)"/>. It can also be called
/// directly when restoring a migrated session with known <see cref="InitializeRequestParams"/>.
/// </remarks>
/// <param name="initParams">The initialization parameters from the client, or <see langword="null"/> if unavailable.</param>
public async ValueTask HandleInitializeRequestAsync(InitializeRequestParams? initParams)
{
// Capture the negotiated protocol version for resumability checks
NegotiatedProtocolVersion = initParams?.ProtocolVersion;
_negotiatedProtocolVersion = initParams?.ProtocolVersion;
if (initParams is not null && OnSessionInitialized is { } callback)
{
await callback(initParams, _transportDisposedCts.Token).ConfigureAwait(false);
}
}
/// <summary>
@ -266,7 +282,7 @@ public sealed partial class StreamableHttpServerTransport : ITransport
internal async ValueTask<ISseEventStreamWriter?> TryCreateEventStreamAsync(string streamId, CancellationToken cancellationToken)
{
if (EventStreamStore is null || !McpSessionHandler.SupportsPrimingEvent(NegotiatedProtocolVersion))
if (EventStreamStore is null || !McpSessionHandler.SupportsPrimingEvent(_negotiatedProtocolVersion))
{
return null;
}