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soulsync/tests/metadata/test_deezer_cover_url_upgrade.py
Broque Thomas 80cf16339c Deezer cover art: upgrade CDN URL to 1900×1900 (was embedding 1000×1000) 
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
2026-05-10 18:15:40 -07:00

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"""Pin the Deezer CDN cover-URL upgrade helper.
Discord report (Tim, 2026-05-XX): downloaded cover art via Deezer
metadata source comes out blurry — visibly low-res in Navidrome.
Cause: Deezer's API returns ``cover_xl`` URLs at 1000×1000 but the
underlying CDN serves up to 1900×1900 by rewriting the size segment
in the URL path. SoulSync wasn't doing the rewrite.
Helper: ``_upgrade_deezer_cover_url(url, target_size=1900)`` — pure
function, lifts to one boundary so cover-download sites don't each
re-implement the regex. Tests pin every input shape:
- Standard Deezer URL → upgraded to target
- Non-Deezer URL → returned unchanged
- Already at/above target → returned unchanged (no needless rewrite)
- Empty / None → returned as-is
- Custom target → applied correctly
- Picture URLs (artist) — same path pattern, also upgraded
"""
from __future__ import annotations
import pytest
from core.deezer_client import _upgrade_deezer_cover_url
# ---------------------------------------------------------------------------
# Standard upgrade — the headline case
# ---------------------------------------------------------------------------
class TestUpgradeStandardDeezerUrl:
def test_default_target_1900(self):
url = 'https://cdn-images.dzcdn.net/images/cover/abc123/1000x1000-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url)
assert upgraded == 'https://cdn-images.dzcdn.net/images/cover/abc123/1900x1900-000000-80-0-0.jpg'
def test_alternate_dzcdn_host(self):
"""Both `cdn-images.dzcdn.net` and `e-cdns-images.dzcdn.net`
are valid Deezer CDN hosts. Helper must catch both."""
url = 'https://e-cdns-images.dzcdn.net/images/cover/xyz/1000x1000-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url)
assert '1900x1900' in upgraded
assert upgraded.startswith('https://e-cdns-images.dzcdn.net/')
def test_artist_picture_url_also_upgrades(self):
"""Artist `picture_xl` URLs follow the same `/SIZExSIZE-` path
pattern and the same CDN. Same upgrade applies."""
url = 'https://cdn-images.dzcdn.net/images/artist/hash/1000x1000-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url)
assert '1900x1900' in upgraded
def test_500x500_upgrades(self):
"""Some albums on Deezer only have cover_big (500×500). Helper
upgrades anything below target, not just 1000×1000."""
url = 'https://cdn-images.dzcdn.net/images/cover/abc/500x500-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url)
assert '1900x1900' in upgraded
# ---------------------------------------------------------------------------
# Custom target size
# ---------------------------------------------------------------------------
class TestCustomTargetSize:
def test_smaller_target(self):
"""Caller can request a smaller size for bandwidth-sensitive
cases (mobile, thumbnails, etc.)."""
url = 'https://cdn-images.dzcdn.net/images/cover/abc/1000x1000-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url, target_size=600)
# 1000 already > 600, so this is a no-op — never DOWNGRADE.
assert upgraded == url
def test_larger_target_works(self):
url = 'https://cdn-images.dzcdn.net/images/cover/abc/250x250-000000-80-0-0.jpg'
upgraded = _upgrade_deezer_cover_url(url, target_size=1400)
assert '1400x1400' in upgraded
# ---------------------------------------------------------------------------
# Already-upgraded URLs — no needless rewrite
# ---------------------------------------------------------------------------
class TestAlreadyUpgraded:
def test_already_at_target_returned_unchanged(self):
"""Re-running the upgrade on an already-upgraded URL should
be a no-op. Idempotent — important for cached URLs that may
have been rewritten by a previous SoulSync version."""
url = 'https://cdn-images.dzcdn.net/images/cover/abc/1900x1900-000000-80-0-0.jpg'
assert _upgrade_deezer_cover_url(url) == url
def test_above_target_returned_unchanged(self):
"""Defensive: if the URL is somehow LARGER than target, don't
downgrade. Cached URL from a future bigger-target setting,
manual edits, etc."""
url = 'https://cdn-images.dzcdn.net/images/cover/abc/3000x3000-000000-80-0-0.jpg'
assert _upgrade_deezer_cover_url(url) == url
# ---------------------------------------------------------------------------
# Defensive — non-Deezer URLs left untouched
# ---------------------------------------------------------------------------
class TestNonDeezerUrls:
@pytest.mark.parametrize('url', [
'https://i.scdn.co/image/spotify-id-thing', # Spotify
'https://is4-ssl.mzstatic.com/image/100x100bb.jpg', # iTunes
'https://coverartarchive.org/release/abc/front', # MB CAA
'https://lastfm.freetls.fastly.net/i/u/770x0/abc.jpg', # Last.fm
'https://example.com/random.jpg', # Random
])
def test_non_dzcdn_returned_unchanged(self, url):
"""Helper must NOT touch non-Deezer URLs. Mirrors the
defensive check pattern the iTunes and Spotify upgrade
helpers use."""
assert _upgrade_deezer_cover_url(url) == url
def test_dzcdn_url_without_size_segment_returned_unchanged(self):
"""Defensive: if Deezer ever changes URL format, don't crash
— return as-is and let the download attempt happen with the
original URL."""
url = 'https://cdn-images.dzcdn.net/images/cover/abc/some-other-format.jpg'
assert _upgrade_deezer_cover_url(url) == url
# ---------------------------------------------------------------------------
# Empty / None inputs
# ---------------------------------------------------------------------------
class TestEmptyInputs:
def test_empty_string(self):
assert _upgrade_deezer_cover_url('') == ''
def test_none(self):
assert _upgrade_deezer_cover_url(None) is None
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