backup-docker-to-local/tests/unit/backup/test_snapshot.py

"""Contract of the filesystem snapshot used to capture volumes atomically."""

from __future__ import annotations

import unittest

from baudolo.backup.shell import BackupError
from baudolo.backup.snapshot import SnapshotError, volume_snapshot


class Runner:
    def __init__(self, replies: dict[str, list[str]] | None = None) -> None:
        self.calls: list[list[str]] = []
        self.replies = replies or {}

    def __call__(self, command: list[str]) -> list[str]:
        self.calls.append(list(command))
        for prefix, reply in self.replies.items():
            if " ".join(command).startswith(prefix):
                return reply
        return []


class Unmountable(Runner):
    def __call__(self, command: list[str]) -> list[str]:
        result = super().__call__(command)
        if command[0] == "mount":
            raise BackupError("permission denied")
        return result


class TestBtrfs(unittest.TestCase):
    def test_it_creates_a_read_only_snapshot_inside_the_subject(self) -> None:
        run = Runner()
        with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertEqual(
            run.calls[0],
            [
                "btrfs",
                "subvolume",
                "snapshot",
                "-r",
                "/var/lib/docker",
                "/var/lib/docker/.baudolo-20260731",
            ],
        )

    def test_it_removes_the_snapshot_afterwards(self) -> None:
        run = Runner()
        with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertEqual(
            run.calls[-1],
            ["btrfs", "subvolume", "delete", "/var/lib/docker/.baudolo-20260731"],
        )

    def test_it_maps_a_volume_path_into_the_snapshot(self) -> None:
        run = Runner()
        with volume_snapshot(
            "btrfs", "/var/lib/docker", "20260731", run=run
        ) as resolve:
            self.assertEqual(
                resolve("/var/lib/docker/volumes/postgres_data/_data"),
                "/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data",
            )

    def test_it_keeps_the_trailing_slash_rsync_reads_as_contents(self) -> None:
        run = Runner()
        with volume_snapshot(
            "btrfs", "/var/lib/docker", "20260731", run=run
        ) as resolve:
            self.assertEqual(
                resolve("/var/lib/docker/volumes/postgres_data/_data/"),
                "/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data/",
            )

    def test_it_removes_the_snapshot_even_when_the_body_raises(self) -> None:
        run = Runner()
        with (
            self.assertRaises(ZeroDivisionError),
            volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run),
        ):
            raise ZeroDivisionError
        self.assertEqual(run.calls[-1][:3], ["btrfs", "subvolume", "delete"])


class TestZfs(unittest.TestCase):
    def _run(self) -> Runner:
        return Runner({"zfs list": ["tank/docker"]})

    def test_it_snapshots_the_dataset_mounted_at_the_subject(self) -> None:
        run = self._run()
        with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertIn(["zfs", "snapshot", "tank/docker@baudolo-20260731"], run.calls)

    def test_it_destroys_the_snapshot_afterwards(self) -> None:
        run = self._run()
        with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertEqual(
            run.calls[-1], ["zfs", "destroy", "tank/docker@baudolo-20260731"]
        )

    def test_it_mounts_the_snapshot_inside_the_subject(self) -> None:
        run = self._run()
        with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertIn(
            [
                "mount",
                "-t",
                "zfs",
                "tank/docker@baudolo-20260731",
                "/var/lib/docker/.baudolo-20260731",
            ],
            run.calls,
        )

    def test_it_maps_a_volume_path_into_the_mounted_snapshot(self) -> None:
        run = self._run()
        with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run) as resolve:
            self.assertEqual(
                resolve("/var/lib/docker/volumes/postgres_data/_data"),
                "/var/lib/docker/.baudolo-20260731/volumes/postgres_data/_data",
            )

    def test_it_unmounts_before_it_destroys(self) -> None:
        run = self._run()
        with volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run):
            pass
        self.assertEqual(
            run.calls[-3:],
            [
                ["umount", "/var/lib/docker/.baudolo-20260731"],
                ["rmdir", "/var/lib/docker/.baudolo-20260731"],
                ["zfs", "destroy", "tank/docker@baudolo-20260731"],
            ],
        )

    def test_a_failed_mount_leaves_no_snapshot_behind(self) -> None:
        run = Unmountable({"zfs list": ["tank/docker"]})
        with (
            self.assertRaises(BackupError),
            volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run),
        ):
            pass
        self.assertEqual(
            run.calls[-2:],
            [
                ["rmdir", "/var/lib/docker/.baudolo-20260731"],
                ["zfs", "destroy", "tank/docker@baudolo-20260731"],
            ],
        )

    def test_an_unmounted_dataset_is_an_error(self) -> None:
        run = Runner({"zfs list": [""]})
        with (
            self.assertRaises(SnapshotError),
            volume_snapshot("zfs", "/var/lib/docker", "20260731", run=run),
        ):
            pass


class TestRejections(unittest.TestCase):
    def test_an_unknown_kind_is_rejected(self) -> None:
        run = Runner()
        with (
            self.assertRaises(SnapshotError),
            volume_snapshot("ext4", "/var/lib/docker", "20260731", run=run),
        ):
            pass
        self.assertEqual(run.calls, [])

    def test_a_path_outside_the_subject_is_rejected(self) -> None:
        run = Runner()
        with (
            volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=run) as resolve,
            self.assertRaises(SnapshotError),
        ):
            resolve("/etc/passwd")

    def test_the_subject_itself_resolves_to_the_snapshot_root(self) -> None:
        run = Runner()
        with volume_snapshot(
            "btrfs", "/var/lib/docker", "20260731", run=run
        ) as resolve:
            self.assertEqual(
                resolve("/var/lib/docker"), "/var/lib/docker/.baudolo-20260731"
            )


class Busy(Runner):
    def __call__(self, command: list[str]) -> list[str]:
        if command[:3] == ["btrfs", "subvolume", "delete"]:
            raise BackupError("target is busy")
        return super().__call__(command)


class TestRemovalFailure(unittest.TestCase):
    def test_a_failed_removal_does_not_fail_a_completed_run(self) -> None:
        with volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()):
            pass

    def test_a_failed_removal_does_not_mask_the_body(self) -> None:
        with (
            self.assertRaises(ZeroDivisionError),
            volume_snapshot("btrfs", "/var/lib/docker", "20260731", run=Busy()),
        ):
            raise ZeroDivisionError


if __name__ == "__main__":
    unittest.main()