Fix markdown formatter for telegram notification

- Always convert context field value to string before pipeline

Author: wanliqun

alert/formatter.go

@@ -192,6 +192,7 @@ type TelegramMarkdownFormatter struct {
 
 func NewTelegramMarkdownFormatter(tags, atUsers []string) (f *TelegramMarkdownFormatter, err error) {
 	funcMap := template.FuncMap{
+		"toString":               toString,
 		"escapeMarkdown":         escapeMarkdown,
 		"formatRFC3339":          formatRFC3339,
 		"truncateStringWithTail": truncateStringWithTail,
@@ -207,6 +208,13 @@ func NewTelegramMarkdownFormatter(tags, atUsers []string) (f *TelegramMarkdownFo
 	return &TelegramMarkdownFormatter{markdownFormatter: mf}, nil
 }
 
+func toString(val interface{}) string {
+	if str, ok := val.(string); ok {
+		return str
+	}
+	return fmt.Sprintf("%v", val)
+}
+
 func escapeMarkdown(v interface{}) string {
 	return bot.EscapeMarkdown(fmt.Sprintf("%v", v))
 }

alert/templates.go

@@ -91,7 +91,7 @@ Reason
 {{.Error | escapeMarkdown}}
 
 {{else}}{{ end }}{{ if .CtxFields }}*Context Fields*:{{ range $Key, $Val := .CtxFields }}
-    *{{$Key | escapeMarkdown}}*: {{$Val | truncateStringWithTail | escapeMarkdown}}{{ end }}{{ end }}
+    *{{$Key | escapeMarkdown}}*: {{$Val | toString | truncateStringWithTail | escapeMarkdown}}{{ end }}{{ end }}
 {{ range mentions }}@{{ . }} {{ end }}
 `,
 	}