fix(telemetry): emit usage events for a request the caller abandoned - #1190
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A request whose downstream client hangs up before the response head is
written leaves no row in the usage log. Every endpoint emits its usage
events from the tail of its own handler, and that is continuation code:
when the client disconnects first, axum drops the handler future and none
of it runs. The request may have reached a provider and spent its tokens,
and the control plane never hears about it — invisible exactly where an
operator most needs it, because the usual reason a caller gives up is a
long time to first token. The already-failed attempts of a fallback chain
were lost the same way, since `RoutingTelemetry` was a local inside the
dispatch loop.
The emission now happens where cancellation cannot skip it. The telemetry
middleware's `ClientCancelGuard` writes, from `Drop`, the events the
handler never reached: one non-terminal event per attempt that had already
failed, then one terminal `499` / `client_disconnected` event with zero
tokens and zero cost. Everything it needs is published to the request's
attribution cell at chokepoints the handlers already pass through — the
`ClientContext` extractor, `model_resolve::resolve_model` and
`RoutingTelemetry` — so no endpoint opts in and none can drift out.
The terminal event names both model identities the request carries:
`requested_model` is the entry the caller addressed (the group, for a
routing request) and `model_id` is the target that was in flight, with
`attempt_index` / `attempt_kind` / `attempt_model` and the provider-key
attribution of that attempt. A cancel before any target was selected
reports no attempt and an empty `model_id`; a routing group's own uuid is
never written there, because it prices nothing.
Behavior changes:
- A head-phase client cancel on `/v1/chat/completions`, `/v1/completions`,
`/v1/embeddings`, `/v1/images/{generations,edits}`, `/v1/messages`,
`/v1/messages/count_tokens`, `/v1/rerank`, `/v1/responses`,
`/v1/audio/{transcriptions,translations,speech}` and `/v1/videos` now
produces usage events where it previously produced none. Rows carry
status `499`, `error_class = "client_disconnected"` and zero tokens, so
they cost nothing and are filterable. Requests that never authenticated
still emit nothing, matching the other pre-dispatch rejections.
- The mid-stream `499` event — a consumer that abandoned a stream already
in flight — now carries `error_class = "client_disconnected"` too, with
a message naming the streaming shape. It previously carried the status
and no class at all, so it could not be filtered for. Stamped at the
emission chokepoint, so all six streaming families report it alike.
- The access log gains `upstream_model` and `provider_key_id`. `model=`
keeps meaning the entry the caller addressed; the new pair names the
target that was actually selected, which the `499` line could not say
before. Both are omitted when no target was selected.
No new field reaches the control plane: every one of these already exists
in the telemetry shape and `499` passes its range check unchanged.
Spawns a real gateway against a routing model whose only target delays 30s before writing its response head, aborts the client mid-dispatch, and asserts the SLS row and the access-log line the request leaves behind: status 499, `client_disconnected`, the GROUP as `requested_model` and the TARGET as `model_id` / `attempt_model`, plus the target's upstream model and provider key on the line. The routing shape is the point. Every earlier cancel test used a single direct model, where the entry the caller addressed and the target the gateway dispatched to are one value — so none of them could tell a row that names the target from one that names the group.
The bypass census requires every UsageEvent literal to either set `guardrail_bypassed_reason` or say why it has no guardrail chain to read. The cancel emitters have none: the chain each handler resolves for itself lives behind no chokepoint the guard can reach, so a cancelled request reports no guardrail attribution rather than a wrong one.
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Included review availability: Your plan provides up to 5 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe proxy now records resolved upstream target attribution in access logs and cancellation telemetry. Client disconnects before response headers can emit terminal ChangesCancellation telemetry and dispatch attribution
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Bug fix · Severity of issue fixed: Medium Sequence Diagram(s)sequenceDiagram
participant Client
participant ClientCancelGuard
participant RequestAttribution
participant cancel_emit
participant UsagePipeline
Client->>ClientCancelGuard: disconnect before response head
ClientCancelGuard->>RequestAttribution: take cancellation context
ClientCancelGuard->>cancel_emit: emit cancellation context
cancel_emit->>UsagePipeline: emit failed attempts and terminal 499 event
UsagePipeline->>RequestAttribution: note usage emitted
Merge Risk: ⚪ Minimal · up to Cancellation telemetry preserves requested routing-group identity without misreporting it as an upstream target, and duplicate terminal events are suppressed. The change is ready to merge. 🚥 Pre-merge checks | ✅ 5 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (5 passed)
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Comment |
The terminal-path section covered the two shapes that RETURN early. A dropped future is the third, and it is the one that costs other work: any value a cancelled request must report has to be published to the attribution cell at a chokepoint, never held only in a handler local.
The guard defers to the handler when the handler already emitted a terminal event, and a streaming handler records that from Drop as cancellation unwinds. That only reaches the cell because tokio keeps the task-local installed while the scoped future is dropped — a property nothing else pinned, and whose loss would turn one cancelled stream into two contradicting terminal rows with nothing failing.
Asserting the new upstream_model / provider_key_id pair only on the 499 line would leave an implementation that fills it from the cancel guard and nowhere else looking entirely correct.
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Inline comments:
In `@crates/aisix-proxy/src/attribution.rs`:
- Around line 288-290: Update note_attempt_settled to retain compact metadata
for the latest successful AttemptRecord after clearing in_flight, and have
cancel::emit use it when no attempt is active so cancellation attribution
preserves the selected model and attempt fields during post-settlement
processing. Clear the retained metadata only at terminal emission or guard
disarm, without emitting a duplicate success event.
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crates/aisix-obs/src/access_log.rscrates/aisix-proxy/AGENTS.mdcrates/aisix-proxy/src/a2a.rscrates/aisix-proxy/src/attempt.rscrates/aisix-proxy/src/attribution.rscrates/aisix-proxy/src/audio.rscrates/aisix-proxy/src/cancel.rscrates/aisix-proxy/src/chat.rscrates/aisix-proxy/src/client_ip.rscrates/aisix-proxy/src/completions.rscrates/aisix-proxy/src/count_tokens.rscrates/aisix-proxy/src/embeddings.rscrates/aisix-proxy/src/images.rscrates/aisix-proxy/src/jobs.rscrates/aisix-proxy/src/lib.rscrates/aisix-proxy/src/mcp.rscrates/aisix-proxy/src/messages.rscrates/aisix-proxy/src/model_resolve.rscrates/aisix-proxy/src/operation.rscrates/aisix-proxy/src/passthrough_route.rscrates/aisix-proxy/src/realtime.rscrates/aisix-proxy/src/reject.rscrates/aisix-proxy/src/rerank.rscrates/aisix-proxy/src/responses.rscrates/aisix-proxy/src/usage_attr.rscrates/aisix-proxy/src/videos.rstests/e2e/src/cases/client-cancel-usage-1571-e2e.test.ts
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…er's attribution Three review findings, all on what the attribution cell is allowed to say about a request. A semantic guardrail, a semantic route and the semantic cache all dispatch to an embedding model, and two of those callers run AFTER the winning attempt settled — the guardrail's output hook and the cache write. Because `resolve_provider_key` commits every target it resolves to the request's cell, an ordinary request that ran a semantic guardrail reported the EMBEDDING model as the upstream it dispatched to, on the very access-log line an operator reads to find out which member of a routing group served them. Wrong rather than absent, and on a field this change introduced. `embed_texts` now runs against a throwaway cell. A cancel also lands in the gaps around an attempt, not only inside one: the retry backoff, and the post-dispatch work after the winner (the output scan, the cache write, the token commit). Those are whole HTTP round trips, and a cancel there used to produce a 499 naming no target at all while carrying that target's provider-key tags. The winning attempt is now kept whole — its own event is the one the handler never wrote, so nothing of the request carries its index yet — and a failed attempt leaves its model id behind, without its index, which a row already claims. Finally, `dispatched` on a cancel inside an in-flight attempt is now false. It states that the event describes work that REACHED an upstream and makes the exporter derive a CLIENT span from the latency, but an attempt is published to the cell before the target's own rate-limit reservation and before the bridge assembles the request — so claiming it would fabricate an upstream span for a call nobody made. A settled winner still reports true, with its own measured duration.
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Problem
A request whose downstream client hangs up before the response head is written leaves no row in the usage log at all.
Every endpoint emits its usage events from the tail of its own handler, and that is continuation code. When the client disconnects first, axum drops the handler future and none of it runs — the request may have reached a provider and kept it busy, and the control plane never hears about it. The gateway's
ClientCancelGuardalready wrote the499access-log line and bumpedaisix_proxy_client_cancelled_requests_total, but nothing that reached the usage log. That is invisible exactly where an operator most needs it, because the usual reason a caller gives up is a long time to first token.The already-failed attempts of a fallback/retry chain were lost the same way:
RoutingTelemetryis a plain local inside the dispatch loop, and its records only ever became events in code the dropped future never reached.Approach
The emission moves to the one thing cancellation cannot skip:
Drop.ClientCancelGuardnow writes, fromDrop, the events the handler never got to — one non-terminal event per attempt that had already failed, then one terminal499event for the request itself. Everything it needs is published to the request's attribution cell at chokepoints the handlers already pass through, so no endpoint opts in and none can drift out:api_keyidClientContextextractormodel_resolve::resolve_modelRoutingTelemetry::begin_attempt/::recorddispatch::resolve_provider_key(already there)The terminal event keeps both model identities the request carries apart:
requested_modelis the entry the caller addressed — the group, for a routing request — andmodel_idis the target the request had committed to, withattempt_index/attempt_kind/attempt_modeland that attempt's provider-key attribution. A cancel before any target was selected reports no attempt and an emptymodel_id; a routing group's own uuid is never written there, because it prices nothing.A cancel also lands in the gaps around an attempt, not only inside one, and those gaps are whole round trips: the retry backoff between two targets, and everything the handler still does after the winner settles — the token commit, the output guardrail scan, the cache write. So the winning attempt is kept whole once it settles (its own event is the one the handler never wrote, so nothing of the request carries its index yet) and a failed attempt leaves its model id behind without its index, which a row already claims.
One thing the guard deliberately does not claim is
dispatched. It states that the event describes work that reached an upstream, and makes the exporter derive a CLIENT span from the latency — but an attempt is published to the cell before the target's own rate-limit reservation and before the bridge assembles the request, so an attempt in flight has not necessarily reached anyone. A settled winner reportstruewith its own measured duration; an in-flight one reportsfalseand no latency, rather than fabricating a span for a call nobody made.Finally, the cell only ever names a target the caller asked for.
embed_texts— the one dispatch the gateway makes on its own behalf, for a semantic guardrail, a semantic route or the semantic cache — now runs against a throwaway cell, because two of its three callers run after the winning attempt has settled and would otherwise have put the embedding model on the request's own access-log line.Nothing is emitted for a request that never authenticated — a caller that hung up during body upload is in the same position as the pre-dispatch rejections in
reject.rs, which emit no usage event either. And if the handler had already got an event out in the microseconds before the future was dropped, the guard defers to it rather than doubling the row.Behavior changes
A head-phase client cancel now produces usage events where it previously produced none, on
/v1/chat/completions,/v1/completions,/v1/embeddings,/v1/images/{generations,edits},/v1/messages,/v1/messages/count_tokens,/v1/rerank,/v1/responses,/v1/audio/{transcriptions,translations,speech}and/v1/videos. Rows carry status499,error_class = "client_disconnected",error_message = "client closed the request before the response head was written", zero tokens and zero cost — so they add spend to nothing and are filterable as a class.The mid-stream
499event now carries the same vocabulary. A consumer that abandoned a stream already in flight was reported with the status and noerror_classat all, so it could not be filtered for; it now carrieserror_class = "client_disconnected"and a message naming the streaming shape ("client closed the request while the response was streaming"). Token and cost content is unchanged. Stamped at the emission chokepoint, so all six streaming families report it alike rather than each through its own helper.The access log gains
upstream_modelandprovider_key_id.model=keeps meaning the entry the caller addressed; the new pair names the target that was actually selected, which a499line could not say before (and which was reachable nowhere else by request id). Both are omitted from the line when no target was selected.An environment's request count rises and its success rate falls, because these rows did not exist before. The control plane derives both from the usage events (
request_countis aCOUNT(*)over distinctrequest_id,success_countaBOOL_OR(2xx)), so an environment with abandoned requests will now see them. Latency percentiles are unaffected — they already filter to successful rows with a positive caller latency.No new field reaches the control plane —
error_class,error_message,model_id,attempt_*andrequested_modelall already exist in the telemetry shape, and499passes its range check unchanged. No metric or label set changes.What is deliberately not covered
/mcp,/a2a/:agentand the passthrough namespace tunnel to an upstream the caller never named a model for, so a cancel there has no model, no attempt and no target to report. They keep the access-log line and the cancel counter they already had./v1/realtimewrites its terminal event from the session task long after the handler returned its upgrade, and the/v1/files|batches|fine_tuningmanagement routes may auto-select the model themselves rather than taking a caller-named one.operation::surface_for_endpointis checked against the router's own parsed routing table, so a new metering route fails the build until it either maps or is named exempt with a reason.applied_guardrails, enforced hits, scores, bypass reason). Those come off a chain each handler resolves for itself, in a crate the guard cannot call back into; there is no chokepoint to read them from, and adding ten opt-in call sites is the drift this design exists to avoid. The emitters declare it in place, which the bypass census enforces.Dropemitter (its generator body has not started) nor the guard (already disarmed). It leaves an access-log line and no usage event.Tests
Rust, in
crates/aisix-proxy— each seeded against a routing model, which is the gap that let this go unpinned: every existing cancel test used a singledirectmodel, where the entry the caller addressed and the target dispatched to are the same value, so none of them could tell a correct row from one naming the group.head_phase_cancel_before_dispatch_reports_the_group_and_no_model_id— cancel during the input guardrail scan: one499event,requested_model= group,model_idempty, no attempt fields.head_phase_cancel_mid_attempt_reports_the_target_in_flight—model_id/attempt_model/attempt_index/attempt_kindof the target being awaited.head_phase_cancel_keeps_the_attempts_that_already_failed— attempt 0 fails, the fallback is in flight, the caller aborts: the failed-attempt event and the terminal499, in that order.head_phase_cancel_after_the_winner_settled_still_names_the_target— the winner answers, the output guardrail scan is what the caller abandons: the row names the target in full rather than reporting a request that reached nothing.head_phase_cancel_on_a_single_target_family_reports_its_model—/v1/embeddings, standing for the families with no attempt loop.a_cancel_before_the_model_is_named_emits_nothing— an authenticated caller that abandons its upload names no model, so it gets no row. (authandClientContextare bothFromRequestPartsand run before the body extractor, so an api_key alone is reached long before a model is.)embedding_does_not_overwrite_the_caller_s_target— a gateway-initiated embedding must leave the caller's target untouched.streaming_chat_telemetry_fires_on_client_disconnect— extended to pin the mid-stream event's new class and message.every_metering_route_decides_what_a_head_phase_cancel_reports— the route census above.the_cell_is_writable_while_the_scoped_future_is_dropped— the double-emission interlock rests on tokio keeping the task-local installed while the scoped future is dropped, which is what lets a streaming handler's ownDropemitter claim the terminal event before the guard looks. Nothing else pinned it, and losing it would turn one cancelled stream into two contradicting terminal rows with nothing failing.E2E,
tests/e2e/src/cases/client-cancel-usage-1571-e2e.test.ts— a real gateway against a routing group whose only target delays 30s before its response head; the client aborts mid-dispatch; the mock SLS sink's row and the access-log line are both asserted. A second case drives an ordinary completed request, because asserting the new access-log pair only on the 499 line would leave an implementation that fills it from the guard and nowhere else looking correct.Every test was mutation-checked: reverting the emission, taking
model_idfrom the entry instead of the attempt, dropping the failed attempts, letting a composite entry write its own uuid, removing the499vocabulary stamp, emptyingAccessLogTarget::current(), and removing the detached scope aroundembed_textseach turn the corresponding test red.Fixes api7/AISIX-Cloud#1571
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Summary by CodeRabbit
New Features
499, cancellation details, routing information, and zero usage.Bug Fixes
Tests