One off jobs (distribworks#137)

One off jobs

.travis.yml

@@ -23,8 +23,4 @@ script:
   - go vet ./...
   # - fgt golint ./...
   - glide install
-  - go test -v ./dkron
-
-env:
-  global:
-    - GO15VENDOREXPERIMENT=1
+  - go test -v $(glide novendor)

cron/doc.go

@@ -100,6 +100,19 @@ Note: The interval does not take the job runtime into account.  For example,
 if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes,
 it will have only 2 minutes of idle time between each run.
 
+Fixed times
+
+You may also schedule a job to execute once and never more. This is supported by
+formatting the cron spec like this:
+
+    @at <datetime>
+
+Where "datetime" is a string accepted by time.Parse in RFC 3339/ISO 8601 format
+(https://golang.org/pkg/time/#Parse).
+
+For example, "@at 2018-01-02T15:04:00" would run the job on the specified date and time
+assuming UTC timezone.
+
 Time zones
 
 All interpretation and scheduling is done in the machine's local time zone (as

cron/parser.go

@@ -236,6 +236,15 @@ func parseDescriptor(spec string) Schedule {
 		return Every(duration)
 	}
 
+	const at = "@at "
+	if strings.HasPrefix(spec, at) {
+		date, err := time.Parse(time.RFC3339, spec[len(at):])
+		if err != nil {
+			log.Panicf("Failed to parse date %s: %s", spec, err)
+		}
+		return At(date)
+	}
+
 	log.Panicf("Unrecognized descriptor: %s", spec)
 	return nil
 }

cron/parser_test.go

@@ -103,6 +103,8 @@ func TestSpecSchedule(t *testing.T) {
 	}{
 		{"* 5 * * * *", &SpecSchedule{all(seconds), 1 << 5, all(hours), all(dom), all(months), all(dow)}},
 		{"@every 5m", ConstantDelaySchedule{time.Duration(5) * time.Minute}},
+		{"@at 2018-01-02T15:04:00Z", SimpleSchedule{time.Date(2018, time.January, 2, 15, 4, 0, 0, time.UTC)}},
+		{"@at 2019-02-04T09:20:00+06:00", SimpleSchedule{time.Date(2019, time.February, 4, 9, 20, 0, 0, time.FixedZone("", 21600))}},
 	}
 
 	for _, c := range entries {

cron/simple.go

@@ -0,0 +1,21 @@
+package cron
+
+import "time"
+
+// SimpleDelaySchedule represents a simple non recurring duration.
+type SimpleSchedule struct {
+	Date time.Time
+}
+
+// Just store the given time for this schedule.
+func At(date time.Time) SimpleSchedule {
+	return SimpleSchedule{
+		Date: date,
+	}
+}
+
+// Next conforms to the Schedule interface but this kind of jobs
+// doesn't need to be run more than once, so it doesn't return a new date but the existing one.
+func (schedule SimpleSchedule) Next(t time.Time) time.Time {
+	return schedule.Date
+}

scripts/test.sh

@@ -3,4 +3,4 @@
 docker-compose up -d etcd
 export COMPOSE_ETCD_PORT=`docker port dkron_etcd_1 4001/tcp | cut -d":" -f 2`
 export DKRON_BACKEND_MACHINE=`docker-machine ip default`:$COMPOSE_ETCD_PORT
-go test -v ./dkron $1
+go test -v $(glide novendor) $1