Stage Android emulator logcat output by sjchmiela · Pull Request #3627 · expo/eas-cli

sjchmiela · 2026-04-23T15:35:46Z

Summary

stream adb logcat -v threadtime for every Android emulator started by eas/start_android_emulator
write live logcat output to a well-known staging directory under the build logs directory
record metadata for each stream so a later step can stop and collect logs safely

Why

When an Android emulator crashes before later diagnostics run, adb logcat -d may no longer work because the device is already gone. Streaming from startup preserves those logs without writing into directories that get archived.

Test plan

cd packages/build-tools && yarn test startAndroidEmulator AndroidEmulatorUtils

linear · 2026-04-23T15:35:50Z

ENG-20762 Stream Android emulator logcat from the emulator start

codecov · 2026-04-23T15:40:55Z

Codecov Report

❌ Patch coverage is 79.41176% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.50%. Comparing base (900ad76) to head (30529e4).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...ages/build-tools/src/utils/AndroidEmulatorUtils.ts	76.67%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3627      +/-   ##
==========================================
- Coverage   55.70%   55.50%   -0.19%     
==========================================
  Files         852      856       +4     
  Lines       36549    36828     +279     
  Branches     7642     7647       +5     
==========================================
+ Hits        20356    20438      +82     
- Misses      14774    16295    +1521     
+ Partials     1419       95    -1324

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Copilot

Pull request overview

Adds early, continuous Android emulator logcat capture during eas/start_android_emulator so logs are preserved even if the emulator dies before later diagnostics can run.

Changes:

Introduces a build-logs staging directory for Android emulator logcat output.
Starts adb logcat -v threadtime streaming immediately after each emulator boot and writes output to staged files.
Adds/updates unit tests for the new streaming behavior and step integration.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
packages/build-tools/src/utils/AndroidEmulatorUtils.ts	Adds logcat staging path helper and `startLogcatStreamingAsync` implementation.
packages/build-tools/src/steps/functions/startAndroidEmulator.ts	Starts logcat streaming for each emulator (including clones) using the build logs staging directory.
packages/build-tools/src/utils/tests/AndroidEmulatorUtils.test.ts	Adds unit tests for logcat streaming success/failure.
packages/build-tools/src/steps/functions/tests/startAndroidEmulator.test.ts	Updates mocks/assertions to cover logcat streaming integration and failure tolerance.

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sjchmiela · 2026-04-24T11:48:37Z

+      const safeSerialId = serialId.replace(/[^a-zA-Z0-9_.-]/g, '_');
+      const outputPath = path.join(outputDir, `${child.pid}-${safeSerialId}.log`);
+      const writeStream = fs.createWriteStream(outputPath);
+      child.stdout.pipe(writeStream);
+      child.stdout.on('error', err => {
+        logger.warn({ err }, `Failed to read Android emulator logcat for ${serialId}.`);
+      });
+      writeStream.on('error', err => {
+        logger.warn({ err }, `Failed to write Android emulator logcat for ${serialId}.`);
+      });
+      child.on('close', () => {
+        writeStream.end();
+      });
+      child.unref();
+
+      void logcatPromise.catch(err => {
+        logger.warn({ err }, `Android emulator logcat stream for ${serialId} stopped.`);
+      });
+
+      logger.info(`Streaming Android emulator logcat for ${serialId} to ${outputPath}.`);
+
+      return { outputPath };
+    } catch (err) {


Keeping this as-is intentionally. We split the work so PR 1 only starts staging logcat for every emulator, and PR 2 only copies the staged .log files into Maestro artifacts. The collection step no longer stops logcat or needs per-stream metadata, so returning outputPath is enough for this branch and avoids reintroducing the metadata/stop path we explicitly removed in the follow-up PR.

Copilot

Pull request overview

This PR adds best-effort, continuous adb logcat streaming for Android emulators started by the eas/start_android_emulator build function, writing output into a predictable subdirectory under the build logs directory so logs are preserved even if the emulator disappears later.

Changes:

Added AndroidEmulatorUtils.startLogcatStreamingAsync to start adb logcat -v threadtime streaming into a staged .log file.
Added AndroidEmulatorUtils.getLogcatStagingDirectoryPath and wired it into eas/start_android_emulator so every started emulator begins streaming logcat immediately.
Added/updated unit tests covering the streaming behavior and the build function integration.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/build-tools/src/utils/AndroidEmulatorUtils.ts	Adds logcat staging path helper and a new async helper to start streaming logcat to a file.
packages/build-tools/src/utils/tests/AndroidEmulatorUtils.test.ts	Adds tests validating logcat streaming writes to a staged file and handles spawn failures.
packages/build-tools/src/steps/functions/startAndroidEmulator.ts	Starts logcat streaming for base emulators and clones immediately after each `startAsync`.
packages/build-tools/src/steps/functions/tests/startAndroidEmulator.test.ts	Updates mocks/assertions to verify logcat streaming is invoked during emulator startup and failures don’t block readiness waits.

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Copilot

Pull request overview

Adds early, continuous Android emulator adb logcat streaming to a predictable staging directory under the build logs directory so logs are preserved even if the emulator crashes before later diagnostics.

Changes:

Add AndroidEmulatorUtils.getLogcatStagingDirectoryPath() and AndroidEmulatorUtils.startLogcatStreamingAsync() to start and persist logcat streaming to disk.
Invoke logcat streaming during base emulator startup and during clone startup in eas/start_android_emulator.
Add unit tests for the new utility and update startAndroidEmulator step tests to assert logcat streaming behavior and ordering.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/build-tools/src/utils/tests/AndroidEmulatorUtils.test.ts	Adds tests for `startLogcatStreamingAsync` and temp-dir cleanup.
packages/build-tools/src/utils/AndroidEmulatorUtils.ts	Introduces logcat staging path helper and streaming implementation.
packages/build-tools/src/steps/functions/startAndroidEmulator.ts	Starts logcat streaming as part of emulator bring-up (base + clones).
packages/build-tools/src/steps/functions/tests/startAndroidEmulator.test.ts	Extends step tests to cover logcat streaming calls and failure tolerance.

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github-actions · 2026-04-24T12:15:41Z

⏩ The changelog entry check has been skipped since the "no changelog" label is present.

Copilot

Pull request overview

This PR adds continuous adb logcat streaming for Android emulators started by the eas/start_android_emulator build function, staging log output under the build logs directory so logs survive emulator crashes.

Changes:

Add AndroidEmulatorUtils.getLogcatStagingDirectoryPath() and startLogcatStreamingAsync() to stream adb logcat -v threadtime into staged files.
Wire logcat streaming into the emulator startup flow (including cloned emulators).
Add unit tests for the new utility and update step tests to assert streaming is invoked before readiness checks and that failures don’t block startup.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/build-tools/src/utils/AndroidEmulatorUtils.ts	Introduces staging path helper and logcat streaming implementation.
packages/build-tools/src/steps/functions/startAndroidEmulator.ts	Starts logcat streaming immediately after emulator start (base + clones) using the build logs directory.
packages/build-tools/src/utils/tests/AndroidEmulatorUtils.test.ts	Adds unit coverage for streaming success and failure paths.
packages/build-tools/src/steps/functions/tests/startAndroidEmulator.test.ts	Verifies streaming is invoked for each emulator and does not block startup when it fails.

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+      const childStdout = child.stdout;
+      const safeSerialId = serialId.replace(/[^a-zA-Z0-9_.-]/g, '_');
+      const outputPath = path.join(outputDir, `${child.pid}-${safeSerialId}.log`);
+      const writeStream = fs.createWriteStream(outputPath);


sjchmiela force-pushed the stanley/eng-20762-stage-emulator-logcat branch from 93e6a3d to 7945c7d Compare April 23, 2026 15:51

Stage Android emulator logcat output

6c0f797

sjchmiela force-pushed the stanley/eng-20762-stage-emulator-logcat branch from 7945c7d to 6c0f797 Compare April 23, 2026 15:56

sjchmiela requested a review from Copilot April 24, 2026 11:31

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Address logcat review feedback

2313ad9

sjchmiela requested a review from Copilot April 24, 2026 11:50

sjchmiela added the no changelog PR that doesn't require a changelog entry label Apr 24, 2026

Copilot started reviewing on behalf of sjchmiela April 24, 2026 11:51 View session

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Comment thread packages/build-tools/src/utils/AndroidEmulatorUtils.ts

Guard missing logcat child pid

40c554e

sjchmiela requested a review from Copilot April 24, 2026 12:01

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Comment thread packages/build-tools/src/utils/AndroidEmulatorUtils.ts

Comment thread packages/build-tools/src/utils/__tests__/AndroidEmulatorUtils.test.ts Outdated

sjchmiela added 2 commits April 24, 2026 14:12

Tighten logcat stream cleanup

d3aeb9b

Use pipeline for logcat streaming

30529e4

sjchmiela requested a review from Copilot April 24, 2026 12:16

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Stage Android emulator logcat output#3627

Stage Android emulator logcat output#3627
sjchmiela wants to merge 5 commits intomainfrom
stanley/eng-20762-stage-emulator-logcat

sjchmiela commented Apr 23, 2026

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sjchmiela commented Apr 23, 2026

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