set restic backup exit code 3 as warning, stream output to log instead

TODO.md

@@ -2,7 +2,7 @@
 # TODO
 
 - [ ] Write README
-- [ ] `restic backup` can take a long time: stream output to logging somehow to keep track of what it's doing.
+- [X] `restic backup` can take a long time: stream output to logging somehow to keep track of what it's doing. Stop using `--json` for `backup`, generates way too much JSON log info.
 - [ ] Make Restictray non-dependent on existing config in `~/.restic`:
   - [ ] Create default files if not existing?
   - [ ] Create a config dialog in https://developer.fyne.io/
@@ -11,4 +11,6 @@
   - [ ] If something goes wrong, menu shows error and app becomes unusable. Perhaps not all errors (e.g. above one) have to be this way.
   - [X] Is backing up while mounted ok? => yes
   - [ ] `restic backup` can result in `Warning: at least one source file could not be read\n: exit status 3`. This returns an error, but the backup itself seems to be all right.
+    - [X] exit code 3: https://restic.readthedocs.io/en/stable/040_backup.html likely to be a permission problem, perhaps ignoring instead of panicking as of now?
+    - [ ] `restic list locks` showed a dangling one; PID of already gone `restic` process. Why? Unable to reproduce? 
   - [ ] Verify backups with `restic check`? If not okay, remove (snapshot/folder?) and rebackup? What's the plan then?

restic/wrapper.go

@@ -1,7 +1,9 @@
 package restic
 
 import (
+	"bufio"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"github.com/rs/zerolog/log"
 	"os/exec"
@@ -139,12 +141,28 @@ func openFolder(folder string) error {
 	return nil
 }
 
+// Backup uses "restic backup" to create a new snapshot. This is a blocking call.
 func (w *Wrapper) Backup(c *Config) error {
-	cmd := resticCmd("--json", "--password-file", PasswordFile(), "-r", c.Repository, "--exclude-file", ExcludeFile(), "backup", c.Backup)
-	out, err := cmd.CombinedOutput()
-	if err != nil {
-		return fmt.Errorf("restic backup cmd: %s: %w", string(out), err)
+	cmd := resticCmd("--password-file", PasswordFile(), "-r", c.Repository, "--exclude-file", ExcludeFile(), "backup", c.Backup, "--no-scan")
+
+	stdout, _ := cmd.StdoutPipe()
+	cmd.Start()
+
+	scanner := bufio.NewScanner(stdout)
+	scanner.Split(bufio.ScanLines)
+	for scanner.Scan() {
+		m := scanner.Text()
+		log.Info().Str("out", m).Msg("backup")
+	}
+	err := cmd.Wait()
+
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) && exitErr.ExitCode() == 3 {
+			log.Warn().Err(err).Msg("At least one file could not be read, permission problem?")
+			return nil
+		}
+		return fmt.Errorf("restic backup cmd: %w", err)
 	}
-	log.Info().Str("out", string(out)).Msg("backup")
 	return nil
 }