Add Time Trigger API and client (#153) (#161)

This change adds a timer trigger API, client, and implementation.  Users can trigger a function with a cron-compatible string. 

This change also moves the publisher interface and webhook-based publisher implementation out of kubewatcher and into a separate `publisher` package.

timer/timer.go

@@ -0,0 +1,143 @@
+/*
+Copyright 2017 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package timer
+
+import (
+	"github.com/robfig/cron"
+
+	"log"
+
+	"github.com/fission/fission"
+	"github.com/fission/fission/publisher"
+)
+
+type requestType int
+
+const (
+	SYNC requestType = iota
+)
+
+type (
+	Timer struct {
+		triggers       map[string]*timerTriggerWithCron
+		requestChannel chan *timerRequest
+		publisher      *publisher.Publisher
+	}
+
+	timerRequest struct {
+		requestType
+		triggers        []fission.TimeTrigger
+		responseChannel chan *timerResponse
+	}
+	timerResponse struct {
+		error
+	}
+	timerTriggerWithCron struct {
+		trigger fission.TimeTrigger
+		cron    *cron.Cron
+	}
+)
+
+func MakeTimer(publisher publisher.Publisher) *Timer {
+	timer := &Timer{
+		triggers:       make(map[string]*timerTriggerWithCron),
+		requestChannel: make(chan *timerRequest),
+		publisher:      &publisher,
+	}
+	go timer.svc()
+	return timer
+}
+
+func (timer *Timer) Sync(triggers []fission.TimeTrigger) error {
+	req := &timerRequest{
+		requestType:     SYNC,
+		triggers:        triggers,
+		responseChannel: make(chan *timerResponse),
+	}
+	timer.requestChannel <- req
+	resp := <-req.responseChannel
+	return resp.error
+}
+
+func (timer *Timer) svc() {
+	for {
+		req := <-timer.requestChannel
+		switch req.requestType {
+		case SYNC:
+			err := timer.syncCron(req.triggers)
+			req.responseChannel <- &timerResponse{error: err}
+		}
+	}
+}
+
+func (timer *Timer) syncCron(triggers []fission.TimeTrigger) error {
+	for _, t := range triggers {
+		if item, ok := timer.triggers[t.Name]; ok {
+			// the item exists, update the item if needed
+			if item.trigger.Uid == t.Uid {
+				continue
+			}
+
+			// update cron if the cron spec changed
+			if item.trigger.Cron != t.Cron {
+				// if there is an cron running, stop it
+				if item.cron != nil {
+					item.cron.Stop()
+				}
+				item.cron = timer.newCron(t)
+			}
+
+			item.trigger = t
+		} else {
+			timer.triggers[t.Name] = &timerTriggerWithCron{
+				trigger: t,
+				cron:    timer.newCron(t),
+			}
+		}
+	}
+
+	for k, v := range timer.triggers {
+		found := false
+		for _, t := range triggers {
+			if t.Name == k {
+				found = true
+				break
+			}
+		}
+		if !found {
+			if v.cron != nil {
+				v.cron.Stop()
+			}
+			delete(timer.triggers, k)
+		}
+	}
+
+	return nil
+}
+
+func (timer *Timer) newCron(t fission.TimeTrigger) *cron.Cron {
+	c := cron.New()
+	c.AddFunc(t.Cron, func() {
+		headers := map[string]string{
+			"X-Fission-Timer-Name": t.Name,
+		}
+		(*timer.publisher).Publish("", headers, fission.UrlForFunction(&t.Function))
+	})
+	c.Start()
+	log.Printf("Updated new cron for %v", t.Name)
+	return c
+}