fix(proxy): abort paid upstream on client disconnect for chat path

[erhnysr]

Describe your changes

The media handlers all abort their upstream on client disconnect (#251, fixed for /v1/images/image2image in v0.12.252 and for audio + chat-path /img2img in v0.12.253). The main /v1/chat/completions path — the highest-traffic one — was the one handler still missing it.

proxyRequest wired its disconnect abort to req.on("close"):

const onClientClose = () => {
  if (!globalController.signal.aborted) { ... globalController.abort(); }
};
req.on("close", onClientClose);

On Node (verified on v24.15.0) an IncomingMessage emits "close" when the request-body readable finishes, not when the client hangs up. The body is fully drained near the top of proxyRequest, so that event had already fired by the time the listener was attached ~1,500 lines below — onClientClose never ran. globalController was therefore only ever aborted by the request timeout, and a caller that hung up mid-request left the paid x402 upstream running to completion for a response nobody would receive — the exact orphan-upstream problem #251 fixed for the media paths.

Change

Move the abort to res.on("close") (guarded by !res.writableEnded), mirroring every media handler — e.g. /v1/images/image2image:

res.on("close", () => {
  if (!res.writableEnded) clientAbort.abort();
});

The four removeListener cleanup sites are migrated from req to res to match.

Reproduction

New regression test src/proxy.chat-abort.test.ts (same harness/style as src/proxy.img2img-abort.test.ts): the client POSTs /v1/chat/completions, the upstream mock holds the socket open, and the client destroy()s mid-request. The mock's res.on("close")-with-!writableEnded counter observes the abort.

• Before the fix: upstreamAborted stays 0 — the upstream is orphaned (surfaces as Response finished with error: Premature close → All 1 models failed (HTTP 500)).
• After the fix: the upstream socket observes the abort (upstreamAborted === 1), and the test also completes far faster since the abort fires immediately instead of waiting out the premature-close path.

Full suite: 64 files / 724 tests passing.

Checklist

• Repo forked and branch created from main
• Commit messages and codestyle follow conventions
• Relevant issues linked (img2img endpoint missing client abort controller charges user on disconnect #251 lineage; sibling PRs fix(proxy): pass clientAbort.signal to asset download fetches + abort guard on chat /imagegen catch #276 / fix(proxy): guard image2image abort errors after client disconnect #278)

Summary by CodeRabbit

• Bug Fixes

  • Client disconnections during chat completions now properly cancel ongoing paid upstream requests.
  • Prevents unnecessary processing and costs after a client connection is closed.

• Tests

  • Added regression coverage to verify upstream requests are aborted exactly once when clients disconnect.

• Chores

  • Released version 0.12.254.

[coderabbitai]

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📒 Files selected for processing (4)

• CHANGELOG.md
• package.json
• src/proxy.chat-abort.test.ts
• src/proxy.ts

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📝 Walkthrough

Walkthrough

The proxy now listens for response closure to abort unfinished paid chat upstream requests. Cleanup paths use the response listener. An end-to-end regression test verifies upstream closure after client disconnect. The package version and changelog were updated to v0.12.254.

Changes

Chat request cancellation

Layer / File(s)	Summary
Response-close abort handling src/proxy.ts	proxyRequest attaches onClientClose to res.on("close") and removes the listener from the response across cleanup paths.
Regression coverage and release update src/proxy.chat-abort.test.ts, package.json, CHANGELOG.md	The regression test verifies upstream socket closure after client disconnect. The package version and changelog move to 0.12.254.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to fe8e8

The change localizes client-disconnect cancellation to the chat request path and adds regression coverage; no actionable merge-blocking risk remains after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant proxyRequest
  participant UpstreamHTTPServer
  Client->>proxyRequest: Send chat completion request
  proxyRequest->>UpstreamHTTPServer: Forward paid request
  Client--xproxyRequest: Close connection
  proxyRequest->>UpstreamHTTPServer: Abort unfinished request

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Suggested reviewers: 1bcmax, killerqueen-z, 0xcheetah1

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: aborting paid upstream requests on client disconnects in the proxy chat path.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (2 skipped: 2 …
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (2 skipped: 2 unsupported.)

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[VickyXAI]

Merged as-is via fast-forward (fe8e871) and shipped in v0.12.254 with two small follow-ups on top (bd13340): a res.destroyed check right after the listener attach (covers a hang-up during the context-compression / balance-check awaits, where close had already fired), and a ClientDisconnectedError so a client cancel no longer surfaces as Request timed out after 300000ms + a balance-cache invalidation. Your test now also asserts onError stays silent and gates the disconnect on the upstream being reached instead of a fixed timer. Great diagnosis — thank you!