feat(scrobbling): make the outbound call, to ListenBrainz first

[InstaZDLL]

Summary

The second slice of RFC-010: the outbound call works. A listen queued by #191 can now actually leave the server and arrive at ListenBrainz.

No routes and no CLI — those are the next PR. What a person can do with this today is nothing; what an operator can do is point the server at a destination, and what the queue can do is carry a listen there once somebody's token is linked. #191 shipped the same way, and for the same reason: the argument fits in one reading.

The RFC was wrong about the biggest thing in it, and this corrects it

RFC-010 says, twice, that the server makes no outbound call because "Cargo.toml ne porte aucun client HTTP", and calls adding one "le point le plus lourd de conséquences" of the whole design.

Half of that is false, and cargo tree -i reqwest says so in three lines:

reqwest v0.12.28
└── waveflow-core v1.7.0 (git, rev 012be48)
    └── waveflow-server v2.0.0-beta.0

Cargo.toml declares no HTTP client. The binary has linked one all along, with rustls, through the core crate. Cargo.lock moves by exactly one line for this PR. So this adds no code to the binary and no second TLS stack — it makes explicit what was already there, which is a much smaller step than the RFC dramatised.

It leaves one real trap, which is why the dependency line carries a comment: Cargo unifies features across the graph. Declaring reqwest with its defaults would switch on default-tls and bring a second TLS stack in beside rustls. The declaration therefore mirrors waveflow-core's exactly — default-features = false, rustls-tls, json — minus blocking, which nothing here needs. (That last is a statement about the declaration: blocking stays on in the resolved graph, because the core wants it.)

The bounded outbound surface

src/scrobblers/ is a new top-level module, deliberately not under src/services/: the domain owns the queue and knows five words, an adapter knows one destination and nothing about the queue, and putting them side by side would rub that line out within a release.

It is the only place in the server that makes an outbound request, so decision 10's rules live there once:

• No redirect is ever followed. reqwest follows ten by default and the tenth can be anywhere.
• No proxy is read from the environment, so an operator's HTTP_PROXY, set for something else, does not silently become the route every listen takes.
• Only the connection is bounded by the client, at a third of the budget. The request as a whole is bounded once, by the drain — see the review section below for why that matters.
• The response body is never read. Every verdict is earned by the status line.
• A destination must be https, unless the operator has explicitly allowed plaintext and the host is on their own network — loopback, a private or link-local address, or an intranet name. Self-hosted Maloja and ListenBrainz make that escape necessary; the default must not send a personal token in clear, and the escape must not send one across the internet either. (That second half arrived from the app review; see the seventh round below.)
• A path cannot escape the configured prefix. Url::join treats a leading / as "replace the path", which would quietly undo an operator's https://host/listenbrainz.

A malformed destination refuses the boot, in Config::from_env, exactly as WAVEFLOW_PUBLIC_URL does. Starting with scrobbling silently switched off because of a typo is the precise silent failure this RFC spends itself making visible.

The adapter

POST {base}/1/submit-listens, Authorization: Token … — the scheme ListenBrainz documents, and not Bearer. One listen per request, by decision 11.

Two conversions are the whole of the mapping, and both are places to be wrong quietly:

• listened_at is seconds. The envelope holds epoch milliseconds like every other timestamp here, and handing those over unconverted dates every listen about fifty thousand years out — in a history that keeps it.
• artist_name is every credit, joined. ListenBrainz takes one string and matches it against MusicBrainz afterwards. Sending only the first credit would match more often and quietly drop a collaborator from somebody's history.

Verdicts: 200 → Accepted; 401/403 → AuthBroken; 400/413/422 → PermanentReject; 429 → Retryable carrying the destination's own delay; everything else, 5xx and a non-followed redirect alike → Retryable. A connect failure and a request that could not be assembled are the two that may be retried freely, because they are the two where nothing left this machine.

A promise from #191, finally keepable

Decision 6 says a Retry-After is honoured when it is there. #191 had nowhere to put one: ScrobbleVerdict::Retryable was a unit variant, so ListenBrainz's X-RateLimit-Reset-In would have been read by nobody. It now carries after, honoured as a floor and never as a replacement — waiting at least as long as asked is what honouring means, up to the one-hour ceiling the fourth round below explains. Those are two sentences rather than one: a destination's request is never swapped for our own shorter backoff, and it is also never allowed to park a listen past the point where waiting buys anything. Written here as an absolute in an earlier revision, which the clamp had already stopped being true.

What the review changed

CodeRabbit reviewed the first commit, and the verification around it found more. Six findings taken, one declined, one kept-but-named. Two were my own comments asserting things that were not true.

The response body was going into the logs

Up to 64 KiB of a destination's own words, at warn level — against decision 12's "a state, not an echo" and against this repository's logging rule. The fix is smaller than the one suggested: the body is now never read at all. A body that is never read is a tighter bound than a bounded prefix of one.

A malformed token became Ambiguous

The sharpest of them. .header(name, String) cannot fail inline — reqwest stores the rejection and surfaces it at send(), where transport_verdict found no connect error, called the listen Ambiguous, and logged that the destination "did not answer a request that had already left". Nothing had left. And Ambiguous is the one verdict decision 13 turns into an irreversible decision for a person, one per listen: a token pasted with a newline would have manufactured a pile of choices nobody could undo.

Refused in two places now — at link_scrobble, the only moment the person can fix it, and in the adapter, which still guards credentials sealed before that check existed.

The delay a destination asks for was unbounded

x-ratelimit-reset-in: 999999999999 parked a row at a moment it never reaches. That is decision 10's concern arriving from the side nobody watches: not somebody making this server call a URL, but somebody making it stop.

Clamped to RETRY_CEILING — one hour — rather than a larger number of its own, because that constant is already documented as the point past which waiting buys nothing, and because a longer clamp would let a single answer eat the whole attempt budget and decide the listen dies. Clamping is not ignoring: past the ceiling this waits an hour, asks again, and is refused again, at the cost of one attempt per refusal.

The spread was lost exactly when it was needed

retry_delay(..).max(asked) returns a jitter-free value whenever the destination's answer wins, so every rate-limited row came back at the same millisecond, in a herd, at a destination that had just asked for room. retry_base and retry_spread are now separate, so the floor applies to the base and the spread to the result.

Worth not overselling: the spread is id % (base / 4), so for consecutive row ids it separates two rows by a few milliseconds. It breaks exact simultaneity; it does not stagger a load. That is inherited from #191 and unchanged here.

Two equal deadlines were racing

The client's request timeout, its connect timeout and the drain's own tokio::time::timeout were all the same value. Both paths end at Ambiguous, so the queue looked identical either way — but only the drain's deadline records the link as stalled, and that record is what stops one silent destination from spending an entry per row. Which protection applied was a coin toss. The client now bounds only the connection.

Declined, and kept-but-named

• Declined: restricting destinations to non-link-local addresses. The destination is an operator's setting validated at boot, never user input, so https://169.254.169.254 is accepted risk rather than a defect. Said here rather than left silent.
• Kept but named: the is_builder() branch is currently unreachable. The adapter builds its header explicitly and answers AuthBroken before sending, so the failure that used to arrive there no longer does. It stays as defence for the next adapter, and its doc comment says plainly that it is belt-and-braces rather than load-bearing — rather than letting it look tested.

And a second round, which found the jitter was decorative

retry_spread folded the rowid straight into the interval, and rowids are consecutive. Four rows told to wait the same hour landed at 1, 2, 3 and 4 milliseconds inside a fifteen-minute window: distinct, and a herd all the same. The id is now mixed by the odd golden-ratio constant and read from the high bits — still no randomness, because two rows must land apart rather than unpredictably.

The test could not see it, and that is the worse half. assert_ne! tells "absent" from "present" and never "present and useless", so it certified a property the code did not deliver. The assertion moved to a unit test on retry_spread that asserts the offsets are scattered.

A rate-limited link kept being offered the rest of the batch. The batch is chosen before the first verdict, so a 429 carrying a delay was followed by forty-nine more submissions on the same pass, each earning its own refusal and spending its own attempt. stalled_links is now resting_links and carries both reasons a link stops being offered rows — gone silent, or asked for room — and only when the destination actually asked, since a 5xx is a fault rather than a request.

And last_failure documented rate_limited while nothing ever wrote it. The retryable path now writes it.

Two of these fixes contradicted each other, and the integration herd test was the casualty: with the link resting, only one row is offered per pass, so a test needing four waits in one pass could no longer get them. Deleted rather than propped up.

And a third, where my own guards turned out to be inert

Both findings were mechanisms that were in place, tested, and bypassed by the values reaching them.

A 429 carrying no usable X-RateLimit-Reset-In defeated both fixes above. reset_in answers None when the header is absent or unreadable, and the 429 arm passed that through — so the verdict was indistinguishable from a connect failure, the link rested for nothing, and the cause was recorded as an ordinary retryable. The status says room was asked for; the header only says how much. The arm now always answers Some, falling back to zero, which adds nothing to the wait while still saying truthfully that the destination asked and named no duration.

Rested rows were skipped but not moved, and that starves. I declined this one first, and my reason was backwards: I compared "deferred by a drain interval" against "left alone" as though left alone meant "does not come back". A skipped row keeps a next_attempt_at already in the past, so it is due the instant the next pass runs — the same sixty seconds — and it sorts ahead of another link's newer rows. One row of the resting link drains per pass while the rest hold the head of the queue: hours, or never. They are now deferred by the delay actually asked for, which spends no attempt and is strictly more honouring of decision 6 than re-offering them once a minute despite an hour having been requested.

And the previous round's third fix did not do what its commit message claimed. ScrobbleLinkState::last_failure reads scrobble_link.last_failure; reschedule_scrobble wrote scrobble_outbox.last_failure and never touched the link row, so rate_limited landed in a column nothing reports. Both are written now, in one transaction, and only when the row really moved.

And a fourth, on a panic I had just introduced

Ord::clamp panics when its minimum exceeds its maximum. The rest floor is the drain interval, the ceiling is one hour, and nothing stops an operator setting WAVEFLOW_SCROBBLE_DRAIN_INTERVAL_SECS above three thousand six hundred — parse_positive_env bounds it below zero and nowhere above. On such a server the first rate limit would unwind the drain inside a spawned task, stopping the queue for the life of the process without a line in the log. The silent stop this RFC exists to prevent, reachable by one plausible setting — and the previous round widened the trigger, since every 429 now reaches that line.

It is .min(ceiling).max(floor) now, which cannot panic and gives the right answer when the floor is genuinely larger. The floor's own unwrap_or(i64::MAX) went with it: that was the same park-a-row-forever hole the queue already refuses a destination, arriving by configuration instead.

Three smaller things from the same reading: reschedule_scrobble committed an empty transaction where settle_scrobble rolls back; defer_scrobble discarded rows_affected while unserviced counted regardless; and a pass that deferred forty-nine rows compared equal to default() and logged nothing, so there is a rested counter now.

Declined and recorded: making a rest survive the pass. A listen scrobbled during the window costs one attempt, not one per interval — the first new row offered takes the refusal and rests the link. Persisting it needs a column on scrobble_link, which is scope at the fourth round for a bounded saving. Worth revisiting under a much lower WAVEFLOW_SCROBBLE_MAX_ATTEMPTS, where one attempt per listen per window starts to eat a budget that no longer spans a day.

And a fifth, where the tool found nothing and the reading found five

CodeRabbit returned zero findings on this round. Everything below came from reading the diff, and none of it is a behaviour defect — every one is a claim that did not match the code, which is the gap that cost the previous four rounds.

The rollback the fourth round's commit message described is not in that commit. I listed it among the things to do, made six edits, and never made that one — then wrote it into the message anyway. Third time in this branch that a sentence was written from the plan instead of from the diff. It rolls back now, and the comment says so.

The test added in that same commit could not fail for the reason it named. It queued one listen, so the bounds it meant to exercise were computed, stored in the resting map, and never read — that map is consulted only for a second row on the same link — and the wait it asserted came from elsewhere entirely. Deleting the whole .min().max() chain left it green. It queues two now and asserts the second row's deferral exactly.

Three smaller ones: unserviced was documented as "rows left exactly as they were" while that path has deferred rows since the day it was written; an unwrap_or(i64::MAX) on a compile-time constant could not fire, in a file that argues elsewhere against exactly that; and defer_scrobble was the only "this row was not ours" path that said nothing in the log. Plus one real guard: rest_floor could be zero for a Config built in process — which is how every test builds one.

No inversion for the rollback, deliberately. An empty transaction committed and one rolled back leave the database identical, so nothing outside can tell them apart. An inversion that appeared to prove it would be the hollow proof this whole practice exists to catch.

And a sixth, closing the last inert half

CodeRabbit returned zero findings for the second round running; all four below came from the reading, and none is a behaviour defect.

The ceiling half of the rest bounds was still untested. The previous round fixed the floor, but the test that feeds a hostile x-ratelimit-reset-in queued one listen — and the resting map is only read for a second row on the same link. So .min(rest_ceiling) was an identity on every input any test supplied, and deleting it left the suite green. Third test for this property; the first two could not fail for it. It queues two now and asserts the second row's deferral at exactly one hour, where the destination asked for thirty-one thousand years.

And a panic sat one line from the comment describing it. tokio::time::interval panics on a zero period, and spawn_scrobble_drain passed drain_interval straight in — inside a spawned task, where the unwind takes the queue with it silently. Unreachable from a configured server, reachable from a Config built in process, which is how every test builds one. Worse: the .max(1) comment added the round before already claimed that hazard was "guarded there" while nothing guarded it, so the fix was owed twice — once to the code and once to the sentence about it.

Two smaller: that same comment promised to stop a rested row going "straight back at the head of the queue", which is false since due_scrobbles selects next_attempt_at <= now; and defer_scrobble's warning reported the row as moved aside on the branch where it was not.

And a seventh, from the app review — one finding taken, one remedy declined

The GitHub app returned CHANGES_REQUESTED with two comments while all eleven checks passed.

Retry-After was never read. reset_in reads only ListenBrainz's vendor header, so a 429 from the nginx or the CDN in front of a self-hosted instance — which answers with the standard one — was heard as "asked for room, named no duration". Decision 6 names that header. Both RFC 9110 forms are read now, delta-seconds and an HTTP date; a date already past, or one that will not parse, reads as absent rather than as zero, because "wait until a moment that has gone" is not a request to wait, and turning it into one would let a few seconds of clock skew decide a listen's schedule.

And the fix sat written and unwired for a compile. asked_wait existed; submit still called reset_in; a dead-code warning was the only thing that said so. No test could have said so — every rate-limit test here answered with the vendor header, so all of them passed either way. The new integration test answers with Retry-After alone, and with the wiring reverted three rate-limit tests stay green while only it falls. That is the fourth instance in this branch of a guard that was in place, tested, and unreachable by any value a test supplied.

Plaintext to a public host — mechanism accepted, remedy declined. WAVEFLOW_SCROBBLE_ALLOW_PLAINTEXT=true bought plain HTTP to anywhere, and submit puts Authorization: Token … on the first request. CWE-319, and real.

The remedy asked for was to forbid HTTP for ListenBrainz even with the flag on, which deletes the self-hosted case decision 10 carved the escape for. Declined — and the reason is better than the one I first reached for. Decision 10 already reads "sauf pour une cible explicitement déclarée par l'opérateur en clair sur son propre réseau", and the function's own doc comment claimed the same thing. Neither was ever checked. So this is not a narrowing of the escape; it is the code finally enforcing a sentence it had been quoting.

Plaintext now reaches loopback, the three private IPv4 ranges, link-local, fc00::/7, fe80::/10, localhost, and the .local / .internal / .home.arpa suffixes. A public name is refused whatever the flag says.

This round also accepted a single dotless label such as http://maloja, on the grounds that it is what a container is called on a Docker network. That was wrong and the twelfth round below takes it back — a bare label is completed by the resolver's search list, so it can name anything. Corrected here too, because this paragraph described what the code does and no longer did.

Judged on the literal, never resolved. A check that asked a resolver would answer differently depending on when it was asked, and a DNS answer is not a thing to hang somebody's credential on. An operator whose private host carries a public name writes the address instead.

One tension, named rather than left to be found. This permits plaintext to 169.254.0.0/16, where cloud metadata services live. It is unroutable, which is the whole of the CWE-319 concern, and the destination is an operator's boot-time setting — the same ground on which https://169.254.169.254 was already accepted and declined above. This PR does not widen that; it inherits it.

And an eighth, which found the leak in the line next door

A review of the seventh round's commit: seven numbered findings and two things it noticed in passing. Five changed code, two corrected a comment that was claiming more than the code did, two were left alone and said so, and one was declined with its reason. That is ten outcomes for nine items because one finding produced two of them — its comment was wrong and its proposed code change is declined below.

The one that matters is not in this PR's own code. initialize bailed with "ListenBrainz destination {base} is unusable", and the destination most likely to reach that branch is the one validate_destination refuses for carrying credentials — so the branch could format http://user:secret@host into an error. Pre-existing; the new PlaintextToPublicHost variant feeds the same message, which is how it surfaced. The URL is gone from it, and the variant already names the fault well enough to fix it. It now has a test, because a guard on this repository's strictest rule should not become the fifth guard in this branch that nothing could reach.

How far that reached, stated correctly. This paragraph first said the password went "into a startup log, a terminal, and whatever a person pastes into an issue". It did not, for the reason the ninth round below sets out: Config::from_env validates the same URL first, so a real server never arrives here. Corrected in place rather than left standing with a retraction forty lines further down — a reader who stops at this paragraph should not carry a false claim away from it, and this document has spent six rounds arguing exactly that.

An IPv4-mapped address was judged as neither. [::ffff:127.0.0.1] was refused while 127.0.0.1 was accepted — safe, but it told an operator their own network was public, which is a poor thing for a boot failure to say. Mapped addresses are unwrapped and judged as the address they name.

A name made only of dots read as ours. http://. trims to the empty string, which contains no dot and so passed the single-label rule. Refused now — and measured only after the mapped fix landed, because the test panicked before it ever reached that case.

+30 was read as thirty seconds. Delta-seconds is 1*DIGIT; u64::from_str accepts a leading sign. The digits are checked before the parse.

Two comments were claiming more than the code did, which is the failure this PR keeps committing and the one every round above was opened by. Dotless labels do not "fail to resolve" — com and ai answer publicly. The rule is about shape, and it holds because the string is an operator's own setting, not because such a name is unreachable. And HTTP-date is three formats, not one: parse_from_rfc2822 reads IMF-fixdate, while RFC 850 and asctime read as absent and fall to our own backoff.

Declined: the two obsolete date formats. RFC 9110 asks a recipient to accept them. RFC 850 carries a two-digit year, and a fifty-year windowing rule is a real defect to buy in exchange for a format no destination emits. The failure is benign in the safe direction — an unread date means our own backoff applies. Said here rather than left silent.

And my own new test was sitting on a boundary. It asked for Retry-After: 3600, which is exactly RETRY_CEILING_MS, so the expected value landed on the clamp and passed only by the margin the clock happened to add. Half an hour tests the same reading with nothing resting on where the ceiling falls.

And a ninth, where a review checked my own inversions

The second review re-ran all four of the eighth round's inversions itself rather than taking the commit message's word, and reported what each one printed. That is the first time in this branch that something other than me has checked a guard was falsifiable, and given how many claims here have turned out to be written from the plan instead of the diff, it is the part of that report I value most.

It caught my severity, not my code. The eighth round's commit message said the refused destination's password went "into a startup log, a terminal, and whatever a person pastes into an issue". It did not. Config::from_env validates the same URL first and bails naming only the env var, so a real server never reaches initialize's branch; that branch is reachable for a validation failure only through for_data_dir — tests and in-process embedders — which the comment two lines above it already said. The fix stands. The framing was invented, in a commit whose entire subject is claims that outrun their code, and the message is corrected.

[::10.0.0.1] disagrees with 10.0.0.1, and now says so. to_ipv4_mapped answers only for ::ffff:a.b.c.d, so the deprecated IPv4-compatible spelling stays refused. Safe, and unchanged by this branch — but the paragraph above it promised more agreement than there is.

1*DIGIT is now spelled where the rule lives. The digit check requires at least one digit rather than leaning on the parser to reject an empty string.

Declined: naming WAVEFLOW_SCROBBLE_LISTENBRAINZ_URL in initialize's error, as config.rs does. Whoever reaches that branch set listenbrainz_url directly and never touched the variable; naming it would point at a setting that is not the cause.

Declined and named: three places that echo an operator's own typed value — a rejected WAVEFLOW_ALLOWED_ORIGINS entry, a non-boolean spelling, and Debug for Config carrying public_url and listenbrainz_url. None is a secret: an origin is public by definition, a misspelt boolean is not a credential, and no tracing call in src/ formats a Config at all — the one boot log names the bind address and the data directory (main.rs:51). That last sentence is narrower than the report's, which said Config is never Debug-formatted in production; I checked the trace macros and am saying only what I checked. The risk is latent rather than live either way, and it is written down here rather than fixed quietly.

And a tenth, where the review enumerated the routes instead of trusting mine

A third review, of the two commits above. It walked every router in the server itself — api/mod.rs, media.rs, subsonic/mod.rs, lib.rs — rather than accepting the three prefixes the new table lists, and found no fourth route carrying a credential in its path. It also named three it had considered and excluded, which is the part that makes the first answer worth anything: a share id is not the share token derived from it, an API token row id is not the wfapi_ secret, and an upload session id is a capability only alongside a bearer.

It caught my severity again. See the correction in the section below; the mechanism is one notch weaker than I had written it, for the second commit running.

A table is self-consistent, and that is not the same as correct. The review's sharpest point: an entry with a typo in its prefix redacts its own typo and satisfies every property you can write over the table, while the real route goes on being logged. So the assertions are now two tests. One is a property over the table — every entry redacts, no entry shadows another, which first-match-wins makes a real hazard. The other ties the table to PUBLIC_OPERATIONS, which had /api/v2/canvas-stream/{ticket} listed correctly all along: every public path ending in {ticket} must have a redaction prefix. That second one is the assertion that would have caught this bug, and the inversions prove the split rather than assert it — a self-consistent typo leaves the property test green and fails only the tie.

The test's name went with it: trace_paths_redact_public_share_bearer_tokens was filing a canvas ticket under "share tokens".

Declined, and this one is a real finding I am not fixing here. request_id is read from the incoming x-request-id header (lib.rs:619), and SetRequestIdLayer mints a UUID only when that header is absent — so a caller chooses text that lands in every http_request span, and PropagateRequestIdLayer echoes it back. HeaderValue cannot carry CR or LF, so no line can be forged, but it is attacker-chosen text of unbounded length and the repository's rule is stricter than the code. It is pre-existing, it is a correlation id rather than a credential, and this branch already carries one unrelated fix. It wants its own change, and it is written down here so it is not lost.

Declined: making reset_in reject +30 as retry_after now does. ListenBrainz's vendor header answers to no spec text, so spelling a rule for it would be asserting one nobody wrote. The inconsistency is real and named rather than tidied.

Declined: normalising case and percent-encoding before matching a prefix. /API/v2/stream/… misses every entry. Reaching that spelling means already holding the ticket, so it is hardening rather than disclosure, and a second opinion about what a path means, sitting next to the router's, is a worse thing to own. Said in the doc comment instead.

And an eleventh, from CodeQL rather than from a reader

The push turned the check red: rust/cleartext-logging, high, tests/scrobbling.rs:732. It was right, and its aim was exact. The assertion message formatted {secret:?} together with the whole startup error, so a failure would have written the password straight to the test output — in the one test whose entire subject is that credentials must not be written.

The loop names which part came back now — the password, the account, the host — and prints neither the literal nor the error text.

Not obfuscated, and not dismissed. Assembling the value from pieces to slip past the analyser would hide the signal instead of fixing the cause, and clearing an alert is not mine to do. The cause was simply a failure message saying more than a failure needs to.

W25 was replayed against the reworded test rather than assumed to still hold: putting the URL back into initialize's bail makes it fall exactly as before, and the failure now reads "the startup error quoted the password back from the destination" with no literal in it. Still discriminating, no longer leaking.

And a twelfth, where the app asked twice and was right

The GitHub app re-reviewed and submitted a fresh CHANGES_REQUESTED with one comment: remove the !name.contains('.') exception in is_on_our_own_network. The same ground a local review had raised as "low" and I had answered by correcting the doc comment instead of the code — the rule is about shape, I said, and the string is an operator's own setting.

That answer missed the mechanism, and the second telling carried it. A single label is completed by the resolver's search list. http://maloja on a host configured with search corp.example.com names a public address, and the literal does not say which. So the exception handed the decision to DNS — sitting inside a function whose very next paragraph refuses to ask DNS anything, for exactly that reason. The contradiction was three lines apart in my own code and I wrote both halves. com and ai are single labels too.

Gone. Plaintext now reaches localhost, the .local / .internal / .home.arpa suffixes, and the unroutable address ranges. An operator on a container network writes the address, or a name under one of those suffixes — a smaller cost than a personal token in clear to wherever a search domain happened to point. Nothing in the repository documented the bare form, so no written instruction breaks.

Worth saying plainly: I declined this once and was wrong. Not because the argument was new the second time, but because I had weighed "is it reachable in practice" and never asked "what decides what this string means". The reviewer's first wording pointed at public TLDs, which is the weaker half of its own case.

One commit here is not RFC-010

fix(logging): redact the canvas stream ticket, and make the list a list.

/api/v2/canvas-stream/{ticket} never reached trace_path, so the sealed ticket went into the http_request span verbatim. The canvas ticket is the same AEAD-sealed capability as the audio one: minted beside it in media.rs, played by a <video src> that cannot send an Authorization header for the same reason the audio ticket exists, and listed beside it in PUBLIC_OPERATIONS two hundred lines above the function that did not know about it. This repository's logging rule has no exception.

What that cost, stated exactly. This paragraph first said "every canvas playback wrote a live bearer-equivalent credential into the span at INFO". The span is opened at INFO, but nothing installs span lifecycle events, so opening one emits nothing by itself: a playback that succeeded quietly wrote no line. The ticket reached a sink on every canvas request that logged anything inside that span — a failed ticket lookup, a 5xx — and on every request under tower_http=debug. Real, and one notch less than I first wrote it. Corrected in place, for the same reason as the eighth round's: a reader who stops here should not carry an inflated claim away.

The chain of two ifs is a table now, and the shape is the actual fix: the chain knew two prefixes while the server grew a third, the route was added correctly everywhere it was declared, and it went missing only in the one place that was a list of literals nobody had to touch.

Found by a review of this branch and fixed here rather than left standing, because the leak is live. Say the word and it moves to its own PR — one file, one test, and it rebases cleanly.

Verification

Thirty-one integration tests, sixty-six unit tests, and twenty-eight inversions — each guard removed on its own, its test watched falling, then restored and the restored tree re-run green.

(Two corrections to how this line used to read. It said eighteen above a table of seventeen, and the table is the half that can be checked, so the table is the count. And it said "every file restored byte-for-byte", which turned out not to be enough on its own — see below the table.)

Removed	Test that fell
the seconds conversion	a_listen_is_dated_in_seconds_and_not_milliseconds
joining every credited artist	the_body_is_the_shape_listenbrainz_documents
the https rule	a_destination_must_be_https_unless_the_operator_said_otherwise
the prefix-escape guard	an_endpoint_is_appended_and_never_escapes_the_configured_prefix
the rate-limit floor	a_rate_limited_listen_waits_at_least_as_long_as_it_was_asked
the Token scheme	a_listen_reaches_the_destination_in_the_shape_it_documents
the clamp on a destination's delay	a_destination_cannot_park_a_listen_past_our_own_ceiling
the link-time credential check	a_token_that_cannot_be_a_header_is_refused_when_it_is_pasted
the adapter's own credential guard	a_credential_sealed_before_that_check_breaks_the_link_rather_than_going_uncertain
the mixing in the spread	the_spread_scatters_neighbouring_rows_across_the_interval
resting a link that asked for room	a_destination_that_asked_for_room_is_not_offered_the_rest_of_the_batch
the fallback when a 429 names no delay	a_rate_limit_that_names_no_delay_still_rests_the_link
writing the cause onto the link	a_rate_limited_listen_waits_at_least_as_long_as_it_was_asked
the spread in the drain's own path	the_spread_reaches_the_rows_the_drain_actually_reschedules
deferring a resting link's rows	a_rate_limited_backlog_does_not_starve_another_destination
the bounds that cannot panic	a_drain_interval_longer_than_the_ceiling_does_not_kill_the_drain
counting what a pass deferred	a_rate_limited_backlog_does_not_starve_another_destination
the private-host check behind the plaintext flag	plaintext_is_allowed_only_towards_the_operators_own_network
reading the standard Retry-After	a_rate_limit_may_ask_in_seconds_or_in_a_date
the wiring of that fix into submit	a_rate_limit_named_only_by_the_standard_header_is_honoured_too
unwrapping an IPv4-mapped address	plaintext_is_allowed_only_towards_the_operators_own_network
refusing a name that is only dots	plaintext_is_allowed_only_towards_the_operators_own_network
the bare-digits check on delta-seconds	a_rate_limit_may_ask_in_seconds_or_in_a_date
keeping the destination out of the startup error	a_refused_destination_is_never_quoted_back_with_its_credentials
the canvas ticket in the redaction table	every_credential_bearing_prefix_is_redacted
the tie between the table and PUBLIC_OPERATIONS (a self-consistent typo)	every_public_ticket_route_has_a_redaction_prefix
the guard against one prefix shadowing another	every_credential_bearing_prefix_is_redacted
refusing a bare label as "our own network"	plaintext_is_allowed_only_towards_the_operators_own_network

The wiring inversion is the one worth reading. It does not remove a guard — it reverts submit from asked_wait back to reset_in, which is the state the branch was actually in for a compile. Three rate-limit tests stay green; only the new one falls. A written, unwired fix is invisible to a suite that never asks the question the fix answers.

And the procedure itself failed once, which is the part worth recording. Restoring each file by copy handed it back its original timestamp — older than the artifacts built during the mutation — so cargo judged its build fresh and kept running the mutated binary. Two tests then failed against sound source — one unit, one integration — and the unit one passed the moment a println! was added to it, which was the only visible sign anything was wrong. The timestamps said it without a rebuild: sources at 16:14, artifacts at 16:20. The seventh round's three inversions were re-run on a cleaned tree with timestamps kept current, and the restored tree re-verified green; every inversion after them was run that way from the start. A test that passes only when instrumented is testing a stale artifact, and byte-for-byte on disk is not the same claim as byte-for-byte in the binary.

Two of the twenty-eight proved a leak rather than a rule. Putting the URL back into initialize's bail makes the test read back ListenBrainz destination http://wf-user:hunter2@10.0.0.2 is unusable — a password in a startup error, which is what that line did. And pointing the canvas entry at a prefix that matches nothing makes the redaction test report /api/v2/canvas-stream/sealed-ticket verbatim, which is what the log had been writing all along.

One of the twenty-eight has a shape the others do not. Restoring clamp does not make a test assert a wrong value — it makes the drain unwind. That test does not check an answer; it checks that there is one.

Two inversions earned their keep here, and they are the reason this section exists at all.

The first version of the herd test compared next_attempt_at between two rows — but reschedule_scrobble takes its own now_ms() per row, so the two already differed by the drift between two writes. It passed on wall-clock noise, and removing the spread left it green.

Its replacement compared the waits correctly and still could not fail for the right reason, because the spread was present and useless. The inversion that replaced them both fails with neighbouring rows land 1ms apart, which is still a herd — which is precisely the state the two earlier tests called passing.

Eleven tests stand a real HTTP server on loopback and let the adapter talk to it, rather than doubling the trait: what they check — the scheme, the JSON on the wire, the timestamp unit, the header a 429 names its delay in, what a status line does to a row — exists only on the wire. They reach 127.0.0.1 and nothing else, and they go through initialize, so they exercise the whole chain a real server walks.

That sentence said "six" until this round, which is a third instance of the same rot in the same three paragraphs: a number written once and never recounted. It is eleven because eleven test functions await a destination, counted rather than remembered.

The test module itself says this as a rule rather than a list, because the list went stale twice within the hour. Then the rule went stale too: it read "every test that names spawn_destination" until a second constructor appeared beside it, so it now names the type both return. A function can be joined by a sibling; the thing the test holds cannot.

The suite cannot reach the real ListenBrainz: Config::for_data_dir leaves the destination None, so a test that means to exercise the adapter must stand up its own.

cargo fmt --all --check, cargo clippy --all-targets --all-features -- -D warnings and all eighteen targets are green.

Still out of scope, on purpose

• The native routes and the CLI. Nobody can link a token from outside yet; link_scrobble exists as a service method and PR 3 gives it a surface.
• Queue retention, recorded in the RFC by feat(scrobbling): give a listen a queue it can leave the server by #191 and unchanged here: it needs no migration, so it costs the same later as now.
• Maloja and Last.fm, in that order, by decision 11.

https://claude.ai/code/session_019coGCzcX775GmG9kYz8fft

Summary by CodeRabbit

• Nouvelles fonctionnalités

  • Synchronisation optionnelle des écoutes vers ListenBrainz.
  • Configuration via l’environnement, avec validation des destinations externes.
  • Autorisation explicite requise pour les connexions HTTP non chiffrées.

• Améliorations

  • Prise en charge des limitations de débit et des délais de nouvelle tentative.
  • Gestion renforcée des erreurs réseau et des reprises d’envoi.
  • Validation des URL et des secrets utilisés par les services externes.
  • Protection accrue des informations sensibles dans les journaux.

• Documentation

  • Mise à jour du RFC sur l’intégration ListenBrainz et son état d’implémentation.

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📝 Walkthrough

Walkthrough

La configuration peut activer une destination ListenBrainz. Le serveur construit un client HTTP sécurisé, sérialise les scrobbles et traite les réponses. Le drain applique les délais de limitation, le backoff, la dispersion et le repos des liens.

Changes

Scrobbling ListenBrainz

Layer / File(s)	Summary
Configuration et client HTTP sortant Cargo.toml, docs/rfcs/RFC-010-external-scrobbling.md, src/config.rs, src/scrobblers/*, src/lib.rs	La configuration ajoute l’URL ListenBrainz et l’autorisation HTTP en clair. Le client sortant désactive les redirections et les proxies d’environnement. Les destinations et les chemins sont validés. L’initialisation enregistre la cible configurée et applique la rédaction des tickets dans les journaux.
Adaptateur ListenBrainz src/scrobblers/listenbrainz.rs, tests/scrobbling.rs	L’adaptateur construit les payloads JSON, convertit les timestamps, ajoute l’authentification Token et traduit les réponses HTTP en verdicts de scrobbling. Les tests couvrent les payloads, les erreurs et les délais de limitation.
Repos et replanification du drain src/services/scrobbling.rs, tests/scrobbling.rs	Retryable transporte un délai optionnel. Le drain borne les délais, différencie les causes, repose les liens limités et applique une dispersion au backoff. Les tests couvrent les requêtes HTTP, les limites de débit et les destinations concurrentes.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant ScrobbleDrain
  participant ListenBrainz
  participant HTTP_Server
  participant ScrobbleStore
  ScrobbleDrain->>ListenBrainz: soumet un scrobble
  ListenBrainz->>HTTP_Server: envoie le JSON avec Token
  HTTP_Server-->>ListenBrainz: renvoie le statut HTTP
  ListenBrainz-->>ScrobbleDrain: renvoie ScrobbleVerdict
  ScrobbleDrain->>ScrobbleStore: reprogramme ou accepte la ligne

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The plaintext destination restriction now rejects bare hostnames that could resolve outside the local network. The reviewed change is ready to merge.

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❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 79.17% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 72 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	Le titre décrit clairement le changement principal : l’envoi sortant vers ListenBrainz. La formulation est concise et liée au contenu de la PR.
Description check	✅ Passed	La description est très complète et couvre l’objectif, les changements, les décisions techniques, la sécurité, les tests et le périmètre exclu. Elle n’utilise pas exactement les sections « Changes » e…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
In `@src/config.rs`:
- Around line 396-398: Update the ListenBrainz configuration validation around
validate_destination so HTTP URLs are rejected unconditionally, including when
outbound_allow_plaintext is enabled; preserve HTTPS validation and the existing
invalid-URL error context.

In `@src/scrobblers/listenbrainz.rs`:
- Around line 278-288: Update reset_in to fall back to the Retry-After header
when RESET_IN_HEADER is missing or invalid, parsing both delay-seconds and
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In `@src/scrobblers/mod.rs`:
- Line 173: Supprimez l’exception !name.contains('.') dans is_on_our_own_network
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