added optional jitter to schedule filter

web/scraping.go

@@ -1220,7 +1220,13 @@ func TriggerSchedule(watchID WatchID, web *Web, scheduleID *FilterID) {
 
 // getCronDebugResult parses the cron schedule string and logs any errors
 func getCronDebugResult(filter *Filter) {
-	_, err := cron.ParseStandard(filter.Var1)
+	scheduleSplit := strings.Split(filter.Var1, "+")
+	scheduleTrimmed := strings.TrimSpace(scheduleSplit[0])
+	_, err := cron.ParseStandard(scheduleTrimmed)
+	if err != nil {
+		filter.Log(err)
+	}
+	_, err = getJittersFromScheduleString(filter.Var1)
 	if err != nil {
 		filter.Log(err)
 	}

web/util.go

@@ -2,6 +2,9 @@ package web
 
 import (
 	"errors"
+	"math/rand"
+	"strings"
+	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/go-playground/validator/v10"
@@ -66,3 +69,27 @@ func buildFilterTree(filters []Filter, connections []FilterConnection) {
 		}
 	*/
 }
+
+func getJittersFromScheduleString(scheduleString string) ([]time.Duration, error) {
+	split := strings.Split(scheduleString, "+")
+	split = split[1:]
+	durations := []time.Duration{}
+	if len(split) == 0 {
+		return durations, nil
+	}
+
+	rand.Seed(time.Now().UnixMilli())
+
+	for _, jitter := range split {
+		trimmed := strings.TrimSpace(jitter)
+
+		duration, err := time.ParseDuration(trimmed)
+		if err != nil {
+			return durations, err
+		}
+
+		duration = time.Duration(float64(duration.Nanoseconds()) * rand.Float64())
+		durations = append(durations, duration)
+	}
+	return durations, nil
+}

web/web.go

@@ -91,7 +91,9 @@ func (web *Web) addCronJobIfCronFilter(filter *Filter, startup bool) {
 	if filter.Var2 != nil && *filter.Var2 == "no" {
 		return
 	}
-	entryID, err := web.cron.AddFunc(filter.Var1, func() { TriggerSchedule(filter.WatchID, web, &filter.ID) })
+	scheduleSplit := strings.Split(filter.Var1, "+")
+	scheduleTrimmed := strings.TrimSpace(scheduleSplit[0])
+	entryID, err := web.cron.AddFunc(scheduleTrimmed, func() { web.addCronJitter(filter.WatchID, filter) })
 	if err != nil {
 		if startup {
 			web.startupWarning("Could not start job for Watch: ", filter.WatchID)
@@ -104,6 +106,20 @@ func (web *Web) addCronJobIfCronFilter(filter *Filter, startup bool) {
 	web.cronWatch[filter.ID] = entryID
 }
 
+func (web *Web) addCronJitter(watchID WatchID, filter *Filter) {
+	durations, err := getJittersFromScheduleString(filter.Var1)
+	if err != nil {
+		log.Println("Could not parse Schedule string:", filter.Var1)
+		return
+	}
+
+	for _, duration := range durations {
+		log.Println("Delaying by:", duration)
+		time.Sleep(duration)
+	}
+	TriggerSchedule(filter.WatchID, web, &filter.ID)
+}
+
 // validateProxyURL calls url.Parse with the proxy.url, if there is an error, it's added to startupWarnings
 func (web *Web) validateProxyURL() {
 	if viper.IsSet("proxy.url") {