Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/Server/McpServerPromptAttribute.cs

@@ -0,0 +1,120 @@
+using Microsoft.Extensions.AI;
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Server;
+
+/// <summary>
+/// Used to indicate that a method should be considered an <see cref="McpServerPrompt"/>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This attribute is applied to methods that should be exposed as prompts in the Model Context Protocol. When a class 
+/// containing methods marked with this attribute is registered with McpServerBuilderExtensions,
+/// these methods become available as prompts that can be called by MCP clients.
+/// </para>
+/// <para>
+/// When methods are provided directly to <see cref="M:McpServerPrompt.Create"/>, the attribute is not required.
+/// </para>
+/// <para>
+/// By default, parameters are sourced from the <see cref="GetPromptRequestParams.Arguments"/> dictionary, which is a collection
+/// of key/value pairs. Those parameters are deserialized from the
+/// <see cref="JsonElement"/> values in that collection. There are a few exceptions to this:
+/// <list type="bullet">
+///   <item>
+///     <description>
+///       <see cref="CancellationToken"/> parameters are automatically bound to a <see cref="CancellationToken"/> provided by the
+///       <see cref="IMcpServer"/> and that respects any <see cref="CancelledNotification"/>s sent by the client for this operation's
+///       <see cref="RequestId"/>.
+///     </description>
+///   </item>
+///   <item>
+///     <description>
+///       <see cref="IServiceProvider"/> parameters are bound from the <see cref="RequestContext{GetPromptRequestParams}"/> for this request.
+///     </description>
+///   </item>
+///   <item>
+///     <description>
+///       <see cref="IMcpServer"/> parameters are bound directly to the <see cref="IMcpServer"/> instance associated
+///       with this request's <see cref="RequestContext{CallPromptRequestParams}"/>. Such parameters may be used to understand
+///       what server is being used to process the request, and to interact with the client issuing the request to that server.
+///     </description>
+///   </item>
+///   <item>
+///     <description>
+///       <see cref="IProgress{ProgressNotificationValue}"/> parameters accepting <see cref="ProgressNotificationValue"/> values
+///       are bound to an <see cref="IProgress{ProgressNotificationValue}"/> instance manufactured to forward progress notifications
+///       from the prompt to the client. If the client included a <see cref="ProgressToken"/> in their request, progress reports issued
+///       to this instance will propagate to the client as <see cref="NotificationMethods.ProgressNotification"/> notifications with
+///       that token. If the client did not include a <see cref="ProgressToken"/>, the instance will ignore any progress reports issued to it.
+///     </description>
+///   </item>
+///   <item>
+///     <description>
+///       When the <see cref="McpServerPrompt"/> is constructed, it may be passed an <see cref="IServiceProvider"/> via 
+///       <see cref="McpServerPromptCreateOptions.Services"/>. Any parameter that can be satisfied by that <see cref="IServiceProvider"/>
+///       according to <see cref="IServiceProviderIsService"/> will be resolved from the <see cref="IServiceProvider"/> provided to the 
+///       prompt invocation rather than from the argument collection.
+///     </description>
+///   </item>
+///   <item>
+///     <description>
+///       Any parameter attributed with <see cref="FromKeyedServicesAttribute"/> will similarly be resolved from the 
+///       <see cref="IServiceProvider"/> provided to the prompt invocation rather than from the argument collection.
+///     </description>
+///   </item>
+/// </list>
+/// </para>
+/// <para>
+/// All other parameters are deserialized from the <see cref="JsonElement"/>s in the <see cref="GetPromptRequestParams.Arguments"/> dictionary.
+/// </para>
+/// <para>
+/// In general, the data supplied via the <see cref="GetPromptRequestParams.Arguments"/>'s dictionary is passed along from the caller and
+/// should thus be considered unvalidated and untrusted. To provide validated and trusted data to the invocation of the prompt, consider having 
+/// the prompt be an instance method, referring to data stored in the instance, or using an instance or parameters resolved from the <see cref="IServiceProvider"/>
+/// to provide data to the method.
+/// </para>
+/// <para>
+/// Return values from a method are used to create the <see cref="GetPromptResult"/> that is sent back to the client:
+/// </para>
+/// <list type="table">
+///   <item>
+///     <term><see cref="string"/></term>
+///     <description>Converted to a list containing a single <see cref="PromptMessage"/> with its <see cref="PromptMessage.Content"/> set to contain the <see cref="string"/>.</description>
+///   </item>
+///   <item>
+///     <term><see cref="PromptMessage"/></term>
+///     <description>Converted to a list containing the single <see cref="PromptMessage"/>.</description>
+///   </item>
+///   <item>
+///     <term><see cref="IEnumerable{PromptMessage}"/> of <see cref="PromptMessage"/></term>
+///     <description>Converted to a list containing all of the returned <see cref="PromptMessage"/> instances.</description>
+///   </item>
+///   <item>
+///     <term><see cref="ChatMessage"/></term>
+///     <description>Converted to a list of <see cref="PromptMessage"/> instances derived from the <see cref="ChatMessage"/> with <see cref="AIContentExtensions.ToPromptMessages"/>.</description>
+///   </item>
+///   <item>
+///     <term><see cref="IEnumerable{ChatMessage}"/> of <see cref="ChatMessage"/></term>
+///     <description>Converted to a list of <see cref="PromptMessage"/> instances derived from all of the <see cref="ChatMessage"/> instances with <see cref="AIContentExtensions.ToPromptMessages"/>.</description>
+///   </item>
+/// </list>
+/// <para>
+/// Other returned types will result in an <see cref="InvalidOperationException"/> being thrown.
+/// </para>
+/// </remarks>
+[AttributeUsage(AttributeTargets.Method)]
+public sealed class McpServerPromptAttribute : Attribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="McpServerPromptAttribute"/> class.
+    /// </summary>
+    public McpServerPromptAttribute()
+    {
+    }
+
+    /// <summary>Gets the name of the prompt.</summary>
+    /// <remarks>If <see langword="null"/>, the method name will be used.</remarks>
+    public string? Name { get; set; }
+}