microsoft/amplifier-bundle-android-tester/android-self-hosted-publishing

Android Self-Hosted Publishing

Getting a build onto a tester's phone repeatedly, without a store, comes down to a small number of rules. All of these were validated by a rail that ran daily against a real device during an extended field project — each rule below fired for real at least once.

versionCode must strictly increase — refuse otherwise

A publish step that would serve changed bytes under an existing versionCode must refuse, naming the collision.

This is not theoretical tidiness. The refusal fired on the rail's first real use, catching a genuine attempt to republish changed bytes under the same version. Without it, that build reaches a device whose updater correctly decides it is already up to date — producing the worst possible failure shape: a tester debugging a bug that was already fixed, on a build that silently never arrived.

Signed APK plus a signed manifest sidecar

The shape that worked:

The in-app updater verifies both the signature on the manifest and the sha256 of the downloaded APK against the manifest before installing. Two independent checks: the signature says who published it, the hash says the bytes are intact.

Two health checks are worth building in, because both failures are silent:

• published-build-is-signed — a debug-signed artifact served from the release channel

installs fine and then fails to update over the previously-installed release build.

• served-build-is-current — the thing the server is actually serving matches the

latest build produced. A publish step that succeeded while writing to the wrong path passes every other check.

HTTPS first, fall back to HTTP only on a TLS failure — never on a 404

The update client tries HTTPS first, reusing the app's own already-pinned CA and trust manager rather than constructing a new permissive one. It falls back to plain HTTP only when the failure is TLS or connect-level.

A 404 is an answer. Falling back to HTTP on a 404 converts "the server does not have this file" into "silently retry the same missing file with less security". The distinction is the whole point: a transport failure means try another transport; an HTTP status means the server responded, and this is what it said.

Reuse the existing trust manager. An updater that builds its own TLS context is the classic place a permissive trust-all implementation gets introduced "temporarily" and stays.

Prove the installed build is the build you just made

Symptom: a fix that is definitely in the code is definitely not in the app. Hours disappear into debugging code that is not running.

Technique: compare hashes, not version strings:

LOCAL=$(sha256sum app-debug.apk | cut -d' ' -f1)
DEV_PATH=$(adb -s "$SERIAL" shell pm path com.example.app | sed 's/package://' | tr -d '\r')
DEV=$(adb -s "$SERIAL" shell sha256sum "$DEV_PATH" | cut -d' ' -f1 | tr -d '\r')
[ "$LOCAL" = "$DEV" ] && echo "installed build IS the local build" || echo "MISMATCH"

Make this the first question of any device bug report, before reproducing anything: what build is on the device, and is it the one containing the fix? A version string can be stale (it is only correct if someone remembered to bump it); a hash cannot.

Source

Full narrative and additional context: docs/FIELD-NOTES-2026-08.md §5, "App publishing and self-hosted update rails".