Rewrite access check in create_archive with EAFP

Signed-off-by: Joffrey F <joffrey@docker.com>

docker/utils/utils.py

@@ -97,10 +97,6 @@ def create_archive(root, files=None, fileobj=None, gzip=False):
     for path in files:
         full_path = os.path.join(root, path)
 
-        if os.lstat(full_path).st_mode & os.R_OK == 0:
-            raise IOError(
-                'Can not access file in context: {}'.format(full_path)
-            )
         i = t.gettarinfo(full_path, arcname=path)
         if i is None:
             # This happens when we encounter a socket file. We can safely
@@ -121,7 +117,9 @@ def create_archive(root, files=None, fileobj=None, gzip=False):
                 with open(full_path, 'rb') as f:
                     t.addfile(i, f)
             except IOError:
-                t.addfile(i, None)
+                raise IOError(
+                    'Can not read file in context: {}'.format(full_path)
+                )
         else:
             # Directories, FIFOs, symlinks... don't need to be read.
             t.addfile(i, None)

tests/unit/utils_test.py

@@ -933,7 +933,10 @@ class TarTest(unittest.TestCase):
             tar_data = tarfile.open(fileobj=archive)
             assert sorted(tar_data.getnames()) == ['bar', 'foo']
 
-    @pytest.mark.skipif(IS_WINDOWS_PLATFORM, reason='No chmod on Windows')
+    @pytest.mark.skipif(
+        IS_WINDOWS_PLATFORM or os.geteuid() == 0,
+        reason='root user always has access ; no chmod on Windows'
+    )
     def test_tar_with_inaccessible_file(self):
         base = tempfile.mkdtemp()
         full_path = os.path.join(base, 'foo')
@@ -944,8 +947,9 @@ class TarTest(unittest.TestCase):
         with pytest.raises(IOError) as ei:
             tar(base)
 
-        assert 'Can not access file in context: {}'.format(full_path) in \
+        assert 'Can not read file in context: {}'.format(full_path) in (
             ei.exconly()
+        )
 
     @pytest.mark.skipif(IS_WINDOWS_PLATFORM, reason='No symlinks on Windows')
     def test_tar_with_file_symlinks(self):