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Add support for MCP prompts
- Add prompt registry class and methods. - Add tests for simple prompts. - Update MCP client test with prompts.
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‎nanoFramework.WebServer.Mcp/McpPromptRegistry.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System;
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using System.Collections;
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using System.Diagnostics;
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using System.Reflection;
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using System.Text;
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namespace nanoFramework.WebServer.Mcp
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{
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/// <summary>
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/// Registry for Model Context Protocol (MCP) prompts, allowing discovery and invocation of prompts defined with the <see cref="McpServerPromptAttribute"/>.
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/// </summary>
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public static class McpPromptRegistry
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{
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private static readonly Hashtable promtps = new Hashtable();
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private static bool isInitialized = false;
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/// <summary>
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/// Discovers MCP prompts by scanning the provided types for methods decorated with the <see cref="McpServerPromptAttribute"/>.
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/// This method should be called once to populate the tool registry.
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/// </summary>
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/// <param name="typesWithPrompts">An array of types to scan for MCP prompts.</param>
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public static void DiscoverPrompts(Type[] typesWithPrompts)
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{
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if (isInitialized)
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{
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// prompts already discovered
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return;
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}
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foreach (Type mcpPrompt in typesWithPrompts)
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{
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MethodInfo[] methods = mcpPrompt.GetMethods();
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foreach (MethodInfo method in methods)
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{
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try
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{
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object[] allAttribute = method.GetCustomAttributes(true);
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foreach (var attrib in allAttribute)
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{
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if (attrib.GetType() != typeof(McpServerPromptAttribute))
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{
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continue;
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}
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McpServerPromptAttribute attribute = (McpServerPromptAttribute)attrib;
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if (attribute != null)
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{
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ParameterInfo[] parameters = method.GetParameters();
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string inputType = string.Empty;
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// We only support no parameters for now
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if (parameters.Length > 1)
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{
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continue;
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}
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promtps.Add(attribute.Name, new PromptMetadata
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{
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Name = attribute.Name,
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Description = attribute.Description,
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Method = method,
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MethodType = parameters.Length > 0 ? parameters[0].ParameterType : null,
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});
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}
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}
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}
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catch (Exception)
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{
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continue;
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}
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}
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}
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isInitialized = true;
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}
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/// <summary>
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/// Gets the metadata of all registered MCP prompts in JSON format.
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/// This method should be called after <see cref="DiscoverPrompts"/> to retrieve the prompt metadata.
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/// </summary>
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/// <returns>A JSON string containing the metadata of all registered prompts.</returns>
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/// <exception cref="Exception">Thrown if there is an error building the prompts list.</exception>
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public static string GetPromptMetadataJson()
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{
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try
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{
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StringBuilder sb = new StringBuilder();
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sb.Append("\"prompts\":[");
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foreach (PromptMetadata prompt in promtps.Values)
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{
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sb.Append(prompt.ToString());
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sb.Append(",");
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}
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sb.Remove(sb.Length - 1, 1);
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sb.Append("],\"nextCursor\":null");
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return sb.ToString();
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}
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catch (Exception)
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{
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throw new Exception("Impossible to build prompts list.");
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}
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}
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private static object CreateInstance(Type type)
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{
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// Get the default constructor
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ConstructorInfo constructor = type.GetConstructor(new Type[0]);
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if (constructor == null)
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{
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throw new Exception($"Type {type.Name} does not have a parameterless constructor");
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}
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return constructor.Invoke(new object[0]);
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}
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/// <summary>
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/// Gets the description of a registered MCP prompt by its name.
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/// </summary>
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/// <param name="promptName">The name of the prompt to invoke.</param>
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/// <returns>A string containing the description of the prompt.</returns>
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/// <exception cref="Exception">Thrown when the specified prompt is not found in the registry.</exception>
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public static string GetPromptDescription(string promptName)
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{
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if (promtps.Contains(promptName))
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{
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PromptMetadata promptMetadata = (PromptMetadata)promtps[promptName];
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return promptMetadata.Description;
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}
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throw new Exception("Prompt not found");
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}
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/// <summary>
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/// Invokes a registered MCP prompt by name and returns the serialized result.
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/// </summary>
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/// <param name="promptName">The name of the prompt to invoke.</param>
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/// <returns>A JSON string containing the serialized result of the prompt invocation.</returns>
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/// <exception cref="Exception">Thrown when the specified prompt is not found in the registry.</exception>
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public static string InvokePrompt(string promptName)
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{
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if (promtps.Contains(promptName))
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{
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PromptMetadata promptMetadata = (PromptMetadata)promtps[promptName];
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MethodInfo method = promptMetadata.Method;
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Debug.WriteLine($"Prompt name: {promptName}, method: {method.Name}");
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object result = method.Invoke(null, new object[] { });
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// Handle serialization based on return type
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if (result == null)
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{
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return "null";
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}
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Type resultType = result.GetType();
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// For strings, return as-is with quotes
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// For primitive types, convert to string and add quotes
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if (resultType == typeof(string))
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{
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return $"\"{result}\"";
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}
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}
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throw new Exception("Prompt not found");
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}
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}
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}

‎nanoFramework.WebServer.Mcp/McpServerController.cs‎

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Original file line numberDiff line numberDiff line change
@@ -120,6 +120,17 @@ public void HandleMcpRequest(WebServerEventArgs e)
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sb.Append($",\"result\":{{\"content\":[{{\"type\":\"text\",\"text\":{result}}}]}}}}");
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}
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else if (request["method"].ToString() == "prompts/list")
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{
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string promptListJson = McpPromptRegistry.GetPromptMetadataJson();
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sb.Append($",\"result\":{{{promptListJson}}}}}");
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}
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else if (request["method"].ToString() == "prompts/get")
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{
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string promptName = ((Hashtable)request["params"])["name"].ToString();
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string result = McpPromptRegistry.InvokePrompt(promptName);
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sb.Append($",\"result\":{{\"description\":\"{McpPromptRegistry.GetPromptDescription(promptName)}\",\"messages\":[{{\"role:\":\"user\",\"type:\"\"text\",\"text\":{result}}}]}}}}");
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}
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else
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{
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sb.Append($",\"error\":{{\"code\":-32601,\"message\":\"Method not found\"}}}}");

‎nanoFramework.WebServer.Mcp/McpServerPromptAttribute.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System;
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namespace nanoFramework.WebServer.Mcp
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{
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/// <summary>
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/// Used to indicate that a method should be considered an <see cref="McpServerPromptAttribute"/>.
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/// </summary>
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/// <remarks>
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/// <para>
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/// This attribute is applied to methods that should be exposed as prompts in the Model Context Protocol. When a class
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/// containing methods marked with this attribute is registered with McpServerBuilderExtensions,
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/// these methods become available as prompts that can be called by MCP clients.
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/// </para>
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[AttributeUsage(AttributeTargets.Method)]
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public class McpServerPromptAttribute : Attribute
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{
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/// <summary>
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/// Gets the name of the prompt.
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/// </summary>
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public string Name { get; }
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/// <summary>
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/// Gets the description of the tool.
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/// </summary>
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public string Description { get; }
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/// <summary>
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/// Initializes a new instance of the <see cref="McpServerPromptAttribute"/> class with the specified name and description.
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/// </summary>
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/// <param name="name">The unique name of the prompt.</param>
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/// <param name="description">The description of the prompt.</param>
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public McpServerPromptAttribute(string name, string description = "")
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{
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Name = name;
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Description = description;
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}
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}
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}

‎nanoFramework.WebServer.Mcp/PromptMetadata.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System;
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using System.Reflection;
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namespace nanoFramework.WebServer.Mcp
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{
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/// <summary>
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/// Represents metadata information for a prompt, including its name, description and associated method.
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/// </summary>
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public class PromptMetadata
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{
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/// <summary>
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/// Gets or sets the unique name of the prompt.
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/// </summary>
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public string Name { get; set; }
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/// <summary>
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/// Gets or sets the description of the prompt.
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/// </summary>
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public string Description { get; set; }
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/// <summary>
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/// Gets or sets the <see cref="MethodInfo"/> representing the method associated with the prompt.
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/// </summary>
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public MethodInfo Method { get; set; }
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/// <summary>
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/// Gets or sets the type of the method associated with the prompt.
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/// </summary>
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public Type MethodType { get; set; }
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/// <summary>
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/// Returns a JSON string representation of the prompt metadata.
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/// </summary>
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/// <returns>A JSON string containing the prompt's name, description schema.</returns>
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public override string ToString()
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{
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string output = $"{{\"name\":\"{Name}\",\"description\":\"{Description}\"}}";
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return output;
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}
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}
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}

‎nanoFramework.WebServer.Mcp/nanoFramework.WebServer.Mcp.nfproj‎

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<Compile Include="HashtableExtension.cs" />
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<Compile Include="McpServerBasicAuthenticationController.cs" />
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<Compile Include="McpServerKeyAuthenticationController.cs" />
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<Compile Include="McpServerPromptAttribute.cs" />
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<Compile Include="McpServerToolAttribute.cs" />
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<Compile Include="McpPromptRegistry.cs" />
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<Compile Include="McpToolRegistry.cs" />
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<Compile Include="McpToolsJsonHelper.cs" />
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<Compile Include="McpServerController.cs" />
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<Compile Include="Properties\AssemblyInfo.cs" />
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<Compile Include="PromptMetadata.cs" />
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<Compile Include="ToolMetadata.cs" />
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</ItemGroup>
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<ItemGroup>

‎tests/McpClientTest/McpClientTest.cs‎

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// Load them as AI functions in the kernel
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#pragma warning disable SKEXP0001
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kernel.Plugins.AddFromFunctions("nanoFramework", tools.Select(aiFunction => aiFunction.AsKernelFunction()));
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// --
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// Check available prompts
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var prompts = await mcpToolboxClient.ListPromptsAsync().ConfigureAwait(false);
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// Print those prompts
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Console.WriteLine("// Available prompts:");
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foreach (var p in prompts) Console.WriteLine($"{p.Name}: {p.Description}");
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Console.WriteLine("// --");
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// load them
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kernel.Plugins.AddFromPromptDirectory("nanoFramework", prompts.Select(prompt => prompt.AsKernelPrompt()));
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var history = new ChatHistory();
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var chatCompletionService = kernel.GetRequiredService<IChatCompletionService>();

‎tests/McpEndToEndTest/McpEndToEndTest.nfproj‎

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</PropertyGroup>
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<Import Project="$(NanoFrameworkProjectSystemPath)NFProjectSystem.props" Condition="Exists('$(NanoFrameworkProjectSystemPath)NFProjectSystem.props')" />
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<ItemGroup>
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<Compile Include="McpPromptsClasses.cs" />
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<Compile Include="McpToolsClasses.cs" />
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<Compile Include="Program.cs" />
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<Compile Include="Properties\AssemblyInfo.cs" />

‎tests/McpEndToEndTest/McpPromptsClasses.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using nanoFramework.WebServer.Mcp;
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namespace McpServerTests
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{
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public class McpPrompts
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{
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[McpServerPrompt("simple_prompt", "A simple test prompt")]
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public static string SimplePrompt()
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{
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return "This is a prompt example";
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}
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[McpServerPrompt("another_simple_prompt", "Another test prompt")]
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public static string AnotherSimplePrompt()
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{
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return "This is another prompt example";
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}
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}
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}

‎tests/McpEndToEndTest/Program.cs‎

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Debug.WriteLine($"Connected with wifi credentials. IP Address: {GetCurrentIPAddress()}");
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McpToolRegistry.DiscoverTools(new Type[] { typeof(McpServerTests.McpTools) });
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Debug.WriteLine("MCP Tools discovered and registered.");
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35+
McpPromptRegistry.DiscoverPrompts(new Type[] { typeof(McpServerTests.McpPrompts) });
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Debug.WriteLine("MCP Prompts discovered and registered.");
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3638
_server = new WebServer(80, HttpProtocol.Http, new Type[] { typeof(McpServerController) });
3739
_server.CommandReceived += ServerCommandReceived;
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// Start the server.

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