fix(downloads): set 0o644 permissions on downloaded files

`NamedTemporaryFile` creates files with mode 0o600, making them
unreadable by external wheel servers (e.g. nginx) that run as a
different user. This caused 403 Forbidden errors when `uv pip install`
tried to fetch wheels from the local package index.

Use `os.fchmod` before close+rename to widen permissions to 0o644,
preserving the atomicity and thread-safety benefits of
`NamedTemporaryFile`.

Closes: #1281
Co-Authored-By: Claude <claude@anthropic.com>
Signed-off-by: Shanmukh Pawan <smoparth@redhat.com>

Author: smoparth

src/fromager/downloads.py

@@ -3,6 +3,7 @@
 import logging
 import os
 import pathlib
+import stat
 import tarfile
 import tempfile
 import typing
@@ -81,6 +82,14 @@ def _download_with_retry() -> pathlib.Path:
                 for chunk in r.iter_content(chunk_size=64 * 1024):
                     if chunk:
                         tmp.write(chunk)
+            # NamedTemporaryFile creates files with mode 0o600. Widen to
+            # 0o644 so external wheel servers (e.g. nginx) running as a
+            # different user can read the file.  Using fchmod before
+            # close+rename avoids a window where the final path exists
+            # with overly restrictive permissions.
+            os.fchmod(
+                tmp.fileno(), stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP | stat.S_IROTH
+            )
             tmp.close()
             # Atomic rename on the same filesystem
             os.rename(temp_path, outfile)

tests/test_downloads.py

@@ -1,7 +1,9 @@
 from __future__ import annotations
 
 import io
+import os
 import pathlib
+import stat
 import tarfile
 import typing
 import zipfile
@@ -72,6 +74,17 @@ def test_download_url_creates_parent_dirs(
     assert download_url(destination_dir=tmp_path / "a" / "b", url=_PKG_URL).exists()
 
 
+def test_download_url_world_readable(
+    requests_mock: requests_mock.Mocker, tmp_path: pathlib.Path
+) -> None:
+    """Downloaded files must be readable by other users (e.g. nginx)."""
+    requests_mock.get(_PKG_URL, content=b"data")
+    result = download_url(destination_dir=tmp_path, url=_PKG_URL)
+    mode = stat.S_IMODE(os.stat(result).st_mode)
+    assert mode & stat.S_IRGRP, "group-read bit must be set"
+    assert mode & stat.S_IROTH, "other-read bit must be set"
+
+
 def test_download_url_cleans_up_on_failure(
     requests_mock: requests_mock.Mocker, tmp_path: pathlib.Path
 ) -> None: