single mode: Cache alert fingerprints

If ntfy-alertmanager breaks alertmanager's grouping feature, it should
take care of caching alerts on its own.

cache.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"sync"
+	"time"
+)
+
+type fingerprint string
+
+type cachedAlert struct {
+	expires time.Time
+}
+
+type cache struct {
+	mu     sync.Mutex
+	alerts map[fingerprint]*cachedAlert
+}
+
+func (a *cachedAlert) expired() bool {
+	return a.expires.Before(time.Now())
+}
+
+func newCache() *cache {
+	c := new(cache)
+	c.alerts = make(map[fingerprint]*cachedAlert)
+
+	return c
+}
+
+func (c *cache) cleanup() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	for key, value := range c.alerts {
+		if value.expired() {
+			delete(c.alerts, key)
+		}
+	}
+}
+
+func (c *cache) set(f fingerprint, d time.Duration) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	alert := new(cachedAlert)
+	alert.expires = time.Now().Add(d)
+
+	c.alerts[f] = alert
+}
+
+func (c *cache) contains(f fingerprint) bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	_, ok := c.alerts[f]
+	return ok
+}

main.go

@@ -26,6 +26,7 @@ var version string
 type receiver struct {
 	cfg    *config
 	logger *log.Logger
+	cache  *cache
 }
 
 type payload struct {
@@ -40,6 +41,7 @@ type alert struct {
 	Status      string                 `json:"status"`
 	Labels      map[string]interface{} `json:"labels"`
 	Annotations map[string]interface{} `json:"annotations"`
+	Fingerprint fingerprint            `json:"fingerprint"`
 }
 
 type notification struct {
@@ -52,6 +54,13 @@ type notification struct {
 func (rcv *receiver) singleAlertNotifications(p *payload) []*notification {
 	var notifications []*notification
 	for _, alert := range p.Alerts {
+		if rcv.cache.contains(alert.Fingerprint) {
+			rcv.logger.Debugf("Alert %s skipped: Still in cache", alert.Fingerprint)
+			continue
+		}
+		// TODO: Make configurable
+		rcv.cache.set(alert.Fingerprint, time.Hour*24)
+
 		n := new(notification)
 
 		// create title
@@ -275,6 +284,15 @@ func (rcv *receiver) basicAuthMiddleware(handler http.HandlerFunc) http.HandlerF
 	}
 }
 
+func (rcv *receiver) runCleanup() {
+	for {
+		// TODO: Make configurable
+		time.Sleep(time.Hour)
+		rcv.logger.Info("Pruning cache")
+		rcv.cache.cleanup()
+	}
+}
+
 func main() {
 	var configPath string
 	flag.StringVar(&configPath, "config", "/etc/ntfy-alertmanager/config", "config file path")
@@ -298,7 +316,7 @@ func main() {
 		logger.Errorf("config: %v", err)
 	}
 
-	receiver := &receiver{cfg: cfg, logger: logger}
+	receiver := &receiver{cfg: cfg, logger: logger, cache: newCache()}
 
 	logger.Infof("Listening on %s, ntfy-alertmanager %s", cfg.HTTPAddress, version)
 
@@ -309,5 +327,6 @@ func main() {
 		http.HandleFunc("/", receiver.handleWebhooks)
 	}
 
+	go receiver.runCleanup()
 	logger.Fatal(http.ListenAndServe(cfg.HTTPAddress, nil))
 }