introduce ITransactionCallback

Author: smdn

src/Smdn.Net.MuninNode/Smdn.Net.MuninNode.Protocol/MuninProtocolHandler.cs

@@ -147,17 +147,28 @@ public ValueTask HandleTransactionStartAsync(
   }
 
   /// <remarks>
-  /// In the default implementation, a banner response is sent back to the client.
+  /// In the default implementation, <see cref="ITransactionCallback.StartTransactionAsync"/> is
+  /// called for <see cref="IPluginProvider"/> and <see cref="IPlugin"/>s,
+  /// and then a banner response is sent back to the client.
   /// </remarks>
-  protected virtual ValueTask HandleTransactionStartAsyncCore(
+  protected virtual async ValueTask HandleTransactionStartAsyncCore(
     IMuninNodeClient client,
     CancellationToken cancellationToken
   )
-    => SendResponseAsync(
+  {
+    if (profile.PluginProvider is ITransactionCallback providerTransactionCallback)
+      await providerTransactionCallback.StartTransactionAsync(cancellationToken).ConfigureAwait(false);
+
+    foreach (var pluginTransactionCallback in plugins.Values.OfType<ITransactionCallback>()) {
+      await pluginTransactionCallback.StartTransactionAsync(cancellationToken).ConfigureAwait(false);
+    }
+
+    await SendResponseAsync(
       client,
       banner,
       cancellationToken
-    );
+    ).ConfigureAwait(false);
+  }
 
   /// <inheritdoc cref="IMuninProtocolHandler.HandleTransactionEndAsync"/>
   public ValueTask HandleTransactionEndAsync(
@@ -178,11 +189,22 @@ public ValueTask HandleTransactionEndAsync(
     return HandleTransactionEndAsyncCore(client, cancellationToken);
   }
 
-  protected virtual ValueTask HandleTransactionEndAsyncCore(
+  /// <remarks>
+  /// In the default implementation, <see cref="ITransactionCallback.EndTransactionAsync"/> is
+  /// called for <see cref="IPluginProvider"/> and <see cref="IPlugin"/>s.
+  /// </remarks>
+  protected virtual async ValueTask HandleTransactionEndAsyncCore(
     IMuninNodeClient client,
     CancellationToken cancellationToken
   )
-    => default; // do nothing in this class
+  {
+    foreach (var pluginTransactionCallback in plugins.Values.OfType<ITransactionCallback>()) {
+      await pluginTransactionCallback.EndTransactionAsync(cancellationToken).ConfigureAwait(false);
+    }
+
+    if (profile.PluginProvider is ITransactionCallback providerTransactionCallback)
+      await providerTransactionCallback.EndTransactionAsync(cancellationToken).ConfigureAwait(false);
+  }
 
   private static bool ExpectCommand(
     ReadOnlySequence<byte> commandLine,

src/Smdn.Net.MuninNode/Smdn.Net.MuninPlugin/ITransactionCallback.cs

@@ -0,0 +1,40 @@
+// SPDX-FileCopyrightText: 2023 smdn <smdn@smdn.jp>
+// SPDX-License-Identifier: MIT
+
+using System.Threading;
+using System.Threading.Tasks;
+
+using Smdn.Net.MuninNode.Protocol;
+
+namespace Smdn.Net.MuninPlugin;
+
+/// <summary>
+/// Defines the callbacks when a request session from the <c>munin-update</c> starts or ends.
+/// </summary>
+public interface ITransactionCallback {
+  /// <summary>
+  /// Implements a callback to be invoked when <c>munin-update</c> starts a transaction.
+  /// </summary>
+  /// <remarks>
+  /// This method is invoked when the <see cref="IMuninProtocolHandler"/> is requested to start
+  /// processing a transaction.
+  /// </remarks>
+  /// <param name="cancellationToken">
+  /// The <see cref="CancellationToken" /> to monitor for cancellation requests.
+  /// </param>
+  /// <seealso cref="IMuninProtocolHandler.HandleTransactionStartAsync"/>
+  ValueTask StartTransactionAsync(CancellationToken cancellationToken);
+
+  /// <summary>
+  /// Implements a callback to be invoked when <c>munin-update</c> ends a transaction.
+  /// </summary>
+  /// <remarks>
+  /// This method is invoked when the <see cref="IMuninProtocolHandler"/> is requested to end
+  /// processing a transaction.
+  /// </remarks>
+  /// <param name="cancellationToken">
+  /// The <see cref="CancellationToken" /> to monitor for cancellation requests.
+  /// </param>
+  /// <seealso cref="Smdn.Net.MuninNode.Protocol.IMuninProtocolHandler.HandleTransactionEndAsync"/>
+  ValueTask EndTransactionAsync(CancellationToken cancellationToken);
+}