`Path.resolve()` is a filesystem call — it lstats every component of the path.
`_resolve_dlc_path` and `safe_join` both re-resolved their ROOT on every single
call, and those run once per song, per art fetch, per scanned row.
Found while profiling a 2-fps report: on a real 50,944-song library the server
was issuing ~23,500 stat/lstat calls per second, re-walking the same three
parent directories over and over, and burning ~50% of a core doing it. It is
worst exactly where big libraries live — the library was on an NTFS-3G (FUSE)
mount, where every stat is a userspace round trip through mount.ntfs-3g (itself
visible in top). The cost was the constant re-resolution, not the work.
A root is fixed for the life of the process, so resolve it once
(safepath.resolved_root, lru_cache). Measured, 5,000 lookups against a real
library path:
before: 15,264 stat syscalls (54.2 ms)
after: 277 stat syscalls ( 0.8 ms) 55x fewer
Containment is unchanged, which is the part that matters:
- safe_join still resolves the CANDIDATE on every call — following its
symlinks IS the zip-slip / traversal defence, so it is never cached. Only
the server-owned root is.
- _resolve_dlc_path keeps its lexical containment check (deliberately does not
follow symlinks, so junction-mounted libraries keep working).
Tradeoff, documented on resolved_root: if a root's symlink is re-pointed at a
NEW target while the server runs, the old target stays in effect until restart.
Fine for a library path fixed at startup; the cache is keyed on the Path, so
switching library dir is a different key.
Tests: root resolved once across 500 lookups (the regression), a different root
is a different entry, and the containment contract re-pinned — traversal,
Windows drive-absolute, backslash, NUL, empty, and a symlink escaping the root
must still be refused. Full suite green.
The keystone for the path-dependent routers (ws_highway, song, audio-local-path,
sloppak): the "where do the song files live + safe containment" layer leaves
server.py so a router can reach it.
- `_resolve_dlc_path` (pure — args only) moves verbatim.
- `_get_dlc_dir` reads the env-derived paths through the appstate seam
(appstate.dlc_dir/dlc_dir_env/config_dir) instead of module globals, so
lib/dlc_paths.py does no import-time IO.
- appstate gains `dlc_dir`/`dlc_dir_env` slots (config_dir already there);
server.py configures them. All three are env-derived, so a setenv+reimport
fixture reconfigures them for free — ZERO setattr retargeting.
- server.py RE-EXPORTS both (`from dlc_paths import _get_dlc_dir,
_resolve_dlc_path`), so its 24+16 call sites AND the tests that reach
`server._get_dlc_dir()` / `server._resolve_dlc_path()` directly
(test_dlc_junction, test_highway_ws_*) resolve unchanged — no test edits.
server.py: 9,085 -> 9,008.
Verified: _resolve_dlc_path byte-identical to origin/main; _get_dlc_dir's only
change is the three path identifiers -> appstate.*; pyflakes clean; route table
identical (143); pytest 2407 passed (test_dlc_junction + both highway_ws suites
green via re-export); packaging guard 52; eslint 0. Boot smoke: library scans
(8 songs, _get_dlc_dir), a real song resolves + serves art (_resolve_dlc_path),
and the highway WS reaches `ready` with notes.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
