🐛 fix(unix): use correct runtime dir path for OpenBSD (#440)

OpenBSD applications using platformdirs were unnecessarily falling back
to temporary directories because the default runtime path
`/var/run/user/{uid}` is not writable by regular users on OpenBSD. 🔒
This issue was reported by OpenBSD package maintainers who noticed the
mismatch with the platform's native XDG implementation.

OpenBSD now has native `XDG_RUNTIME_DIR` support in libc via the
`setxdgenv()` function in
[`lib/libc/gen/login_cap.c`](https://github.com/openbsd/src/blob/master/lib/libc/gen/login_cap.c),
which creates directories at `/tmp/run/user/{uid}` with proper ownership
and permissions. The fix splits the BSD platform detection to handle
OpenBSD separately from FreeBSD and NetBSD, which both continue using
`/var/run/user/{uid}`. ✨

This change aligns platformdirs with OpenBSD's official implementation
while preserving existing behavior for FreeBSD and NetBSD. Applications
on OpenBSD will now correctly use the runtime directory created by the
system during login instead of falling back to temporary directories.

## Documentation References

During investigation, the following official platform documentation was
reviewed:

- **OpenBSD**: [`setxdgenv()` in
login_cap.c](https://github.com/openbsd/src/blob/master/lib/libc/gen/login_cap.c)
- uses `/tmp/run/user/{uid}`
- **FreeBSD**: [`pam_xdg`
module](https://github.com/freebsd/freebsd-src/blob/main/lib/libpam/modules/pam_xdg/pam_xdg.c)
- uses `/var/run/xdg/{username}` (platformdirs fallback of
`/var/run/user/{uid}` is reasonable)
- **NetBSD**: No native XDG support found; [pkgsrc
patches](https://github.com/NetBSD/pkgsrc/blob/trunk/misc/py-platformdirs/patches/patch-tests_test__unix.py)
treat it same as FreeBSD

Fixes #436

Author: gaborbernat

src/platformdirs/unix.py

@@ -150,11 +150,13 @@ def user_runtime_dir(self) -> str:
         """
         :return: runtime directory tied to the user, e.g. ``$XDG_RUNTIME_DIR/$appname/$version``.
 
-        If ``$XDG_RUNTIME_DIR`` is unset, tries the platform default (``/var/run/user/$(id -u)`` on
-        FreeBSD/OpenBSD/NetBSD, ``/run/user/$(id -u)`` otherwise). If the default is not writable,
-        falls back to a temporary directory.
+        If ``$XDG_RUNTIME_DIR`` is unset, tries the platform default (``/tmp/run/user/$(id -u)`` on
+        OpenBSD, ``/var/run/user/$(id -u)`` on FreeBSD/NetBSD, ``/run/user/$(id -u)`` otherwise).
+        If the default is not writable, falls back to a temporary directory.
         """
-        if sys.platform.startswith(("freebsd", "openbsd", "netbsd")):
+        if sys.platform.startswith("openbsd"):
+            path = f"/tmp/run/user/{getuid()}"  # noqa: S108
+        elif sys.platform.startswith(("freebsd", "netbsd")):
             path = f"/var/run/user/{getuid()}"
         else:
             path = f"/run/user/{getuid()}"

tests/test_unix.py

@@ -169,18 +169,57 @@ def test_site_state_dir_fixed_path() -> None:
 
 
 @pytest.mark.usefixtures("_getuid")
-@pytest.mark.parametrize("platform", ["freebsd", "openbsd", "netbsd"])
-def test_platform_on_bsd(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture, platform: str) -> None:
+@pytest.mark.parametrize("platform", [pytest.param("freebsd", id="freebsd"), pytest.param("netbsd", id="netbsd")])
+def test_freebsd_netbsd_site_runtime_dir(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture, platform: str) -> None:
     monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
     mocker.patch("sys.platform", platform)
+    assert Unix().site_runtime_dir == "/var/run"
+
+
+@pytest.mark.usefixtures("_getuid")
+@pytest.mark.parametrize("platform", [pytest.param("freebsd", id="freebsd"), pytest.param("netbsd", id="netbsd")])
+def test_freebsd_netbsd_user_runtime_dir_writable(
+    monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture, platform: str
+) -> None:
+    monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
+    mocker.patch("sys.platform", platform)
+    mocker.patch("os.access", return_value=True)
+    assert Unix().user_runtime_dir == "/var/run/user/1234"
+
+
+@pytest.mark.usefixtures("_getuid")
+@pytest.mark.parametrize("platform", [pytest.param("freebsd", id="freebsd"), pytest.param("netbsd", id="netbsd")])
+def test_freebsd_netbsd_user_runtime_dir_not_writable(
+    monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture, platform: str
+) -> None:
+    monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
+    mocker.patch("sys.platform", platform)
+    mocker.patch("os.access", return_value=False)
     mocker.patch("tempfile.tempdir", "/tmp")  # noqa: S108
+    assert Unix().user_runtime_dir == "/tmp/runtime-1234"  # noqa: S108
+
 
+@pytest.mark.usefixtures("_getuid")
+def test_openbsd_site_runtime_dir(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture) -> None:
+    monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
+    mocker.patch("sys.platform", "openbsd")
     assert Unix().site_runtime_dir == "/var/run"
 
+
+@pytest.mark.usefixtures("_getuid")
+def test_openbsd_user_runtime_dir_writable(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture) -> None:
+    monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
+    mocker.patch("sys.platform", "openbsd")
     mocker.patch("os.access", return_value=True)
-    assert Unix().user_runtime_dir == "/var/run/user/1234"
+    assert Unix().user_runtime_dir == "/tmp/run/user/1234"  # noqa: S108
+
 
+@pytest.mark.usefixtures("_getuid")
+def test_openbsd_user_runtime_dir_not_writable(monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture) -> None:
+    monkeypatch.delenv("XDG_RUNTIME_DIR", raising=False)
+    mocker.patch("sys.platform", "openbsd")
     mocker.patch("os.access", return_value=False)
+    mocker.patch("tempfile.tempdir", "/tmp")  # noqa: S108
     assert Unix().user_runtime_dir == "/tmp/runtime-1234"  # noqa: S108