[build-tools] Collect shared simulator logs by sjkim-expo · Pull Request #4463 · expo/eas-cli

sjkim-expo · 2026-09-23T20:34:08Z

Why

User-app logs should be available across iOS session types, not just Agent Device. This follows the workflow approach Gabe and I discussed for ENG-26642 and replaces #4429.

How

I added background collection and final upload steps using the same pattern as serve-sim metrics. The collector requests /logs?scope=user-apps and uploads the result as an App logs artifact. Replay cursors prevent duplicate records on reconnect.

The collector checks that serve-sim acknowledged the filter. Older servers are skipped with a warning rather than falling back to all simulator logs. Collection remains best effort, capped at 20 MiB per device and 30 minutes, with a 30-second upload limit per device. A hard-killed worker can still lose its logs.

Rollout order is serve-sim filter support (expo/serve-sim#196), then the worker functions, then the WWW companion: https://github.com/expo/universe/pull/31439. The serve-sim filter must be released, not just merged, before the collector can use it.

Test Plan

Collector, artifact, function, and local HTTP tests pass, along with build-tools typechecking, focused lint and formatting. They cover filter acknowledgement, replay deduplication, aborts, byte limits, and uploading the exact collected bytes.

I also ran the real local WWW/worker workflow with a patched serve-sim build. The native fixture produced logs before and after a process relaunch. Stopping the session uploaded an artifact with 499 valid records and 68 fixture markers, all attributed to the app. Downloading it through the API and staging storage returned exactly the local file's bytes.

I also downloaded the artifact from the dashboard and verified that its bytes matched. The local supervisor needed a startup workaround, and verification with released package versions remains a separate check. This does not guarantee logs from before serve-sim starts.

linear-code · 2026-09-23T20:34:20Z

ENG-26642

codecov · 2026-09-23T20:41:24Z

Codecov Report

❌ Patch coverage is 94.71366% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.63%. Comparing base (e690ac0) to head (cabeea9).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
...uild-tools/src/steps/utils/serveSimLogsRecorder.ts	93.15%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4463      +/-   ##
==========================================
+ Coverage   72.52%   72.63%   +0.11%     
==========================================
  Files         974      978       +4     
  Lines       46505    46728     +223     
  Branches    10015    10099      +84     
==========================================
+ Hits        33725    33936     +211     
- Misses      11786    11798      +12     
  Partials      994      994

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github-actions · 2026-09-23T22:00:55Z

✅ Thank you for adding the changelog entry!

gwdp

Very nice 💪 ! few comments above

gwdp · 2026-09-25T18:10:25Z

+      deviceRunSessionId,
+      artifactId: `simulator-log-${udid}`,
+      name: `App logs (${udid.slice(0, 8)})`,
+      filename: 'simulator.ndjson',


suggestion/nit: would app-logs.ndjson make sense?

gwdp · 2026-09-25T18:18:49Z

+    await uploadDeviceRunSessionArtifactAsync(ctx, {
+      deviceRunSessionId,
+      artifactId: `simulator-log-${udid}`,
+      name: `App logs (${udid.slice(0, 8)})`,


What do you think about a follow-up to expose and use the device name as the name? Could a device ID have little meaning to users?

gwdp · 2026-09-25T18:59:59Z

+          return;
+        }
+        const deviceRunSessionId = getDeviceRunSessionIdOrThrow(env);
+        const signal = AbortSignal.timeout(30_000);


Would it make sense to move the timeout to be per device/upload? eg.: one upload can get stuck but we don't fail all?

gwdp · 2026-09-25T19:01:51Z

+          });
+        }
+      } catch (err) {
+        logger.warn({ err }, 'Could not finalize simulator logs; the session result is unchanged.');


Could we add Sentry.capture here so we gain visibility of this failure?

gwdp · 2026-09-25T19:02:42Z

+      try {
+        await ServeSimLogsRecorder.startAsync({ logger });
+      } catch (err) {
+        logger.warn(


Same comment from above, adding Sentry here would give us visibility on this failure

gwdp · 2026-09-25T19:04:00Z

+  let file: Awaited<ReturnType<typeof open>> | undefined;
+  let body: NodeJS.ReadableStream | undefined;
+  const closeBody = (): void => {
+    (body as import('node:stream').Readable | undefined)?.destroy?.();


Might be against repo convention, import type would be recommended

gwdp · 2026-09-25T19:06:57Z

+            payload = JSON.stringify(JSON.parse(parsed.raw));
+          }
+        } catch {
+          continue;


Might be a silent failure we want to avoid; If serv-sim is somehow producing bad/incompatible output we want a loud failure that even bubbles up on sentry?

gwdp · 2026-09-25T19:11:47Z

+        let sequence: number | undefined;
+        try {
+          const parsed: unknown = JSON.parse(payload);
+          if (


What do you think about using a Zod schema to validate here?

devin-ai-integration

Devin Review found 3 potential issues.

devin-ai-integration · 2026-09-25T19:19:48Z

startAsync

+}> {
+  let bytesWritten = 0;
+  let limitReached = maxBytes <= 0;
+  let lastSequence = since;


🟡 Legacy reconnect duplicates simulator logs

When a server switches to legacy records after a cursor-bearing stream, lastSequence retains the old cursor. The poller reconnects instead of capping that stream, repeatedly appending replayed records.

Learn more

A replay cursor is a sequence number returned by the envelope log protocol. The parser initializes lastSequence from since, so it returns a cursor even when the new response contains only legacy records. startAsync caps a stream without a cursor, but never caps this one. A legacy server can replay buffered logs on every reconnect, producing duplicates until collection ends.

Example: The first server emits envelope sequence 7 and disconnects. Its replacement returns data: {"pid":42} without envelopes on each connection; the client appends that record on every reconnect because it still reports sequence 7.

Recommended fix: Track whether the current response actually yielded envelope sequences separately from the incoming since. Cap reconnects after receiving legacy data even if since was supplied, and only update the replay cursor from sequences successfully written.

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devin-ai-integration · 2026-09-25T19:19:49Z

finishAsync

+        const collected = await ServeSimLogsRecorder.finishAsync({ logger });
+        if (collected.length === 0) {
+          logger.info('No simulator logs collected; skipping upload.');
+          return;
+        }
+        const deviceRunSessionId = getDeviceRunSessionIdOrThrow(env);


🟡 Failed collection discards recorded logs

If getDeviceRunSessionIdOrThrow fails after finishAsync, the recorder clears its session and subsequent collection returns no files. Logs remain on disk but cannot be uploaded by a retry.

Learn more

Finalization transfers the recorded files to its first caller and clears the global session in finishAsync. Here the session ID is read only after finalization. If that lookup fails, the catch logs the error and the caller loses the file list; rerunning collection gets an empty list.

Example: Collection is invoked before DEVICE_RUN_SESSION_ID is available. Finalization returns one app log, then the ID lookup throws. A later call with a valid ID finds no session and uploads nothing.

Recommended fix: Validate the destination session ID before consuming the recorder result, or retain the file list for a later upload attempt.

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devin-ai-integration · 2026-09-25T19:19:50Z

+    activeSession = session;
+    // Reserve the session before asynchronous setup so concurrent starts are harmless.
+    session.polling = (async () => {
+      const outputDirectory = await mkdtemp(path.join(os.tmpdir(), 'serve-sim-logs-'));


🔍 Temporary logs outlive collection

Each collection creates a temporary directory, and neither finalization nor upload removes it. Confirm whether worker teardown removes these files between sessions.

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…ecords (ENG-26642)

sjkim-expo · 2026-09-25T19:38:40Z

@gwdp Addressed everything:

Renamed to app-logs.ndjson
Each upload now has its own 30 s timeout, so one stuck device doesn't cancel the others
Sentry on the start and finish failures
import type
Zod schema for the log envelope. Malformed records are counted and reported to Sentry once per stream, but still skipped rather than thrown, so a bad line can't lose the logs already collected

Device name makes sense as a follow-up.

[build-tools] Collect shared simulator logs (ENG-26642)

d27b961

sjkim-expo added 2 commits September 23, 2026 16:42

[build-tools] Link simulator log changelog entry (ENG-26642)

dd35213

[build-tools] Require user-app scope for session logs (ENG-26642)

cabeea9

sjkim-expo mentioned this pull request Sep 23, 2026

[serve-sim] Add opt-in user-app log filtering expo/serve-sim#196

Merged

7 tasks

sjkim-expo marked this pull request as ready for review September 24, 2026 17:03

sjkim-expo requested a review from gwdp September 24, 2026 17:03

This was referenced Sep 24, 2026

[build-tools] Preserve captured simulator app logs #4429

Closed

[build-tools] add device run session runner #4413

Draft

sjkim-expo requested a review from sjchmiela September 25, 2026 17:55

gwdp requested changes Sep 25, 2026

View reviewed changes

sjkim-expo added 2 commits September 25, 2026 15:19

[build-tools] Name simulator log artifacts app-logs.ndjson (ENG-26642)

714dbc7

[build-tools] Time out simulator log uploads per device (ENG-26642)

9aaa481

devin-ai-integration Bot reviewed Sep 25, 2026

View reviewed changes

sjkim-expo added 3 commits September 25, 2026 15:32

[build-tools] Report simulator log failures to Sentry (ENG-26642)

6509280

[build-tools] Use a type import for the log stream body (ENG-26642)

9ec6362

[build-tools] Validate serve-sim log envelopes and report malformed r…

fdfb50b

…ecords (ENG-26642)

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