Fix #522: add -volume-adjust-pct CLI arg

backend/app.go

@@ -435,6 +435,8 @@ func (a *App) checkFlagsAndSendIPCMsg(cli *ipc.Client) error {
 		return cli.SeekNext()
 	case VolumeCLIArg >= 0:
 		return cli.SetVolume(VolumeCLIArg)
+	case VolumePctCLIArg != 0:
+		return cli.AdjustVolumePct(VolumePctCLIArg)
 	case SeekToCLIArg >= 0:
 		return cli.SeekSeconds(SeekToCLIArg)
 	case SeekByCLIArg != 0:

backend/cmdlineoptions.go

@@ -3,12 +3,14 @@ package backend
 import (
 	"flag"
 	"strconv"
+	"strings"
 )
 
 var (
 	VolumeCLIArg    int     = -1
 	SeekToCLIArg    float64 = -1
 	SeekByCLIArg    float64 = 0
+	VolumePctCLIArg float64 = 0
 
 	FlagPlay      = flag.Bool("play", false, "unpause or begin playback")
 	FlagPause     = flag.Bool("pause", false, "pause playback")
@@ -36,6 +38,14 @@ func init() {
 		SeekByCLIArg = v
 		return err
 	})
+	flag.Func("volume-adjust-pct", "adjusts volume up or down by the given percentage (positive or negative)", func(s string) error {
+		if strings.HasSuffix(s, "%") {
+			s = s[:len(s)-1]
+		}
+		v, err := strconv.ParseFloat(s, 64)
+		VolumePctCLIArg = v
+		return err
+	})
 }
 
 func HaveCommandLineOptions() bool {

backend/ipc/api.go

@@ -13,6 +13,7 @@ const (
 	TimePosPath      = "/transport/timepos" // ?s=<seconds>
 	SeekByPath       = "/transport/seek-by" // ?s=<+/- seconds>
 	VolumePath       = "/volume"            // ?v=<vol>
+	VolumeAdjustPath = "/volume/adjust"     // ?pct=<+/- percentage>
 	ShowPath         = "/window/show"
 	QuitPath         = "/window/quit"
 )
@@ -25,6 +26,10 @@ func SetVolumePath(vol int) string {
 	return fmt.Sprintf("%s?v=%d", VolumePath, vol)
 }
 
+func AdjustVolumePctPath(pct float64) string {
+	return fmt.Sprintf("%s?pct=%0.2f", VolumeAdjustPath, pct)
+}
+
 func SeekToSecondsPath(secs float64) string {
 	return fmt.Sprintf("%s?s=%0.2f", TimePosPath, secs)
 }

backend/ipc/client.go

@@ -68,6 +68,10 @@ func (c *Client) SetVolume(vol int) error {
 	return c.sendRequest(SetVolumePath(vol))
 }
 
+func (c *Client) AdjustVolumePct(pct float64) error {
+	return c.sendRequest(AdjustVolumePctPath(pct))
+}
+
 func (c *Client) Show() error {
 	return c.sendRequest(ShowPath)
 }

backend/ipc/server.go

@@ -70,8 +70,8 @@ func (s *serverImpl) createHandler() http.Handler {
 	m.HandleFunc(StopPath, s.makeSimpleEndpointHandler(s.pbHandler.Stop))
 	m.HandleFunc(PreviousPath, s.makeSimpleEndpointHandler(s.pbHandler.SeekBackOrPrevious))
 	m.HandleFunc(NextPath, s.makeSimpleEndpointHandler(s.pbHandler.SeekNext))
-	m.HandleFunc(TimePosPath, s.makeFloatEndpointHandler(s.pbHandler.SeekSeconds, "s"))
-	m.HandleFunc(SeekByPath, s.makeFloatEndpointHandler(s.pbHandler.SeekBySeconds, "s"))
+	m.HandleFunc(TimePosPath, s.makeFloatEndpointHandler("s", s.pbHandler.SeekSeconds))
+	m.HandleFunc(SeekByPath, s.makeFloatEndpointHandler("s", s.pbHandler.SeekBySeconds))
 	m.HandleFunc(VolumePath, func(w http.ResponseWriter, r *http.Request) {
 		v := r.URL.Query().Get("v")
 		if vol, err := strconv.Atoi(v); err == nil {
@@ -81,6 +81,11 @@ func (s *serverImpl) createHandler() http.Handler {
 			s.writeErr(w, err)
 		}
 	})
+	m.HandleFunc(VolumeAdjustPath, s.makeFloatEndpointHandler("pct", func(pct float64) {
+		vol := s.pbHandler.Volume()
+		vol = vol + int(float64(vol)*(pct/100))
+		s.pbHandler.SetVolume(vol) // will clamp to range for us
+	}))
 	return m
 }
 
@@ -91,7 +96,7 @@ func (s *serverImpl) makeSimpleEndpointHandler(f func()) func(http.ResponseWrite
 	}
 }
 
-func (s *serverImpl) makeFloatEndpointHandler(f func(float64), queryParam string) func(http.ResponseWriter, *http.Request) {
+func (s *serverImpl) makeFloatEndpointHandler(queryParam string, f func(float64)) func(http.ResponseWriter, *http.Request) {
 	return func(w http.ResponseWriter, r *http.Request) {
 		v := r.URL.Query().Get(queryParam)
 		if val, err := strconv.ParseFloat(v, 64); err == nil {