feeder rework

feeder-plugin/youtube-feeder/src/consts.rs

@@ -0,0 +1,57 @@
+//! Constants for `youtube-feeder`.
+
+/// User-Agent for outbound HTTP.
+///
+/// ⚠ **Not cosmetic.** Several upstreams reject a generic or absent
+/// User-Agent, and a 403 there looks exactly like a rate-limit — easy to
+/// misdiagnose. Identify the application and carry contact information.
+pub const USER_AGENT: &str = concat!(
+    "youtube-feeder/",
+    env!("CARGO_PKG_VERSION"),
+    " ( https://github.com/worph/meta-feeder-youtube )"
+);
+
+/// Piped instances, tried in order, rotating past a dead one.
+///
+/// **A pool, not a hostname — measured.** Of four instances tried during the
+/// study, one returned `502`, two `301`-redirected away, and one answered in
+/// ~1 s. That is the failure profile to design for. It is cheap to survive
+/// because we take only the 11-character video id: a dead instance is a retry,
+/// not a broken stream (contrast the *bytes* argument against Piped in
+/// `youtube-source-integration-study.md` §2.2, which does not apply here).
+pub const PIPED_INSTANCES: &[&str] = &[
+    "https://api.piped.private.coffee",
+    "https://pipedapi.kavin.rocks",
+    "https://pipedapi.adminforge.de",
+    "https://api.piped.yt",
+];
+/// Per-request timeout against a Piped instance.
+pub const PIPED_TIMEOUT_SECS: u64 = 15;
+/// Artwork for a YouTube rendition. `hqdefault` exists for every video, unlike
+/// `maxresdefault`, which 404s on anything not uploaded in HD — and a 404 here
+/// is **silent**, gating the record out with no error anywhere.
+pub const YT_THUMB_BASE: &str = "https://i.ytimg.com/vi";
+/// How far a candidate's runtime may sit from the MusicBrainz recording length
+/// and still be the same recording.
+///
+/// ±10 s is what the study measured at, and it is doing two jobs: absorbing
+/// fade-in/out and pre-gap differences between a CD master and an uploaded
+/// Art Track, while staying tight enough to separate a radio edit (249 s) from
+/// an album cut (370 s).
+pub const YT_DURATION_TOLERANCE_SECS: i64 = 10;
+/// Ceiling on Piped `music_songs` candidates examined per track.
+pub const YT_CANDIDATES_PER_TRACK: usize = 8;
+/// How many ranked YouTube references one recording may carry.
+///
+/// §3's mitigation for reference rot: the video **id** is immutable, but its
+/// *availability* is not — takedowns, geo-blocks and embed-disabled uploads all
+/// kill a reference whose CID stays valid forever. One reference per recording
+/// means a takedown kills the track; several let the client fall through.
+///
+/// Three rather than "all of them" because each is a record replicated across
+/// the mesh, and the tail past three is candidates the resolver already ranked
+/// as worse matches.
+pub const MAX_REFS_PER_RECORDING: usize = 3;
+
+// MusicBrainz's published rate ceiling, from the crate that owns that client.
+pub use musicbrainz_feeder::consts::{MB_BURST, MB_RATE_PER_SEC, MB_TIMEOUT_SECS};