Files
buzz/mobile/test/shared
Tom Brow 2e0abbcc0c fix(mobile): let slow image downloads finish (#8881)
On a slow link, a large image could never appear. Every image fetch was
aborted 30s after it started, even while bytes were still arriving, and
a failed fetch then sat on a 30s cooldown before it could be retried. At
240 kbps, anything over about 900 KB could not finish. On a shaped
iPhone SE, a 1.45 MB avatar was fetched, aborted at 30s and never shown.

- **Abort stalls, not slow downloads.** A fetch is now aborted when no
headers or body bytes arrive for 20s, so a dead connection still frees
up quickly. A download that keeps making progress can run for up to 5
minutes, so a server that trickles bytes cannot hold a connection
forever. The 20 MiB response cap still bounds its size.
- **Cancel previews scrolled past in the iOS carousel.** The carousel
loads at most four previews at a time, and a preview scrolled past kept
its slot until its download ended. With the longer limit, four slow
previews could block the visible one for minutes. Now the carousel drops
a cancelled preview's pending image-cache entry, and with no one left
listening, the image loader aborts its HTTP request. Scrolling back
starts a fresh download with no failure cooldown. A download that
another consumer, such as the full-screen viewer or a gallery prefetch,
is still listening to keeps going, and its finished image is still
cached. Closing the carousel aborts its pending previews the same way.
- **Cancel gallery prefetches that leave the window.** The message
gallery prefetches a few pages around the current one with two workers.
Each prefetch used to hold its download until it ended, which also kept
the carousel's cancel from aborting it. Now a prefetch that leaves the
window, or whose gallery goes away, lets go and aborts the same way.

### Validation

Added tests (each fails without its fix):

- A body that trickles in for longer than the stall timeout still loads,
and one that never ends is aborted at the overall cap.
- In the iOS carousel, previews scrolled past abort their stalled
downloads (before headers and mid-body), the next preview loads, and
scrolling back starts a new download. The test fails if the carousel
doesn't evict, if the loader doesn't abort, or if the abort leaves a
cooldown.
- Closing the carousel aborts its stalled previews.
- In a message gallery, jumping to the end and back aborts both
in-flight prefetches and moves the workers to the new window.
- Abandoning a load another consumer still waits for keeps the finished
image cached with no second fetch; abandoning one nobody else waits for
aborts it.
- Rapid scrolling releases each cancelled carousel load at once, and
cancelled loads never reach UIKit.

The full mobile suite passes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Signed-off-by: Tom Brow <tomb@squareup.com>
Co-authored-by: Tom Brow <tomb@squareup.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
2026-11-01 13:57:11 -08:00
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