[core][sandbox] Preserve archived mtimes when extracting image layers

python/ray/experimental/sandbox/_internal/image_utils.py

@@ -180,6 +180,7 @@ def extract_tar_layer(
     else:
         tar_fileobj = tar_input
 
+    dir_mtimes = []
     with tarfile.open(fileobj=tar_fileobj, mode="r:*") as tar:
         for member in tar.getmembers():
             name = member.name.lstrip("/")
@@ -261,8 +262,22 @@ def extract_tar_layer(
                         shutil.copyfileobj(f_in, f_out)
                 if member.mode:
                     os.chmod(target_path, member.mode)
+                # Preserve the archived mtime: tools inside the sandbox rely
+                # on it (apt revalidates its package lists with
+                # If-Modified-Since from the file mtime, and a reset-to-now
+                # mtime makes mirrors answer 304 for stale baked lists).
+                # Best-effort, like the directory pass below.
+                try:
+                    os.utime(target_path, (member.mtime, member.mtime))
+                except OSError:
+                    pass
             elif member.isdir():
                 os.makedirs(target_path, exist_ok=True)
+                # Applied after the loop: extracting children would bump it.
+                # Skip preserved symlinks (UsrMerge /bin -> usr/bin): utime
+                # would follow them and stamp the target with the wrong time.
+                if not os.path.islink(target_path):
+                    dir_mtimes.append((target_path, member.mtime))
             elif member.issym():
                 os.makedirs(parent_dir, exist_ok=True)
                 try:
@@ -280,6 +295,12 @@ def extract_tar_layer(
                     except OSError:
                         pass
 
+    for dir_path, mtime in dir_mtimes:
+        try:
+            os.utime(dir_path, (mtime, mtime))
+        except OSError:
+            pass
+
 
 def pull_and_extract_container_image(
     image: str,

python/ray/experimental/sandbox/tests/test_image_manager.py

@@ -510,5 +510,37 @@ def test_prepare_oci_bundle_no_resolv_without_host_side_networking(tmp_path):
         assert _prepare(mgr, tmp_path, network=network) is None
 
 
+def test_extract_tar_layer_preserves_mtimes(tmp_path):
+    """Archived mtimes survive extraction: apt inside the sandbox validates
+    its package lists with If-Modified-Since from the file mtime, so a
+    reset-to-extraction-time mtime makes mirrors answer 304 for stale
+    image-baked lists."""
+    import io
+    import os
+    import tarfile
+
+    from ray.experimental.sandbox._internal.image_utils import extract_tar_layer
+
+    archived_mtime = 1_600_000_000  # 2020-09-13, clearly not "now"
+    buf = io.BytesIO()
+    with tarfile.open(fileobj=buf, mode="w") as tar:
+        dir_info = tarfile.TarInfo("etc")
+        dir_info.type = tarfile.DIRTYPE
+        dir_info.mtime = archived_mtime
+        tar.addfile(dir_info)
+        file_info = tarfile.TarInfo("etc/os-release")
+        data = b"ID=debian\n"
+        file_info.size = len(data)
+        file_info.mtime = archived_mtime
+        tar.addfile(file_info, io.BytesIO(data))
+
+    dest = tmp_path / "rootfs"
+    dest.mkdir()
+    extract_tar_layer(buf.getvalue(), str(dest))
+
+    assert int(os.path.getmtime(dest / "etc" / "os-release")) == archived_mtime
+    assert int(os.path.getmtime(dest / "etc")) == archived_mtime
+
+
 if __name__ == "__main__":
     sys.exit(pytest.main(["-v", __file__]))