adding max_alerts parameter to slack webhook config

Signed-off-by: Prashant Balachandran <pnair@redhat.com>

correcting formatting errors

config/notifiers.go

@@ -338,6 +338,11 @@ type SlackConfig struct {
 
 	HTTPConfig *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
 
+	// MaxAlerts is the maximum number of alerts to be sent per webhook message.
+	// Alerts exceeding this threshold will be truncated. Setting this to 0
+	// allows an unlimited number of alerts.
+	MaxAlerts uint64 `yaml:"max_alerts" json:"max_alerts"`
+
 	APIURL     *SecretURL `yaml:"api_url,omitempty" json:"api_url,omitempty"`
 	APIURLFile string     `yaml:"api_url_file,omitempty" json:"api_url_file,omitempty"`
 

notify/slack/slack.go

@@ -84,11 +84,19 @@ type attachment struct {
 	MrkdwnIn   []string             `json:"mrkdwn_in,omitempty"`
 }
 
+func truncateAlerts(maxAlerts uint64, alerts []*types.Alert) []*types.Alert {
+	if maxAlerts != 0 && uint64(len(alerts)) > maxAlerts {
+		return alerts[:maxAlerts]
+	}
+	return alerts
+}
+
 // Notify implements the Notifier interface.
 func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error) {
+	alerts := truncateAlerts(n.conf.MaxAlerts, as)
 	var err error
 	var (
-		data     = notify.GetTemplateData(ctx, n.tmpl, as, n.logger)
+		data     = notify.GetTemplateData(ctx, n.tmpl, alerts, n.logger)
 		tmplText = notify.TmplText(n.tmpl, data, &err)
 	)
 	var markdownIn []string