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| 1 | +using Microsoft.AspNetCore.Http; |
| 2 | +using Microsoft.AspNetCore.Routing; |
| 3 | +using Microsoft.AspNetCore.WebUtilities; |
| 4 | +using Microsoft.Extensions.DependencyInjection; |
| 5 | +using Microsoft.Extensions.Logging; |
| 6 | +using Microsoft.Extensions.Options; |
| 7 | +using ModelContextProtocol.Protocol.Messages; |
| 8 | +using ModelContextProtocol.Protocol.Transport; |
| 9 | +using ModelContextProtocol.Server; |
| 10 | +using ModelContextProtocol.Utils.Json; |
| 11 | +using System.Collections.Concurrent; |
| 12 | +using System.Security.Cryptography; |
| 13 | + |
| 14 | +namespace Microsoft.AspNetCore.Builder; |
| 15 | + |
| 16 | +/// <summary> |
| 17 | +/// Extension methods for <see cref="IEndpointRouteBuilder"/> to add MCP endpoints. |
| 18 | +/// </summary> |
| 19 | +public static class McpEndpointRouteBuilderExtensions |
| 20 | +{ |
| 21 | + /// <summary> |
| 22 | + /// Sets up endpoints for handling MCP HTTP Streaming transport. |
| 23 | + /// </summary> |
| 24 | + /// <param name="endpoints">The web application to attach MCP HTTP endpoints.</param> |
| 25 | + /// <param name="runSession">Provides an optional asynchronous callback for handling new MCP sessions.</param> |
| 26 | + /// <returns>Returns a builder for configuring additional endpoint conventions like authorization policies.</returns> |
| 27 | + public static IEndpointConventionBuilder MapMcp(this IEndpointRouteBuilder endpoints, Func<HttpContext, IMcpServer, CancellationToken, Task>? runSession = null) |
| 28 | + { |
| 29 | + ConcurrentDictionary<string, SseResponseStreamTransport> _sessions = new(StringComparer.Ordinal); |
| 30 | + |
| 31 | + var loggerFactory = endpoints.ServiceProvider.GetRequiredService<ILoggerFactory>(); |
| 32 | + var mcpServerOptions = endpoints.ServiceProvider.GetRequiredService<IOptions<McpServerOptions>>(); |
| 33 | + |
| 34 | + var routeGroup = endpoints.MapGroup(""); |
| 35 | + |
| 36 | + routeGroup.MapGet("/sse", async context => |
| 37 | + { |
| 38 | + var response = context.Response; |
| 39 | + var requestAborted = context.RequestAborted; |
| 40 | + |
| 41 | + response.Headers.ContentType = "text/event-stream"; |
| 42 | + response.Headers.CacheControl = "no-store"; |
| 43 | + |
| 44 | + var sessionId = MakeNewSessionId(); |
| 45 | + await using var transport = new SseResponseStreamTransport(response.Body, $"/message?sessionId={sessionId}"); |
| 46 | + if (!_sessions.TryAdd(sessionId, transport)) |
| 47 | + { |
| 48 | + throw new Exception($"Unreachable given good entropy! Session with ID '{sessionId}' has already been created."); |
| 49 | + } |
| 50 | + await using var server = McpServerFactory.Create(transport, mcpServerOptions.Value, loggerFactory, endpoints.ServiceProvider); |
| 51 | + |
| 52 | + try |
| 53 | + { |
| 54 | + var transportTask = transport.RunAsync(cancellationToken: requestAborted); |
| 55 | + |
| 56 | + try |
| 57 | + { |
| 58 | + runSession ??= RunSession; |
| 59 | + await runSession(context, server, requestAborted); |
| 60 | + } |
| 61 | + finally |
| 62 | + { |
| 63 | + await transport.DisposeAsync(); |
| 64 | + await transportTask; |
| 65 | + } |
| 66 | + } |
| 67 | + catch (OperationCanceledException) when (requestAborted.IsCancellationRequested) |
| 68 | + { |
| 69 | + // RequestAborted always triggers when the client disconnects before a complete response body is written, |
| 70 | + // but this is how SSE connections are typically closed. |
| 71 | + } |
| 72 | + finally |
| 73 | + { |
| 74 | + _sessions.TryRemove(sessionId, out _); |
| 75 | + } |
| 76 | + }); |
| 77 | + |
| 78 | + routeGroup.MapPost("/message", async context => |
| 79 | + { |
| 80 | + if (!context.Request.Query.TryGetValue("sessionId", out var sessionId)) |
| 81 | + { |
| 82 | + await Results.BadRequest("Missing sessionId query parameter.").ExecuteAsync(context); |
| 83 | + return; |
| 84 | + } |
| 85 | + |
| 86 | + if (!_sessions.TryGetValue(sessionId.ToString(), out var transport)) |
| 87 | + { |
| 88 | + await Results.BadRequest($"Session {sessionId} not found.").ExecuteAsync(context); |
| 89 | + return; |
| 90 | + } |
| 91 | + |
| 92 | + var message = await context.Request.ReadFromJsonAsync<IJsonRpcMessage>(McpJsonUtilities.DefaultOptions, context.RequestAborted); |
| 93 | + if (message is null) |
| 94 | + { |
| 95 | + await Results.BadRequest("No message in request body.").ExecuteAsync(context); |
| 96 | + return; |
| 97 | + } |
| 98 | + |
| 99 | + await transport.OnMessageReceivedAsync(message, context.RequestAborted); |
| 100 | + context.Response.StatusCode = StatusCodes.Status202Accepted; |
| 101 | + await context.Response.WriteAsync("Accepted"); |
| 102 | + }); |
| 103 | + |
| 104 | + return routeGroup; |
| 105 | + } |
| 106 | + |
| 107 | + private static Task RunSession(HttpContext httpContext, IMcpServer session, CancellationToken requestAborted) |
| 108 | + => session.RunAsync(requestAborted); |
| 109 | + |
| 110 | + private static string MakeNewSessionId() |
| 111 | + { |
| 112 | + // 128 bits |
| 113 | + Span<byte> buffer = stackalloc byte[16]; |
| 114 | + RandomNumberGenerator.Fill(buffer); |
| 115 | + return WebEncoders.Base64UrlEncode(buffer); |
| 116 | + } |
| 117 | +} |
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