improve error handling

devices/libgpiod.go

@@ -7,6 +7,7 @@ import (
 	"time"
 )
 
+// TODO: Do not use subprocesses here, they are unreliable, provide hidden dependencies and are a common target for vulnerabilities.
 func NewLibgpiod(gpiochip string, powerButtonPin int, powerLEDPin int) Device {
 	device := &libgpiod{
 		gpiochip:       gpiochip,

routes/api.go

@@ -37,7 +37,11 @@ func APIEndSession(storage sessions.Storage) http.HandlerFunc {
 		sessionId := req.PathValue("session_id")
 
 		err := storage.EndSession(sessionId)
-		if err != nil {
+		switch {
+		case err == sessions.ErrUnknownSession:
+			http.Error(res, "", http.StatusNotFound)
+			return
+		case err != nil:
 			http.Error(res, "", http.StatusInternalServerError)
 			return
 		}

routes/index.go

@@ -62,7 +62,11 @@ func EndSession(storage sessions.Storage) http.HandlerFunc {
 
 		sessionId := req.FormValue("session_id")
 		err = storage.EndSession(sessionId)
-		if err != nil {
+		switch {
+		case err == sessions.ErrUnknownSession:
+			http.Error(res, "", http.StatusNotFound)
+			return
+		case err != nil:
 			http.Error(res, "", http.StatusInternalServerError)
 			return
 		}

sessions/mem.go

@@ -66,7 +66,7 @@ func (s *memStorage) EndSession(id string) error {
 
 	_, found := s.sessions[id]
 	if !found {
-		//return ErrNotFound
+		return ErrUnknownSession
 	}
 
 	delete(s.sessions, id)

sessions/sessions.go

@@ -1,6 +1,9 @@
 package sessions
 
-import "time"
+import (
+	"errors"
+	"time"
+)
 
 type Session struct {
 	Id          string
@@ -12,16 +15,21 @@ func (s *Session) ExistsFor() time.Duration {
 	return time.Now().Sub(s.CreatedAt)
 }
 
+var (
+	ErrUnknownSession = errors.New("unknown session")
+)
+
 type Storage interface {
-	// Check if the storage contains any sessions
+	// Check if the storage contains any sessions.
 	HasSessions() (bool, error)
 
-	// List all sessions
+	// List all sessions.
 	GetSessions() ([]Session, error)
 
-	// Start a new session
+	// Start a new session.
 	StartSession(description string, createdAt time.Time) (Session, error)
 
-	// End an old session
+	// End an old session.
+	// Should return [ErrUnknownSession] if the session couldn't be found.
 	EndSession(id string) error
 }