Add TTL cache for stops index.

pkg/cafes/common.go

@@ -0,0 +1,87 @@
+package cafes
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/dhconnelly/rtreego"
+)
+
+type RefreshmentStop struct {
+	Name     string
+	Url      string
+	Easting  float64
+	Northing float64
+}
+
+func (s *RefreshmentStop) Bounds() *rtreego.Rect {
+	p := rtreego.Point{s.Easting, s.Northing}
+	return p.ToRect(100)
+}
+
+func (s *RefreshmentStop) Contains(p rtreego.Point) bool {
+	if len(p) != 2 {
+		panic("Expected a 2-dimensional point")
+	}
+	bounds := s.Bounds()
+	for i := 0; i < 2; i++ {
+		if p[i] < bounds.PointCoord(i) || p[i] > bounds.PointCoord(i)+bounds.LengthsCoord(i) {
+			return false
+		}
+	}
+	return true
+}
+
+// TTL cache based on "9.7 Example: Concurrent Non-Blocking Cache" from
+// "The Go Programming Language", Alan A. A. Dovovan and Brian W. Kernighan
+
+type result struct {
+	value *rtreego.Rtree
+	err   error
+}
+
+type entry struct {
+	res     result
+	expires time.Time
+	ready   chan struct{} // closed when res is ready
+}
+
+type Cache struct {
+	mu      sync.Mutex
+	entries map[string]*entry
+}
+
+func New() *Cache {
+	return &Cache{entries: make(map[string]*entry)}
+}
+
+func (c *Cache) Get(k string) (*rtreego.Rtree, error) {
+	c.mu.Lock()
+	e := c.entries[k]
+	if e == nil || e.expires.Before(time.Now()) {
+		e = &entry{ready: make(chan struct{}), expires: time.Now().Add(4 * time.Hour)}
+		c.entries[k] = e
+		c.mu.Unlock()
+		e.res.value, e.res.err = FetchStops(k)
+		close(e.ready)
+	} else {
+		c.mu.Unlock()
+		<-e.ready
+	}
+	return e.res.value, e.res.err
+}
+
+var ErrInvalidStops = errors.New("invalid stops")
+
+func FetchStops(k string) (*rtreego.Rtree, error) {
+	switch k {
+	case "ctccambridge":
+		return FetchCtcCamIndex()
+	case "cyclingmaps":
+		return FetchCyclingMapsIndex()
+	default:
+		return nil, fmt.Errorf("%w: %s", ErrInvalidStops, k)
+	}
+}

pkg/cafes/ctccam.go

@@ -4,6 +4,7 @@ import (
 	"encoding/xml"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 
 	"github.com/dhconnelly/rtreego"
@@ -23,31 +24,6 @@ type Waypoints struct {
 	Waypoints []Waypoint `xml:"wpt"`
 }
 
-type RefreshmentStop struct {
-	Name     string
-	Url      string
-	Easting  float64
-	Northing float64
-}
-
-func (s *RefreshmentStop) Bounds() *rtreego.Rect {
-	p := rtreego.Point{s.Easting, s.Northing}
-	return p.ToRect(100)
-}
-
-func (s *RefreshmentStop) Contains(p rtreego.Point) bool {
-	if len(p) != 2 {
-		panic("Expected a 2-dimensional point")
-	}
-	bounds := s.Bounds()
-	for i := 0; i < 2; i++ {
-		if p[i] < bounds.PointCoord(i) || p[i] > bounds.PointCoord(i)+bounds.LengthsCoord(i) {
-			return false
-		}
-	}
-	return true
-}
-
 func BuildCtcCamIndex(r io.Reader) (*rtreego.Rtree, error) {
 	dec := xml.NewDecoder(r)
 	var wpt Waypoints
@@ -77,6 +53,7 @@ func BuildCtcCamIndex(r io.Reader) (*rtreego.Rtree, error) {
 }
 
 func FetchCtcCamIndex() (*rtreego.Rtree, error) {
+	log.Printf("Fetching %s", ctcCamWaypointsUrl)
 	res, err := http.Get(ctcCamWaypointsUrl)
 	if err != nil {
 		return nil, fmt.Errorf("error getting %s: %v", ctcCamWaypointsUrl, err)
@@ -89,5 +66,6 @@ func FetchCtcCamIndex() (*rtreego.Rtree, error) {
 	if err != nil {
 		return nil, fmt.Errorf("error building CTC Cambridge stops index: %v", err)
 	}
+	log.Printf("Loaded %d CTC Cambridge stops", index.Size())
 	return index, nil
 }

pkg/cafes/cyclingmaps.go

@@ -54,6 +54,7 @@ func BuildCyclingMapsIndex(r io.Reader) (*rtreego.Rtree, error) {
 }
 
 func FetchCyclingMapsIndex() (*rtreego.Rtree, error) {
+	log.Printf("Fetching %s", cyclingMapsCafesUrl)
 	res, err := http.Get(cyclingMapsCafesUrl)
 	if err != nil {
 		return nil, fmt.Errorf("error getting %s: %v", cyclingMapsCafesUrl, err)
@@ -66,5 +67,6 @@ func FetchCyclingMapsIndex() (*rtreego.Rtree, error) {
 	if err != nil {
 		return nil, fmt.Errorf("error building cyclingmaps.net cafe stops index: %v", err)
 	}
+	log.Printf("Loaded %d cyclingmaps.net stops", index.Size())
 	return index, nil
 }