device/raspistill/imp_release.go: improve error checking routine and removed unused const

device/raspistill/imp_release.go

@@ -33,7 +33,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
+	"bufio"
 	"os/exec"
 	"strings"
 
@@ -73,7 +73,6 @@ func (r *Raspistill) stop() error {
 }
 
 func (r *Raspistill) start() error {
-	const disabled = "0"
 	args := []string{
 		"--output", "-",
 		"--nopreview",
@@ -99,23 +98,25 @@ func (r *Raspistill) start() error {
 		return fmt.Errorf("could not pipe command error: %w", err)
 	}
 
+
 	go func() {
+		errScnr := bufio.NewScanner(stderr)
 		for {
 			select {
 			case <-r.done:
 				r.log.Info("raspistill.Stop() called, finished checking stderr")
 				return
 			default:
-				buf, err := ioutil.ReadAll(stderr)
-				if err != nil {
-					r.log.Error("could not read stderr", "error", err)
-					return
-				}
+			}
 
-				if len(buf) != 0 {
-					r.log.Error("error from raspistill stderr", "error", string(buf))
-					return
-				}
+			if errScnr.Scan() {
+				r.log.Error("error line from raspistill stderr","error",errScnr.Text())
+				continue
+			}
+
+			err := errScnr.Err()
+			if err != nil {
+				r.log.Error("error from stderr scan","error",err)
 			}
 		}
 	}()