Call through to cp -p for copying

cmd/backup/main.go

@@ -14,7 +14,6 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
-	"syscall"
 	"time"
 
 	"github.com/docker/docker/api/types"
@@ -449,7 +448,7 @@ func (s *script) copyBackup() error {
 		if err := os.Chown(s.file, s.c.BackupUID, s.c.BackupGID); err != nil {
 			return fmt.Errorf("copyBackup: error changing owner on temp file: %w", err)
 		}
-		if err := copyFile(s.file, path.Join(s.c.BackupArchive, name), s.c.BackupGID, s.c.BackupUID); err != nil {
+		if err := copyFile(s.file, path.Join(s.c.BackupArchive, name)); err != nil {
 			return fmt.Errorf("copyBackup: error copying file to local archive: %w", err)
 		}
 		s.logger.Infof("Stored copy of backup `%s` in local archive `%s`.", s.file, s.c.BackupArchive)
@@ -688,45 +687,9 @@ func lock(lockfile string) func() error {
 }
 
 // copy creates a copy of the file located at `dst` at `src`.
-func copyFile(src, dst string, uid, gid int) error {
+func copyFile(src, dst string) error {
-	in, err := os.Open(src)
+	cmd := exec.Command("cp", "-p", src, dst)
-	if err != nil {
+	return cmd.Run()
-		return fmt.Errorf("copyFile: error opening source file: %w", err)
-	}
-	defer in.Close()
-
-	out, err := touch(dst, uid, gid)
-	if err != nil {
-		return fmt.Errorf("copyFile: error creating destination: %w", err)
-	}
-
-	_, err = io.Copy(out, in)
-	if err != nil {
-		out.Close()
-		return fmt.Errorf("copyFile: error copying: %w", err)
-	}
-	return out.Close()
-}
-
-func touch(file string, uid, gid int) (*os.File, error) {
-	if uid < 1 || gid < 1 {
-		out, err := os.Create(file)
-		if err != nil {
-			return nil, fmt.Errorf("touch: error creating destination: %w", err)
-		}
-		return out, nil
-	}
-	cmd := exec.Command("sudo", "-u", fmt.Sprintf("%d", uid), "touch", file)
-
-	syscall.Umask(0077)
-
-	cmd.SysProcAttr = &syscall.SysProcAttr{}
-	cmd.SysProcAttr.Credential = &syscall.Credential{Uid: uint32(uid), Gid: uint32(gid)}
-
-	if err := cmd.Run(); err != nil {
-		return nil, fmt.Errorf("touch: error creating destination for owner %d:%d: %w", uid, gid, err)
-	}
-	return os.Open(file)
 }
 
 // join takes a list of errors and joins them into a single error

test/compose/docker-compose.yml

@@ -30,8 +30,8 @@ services:
       BACKUP_PRUNING_LEEWAY: 5s
       BACKUP_PRUNING_PREFIX: test
       GPG_PASSPHRASE: 1234secret
-      BACKUP_UID: '1000'
+      BACKUP_UID: ${BACKUP_UID:-1000}
-      BACKUP_GID: '1000'
+      BACKUP_GID: ${BACKUP_GID:-1000}
     volumes:
       - ./local:/archive
       - app_data:/backup/app_data:ro

test/compose/run.sh

@@ -6,11 +6,11 @@ cd $(dirname $0)
 
 mkdir -p local
 
-docker-compose up -d
+BACKUP_UID=$(id -u) BACKUP_GID=$(id -g) docker-compose up -d
 sleep 5
 
-docker-compose exec offen ln -s /var/opt/offen/offen.db /var/opt/offen/db.link
+BACKUP_UID=$(id -u) BACKUP_GID=$(id -g) docker-compose exec offen ln -s /var/opt/offen/offen.db /var/opt/offen/db.link
-docker-compose exec backup backup
+BACKUP_UID=$(id -u) BACKUP_GID=$(id -g) docker-compose exec backup backup
 
 docker run --rm -it \
   -v compose_backup_data:/data alpine \
@@ -21,8 +21,8 @@ echo "[TEST:PASS] Found relevant files in untared remote backup."
 test -L ./local/test.latest.tar.gz.gpg
 
 owner=$(stat -c '%U:%G' ./local/test.tar.gz.gpg)
-if [ "$owner" != "1000:1000" ]; then
+if [ "$owner" != "$(id -un):$(id -gn)" ]; then
-  echo "[TEST:FAIL] Expected backup file to have correct owners, got $owner"
+  echo "[TEST:FAIL] Expected backup file to have correct owners, expected "$(id -un):$(id -gn)", got $owner"
   exit 1
 fi