Truncate payload printed in the UI

Added a flag --max-payload-length to allow customizing the value

cmd/asynqmon/main.go

@@ -26,6 +26,7 @@ var (
 	flagRedisURL          string
 	flagRedisInsecureTLS  bool
 	flagRedisClusterNodes string
+	flagMaxPayloadLength  int
 )
 
 func init() {
@@ -37,6 +38,7 @@ func init() {
 	flag.StringVar(&flagRedisURL, "redis-url", "", "URL to redis server")
 	flag.BoolVar(&flagRedisInsecureTLS, "redis-insecure-tls", false, "disable TLS certificate host checks")
 	flag.StringVar(&flagRedisClusterNodes, "redis-cluster-nodes", "", "comma separated list of host:port addresses of cluster nodes")
+	flag.IntVar(&flagMaxPayloadLength, "max-payload-length", 200, "maximum number of utf8 characters printed in the payload cell in the Web UI")
 }
 
 // TODO: Write test and refactor this code.
@@ -99,6 +101,7 @@ func main() {
 
 	h := asynqmon.New(asynqmon.Options{
 		RedisConnOpt:     redisConnOpt,
+		PayloadFormatter: asynqmon.PayloadFormatterFunc(formatPayload),
 	})
 	defer h.Close()
 
@@ -116,3 +119,20 @@ func main() {
 	fmt.Printf("Asynq Monitoring WebUI server is listening on port %d\n", flagPort)
 	log.Fatal(srv.ListenAndServe())
 }
+
+func formatPayload(taskType string, payload []byte) string {
+	payloadStr := asynqmon.DefaultPayloadFormatter.FormatPayload(taskType, payload)
+	return truncate(payloadStr, flagMaxPayloadLength)
+}
+
+// truncates string s to limit length (in utf8).
+func truncate(s string, limit int) string {
+	i := 0
+	for pos := range s {
+		if i == limit {
+			return s[:pos] + "…"
+		}
+		i++
+	}
+	return s
+}

conversion_helpers.go

@@ -27,7 +27,10 @@ func (f PayloadFormatterFunc) FormatPayload(taskType string, payload []byte) str
 	return f(taskType, payload)
 }
 
-var defaultPayloadFormatter = PayloadFormatterFunc(func(_ string, payload []byte) string {
+// DefaultPayloadFormatter is the PayloadFormater used by default.
+// It prints the given payload bytes as is if the bytes are printable, otherwise it prints a message to indicate
+// that the bytes are not printable.
+var DefaultPayloadFormatter = PayloadFormatterFunc(func(_ string, payload []byte) string {
 	if !isPrintable(payload) {
 		return "non-printable bytes"
 	}

handler.go

@@ -88,7 +88,7 @@ var staticContents embed.FS
 func muxRouter(opts Options, rc redis.UniversalClient, inspector *asynq.Inspector) *mux.Router {
 	router := mux.NewRouter().PathPrefix(opts.RootPath).Subrouter()
 
-	var pf PayloadFormatter = defaultPayloadFormatter
+	var pf PayloadFormatter = DefaultPayloadFormatter
 	if opts.PayloadFormatter != nil {
 		pf = opts.PayloadFormatter
 	}