feature: expired sessions can be deleted via a background goroutine.

- Call defer store.StopCleanup(store.Cleanup(time.Minute * 5)) after store creation.
- Does not break the existing API (optional, but recommended)
- Based on https://github.com/yosssi/boltstore/reaper
- Deletes expired sessions (where expireson > now())
- Includes tests

cleanup.go

@@ -0,0 +1,64 @@
+package pgstore
+
+import (
+	"log"
+	"time"
+)
+
+var defaultInterval = time.Minute * 5
+
+// Cleanup runs a background goroutine every interval that deletes expired
+// sessions from the database.
+//
+// The design is based on https://github.com/yosssi/boltstore
+func (db *PGStore) Cleanup(interval time.Duration) (chan<- struct{}, <-chan struct{}) {
+	if interval <= 0 {
+		interval = defaultInterval
+	}
+
+	quit, done := make(chan struct{}), make(chan struct{})
+	go db.cleanup(interval, quit, done)
+	return quit, done
+}
+
+// StopCleanup stops the background cleanup from running.
+func (db *PGStore) StopCleanup(quit chan<- struct{}, done <-chan struct{}) {
+	quit <- struct{}{}
+	<-done
+}
+
+// cleanup deletes expired sessions at set intervals.
+func (db *PGStore) cleanup(interval time.Duration, quit <-chan struct{}, done chan<- struct{}) {
+	ticker := time.NewTicker(interval)
+
+	defer func() {
+		ticker.Stop()
+	}()
+
+	for {
+		select {
+		case <-quit:
+			// Handle the quit signal
+			done <- struct{}{}
+			return
+		case <-ticker.C:
+			// Delete expired sessions on each tick
+			err := db.deleteExpired()
+			if err != nil {
+				log.Printf("pgstore: unable to delete expired sessions: %v", err)
+			}
+		}
+
+	}
+
+}
+
+// deleteExpired deletes expired sessions from the database.
+func (db *PGStore) deleteExpired() error {
+	_, err := db.DbMap.Exec("DELETE FROM http_sessions WHERE expireson < now()")
+	if err != nil {
+		return err
+	}
+
+	return nil
+}