ADR-0016: A Source Can Be Reported Without Its Cover, and Spotify Is

Context

The stand was built to stand beside a record that is playing. iTunes plays a library of albums the owner chose, and the stand follows it.

Spotify is a different kind of listening, and the owner decided the lights should not follow it. It should still be known: the next thing wanted from Spotify is a voice asking for an album, and whatever answers “what is playing?” or starts playback will need the same report.

There is also a reason that is not a preference. ADR-0012 recorded a line from Spotify’s API pages about not synchronizing recordings with visual media, and left it as the owner’s judgment. Not lighting the stand for Spotify, and never fetching its artwork, steps around that question.

lightd reacts to one thing: a cover arriving on nowplaying/current/art (ADR-0009). It does not know which source a cover came from, and should not.

Options considered

Leave Spotify out of arbitration. Simplest: nowplayd would ignore the source. But then current would name a paused iTunes track while Spotify plays, and nothing downstream could ever know otherwise.

Teach lightd which sources to follow. It would have to read current as well as the cover, and learn what a source is. That is the knowledge ADR-0009 kept out of it.

Publish no cover for the source. current tells the truth about what is playing; the cover topic, which is the only thing the stand follows, is left alone.

Decision

A source can be named as coverless (NP_COVERLESS_SOURCES on nowplayd). When such a source is current, nowplayd:

• publishes current with the track and no art;
• publishes nothing to current/art, which keeps whatever it last held;
• does not look a cover up in a catalog. A catalog’s cover would light the stand exactly as the player’s own would.

Spotify is named. Its driver goes further and never asks Spotify for an image at all, so there is no artwork to mishandle anywhere in the path.

Consequences

• ADR-0008’s promise now has an exception. A subscriber to current may see a playing track with no art. The contract always allowed art to be absent; what changes is that it can now be absent on purpose.
• While Spotify plays, the stand holds the last cover it was given. It shows a record that is not the one playing. That is the decision, and it will look like a fault to anyone who has not read this.
• current/art and current can disagree: the cover is the last lit one, not the current track’s. A subscriber that wants the current track’s cover must check that current.art.sha256 exists and matches, as the contract already said to.
• It rests on one setting. Without NP_COVERLESS_SOURCES=spotify on the workload, nowplayd would look Spotify’s tracks up and the stand would follow them. The setting is committed with the deployment, and the check that proves it is in CHG-0004.
• The relay’s broker account is granted Spotify’s art topic although nothing publishes to it, so that reversing this is a setting and not also a change of account.
• Reversing it is small: remove the setting, and the stand follows Spotify through catalog covers. Using Spotify’s own artwork would be a further decision, with the terms question to answer first.