Discord report (Tim): downloaded cover art via Deezer metadata
source came out visibly blurry in Navidrome / on phones — large
displays exposed the limited resolution.
# Cause
Deezer's API returns `cover_xl` URLs at 1000×1000. The underlying
CDN actually serves up to 1900×1900 by rewriting the size segment
in the URL path (same trick the iTunes mzstatic + Spotify scdn
upgrades already use). SoulSync wasn't doing the rewrite — every
Deezer-sourced cover got embedded at 1000×1000 regardless of how
much higher resolution the CDN had available.
# Verified empirically
```
$ for size in 1000 1400 1800 1900 2000; do curl -I "...{size}x{size}-..."; done
1000: 200 OK 106 KB
1400: 200 OK 198 KB
1800: 200 OK 331 KB
1900: 200 OK 371 KB
2000: 403 Forbidden
```
1900 is the safe ceiling. Above that the CDN returns 403. CDN
serves source-native bytes when source < target (smaller-source
albums get same bytes whether we ask for 1000 or 1900), so asking
for 1900 universally is safe.
# Fix
New `_upgrade_deezer_cover_url(url, target_size=1900)` helper in
`core/deezer_client.py`. Pure function, mirrors the
`_upgrade_spotify_image_url` pattern that already lives in
`core/spotify_client.py`. Defensive on every input shape:
- Empty / None → returned as-is
- Non-Deezer URL (no `dzcdn`) → returned as-is
- No size segment in URL → returned as-is
- Already at/above target → returned as-is (idempotent, never
downgrades)
Applied at both cover-download sites:
- `core/metadata/artwork.py::download_cover_art` — auto post-process
flow. Mirrors the existing iTunes mzstatic upgrade right above it.
- `core/tag_writer.py::download_cover_art` — enhanced library view's
"Write Tags to File" feature.
# Scope discipline
- Helper applied at the DOWNLOAD boundary, not the source extraction
point in `deezer_client.py`. Means cached entries in the metadata
cache + DB row `image_url` columns keep the original 1000×1000 URL
Deezer's API returned. Future CDN behavior changes only affect the
download path, not stored data.
- Pre-existing `prefer_caa_art` toggle (Settings → Library →
Post-Processing) untouched — orthogonal workaround for users who
want even higher quality (MusicBrainz Cover Art Archive, often
3000×3000+).
- iTunes / Spotify upgrade paths untouched — they already worked.
# Tests added (16)
`tests/metadata/test_deezer_cover_url_upgrade.py`:
- Standard upgrade: default target 1900 on cover URL, alternate
dzcdn host (`e-cdns-images.dzcdn.net` vs `cdn-images.dzcdn.net`),
artist picture URLs (same path pattern), 500×500 source upgrades
too
- Custom target size: smaller target = no-op (never downgrade),
larger target works
- Idempotent: already at/above target returned unchanged
- Defensive on non-Deezer URLs: parametrised across 5 hosts
(Spotify scdn, iTunes mzstatic, MB CAA, Last.fm, random) — all
returned untouched
- Defensive on malformed Deezer URL (no size segment) → returned
as-is
- Empty / None handling
# Verification
- 16/16 helper tests pass
- 560/560 metadata + imports tests pass (no regression)
- 2559 full suite passes
- Ruff clean
80cf16339c