Add periodic garbage collection of webhook rate limit cache

PluralKit.Bot/Bot.cs

@@ -102,13 +102,16 @@ namespace PluralKit.Bot
         private IMetrics _metrics;
         private PeriodicStatCollector _collector;
         private ILogger _logger;
+        private WebhookRateLimitService _webhookRateLimit;
+        private int _periodicUpdateCount;
 
-        public Bot(ILifetimeScope services, IDiscordClient client, IMetrics metrics, PeriodicStatCollector collector, ILogger logger)
+        public Bot(ILifetimeScope services, IDiscordClient client, IMetrics metrics, PeriodicStatCollector collector, ILogger logger, WebhookRateLimitService webhookRateLimit)
         {
             _services = services;
             _client = client as DiscordShardedClient;
             _metrics = metrics;
             _collector = collector;
+            _webhookRateLimit = webhookRateLimit;
             _logger = logger.ForContext<Bot>();
         }
 
@@ -161,7 +164,13 @@ namespace PluralKit.Bot
         {
             // Change bot status
             await _client.SetGameAsync($"pk;help | in {_client.Guilds.Count} servers");
-            
+
+            // Run webhook rate limit GC every 10 minutes
+            if (_periodicUpdateCount++ % 10 == 0)
+            {
+                var _ = Task.Run(() => _webhookRateLimit.GarbageCollect());
+            }
+
             await _collector.CollectStats();
             
             _logger.Information("Submitted metrics to backend");

PluralKit.Bot/Services/WebhookRateLimitService.cs

@@ -87,6 +87,23 @@ namespace PluralKit.Bot
             }
         }
 
+        public void GarbageCollect()
+        {
+            _logger.Information("Garbage-collecting webhook rate limit buckets...");
+            
+            var collected = 0;
+            foreach (var channel in _info.Keys)
+            {
+                if (!_info.TryGetValue(channel, out var info)) continue;
+                
+                // Remove all keys that expired more than an hour ago (and of course, haven't been reset)
+                if (info.resetTime < SystemClock.Instance.GetCurrentInstant() - Duration.FromHours(1))
+                    if (_info.TryRemove(channel, out _)) collected++;
+            }
+            
+            _logger.Information("Garbage-collected {ChannelCount} channels from the webhook rate limit buckets.", collected);
+        }
+
         private string GetHeader(HttpResponseMessage response, string key)
         {
             var firstPair = response.Headers.FirstOrDefault(pair => pair.Key.Equals(key, StringComparison.InvariantCultureIgnoreCase));