internal/restic: Fix UID/GID parsing

The helper function uidGidInt used strconv.ParseInt instead of
ParseUint, so it silently ignored some invalid user/group IDs.

Also, improve the error message. "Invalid UID" is more informative than
having "ParseInt" twice (*strconv.NumError displays the function name).

Finally, the user.User struct can be passed by pointer to get reduce
code size.

internal/restic/lock.go

@@ -126,7 +126,7 @@ func (l *Lock) fillUserInfo() error {
 	}
 	l.Username = usr.Username
 
-	l.UID, l.GID, err = uidGidInt(*usr)
+	l.UID, l.GID, err = uidGidInt(usr)
 	return err
 }
 

internal/restic/lock_unix.go

@@ -9,25 +9,21 @@ import (
 	"strconv"
 	"syscall"
 
-	"github.com/restic/restic/internal/errors"
-
 	"github.com/restic/restic/internal/debug"
+	"github.com/restic/restic/internal/errors"
 )
 
 // uidGidInt returns uid, gid of the user as a number.
-func uidGidInt(u user.User) (uid, gid uint32, err error) {
-	var ui, gi int64
-	ui, err = strconv.ParseInt(u.Uid, 10, 32)
+func uidGidInt(u *user.User) (uid, gid uint32, err error) {
+	ui, err := strconv.ParseUint(u.Uid, 10, 32)
 	if err != nil {
-		return uid, gid, errors.Wrap(err, "ParseInt")
+		return 0, 0, errors.Errorf("invalid UID %q", u.Uid)
 	}
-	gi, err = strconv.ParseInt(u.Gid, 10, 32)
+	gi, err := strconv.ParseUint(u.Gid, 10, 32)
 	if err != nil {
-		return uid, gid, errors.Wrap(err, "ParseInt")
+		return 0, 0, errors.Errorf("invalid GID %q", u.Gid)
 	}
-	uid = uint32(ui)
-	gid = uint32(gi)
-	return
+	return uint32(ui), uint32(gi), nil
 }
 
 // checkProcess will check if the process retaining the lock

internal/restic/lock_windows.go

@@ -8,7 +8,7 @@ import (
 )
 
 // uidGidInt always returns 0 on Windows, since uid isn't numbers
-func uidGidInt(u user.User) (uid, gid uint32, err error) {
+func uidGidInt(u *user.User) (uid, gid uint32, err error) {
 	return 0, 0, nil
 }
 

internal/restic/snapshot.go

@@ -154,7 +154,7 @@ func (sn *Snapshot) fillUserInfo() error {
 	sn.Username = usr.Username
 
 	// set userid and groupid
-	sn.UID, sn.GID, err = uidGidInt(*usr)
+	sn.UID, sn.GID, err = uidGidInt(usr)
 	return err
 }