rarbg: implement retry strategy with 429 response (#14000)

src/Jackett.Common/Exceptions/TooManyRequestsException.cs

@@ -0,0 +1,27 @@
+using System;
+using Jackett.Common.Utils.Clients;
+
+namespace Jackett.Common.Exceptions
+{
+    public class TooManyRequestsException : Exception
+    {
+        public TimeSpan RetryAfter { get; private set; }
+
+        public TooManyRequestsException(string message, TimeSpan retryWait)
+            : base(message) => RetryAfter = retryWait;
+
+        public TooManyRequestsException(string message, WebResult response)
+            : base(message)
+        {
+            if (response.Headers.ContainsKey("Retry-After"))
+            {
+                var retryAfter = response.Headers["Retry-After"].ToString();
+
+                if (int.TryParse(retryAfter, out var seconds))
+                    RetryAfter = TimeSpan.FromSeconds(seconds);
+                else if (DateTime.TryParse(retryAfter, out var date))
+                    RetryAfter = date.ToUniversalTime() - DateTime.UtcNow;
+            }
+        }
+    }
+}