Allow postgres subscriptions to be configured in publish only mode

src/HotChocolate/Core/src/Subscriptions.Postgres/PostgresSubscriptionTransportExtensions.cs

@@ -40,9 +40,31 @@ public static IRequestExecutorBuilder AddPostgresSubscriptions(
         this IRequestExecutorBuilder builder,
         Action<IServiceProvider, PostgresSubscriptionOptions> configure)
     {
-        builder.AddSubscriptionDiagnostics();
-
         var services = builder.Services;
+
+        services.AddPostgresSubscriptionPublisher(configure);
+
+        services.TryAddSingleton<ITopicEventReceiver>(
+                sp => sp.GetRequiredService<PostgresPubSub>());
+
+        return builder;
+    }
+    /// <summary>
+    /// Registers the Postgres subscription provider for use in publisher scenarios where the graphql server is
+    /// not running, but you still want to publish events via Postgres for another process to receive.
+    /// </summary>
+    /// <param name="builder">
+    /// The service collecion builder.
+    /// </param>
+    /// <param name="configure">
+    /// A delegate that configures the Postgres subscription provider options.
+    /// </param>
+    public static IServiceCollection AddPostgresSubscriptionPublisher(
+        this IServiceCollection services,
+        Action<IServiceProvider, PostgresSubscriptionOptions> configure)
+    {
+        services.AddSubscriptionDiagnostics();
+
         services.AddSingleton(sp =>
         {
             var options = new PostgresSubscriptionOptions();
@@ -61,9 +83,7 @@ public static IRequestExecutorBuilder AddPostgresSubscriptions(
         services.AddSingleton<PostgresPubSub>();
         services.TryAddSingleton<ITopicEventSender>(
             sp => sp.GetRequiredService<PostgresPubSub>());
-        services.TryAddSingleton<ITopicEventReceiver>(
-            sp => sp.GetRequiredService<PostgresPubSub>());
 
-        return builder;
+        return services;
     }
 }

src/HotChocolate/Core/src/Subscriptions/DependencyInjection/CoreSubscriptionsServiceCollectionExtensions.cs

@@ -30,7 +30,32 @@ public static IRequestExecutorBuilder AddSubscriptionDiagnostics(
             throw new ArgumentNullException(nameof(builder));
         }
 
-        builder.Services.TryAddSingleton<ISubscriptionDiagnosticEvents>(
+        builder.Services.AddSubscriptionDiagnostics();
+
+        return builder;
+    }
+
+    /// <summary>
+    /// Adds the subscription provider diagnostics.
+    /// </summary>
+    /// <param name="services">
+    /// The ServiceCollection.
+    /// </param>
+    /// <returns>
+    /// Returns the ServiceCollection for configuration chaining.
+    /// </returns>
+    /// <exception cref="ArgumentNullException">
+    /// <paramref name="services"/> is <c>null</c>.
+    /// </exception>
+    public static IServiceCollection AddSubscriptionDiagnostics(
+        this IServiceCollection services)
+    {
+        if (services is null)
+        {
+            throw new ArgumentNullException(nameof(services));
+        }
+
+        services.TryAddSingleton<ISubscriptionDiagnosticEvents>(
             sp =>
             {
                 var listeners = sp.GetService<IEnumerable<ISubscriptionDiagnosticEventsListener>>();
@@ -61,6 +86,6 @@ public static IRequestExecutorBuilder AddSubscriptionDiagnostics(
                 return new AggregateSubscriptionDiagnosticEventsListener(listenerArray);
             });
 
-        return builder;
+        return services;
     }
 }