A bunch of cleanup for DI namespaces, ext methods and dist cache classes

src/Umbraco.Infrastructure/Cache/DatabaseServerMessengerNotificationHandler.cs

@@ -0,0 +1,93 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Umbraco.Core.Events;
+using Umbraco.Core.Persistence;
+using Umbraco.Core.Sync;
+using Umbraco.Web;
+using Umbraco.Web.Cache;
+using Umbraco.Web.Routing;
+
+namespace Umbraco.Infrastructure.Cache
+{
+    /// <summary>
+    /// Ensures that distributed cache events are setup and the <see cref="IServerMessenger"/> is initialized
+    /// </summary>
+    public sealed class DatabaseServerMessengerNotificationHandler : INotificationHandler<UmbracoApplicationStarting>
+    {
+        private readonly IBatchedDatabaseServerMessenger _messenger;
+        private readonly IRequestAccessor _requestAccessor;
+        private readonly IUmbracoDatabaseFactory _databaseFactory;
+        private readonly IDistributedCacheBinder _distributedCacheBinder;
+        private readonly ILogger<DatabaseServerMessengerNotificationHandler> _logger;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="DatabaseServerMessengerNotificationHandler"/> class.
+        /// </summary>
+        public DatabaseServerMessengerNotificationHandler(
+            IServerMessenger serverMessenger,
+            IRequestAccessor requestAccessor,
+            IUmbracoDatabaseFactory databaseFactory,
+            IDistributedCacheBinder distributedCacheBinder,
+            ILogger<DatabaseServerMessengerNotificationHandler> logger)
+        {
+            _requestAccessor = requestAccessor;
+            _databaseFactory = databaseFactory;
+            _distributedCacheBinder = distributedCacheBinder;
+            _logger = logger;
+            _messenger = serverMessenger as IBatchedDatabaseServerMessenger;
+        }
+
+        /// <inheritdoc/>
+        public Task HandleAsync(UmbracoApplicationStarting notification, CancellationToken cancellationToken)
+        {
+            // The scheduled tasks - TouchServerTask and InstructionProcessTask - run as .NET Core hosted services.
+            // The former (as well as other hosted services that run outside of an HTTP request context) depends on the application URL
+            // being available (via IRequestAccessor), which can only be retrieved within an HTTP request (unless it's explicitly configured).
+            // Hence we hook up a one-off task on an HTTP request to ensure this is retrieved, which caches the value and makes it available
+            // for the hosted services to use when the HTTP request is not available.
+            _requestAccessor.RouteAttempt += EnsureApplicationUrlOnce;
+            _requestAccessor.EndRequest += UmbracoModule_EndRequest;
+
+            Startup();
+
+            return Task.CompletedTask;
+        }
+
+        private void Startup()
+        {
+            if (_databaseFactory.CanConnect == false)
+            {
+                _logger.LogWarning("Cannot connect to the database, distributed calls will not be enabled for this server.");
+            }
+            else
+            {
+                _distributedCacheBinder.BindEvents();
+
+                // Sync on startup, this will run through the messenger's initialization sequence
+                _messenger?.Sync();
+            }
+        }
+
+        // TODO: I don't really know or think that the Application Url plays a role anymore with the DB dist cache,
+        // this might be really old stuff
+        private void EnsureApplicationUrlOnce(object sender, RoutableAttemptEventArgs e)
+        {
+            if (e.Outcome == EnsureRoutableOutcome.IsRoutable || e.Outcome == EnsureRoutableOutcome.NotDocumentRequest)
+            {
+                _requestAccessor.RouteAttempt -= EnsureApplicationUrlOnce;
+                EnsureApplicationUrl();
+            }
+        }
+
+        // By retrieving the application URL within the context of a request (as we are here in responding
+        // to the IRequestAccessor's RouteAttempt event), we'll get it from the HTTP context and save it for
+        // future requests that may not be within an HTTP request (e.g. from hosted services).
+        private void EnsureApplicationUrl() => _requestAccessor.GetApplicationUrl();
+
+        /// <summary>
+        /// Clear the batch on end request
+        /// </summary>
+        private void UmbracoModule_EndRequest(object sender, UmbracoRequestEventArgs e) => _messenger?.FlushBatch();
+    }
+}