perf(mobile): use HTTP/2 on Android through app-wide Cronet engines by brow · Pull Request #9435 · block/buzz

brow · 2026-11-13T00:57:18Z

Follows #8897 (iOS HTTP/2), now on main.

What

Android gets the same app-wide shared sessions as iOS, backed by Cronet (cronet_http) instead of NSURLSession:

One Cronet engine per traffic class (API, media), so requests to a host multiplex over one HTTP/2 connection and gzip is inflated natively, off the Dart isolate.
HTTP/2 on, HTTP cache off, QUIC off. QUIC would be a separate behavior change, and cronet_http's changelog lists DNS failures with QUIC on cellular.
Streamed uploads (media and voice notes) stay on dart:io on Android: CronetClient reads a request body into memory before sending it, which would break upload progress and copy large attachments in full.
If no Cronet provider is available (no Google Play services), the engine fails to build and the app keeps dart:io, as today.
Transport error classification covers Cronet failures alongside NSURLSession ones, so invite and pairing errors keep their friendly messages.

Measurements

Android emulator (API 36, arm64), profile builds of this branch and main, signed in to the Feedback community. 8 cold starts per build, alternating builds in blocks of 4. Times are for relay /query requests started in the first 8 s.

	main (`dart:io`)	this branch (Cronet)
First query response	6.99 s	1.99 s
Startup burst settled	8.36 s	2.78 s
Burst after the first connection	1.44 s	0.77 s
Query latency after the first connection, median / p90	165 / 1567 ms	106 / 158 ms

Unexplained stall: most of main's startup gap is a ~5 s stall before its first response on every cold start. Its cause is unconfirmed; my guess is dart:io loading its CA store on the emulator, which HTTP/2 itself wouldn't fix, so the first two rows likely overstate the win on real devices. The rows after the first connection exclude the stall and are the fairer comparison. I also tried emulated EDGE throttling, but the emulator's throttle did not slow its traffic, so there are no slow-link numbers yet.

Regressions

None found. Devices without Play services keep dart:io. Cleartext http:// requests keep the handle's own dart:io client, as on iOS.

Testing

Full mobile suite passes (flutter test, 4784 tests).
Automated app run on the emulator: onboarding, Feedback nsec import, channel and DM list load, and 16 cold starts with request timing. Media loading wasn't separately exercised.
No visible UI change, so no screenshots.

chatgpt-codex-connector · 2026-11-13T19:06:31Z

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📝 Code Review	✅ Completed 2026-11-13T19:11:38.324920Z	`490ca3f`	Draft marked ready

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github-actions · 2026-11-13T19:09:26Z

🔐 Codex Security Review

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Use it as a supplement to human review; false positives are possible.

Scope

Exact PR diff: 59ae028a360242d43ffbfdafca8a76eda00484d9...96aff9233f532b4005c9df56975373f355753a0b

Model: gpt-6.1-sol

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Cronet dependency source was unavailable locally, limiting verification of native transport behavior.

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chatgpt-codex-connector · 2026-11-13T19:11:35Z

+    debugPrint('Cronet is unavailable, using dart:io: ${error.message}');
+    return null;
+  }
+  return CronetClient.fromCronetEngine(engine);


Preserve streaming uploads when selecting the Android transport

For Android HTTPS media uploads, this also replaces the streaming transport used by MediaUploadService._sendUploadRequest. However, CronetClient.send in cronet_http 1.10.1 drains the entire request with await stream.toBytes() and copies it into a Java buffer before starting the network request. Consequently, the composer's upload progress reaches 100% before transmission begins, and supported 100 MB attachments require additional full-body allocations that can cause memory failures on constrained devices. Keep streamed uploads on dart:io or use a genuinely streaming Cronet upload implementation. Validate backpressure through the selected production transport: the existing test uses _AbortRecorder, so it cannot detect this regression.

AGENTS.md reference: AGENTS.md:L243-L247

Useful? React with 👍 / 👎.

🤖 Fixed in 96aff92. On Android, streamed requests with a body (media and voice note uploads) now keep the handle's dart:io client, so upload progress and memory behave as before; streamed GETs and buffered requests still use Cronet. A new test covers the routing.

Signed-off-by: Tom Brow <[email protected]>

CronetClient reads a request body into memory before sending it, so upload progress would reach 100% before transmission and large attachments would be copied in full. Streamed requests with a body keep the handle's dart:io client on Android. Signed-off-by: Tom Brow <[email protected]>

kazemek21

Kyle reviewed this PR and the Nexus review-tracker notes and approved with no comments.

Posted by Codex (gpt-6.1-sol) on behalf of kylez

brow force-pushed the mobile-http2 branch from aae7bbc to 12ec456 Compare November 13, 2026 01:28

brow force-pushed the mobile-http2-android branch from eb00637 to d926e06 Compare November 13, 2026 01:34

brow force-pushed the mobile-http2 branch from 12ec456 to 7eee728 Compare November 13, 2026 02:23

brow force-pushed the mobile-http2-android branch from d926e06 to dd58314 Compare November 13, 2026 02:27

brow force-pushed the mobile-http2 branch from 7eee728 to 96d2eac Compare November 13, 2026 15:15

brow force-pushed the mobile-http2-android branch 2 times, most recently from 6e7070b to 36d8868 Compare November 13, 2026 15:29

Base automatically changed from mobile-http2 to main November 13, 2026 18:49

brow force-pushed the mobile-http2-android branch from 36d8868 to 490ca3f Compare November 13, 2026 18:51

brow marked this pull request as ready for review November 13, 2026 19:06

brow requested a review from a team as a code owner November 13, 2026 19:06

brow deployed to codex-review November 13, 2026 19:06 — with GitHub Actions Active

github-actions Bot added the codex-security-review-current The posted Codex security review matches its recorded range. label Nov 13, 2026

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square-tomb added 2 commits November 13, 2026 11:14

feat(mobile): use HTTP/2 on Android through app-wide Cronet engines

3d1aada

Signed-off-by: Tom Brow <[email protected]>

brow force-pushed the mobile-http2-android branch from 490ca3f to 96aff92 Compare November 13, 2026 19:17

brow deployed to codex-review November 13, 2026 19:17 — with GitHub Actions Active

github-actions Bot added codex-security-review-current The posted Codex security review matches its recorded range. and removed codex-security-review-current The posted Codex security review matches its recorded range. labels Nov 13, 2026

kazemek21 approved these changes Nov 13, 2026

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brow merged commit d1a8c36 into main Nov 13, 2026
53 checks passed

brow deleted the mobile-http2-android branch November 13, 2026 21:34

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perf(mobile): use HTTP/2 on Android through app-wide Cronet engines - #9435

perf(mobile): use HTTP/2 on Android through app-wide Cronet engines#9435
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