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SoulStream/crates
KeelrLeek 6d6968e9b1 artist art: a provider's API being up is no promise its CDN is
On 2026-07-28 `webservice.fanart.tv` answered every request normally while
`assets.fanart.tv` refused TCP on both :443 and :80. The two are different
machines, and the hero chain only ever asked the first one anything.

Every gate in that chain tests whether a provider RETURNED URLS, never whether
those URLs load. So Fanart.tv handed back its usual eight banners and four
logos, `banners.is_empty()` was false, and the two fallbacks that exist for
exactly this situation -- TheAudioDB, then Bing -- were both skipped. The page
then fell back to a blown-up square portrait. The tell that this was a provider
outage rather than a regression in the hero code is that it was artist-shaped:
every artist Fanart.tv covers lost its hero, and the ones it does not cover
(Tame Impala) were untouched. Worth recording that browsing fanart.tv proves
nothing here -- that is a third host, on Cloudflare, and it was up throughout.

The check is a one-byte ranged GET, so it is proof the host serves image bytes
without pulling a 4K background to find out. Any HTTP answer counts as alive: a
404 on one image is not an outage, so only a transport failure or a 5xx marks a
host dead. Cached per host for 5 minutes, which is long enough that a dead CDN
costs one probe rather than one per artist, and short enough that the hero comes
back within minutes of the host recovering -- no restart, no cache clearing. The
probe races the page, hence the 3s ceiling.

It has to be applied in three places, and the third is the one that is easy to
miss:

- Discovery, after Fanart and again after TheAudioDB, so an unreachable CDN
  reads downstream as "this provider had nothing" -- precisely the state the
  fallback chain already knows how to handle.
- The persisted manifest, because a manifest outlives the CDN behind it. A
  stored answer short-circuits discovery entirely, so replaying one produces a
  hero that never loads AND no path to the fallback that would have worked.
- The "keep previous banners as a floor" clause. Restoring unreachable banners
  would undo the whole point of falling through: discovery correctly dropped a
  dead CDN, and the floor would put it straight back.

Note for the next time this looks like a renderer bug: a 1x1 hero canvas is a
SYMPTOM, not the cause. It means no image ever decoded, so the GPU renderer
never sized itself.
2026-07-28 09:39:14 -05:00
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