fix: rss failures with exponential blacklist (#1362)

* fix: rss failures with exponential blacklist

failed rss feed urls are marked as blacklisted upto
24 hours, if it's a dead url it notifies with error log
for admin to remove it.

* refactor: helper and magic numbers

moves numbers used for backing off hours
to constants and adds a helper to calculate backing off
hours duration

* chore: log level for skips to debug

* refactor: move failure state record to seperate file

Author: ankitsmt211

application/src/main/java/org/togetherjava/tjbot/features/rss/FailureState.java

@@ -0,0 +1,6 @@
+package org.togetherjava.tjbot.features.rss;
+
+import java.time.ZonedDateTime;
+
+record FailureState(int count, ZonedDateTime lastFailure) {
+}

application/src/main/java/org/togetherjava/tjbot/features/rss/RSSHandlerRoutine.java

@@ -2,6 +2,8 @@
 
 import com.apptasticsoftware.rssreader.Item;
 import com.apptasticsoftware.rssreader.RssReader;
+import com.github.benmanes.caffeine.cache.Cache;
+import com.github.benmanes.caffeine.cache.Caffeine;
 import net.dv8tion.jda.api.EmbedBuilder;
 import net.dv8tion.jda.api.JDA;
 import net.dv8tion.jda.api.entities.channel.concrete.TextChannel;
@@ -48,7 +50,7 @@
  * <p>
  * To include a new RSS feed, simply define an {@link RSSFeed} entry in the {@code "rssFeeds"} array
  * within the configuration file, adhering to the format shown below:
- * 
+ *
  * <pre>
  * {@code
  * {
@@ -58,7 +60,7 @@
  * }
  * }
  * </pre>
- * 
+ * <p>
  * Where:
  * <ul>
  * <li>{@code url} represents the URL of the RSS feed.</li>
@@ -84,6 +86,14 @@ public final class RSSHandlerRoutine implements Routine {
     private final int interval;
     private final Database database;
 
+    private final Cache<String, FailureState> circuitBreaker =
+            Caffeine.newBuilder().expireAfterWrite(7, TimeUnit.DAYS).maximumSize(500).build();
+
+    private static final int DEAD_RSS_FEED_FAILURE_THRESHOLD = 15;
+    private static final double BACKOFF_BASE = 2.0;
+    private static final double BACKOFF_EXPONENT_OFFSET = 1.0;
+    private static final double MAX_BACKOFF_HOURS = 24.0;
+
     /**
      * Constructs an RSSHandlerRoutine with the provided configuration and database.
      *
@@ -117,7 +127,14 @@ public Schedule createSchedule() {
 
     @Override
     public void runRoutine(@Nonnull JDA jda) {
-        this.config.feeds().forEach(feed -> sendRSS(jda, feed));
+        this.config.feeds().forEach(feed -> {
+            if (isBackingOff(feed.url())) {
+                logger.debug("Skipping RSS feed (Backing off): {}", feed.url());
+                return;
+            }
+
+            sendRSS(jda, feed);
+        });
     }
 
     /**
@@ -257,7 +274,6 @@ private void postItem(List<TextChannel> textChannels, Item rssItem, RSSFeed feed
      * @param rssFeedRecord the record representing the RSS feed, can be null if not found in the
      *        database
      * @param lastPostedDate the last posted date to be updated
-     *
      * @throws DateTimeParseException if the date cannot be parsed
      */
     private void updateLastDateToDatabase(RSSFeed feedConfig, @Nullable RssFeedRecord rssFeedRecord,
@@ -400,9 +416,26 @@ private MessageCreateData constructMessage(Item item, RSSFeed feedConfig) {
      */
     private List<Item> fetchRSSItemsFromURL(String rssUrl) {
         try {
-            return rssReader.read(rssUrl).toList();
+            List<Item> items = rssReader.read(rssUrl).toList();
+            circuitBreaker.invalidate(rssUrl);
+            return items;
         } catch (IOException e) {
-            logger.error("Could not fetch RSS from URL ({})", rssUrl, e);
+            FailureState oldState = circuitBreaker.getIfPresent(rssUrl);
+            int newCount = (oldState == null) ? 1 : oldState.count() + 1;
+
+            if (newCount >= DEAD_RSS_FEED_FAILURE_THRESHOLD) {
+                logger.error(
+                        "Possibly dead RSS feed URL: {} - Failed {} times. Please remove it from config.",
+                        rssUrl, newCount);
+            }
+            circuitBreaker.put(rssUrl, new FailureState(newCount, ZonedDateTime.now()));
+
+            long blacklistedHours = calculateWaitHours(newCount);
+
+            logger.warn(
+                    "RSS fetch failed for {} (Attempt #{}). Backing off for {} hours. Reason: {}",
+                    rssUrl, newCount, blacklistedHours, e.getMessage(), e);
+
             return List.of();
         }
     }
@@ -424,4 +457,20 @@ private static ZonedDateTime getZonedDateTime(@Nullable String date, String form
 
         return ZonedDateTime.parse(date, DateTimeFormatter.ofPattern(format));
     }
+
+    private long calculateWaitHours(int failureCount) {
+        return (long) Math.min(Math.pow(BACKOFF_BASE, failureCount - BACKOFF_EXPONENT_OFFSET),
+                MAX_BACKOFF_HOURS);
+    }
+
+    private boolean isBackingOff(String url) {
+        FailureState state = circuitBreaker.getIfPresent(url);
+        if (state == null)
+            return false;
+
+        long waitHours = calculateWaitHours(state.count());
+        ZonedDateTime retryAt = state.lastFailure().plusHours(waitHours);
+
+        return ZonedDateTime.now().isBefore(retryAt);
+    }
 }