connection retry added

TimetableDesigner.Backend.Events.Providers.RabbitMQ/RabbitMQEventQueue.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using RabbitMQ.Client;
+using RabbitMQ.Client.Exceptions;
 
 namespace TimetableDesigner.Backend.Events.Providers.RabbitMQ;
 
@@ -20,6 +21,16 @@ public class RabbitMQEventQueue : EventQueue<RabbitMQEventQueue>
         string password = connectionParameters["Password"];
         string exchangeName = connectionParameters["ExchangeName"];
         string queuePrefix = connectionParameters["QueuePrefix"];
+        if (!connectionParameters.TryGetValue("Retries", out string retriesStr))
+        {
+            retriesStr = "0";
+        }
+        int retries = int.Parse(retriesStr);
+        if (!connectionParameters.TryGetValue("RetryCooldown", out string retryCooldownStr))
+        {
+            retryCooldownStr = "1000";
+        }
+        int retryCooldown = int.Parse(retryCooldownStr);
             
         ConnectionFactory factory = new ConnectionFactory
         {
@@ -29,9 +40,33 @@ public class RabbitMQEventQueue : EventQueue<RabbitMQEventQueue>
             Password = password,
         };
         
-        Task<IConnection> createConnectionTask = factory.CreateConnectionAsync();
+        IConnection? connection = null;
+        int retryCount = 0;
+        Exception lastException = new Exception("Cannot connect to RabbitMQ");
+        while (connection is null && (retries < 0 || retryCount < retries))
+        {
+            try
+            {
+                using (Task<IConnection> createConnectionTask = factory.CreateConnectionAsync())
+                {
                     createConnectionTask.Wait();
-        services.AddSingleton(createConnectionTask.Result);
+                    connection = createConnectionTask.Result;
+                }
+            }
+            catch (Exception ex)
+            {
+                Thread.Sleep(retryCooldown);
+                retryCount++;
+                lastException = ex;
+            }
+        }
+
+        if (connection is null)
+        {
+            throw lastException;
+        }
+        
+        services.AddSingleton(connection);
         services.AddSingleton<IEventQueuePublisher, RabbitMQEventQueuePublisher>(sp => new RabbitMQEventQueuePublisher(sp.GetRequiredService<IConnection>(), exchangeName));
         services.AddSingleton<IEventQueueSubscriber, RabbitMQEventQueueSubscriber>(sp => new RabbitMQEventQueueSubscriber(sp.GetRequiredService<IConnection>(), exchangeName, queuePrefix));
     }