Adding subscriptions

Author: aaronpowell

samples/EverythingServer/Program.cs

@@ -3,9 +3,14 @@
 using ModelContextProtocol.Protocol.Types;
 using EverythingServer.Tools;
 using EverythingServer;
+using ModelContextProtocol.Server;
+using Microsoft.Extensions.AI;
+using Microsoft.Extensions.DependencyInjection;
 
 var builder = Host.CreateEmptyApplicationBuilder(settings: null);
 
+HashSet<string> subscriptions = [];
+
 builder.Services
     .AddMcpServer()
     .WithStdioServerTransport()
@@ -97,6 +102,43 @@
             });
         }
     })
+    .WithSubscribeToResourcesHandler(async (ctx, ct) =>
+    {
+        var uri = ctx.Params?.Uri;
+
+        if (uri is not null)
+        {
+            subscriptions.Add(uri);
+
+            await ctx.Server.RequestSamplingAsync([
+                new ChatMessage(ChatRole.System, "You are a helpful test server"),
+                new ChatMessage(ChatRole.User, $"Resource {uri}, context: A new subscription was started"),
+            ],
+            options: new ChatOptions
+            {
+                MaxOutputTokens = 100,
+                Temperature = 0.7f,
+            },
+            cancellationToken: ct);
+        }
+
+        return new EmptyResult();
+    })
+    .WithUnsubscribeFromResourcesHandler((ctx, ct) =>
+    {
+        var uri = ctx.Params?.Uri;
+        if (uri is not null)
+        {
+            subscriptions.Remove(uri);
+        }
+        return Task.FromResult(new EmptyResult());
+    })
     ;
 
-await builder.Build().RunAsync();
+builder.Services.AddHostedService(sp =>
+{
+    var server = sp.GetRequiredService<IMcpServer>();
+    return new SubscriptionMessageSender(server, subscriptions);
+});
+
+await builder.Build().RunAsync();

samples/EverythingServer/SubscriptionMessageSender.cs

@@ -0,0 +1,32 @@
+using Microsoft.Extensions.Hosting;
+using ModelContextProtocol.Protocol.Types;
+using ModelContextProtocol.Server;
+using ModelContextProtocol.Protocol.Messages;
+
+internal class SubscriptionMessageSender(IMcpServer server, HashSet<string> subscriptions) : IHostedService
+{
+    public async Task StartAsync(CancellationToken cancellationToken)
+    {
+        while (!cancellationToken.IsCancellationRequested)
+        {
+            foreach (var uri in subscriptions)
+            {
+                await server.SendMessageAsync(new JsonRpcNotification
+                {
+                    Method = "notifications/resource/updated",
+                    Params = new ResourceUpdatedNotificationParams
+                    {
+                        Uri = uri,
+                    }
+                }, cancellationToken);
+            }
+
+            await Task.Delay(5000, cancellationToken);
+        }
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+}