safe file writer

esphome/dashboard/util/file.py

@@ -0,0 +1,43 @@
+import logging
+import os
+import tempfile
+from pathlib import Path
+
+_LOGGER = logging.getLogger(__name__)
+
+
+# from https://github.com/home-assistant/core/blob/dev/homeassistant/util/file.py
+def write_utf8_file(
+    filename: Path,
+    utf8_data: str,
+    private: bool = False,
+) -> None:
+    """Write a file and rename it into place.
+
+    Writes all or nothing.
+    """
+
+    tmp_filename = ""
+    try:
+        # Modern versions of Python tempfile create this file with mode 0o600
+        with tempfile.NamedTemporaryFile(
+            mode="w", encoding="utf-8", dir=os.path.dirname(filename), delete=False
+        ) as fdesc:
+            fdesc.write(utf8_data)
+            tmp_filename = fdesc.name
+            if not private:
+                os.fchmod(fdesc.fileno(), 0o644)
+        os.replace(tmp_filename, filename)
+    finally:
+        if os.path.exists(tmp_filename):
+            try:
+                os.remove(tmp_filename)
+            except OSError as err:
+                # If we are cleaning up then something else went wrong, so
+                # we should suppress likely follow-on errors in the cleanup
+                _LOGGER.error(
+                    "File replacement cleanup failed for %s while saving %s: %s",
+                    tmp_filename,
+                    filename,
+                    err,
+                )

tests/dashboard/util/test_file.py

@@ -0,0 +1,48 @@
+import os
+from pathlib import Path
+from unittest.mock import patch
+
+import py
+import pytest
+
+from esphome.dashboard.util.file import write_utf8_file
+
+
+def test_write_utf8_file(tmp_path: Path) -> None:
+    write_utf8_file(tmp_path.joinpath("foo.txt"), "foo")
+    assert tmp_path.joinpath("foo.txt").read_text() == "foo"
+
+    with pytest.raises(OSError):
+        write_utf8_file(Path("/not-writable"), "bar")
+
+
+def test_write_utf8_file_fails_at_rename(
+    tmpdir: py.path.local, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Test that if rename fails not not remove, we do not log the failed cleanup."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    with pytest.raises(OSError), patch(
+        "esphome.dashboard.util.file.os.replace", side_effect=OSError
+    ):
+        write_utf8_file(test_file, '{"some":"data"}', False)
+
+    assert not os.path.exists(test_file)
+
+    assert "File replacement cleanup failed" not in caplog.text
+
+
+def test_write_utf8_file_fails_at_rename_and_remove(
+    tmpdir: py.path.local, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Test that if rename and remove both fail, we log the failed cleanup."""
+    test_dir = tmpdir.mkdir("files")
+    test_file = Path(test_dir / "test.json")
+
+    with pytest.raises(OSError), patch(
+        "esphome.dashboard.util.file.os.remove", side_effect=OSError
+    ), patch("esphome.dashboard.util.file.os.replace", side_effect=OSError):
+        write_utf8_file(test_file, '{"some":"data"}', False)
+
+    assert "File replacement cleanup failed" in caplog.text