McpSession.cs

using ModelContextProtocol.Client;
using ModelContextProtocol.Protocol;
using ModelContextProtocol.Server;

namespace ModelContextProtocol;

/// <summary>
/// Represents a client or server Model Context Protocol (MCP) session.
/// </summary>
/// <remarks>
/// <para>
/// The MCP session provides the core communication functionality used by both clients and servers:
/// <list type="bullet">
///   <item>Sending JSON-RPC requests and receiving responses.</item>
///   <item>Sending notifications to the connected session.</item>
///   <item>Registering handlers for receiving notifications.</item>
/// </list>
/// </para>
/// <para>
/// <see cref="McpSession"/> serves as the base class for both <see cref="McpClient"/> and
/// <see cref="McpServer"/>, providing the common functionality needed for MCP protocol
/// communication. Most applications will use these more specific interfaces rather than working with
/// <see cref="McpSession"/> directly.
/// </para>
/// <para>
/// All MCP sessions should be properly disposed after use as they implement <see cref="IAsyncDisposable"/>.
/// </para>
/// </remarks>
public abstract partial class McpSession : IAsyncDisposable
{
    /// <summary>Gets an identifier associated with the current MCP session.</summary>
    /// <remarks>
    /// Typically populated in transports supporting multiple sessions, such as Streamable HTTP or SSE.
    /// Can return <see langword="null"/> if the session hasn't initialized or if the transport doesn't
    /// support multiple sessions (as is the case with STDIO).
    /// </remarks>
    public abstract string? SessionId { get; }

    /// <summary>
    /// Gets the negotiated protocol version for the current MCP session.
    /// </summary>
    /// <remarks>
    /// Returns the protocol version negotiated during session initialization,
    /// or <see langword="null"/> if initialization hasn't yet occurred.
    /// </remarks>
    public abstract string? NegotiatedProtocolVersion { get; }

    /// <summary>
    /// Gets a value indicating whether the negotiated protocol version is <c>2026-07-28</c> or later: the
    /// revision that removed the <c>initialize</c> handshake (SEP-2575) and <c>Mcp-Session-Id</c> (SEP-2567)
    /// and enabled MRTR (SEP-2322).
    /// </summary>
    /// <remarks>
    /// Returns <see langword="false"/> when no version has been negotiated yet. This is the shared
    /// definition of "is this peer speaking the 2026-07-28 or later revision" used by both the client and server.
    /// </remarks>
    internal bool IsJuly2026OrLaterProtocol() =>
        McpHttpHeaders.IsJuly2026OrLaterProtocolVersion(NegotiatedProtocolVersion);

    /// <summary>
    /// Gets a value indicating whether the negotiated protocol version supports the draft protocol
    /// features (the <c>2026-07-28</c> revision or later).
    /// </summary>
    /// <remarks>
    /// This is a public seam used by bolt-on extensions (such as the Tasks extension) to gate
    /// functionality that requires the <c>2026-07-28</c> or later protocol revision.
    /// </remarks>
    public bool IsDraftProtocol() => IsJuly2026OrLaterProtocol();

    /// <summary>
    /// Sends a JSON-RPC request to the connected session and waits for a response.
    /// </summary>
    /// <param name="request">The JSON-RPC request to send.</param>
    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
    /// <returns>A task containing the session's response.</returns>
    /// <exception cref="InvalidOperationException">The transport is not connected, or another error occurred during request processing.</exception>
    /// <exception cref="McpException">An error occurred during request processing.</exception>
    /// <remarks>
    /// This method provides low-level access to send raw JSON-RPC requests. For most use cases,
    /// consider using the strongly-typed methods that provide a more convenient API.
    /// </remarks>
    public abstract Task<JsonRpcResponse> SendRequestAsync(JsonRpcRequest request, CancellationToken cancellationToken = default);

    /// <summary>
    /// Sends a JSON-RPC message to the connected session.
    /// </summary>
    /// <param name="message">
    /// The JSON-RPC message to send. This can be any type that implements JsonRpcMessage, such as
    /// JsonRpcRequest, JsonRpcResponse, JsonRpcNotification, or JsonRpcError.
    /// </param>
    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
    /// <returns>A task that represents the asynchronous send operation.</returns>
    /// <exception cref="InvalidOperationException">The transport is not connected, or <paramref name="message"/> is a <see cref="JsonRpcRequest"/>. Use <see cref="SendRequestAsync"/> for requests.</exception>
    /// <exception cref="ArgumentNullException"><paramref name="message"/> is <see langword="null"/>.</exception>
    /// <remarks>
    /// <para>
    /// This method provides low-level access to send any JSON-RPC message. For specific message types,
    /// consider using the higher-level methods such as <see cref="SendRequestAsync"/> or methods
    /// on this class that provide a simpler API.
    /// </para>
    /// <para>
    /// The method serializes the message and transmits it using the underlying transport mechanism.
    /// </para>
    /// </remarks>
    public abstract Task SendMessageAsync(JsonRpcMessage message, CancellationToken cancellationToken = default);

    /// <summary>Registers a handler to be invoked when a notification for the specified method is received.</summary>
    /// <param name="method">The notification method.</param>
    /// <param name="handler">The handler to be invoked.</param>
    /// <returns>An <see cref="IAsyncDisposable"/> that will remove the registered handler when disposed.</returns>
    /// <exception cref="ArgumentNullException"><paramref name="method"/> or <paramref name="handler"/> is <see langword="null"/>.</exception>
    /// <exception cref="ArgumentException"><paramref name="method"/> is empty or composed entirely of whitespace.</exception>
    public abstract IAsyncDisposable RegisterNotificationHandler(string method, Func<JsonRpcNotification, CancellationToken, ValueTask> handler);

    /// <inheritdoc/>
    public abstract ValueTask DisposeAsync();
}