Fix: Delete join service message for auto-banned users (#22)

When a user joins, the bot might receive a `ChatMemberUpdated` event before the `NewChatMembers` service message. If the auto-ban is triggered by the `ChatMemberUpdated` event, the service message ID is not yet known, leaving the "X joined the group" message visible.

This change introduces a structured `JoinProcessedCache` that tracks the `JoinMsgID` and `IsBanned` status. If a join message ID arrives for an already banned user (within 10 seconds of the initial join detection), it is now retroactively deleted.

Changes:
- Replaced `JoinProcessedCache map[int64]time.Time` with `map[int64]*JoinProcessedEntry`.
- Added `JoinProcessedEntry` struct in `telegram/telegram.go`.
- Updated `processJoin` in `telegram/autoban.go` to handle late message IDs and mark banned users.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: birabittoh <26506860+birabittoh@users.noreply.github.com>

Author: birabittoh

telegram/autoban.go

@@ -59,15 +59,24 @@ func processJoin(escarbot *EscarBot, chatID int64, user tgbotapi.User, joinMsgID
 	escarbot.JoinCacheMutex.Lock()
 	// Cleanup old entries (older than 1 minute) periodically
 	// We do it here for simplicity
-	for id, t := range escarbot.JoinProcessedCache {
-		if time.Since(t) > 1*time.Minute {
+	for id, entry := range escarbot.JoinProcessedCache {
+		if time.Since(entry.Time) > 1*time.Minute {
 			delete(escarbot.JoinProcessedCache, id)
 		}
 	}
 
 	lastProcessed, exists := escarbot.JoinProcessedCache[user.ID]
 	// If processed in the last 10 seconds, it's a duplicate
-	if exists && time.Since(lastProcessed) < 10*time.Second {
+	if exists && time.Since(lastProcessed.Time) < 10*time.Second {
+		// If we now have a JoinMsgID but didn't before
+		if joinMsgID != 0 && lastProcessed.JoinMsgID == 0 {
+			lastProcessed.JoinMsgID = joinMsgID
+			if lastProcessed.IsBanned {
+				// User was already banned, delete this new join message
+				deleteMessages(escarbot, chatID, joinMsgID)
+				log.Printf("Deleted late join message %d for banned user %d", joinMsgID, user.ID)
+			}
+		}
 		escarbot.JoinCacheMutex.Unlock()
 
 		// Even if it's a duplicate, we might want to update the joinMsgID for captcha
@@ -81,7 +90,13 @@ func processJoin(escarbot *EscarBot, chatID int64, user tgbotapi.User, joinMsgID
 		escarbot.CaptchaMutex.Unlock()
 		return
 	}
-	escarbot.JoinProcessedCache[user.ID] = time.Now()
+
+	entry := &JoinProcessedEntry{
+		Time:      time.Now(),
+		JoinMsgID: joinMsgID,
+		IsBanned:  false,
+	}
+	escarbot.JoinProcessedCache[user.ID] = entry
 	escarbot.JoinCacheMutex.Unlock()
 
 	escarbot.StateMutex.RLock()
@@ -97,6 +112,11 @@ func processJoin(escarbot *EscarBot, chatID int64, user tgbotapi.User, joinMsgID
 		// Ban user and cleanup join message
 		banAndCleanup(escarbot, chatID, user, joinMsgID)
 
+		// Mark as banned in join cache to handle potential late service messages
+		escarbot.JoinCacheMutex.Lock()
+		entry.IsBanned = true
+		escarbot.JoinCacheMutex.Unlock()
+
 		return
 	}
 

telegram/telegram.go

@@ -42,10 +42,17 @@ type EscarBot struct {
 	EnabledReplacers   map[string]bool
 	PendingCaptchas    map[int64]*PendingCaptcha
 	CaptchaMutex       sync.RWMutex
-	JoinProcessedCache map[int64]time.Time
+	JoinProcessedCache map[int64]*JoinProcessedEntry
 	JoinCacheMutex     sync.Mutex
 }
 
+// JoinProcessedEntry represents a join event that was already processed
+type JoinProcessedEntry struct {
+	Time      time.Time
+	JoinMsgID int
+	IsBanned  bool
+}
+
 // MessageHistory represents a previous version of a message
 type MessageHistory struct {
 	Text     string `json:"text"`
@@ -231,7 +238,7 @@ func NewBot(botToken string, channelId string, groupId string, adminId, logChann
 		CaptchaText:        os.Getenv("CAPTCHA_TEXT"),
 		EnabledReplacers:   enabledReplacers,
 		PendingCaptchas:    make(map[int64]*PendingCaptcha),
-		JoinProcessedCache: make(map[int64]time.Time),
+		JoinProcessedCache: make(map[int64]*JoinProcessedEntry),
 	}
 
 	availableReactionsMap[groupIdInt] = getAvailableReactions(escarbot, groupIdInt)