Add --lazy to open the camera only while clients are connected, issue #21

README.md

@@ -65,6 +65,8 @@ Usage: cam2ip [<flags>]
     	Bind address [CAM2IP_BIND_ADDR] (default ":56000")
   --htpasswd-file
     	Path to htpasswd file, if empty auth is disabled [CAM2IP_HTPASSWD_FILE] (default "")
+  --lazy
+    	Open the camera only while clients are connected [CAM2IP_LAZY] (default "false")
   --list-devices
     	List available cameras and exit (default "false")
   --version

cmd/cam2ip/main.go

@@ -10,6 +10,7 @@ import (
 	"go.senan.xyz/flagconf"
 
 	"github.com/gen2brain/cam2ip/camera"
+	"github.com/gen2brain/cam2ip/handlers"
 	"github.com/gen2brain/cam2ip/server"
 )
 
@@ -57,6 +58,7 @@ func main() {
 	flag.StringVar(&srv.TimeFormat, "time-format", "2006-01-02 15:04:05", "Time format [CAM2IP_TIME_FORMAT]")
 	flag.StringVar(&srv.Bind, "bind-addr", ":56000", "Bind address [CAM2IP_BIND_ADDR]")
 	flag.StringVar(&srv.Htpasswd, "htpasswd-file", "", "Path to htpasswd file, if empty auth is disabled [CAM2IP_HTPASSWD_FILE]")
+	flag.BoolVar(&srv.Lazy, "lazy", false, "Open the camera only while clients are connected [CAM2IP_LAZY]")
 
 	var showVersion bool
 	flag.BoolVar(&showVersion, "version", false, "Print version and exit")
@@ -69,7 +71,7 @@ func main() {
 
 		stderr("%s %s [<flags>]\n", colorize(color, colorBold, "Usage:"), name)
 		order := []string{"index", "device", "delay", "width", "height", "quality", "rotate", "flip", "no-webgl",
-			"timestamp", "time-format", "bind-addr", "htpasswd-file", "list-devices", "version"}
+			"timestamp", "time-format", "bind-addr", "htpasswd-file", "lazy", "list-devices", "version"}
 
 		for _, name := range order {
 			f := flag.Lookup(name)
@@ -121,7 +123,7 @@ func main() {
 		}
 	}
 
-	cam, err := camera.New(camera.Options{
+	opts := camera.Options{
 		Index:      srv.Index,
 		Rotate:     srv.Rotate,
 		Flip:       srv.Flip,
@@ -129,26 +131,37 @@ func main() {
 		Height:     srv.Height,
 		Timestamp:  srv.Timestamp,
 		TimeFormat: srv.TimeFormat,
-	})
-	if err != nil {
-		stderr("%s\n", err.Error())
-		os.Exit(1)
 	}
 
-	srv.Reader = cam
-
-	defer srv.Reader.Close()
-
-	info := cam.Info()
-	desc := fmt.Sprintf("%dx%d %s", info.Width, info.Height, info.Format)
-	if dn := deviceName(srv.Index); dn != "" {
-		desc = dn + ", " + desc
+	srv.Open = func() (handlers.ImageReader, error) {
+		return camera.New(opts)
 	}
 
-	stderr("%s %s [%s] listening on %s\n", name, version, desc, srv.Bind)
+	if srv.Lazy {
+		stderr("%s %s [lazy] listening on %s\n", name, version, srv.Bind)
+	} else {
+		cam, err := camera.New(opts)
+		if err != nil {
+			stderr("%s\n", err.Error())
+			os.Exit(1)
+		}
 
-	err = srv.ListenAndServe()
-	if err != nil {
+		defer cam.Close()
+
+		srv.Open = func() (handlers.ImageReader, error) {
+			return cam, nil
+		}
+
+		info := cam.Info()
+		desc := fmt.Sprintf("%dx%d %s", info.Width, info.Height, info.Format)
+		if dn := deviceName(srv.Index); dn != "" {
+			desc = dn + ", " + desc
+		}
+
+		stderr("%s %s [%s] listening on %s\n", name, version, desc, srv.Bind)
+	}
+
+	if err := srv.ListenAndServe(); err != nil {
 		stderr("%s\n", err.Error())
 		os.Exit(1)
 	}

handlers/stream.go

@@ -13,25 +13,33 @@ const errorBackoff = 100 * time.Millisecond
 
 // Stream captures frames in a single loop and broadcasts the encoded JPEG to all subscribers.
 type Stream struct {
-	reader  ImageReader
+	open    func() (ImageReader, error)
+	lazy    bool
 	delay   int
 	quality int
 
+	reader ImageReader
+
 	mu   sync.Mutex
 	cond *sync.Cond
 	subs map[chan []byte]struct{}
 }
 
-// NewStream returns a new Stream and starts its capture loop.
-func NewStream(reader ImageReader, delay, quality int) *Stream {
+// NewStream returns a new Stream and starts its capture loop. open acquires the camera: once up front, or while clients are connected when lazy.
+func NewStream(open func() (ImageReader, error), delay, quality int, lazy bool) *Stream {
 	s := &Stream{
-		reader:  reader,
+		open:    open,
+		lazy:    lazy,
 		delay:   delay,
 		quality: quality,
 		subs:    make(map[chan []byte]struct{}),
 	}
 	s.cond = sync.NewCond(&s.mu)
 
+	if !lazy {
+		s.reader, _ = open()
+	}
+
 	go s.capture()
 
 	return s
@@ -42,10 +50,27 @@ func (s *Stream) capture() {
 	for {
 		s.mu.Lock()
 		for len(s.subs) == 0 {
+			if s.lazy && s.reader != nil {
+				s.reader.Close()
+				s.reader = nil
+			}
+
 			s.cond.Wait()
 		}
 		s.mu.Unlock()
 
+		if s.reader == nil {
+			reader, err := s.open()
+			if err != nil {
+				log.Printf("stream: open: %v", err)
+				time.Sleep(errorBackoff)
+
+				continue
+			}
+
+			s.reader = reader
+		}
+
 		img, err := s.reader.Read()
 		if err != nil {
 			log.Printf("stream: read: %v", err)

server/server.go

@@ -36,7 +36,8 @@ type Server struct {
 	Bind     string
 	Htpasswd string
 
-	Reader handlers.ImageReader
+	Lazy bool
+	Open func() (handlers.ImageReader, error)
 }
 
 // NewServer returns new Server.
@@ -54,7 +55,7 @@ func (s *Server) ListenAndServe() error {
 		basic = auth.NewBasicAuthenticator(realm, auth.HtpasswdFileProvider(s.Htpasswd))
 	}
 
-	stream := handlers.NewStream(s.Reader, s.Delay, s.Quality)
+	stream := handlers.NewStream(s.Open, s.Delay, s.Quality, s.Lazy)
 
 	mux := http.NewServeMux()