Tom Brow d1a8c3607d perf(mobile): use HTTP/2 on Android through app-wide Cronet engines (#9435) ...

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.

---------

Signed-off-by: Tom Brow <tomb@squareup.com>
Co-authored-by: Tom Brow <tomb@squareup.com>

2026-11-13 13:33:58 -08:00

..

app_http_client.dart

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

2026-11-13 13:33:58 -08:00