Use lastPoll time as cutoff on subsequent polls

This also renames the `cutoff_delta` configuration option to
`poll_rate`, updating the README to better reflect its behaviour

README.md

@@ -41,18 +41,19 @@ publisher:
 
 http_port: 8080
 
-cutoff_delta: 5m
+poll_rate: 5m
 
 timer: false
 ```
 
-`cutoff_delta` string formatted for [duration parser](https://golang.org/pkg/time/#ParseDuration).
-`timer` will configure interal polling of the `enabled_feeds` at the given `cutoff_delta` period. To specify this configuration file, define its path in your environment under the `PACKAGE_FEEDS_CONFIG_PATH` variable.
+`poll_rate` string formatted for [duration parser](https://golang.org/pkg/time/#ParseDuration).This is used as an initial value to generate a cutoff point for feed events relative to the given time at execution, with subsequent events using the previous time at execution as the cutoff point.
+`timer` will configure interal polling of the `enabled_feeds` at the given `poll_rate` period. To specify this configuration file, define its path in your environment under the `PACKAGE_FEEDS_CONFIG_PATH` variable.
 
 ## Legacy Configuration
 
 Legacy configuration methods are still supported. By default, without a configuration file all feeds will be enabled. The environment variable `OSSMALWARE_TOPIC_URL` can be used to select the GCP pubsub publisher and `PORT` will configure the port for the HTTP server.
-The default `cutoff_delta` is 5 minutes, this is used to generate a cutoff point for feed events relative to the given time at execution.
+The default `poll_rate` is 5 minutes, it is assumed that an external service is dispatching requests to the configured HTTP server at this frequency.
+
 
 # Contributing
 

cmd/scheduled-feed/main.go

@@ -21,11 +21,13 @@ import (
 type FeedHandler struct {
 	scheduler *scheduler.Scheduler
 	pub       publisher.Publisher
-	delta     time.Duration
+	pollRate  time.Duration
+	lastPoll  time.Time
 }
 
 func (handler *FeedHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	cutoff := time.Now().UTC().Add(-handler.delta)
+	cutoff := handler.getCutoff()
+	handler.lastPoll = time.Now().UTC()
 	pkgs, errs := handler.scheduler.Poll(cutoff)
 	if len(errs) > 0 {
 		for _, err := range errs {
@@ -62,6 +64,16 @@ func (handler *FeedHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (handler FeedHandler) getCutoff() time.Time {
+	var cutoff time.Time
+	if handler.lastPoll.IsZero() {
+		cutoff = time.Now().UTC().Add(-handler.pollRate)
+	} else {
+		cutoff = handler.lastPoll
+	}
+	return cutoff
+}
+
 func main() {
 	configPath, useConfig := os.LookupEnv("PACKAGE_FEEDS_CONFIG_PATH")
 	var err error
@@ -92,19 +104,19 @@ func main() {
 	sched := scheduler.New(feeds)
 
 	log.Printf("listening on port %v", appConfig.HTTPPort)
-	delta, err := time.ParseDuration(appConfig.CutoffDelta)
+	pollRate, err := time.ParseDuration(appConfig.PollRate)
 	if err != nil {
 		log.Fatal(err)
 	}
 	handler := &FeedHandler{
 		scheduler: sched,
 		pub:       pub,
-		delta:     delta,
+		pollRate:  pollRate,
 	}
 
 	if appConfig.Timer {
 		cronjob := cron.New()
-		crontab := fmt.Sprintf("@every %s", delta.String())
+		crontab := fmt.Sprintf("@every %s", pollRate.String())
 		log.Printf("Running a timer %s", crontab)
 		err := cronjob.AddFunc(crontab, func() { cronRequest(appConfig.HTTPPort) })
 		if err != nil {

config/config_test.go

@@ -22,7 +22,7 @@ publisher:
     endpoint: "https://foobaz.com"
 
 http_port: 8080
-cutoff_delta: 5m
+poll_rate: 5m
 timer: true
 `
 	TestConfigStrUnknownFeedType = `

config/scheduledfeed.go

@@ -167,9 +167,9 @@ func Default() *ScheduledFeedConfig {
 		PubConfig: PublisherConfig{
 			Type: stdout.PublisherType,
 		},
-		HTTPPort:    8080,
-		CutoffDelta: "5m",
-		Timer:       false,
+		HTTPPort: 8080,
+		PollRate: "5m",
+		Timer:    false,
 	}
 	config.applyEnvVars()
 	return config

config/structs.go

@@ -4,7 +4,7 @@ type ScheduledFeedConfig struct {
 	PubConfig    PublisherConfig `yaml:"publisher"`
 	EnabledFeeds []string        `yaml:"enabled_feeds"`
 	HTTPPort     int             `yaml:"http_port,omitempty"`
-	CutoffDelta  string          `yaml:"cutoff_delta"`
+	PollRate     string          `yaml:"poll_rate"`
 	Timer        bool            `yaml:"timer"`
 }