iplimit: dont count idle db-only ips toward the per-client limit

after #4083 the staleness window is 30 minutes, which still lets an ip
that stopped connecting a few minutes ago sit in the db blob and keep
the protected slot on the ascending sort. the ip that is actually
connecting right now gets classified as excess and sent to fail2ban,
and never lands in inbound_client_ips.ips so the panel doesnt show it
until you clear the log by hand.

only count ips observed in the current scan toward the limit. db-only
entries stay in the blob for display but dont participate in the ban
decision. live subset still uses the "protect oldest, ban newcomer"
rule.

closes #4091. followup to #4077.

web/job/check_client_ip_job.go

@@ -246,6 +246,37 @@ func mergeClientIps(old, new []IPWithTimestamp, staleCutoff int64) map[string]in
 	return ipMap
 }
 
+// partitionLiveIps splits the merged ip map into live (seen in the
+// current scan) and historical (only in the db blob, still inside the
+// staleness window).
+//
+// only live ips count toward the per-client limit. historical ones stay
+// in the db so the panel keeps showing them, but they must not take a
+// protected slot. the 30min cutoff alone isn't tight enough: an ip that
+// stopped connecting a few minutes ago still looks fresh to
+// mergeClientIps, and since the over-limit picker sorts ascending and
+// keeps the oldest, those idle entries used to win the slot while the
+// ip actually connecting got classified as excess and sent to fail2ban
+// every tick. see #4077 / #4091.
+//
+// live is sorted ascending so the "protect original, ban newcomer"
+// rule still holds when several ips are really connecting at once.
+func partitionLiveIps(ipMap map[string]int64, observedThisScan map[string]bool) (live, historical []IPWithTimestamp) {
+	live = make([]IPWithTimestamp, 0, len(observedThisScan))
+	historical = make([]IPWithTimestamp, 0, len(ipMap))
+	for ip, ts := range ipMap {
+		entry := IPWithTimestamp{IP: ip, Timestamp: ts}
+		if observedThisScan[ip] {
+			live = append(live, entry)
+		} else {
+			historical = append(historical, entry)
+		}
+	}
+	sort.Slice(live, func(i, j int) bool { return live[i].Timestamp < live[j].Timestamp })
+	sort.Slice(historical, func(i, j int) bool { return historical[i].Timestamp < historical[j].Timestamp })
+	return live, historical
+}
+
 func (j *CheckClientIpJob) checkFail2BanInstalled() bool {
 	cmd := "fail2ban-client"
 	args := []string{"-h"}
@@ -358,15 +389,13 @@ func (j *CheckClientIpJob) updateInboundClientIps(inboundClientIps *model.Inboun
 	// re-observed in a while. See mergeClientIps / #4077 for why.
 	ipMap := mergeClientIps(oldIpsWithTime, newIpsWithTime, time.Now().Unix()-ipStaleAfterSeconds)
 
-	// Convert back to slice and sort by timestamp (oldest first)
-	// This ensures we always protect the original/current connections and ban new excess ones.
-	allIps := make([]IPWithTimestamp, 0, len(ipMap))
-	for ip, timestamp := range ipMap {
-		allIps = append(allIps, IPWithTimestamp{IP: ip, Timestamp: timestamp})
+	// only ips seen in this scan count toward the limit. see
+	// partitionLiveIps.
+	observedThisScan := make(map[string]bool, len(newIpsWithTime))
+	for _, ipTime := range newIpsWithTime {
+		observedThisScan[ipTime.IP] = true
 	}
-	sort.Slice(allIps, func(i, j int) bool {
-		return allIps[i].Timestamp < allIps[j].Timestamp // Ascending order (oldest first)
-	})
+	liveIps, historicalIps := partitionLiveIps(ipMap, observedThisScan)
 
 	shouldCleanLog := false
 	j.disAllowedIps = []string{}
@@ -381,35 +410,39 @@ func (j *CheckClientIpJob) updateInboundClientIps(inboundClientIps *model.Inboun
 	log.SetOutput(logIpFile)
 	log.SetFlags(log.LstdFlags)
 
-	// Check if we exceed the limit
-	if len(allIps) > limitIp {
+	// historical db-only ips are excluded from this count on purpose.
+	var keptLive []IPWithTimestamp
+	if len(liveIps) > limitIp {
 		shouldCleanLog = true
 
-		// Keep the oldest IPs (currently active connections) and ban the new excess ones.
-		keptIps := allIps[:limitIp]
-		bannedIps := allIps[limitIp:]
+		// protect the oldest live ip, ban newcomers.
+		keptLive = liveIps[:limitIp]
+		bannedLive := liveIps[limitIp:]
 
-		// Log banned IPs in the format fail2ban filters expect: [LIMIT_IP] Email = X || Disconnecting OLD IP = Y || Timestamp = Z
-		for _, ipTime := range bannedIps {
+		// log format is load-bearing: x-ui.sh create_iplimit_jails builds
+		// filter.d/3x-ipl.conf with
+		//   failregex = \[LIMIT_IP\]\s*Email\s*=\s*<F-USER>.+</F-USER>\s*\|\|\s*Disconnecting OLD IP\s*=\s*<ADDR>\s*\|\|\s*Timestamp\s*=\s*\d+
+		// don't change the wording.
+		for _, ipTime := range bannedLive {
 			j.disAllowedIps = append(j.disAllowedIps, ipTime.IP)
 			log.Printf("[LIMIT_IP] Email = %s || Disconnecting OLD IP = %s || Timestamp = %d", clientEmail, ipTime.IP, ipTime.Timestamp)
 		}
 
-		// Actually disconnect banned IPs by temporarily removing and re-adding user
-		// This forces Xray to drop existing connections from banned IPs
-		if len(bannedIps) > 0 {
-			j.disconnectClientTemporarily(inbound, clientEmail, clients)
-		}
-
-		// Update database with only the currently active (kept) IPs
-		jsonIps, _ := json.Marshal(keptIps)
-		inboundClientIps.Ips = string(jsonIps)
+		// force xray to drop existing connections from banned ips
+		j.disconnectClientTemporarily(inbound, clientEmail, clients)
 	} else {
-		// Under limit, save all IPs
-		jsonIps, _ := json.Marshal(allIps)
-		inboundClientIps.Ips = string(jsonIps)
+		keptLive = liveIps
 	}
 
+	// keep kept-live + historical in the blob so the panel keeps showing
+	// recently seen ips. banned live ips are already in the fail2ban log
+	// and will reappear in the next scan if they reconnect.
+	dbIps := make([]IPWithTimestamp, 0, len(keptLive)+len(historicalIps))
+	dbIps = append(dbIps, keptLive...)
+	dbIps = append(dbIps, historicalIps...)
+	jsonIps, _ := json.Marshal(dbIps)
+	inboundClientIps.Ips = string(jsonIps)
+
 	db := database.GetDB()
 	err = db.Save(inboundClientIps).Error
 	if err != nil {
@@ -418,7 +451,7 @@ func (j *CheckClientIpJob) updateInboundClientIps(inboundClientIps *model.Inboun
 	}
 
 	if len(j.disAllowedIps) > 0 {
-		logger.Infof("[LIMIT_IP] Client %s: Kept %d current IPs, queued %d new IPs for fail2ban", clientEmail, limitIp, len(j.disAllowedIps))
+		logger.Infof("[LIMIT_IP] Client %s: Kept %d live IPs, queued %d new IPs for fail2ban", clientEmail, len(keptLive), len(j.disAllowedIps))
 	}
 
 	return shouldCleanLog