skeleton of IPC mechanism to allow playback control with cmdline flags

backend/ipc/server.go

@@ -0,0 +1,73 @@
+package ipc
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+type Handler interface {
+	PlayPause() error
+	Stop() error
+	Pause() error
+	Continue() error
+	SeekBackOrPrevious() error
+	SeekNext() error
+	SeekSeconds(float64) error
+	Volume() int
+	SetVolume(int) error
+}
+
+type serverImpl struct {
+	handler Handler
+}
+
+func NewServer(handler Handler) *http.Server {
+	s := serverImpl{handler: handler}
+	return &http.Server{
+		Handler: s.createHandler(),
+	}
+}
+
+func (s *serverImpl) createHandler() http.Handler {
+	m := http.NewServeMux()
+	m.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		w.Write([]byte("The given path is not valid"))
+	})
+	m.HandleFunc(PlayPath, s.makeSimpleEndpointHandler(s.handler.Continue))
+	m.HandleFunc(PausePath, s.makeSimpleEndpointHandler(s.handler.Pause))
+	m.HandleFunc(PlayPausePath, s.makeSimpleEndpointHandler(s.handler.PlayPause))
+	m.HandleFunc(StopPath, s.makeSimpleEndpointHandler(s.handler.Stop))
+	m.HandleFunc(PreviousPath, s.makeSimpleEndpointHandler(s.handler.SeekBackOrPrevious))
+	m.HandleFunc(NextPath, s.makeSimpleEndpointHandler(s.handler.SeekNext))
+	return m
+}
+
+func (s *serverImpl) makeSimpleEndpointHandler(f func() error) func(http.ResponseWriter, *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if err := f(); err == nil {
+			s.writeOK(w)
+		} else {
+			s.writeErr(w, err)
+		}
+	}
+}
+
+func (s *serverImpl) writeOK(w http.ResponseWriter) (int, error) {
+	var r Response
+	b, err := json.Marshal(&r)
+	if err != nil {
+		return 0, err
+	}
+	return w.Write(b)
+}
+
+func (s *serverImpl) writeErr(w http.ResponseWriter, err error) (int, error) {
+	r := Response{Error: err.Error()}
+	b, err := json.Marshal(&r)
+	if err != nil {
+		return 0, err
+	}
+	w.WriteHeader(http.StatusInternalServerError)
+	return w.Write(b)
+}