Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/RequestHandlers.cs

@@ -0,0 +1,48 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using System.Text.Json.Serialization.Metadata;
+
+namespace ModelContextProtocol;
+
+internal sealed class RequestHandlers : Dictionary<string, Func<JsonRpcRequest, CancellationToken, Task<JsonNode?>>>
+{
+    /// <summary>
+    /// Registers a handler for incoming requests of a specific method in the MCP protocol.
+    /// </summary>
+    /// <typeparam name="TRequest">Type of request payload that will be deserialized from incoming JSON</typeparam>
+    /// <typeparam name="TResponse">Type of response payload that will be serialized to JSON (not full RPC response)</typeparam>
+    /// <param name="method">Method identifier to register for (e.g., "tools/list", "logging/setLevel")</param>
+    /// <param name="handler">Handler function to be called when a request with the specified method identifier is received</param>
+    /// <param name="requestTypeInfo">The JSON contract governing request parameter deserialization</param>
+    /// <param name="responseTypeInfo">The JSON contract governing response serialization</param>
+    /// <remarks>
+    /// <para>
+    /// This method is used internally by the MCP infrastructure to register handlers for various protocol methods.
+    /// When an incoming request matches the specified method, the registered handler will be invoked with the
+    /// deserialized request parameters.
+    /// </para>
+    /// <para>
+    /// The handler function receives the deserialized request object and a cancellation token, and should return
+    /// a response object that will be serialized back to the client.
+    /// </para>
+    /// </remarks>
+    public void Set<TRequest, TResponse>(
+        string method,
+        Func<TRequest?, ITransport?, CancellationToken, ValueTask<TResponse>> handler,
+        JsonTypeInfo<TRequest> requestTypeInfo,
+        JsonTypeInfo<TResponse> responseTypeInfo)
+    {
+        Throw.IfNull(method);
+        Throw.IfNull(handler);
+        Throw.IfNull(requestTypeInfo);
+        Throw.IfNull(responseTypeInfo);
+
+        this[method] = async (request, cancellationToken) =>
+        {
+            TRequest? typedRequest = JsonSerializer.Deserialize(request.Params, requestTypeInfo);
+            object? result = await handler(typedRequest, request.RelatedTransport, cancellationToken).ConfigureAwait(false);
+            return JsonSerializer.SerializeToNode(result, responseTypeInfo);
+        };
+    }
+}