Alerting: Telegram: truncate long messages (#54339)

Truncate messages longer than 4096 characters

pkg/services/ngalert/notifier/channels/telegram.go

@@ -9,6 +9,7 @@ import (
 	"mime/multipart"
 	"os"
 
+	"github.com/prometheus/alertmanager/notify"
 	"github.com/prometheus/alertmanager/template"
 	"github.com/prometheus/alertmanager/types"
 
@@ -158,8 +159,14 @@ func (tn *TelegramNotifier) buildTelegramMessage(ctx context.Context, as []*type
 	}()
 
 	tmpl, _ := TmplText(ctx, tn.tmpl, as, tn.log, &tmplErr)
+	// Telegram supports 4096 chars max
+	messageText, truncated := notify.Truncate(tmpl(tn.Message), 4096)
+	if truncated {
+		tn.log.Warn("Telegram message too long, truncate message", "original_message", tn.Message)
+	}
+
 	m := make(map[string]string)
-	m["text"] = tmpl(tn.Message)
+	m["text"] = messageText
 	m["parse_mode"] = "html"
 	return m, nil
 }

pkg/services/ngalert/notifier/channels/telegram_test.go

@@ -3,6 +3,7 @@ package channels
 import (
 	"context"
 	"net/url"
+	"strings"
 	"testing"
 
 	"github.com/grafana/grafana/pkg/components/simplejson"
@@ -76,6 +77,25 @@ func TestTelegramNotifier(t *testing.T) {
 				"text":       "__Custom Firing__\n2 Firing\n\nValue: [no value]\nLabels:\n - alertname = alert1\n - lbl1 = val1\nAnnotations:\n - ann1 = annv1\nSource: a URL\nSilence: http://localhost/alerting/silence/new?alertmanager=grafana&matcher=alertname%3Dalert1&matcher=lbl1%3Dval1\n\nValue: [no value]\nLabels:\n - alertname = alert1\n - lbl1 = val2\nAnnotations:\n - ann1 = annv2\nSilence: http://localhost/alerting/silence/new?alertmanager=grafana&matcher=alertname%3Dalert1&matcher=lbl1%3Dval2\n",
 			},
 			expMsgError: nil,
+		}, {
+			name: "Truncate long message",
+			settings: `{
+				"bottoken": "abcdefgh0123456789",
+				"chatid": "someid",
+				"message": "{{ .CommonLabels.alertname }}"
+			}`,
+			alerts: []*types.Alert{
+				{
+					Alert: model.Alert{
+						Labels: model.LabelSet{"alertname": model.LabelValue(strings.Repeat("1", 4097))},
+					},
+				},
+			},
+			expMsg: map[string]string{
+				"parse_mode": "html",
+				"text":       strings.Repeat("1", 4096-3) + "...",
+			},
+			expMsgError: nil,
 		}, {
 			name:         "Error in initing",
 			settings:     `{}`,