Feature: Android mobile wallet — build a signed APK from the existing QML / contrib/android pipeline

[melvincarvalho]

Summary

Produce a signed Bitmark Android APK. Almost all the work is already in this repo (inherited from upstream Electrum 4.x): the QML mobile GUI and the complete Android build pipeline. This is mostly build-system wrangling + Bitmark-specific tweaks, not new wallet code.

What's already here

• electrum/gui/qml/ — the QML mobile GUI (Electrum 4.x's mobile UI; ~35 components, android_res, java_classes). Already Bitmark-aware, already speaks to ElectrumX.
• contrib/android/ — the full Android build pipeline: buildozer_qml.spec, make_apk.sh, build.sh, a Dockerfile (reproducible), p4a_recipes, NDK fetch scripts, barcode scanner. This is the same machinery upstream uses to ship official APKs.

So the wallet logic, the mobile UI, and the build system are done — the task is operational.

Scope / tasks

1. Get the APK build green via contrib/android/ (Docker-based). The fiddly part: buildozer / python-for-android / NDK, plus native builds (secp256k1, cryptography). Solved problem upstream, but expect toolchain wrangling the first time.
2. Bitmark tweaks:
   • app id + name + BTMK branding/icon
   • default server(s): electrum.bitmark.rocks:50002 (SSL), or a server list
   • disable SegWit / force legacy-only — mobile would otherwise generate unsafe btm1... addresses (Bitmark is pre-SegWit). Same fix the desktop needs.
3. Sign + distribute: direct APK download or F-Droid (Google Play is hostile to crypto wallets).

Out of scope (for now)

• iOS — no scaffolding here; Electrum doesn't officially support iOS (QML-on-iOS is painful). Separate, large effort.

Notes

• The Android build is Dockerized -> reproducible, matching the project's reproducible-build approach (cf. daemon build).
• Depends on the legacy-only / disable-SegWit fix — that change benefits desktop and mobile at once, so worth doing first.

Effort

A few days for a first signed APK, almost entirely build-toolchain work. The code is free.

References

• Mobile GUI: electrum/gui/qml/
• Build pipeline: contrib/android/ (buildozer_qml.spec, make_apk.sh, Dockerfile)
• Related: on-chain Marking feature Feature: add Marking (on-chain endorsements via OP_RETURN) to the wallet #2

[melvincarvalho]

✅ APK build works end-to-end

Built a working debug APK straight from the existing contrib/android/ pipeline — no changes needed beyond what's already in main.

Command:

cd contrib/android
./build.sh qml arm64-v8a debug

Result: dist/Electrum-4.7.2-arm64-v8a-debug.apk (~191 MB, debug-signed)

• 8 dex files, 76 arm64 native libs (full Qt6 set + python + secp256k1), META-INF signed -> sideloads/installs fine.
• Built from main, so it includes the legacy-only / disable-SegWit fix (Safety bug: wallet can create SegWit (btm1...) addresses — unsafe on pre-SegWit Bitmark; force legacy-only #4) — new wallets get b... addresses.

Build notes:

• Docker-based (reproducible). ~2h on a 6-core machine the first time: it compiles Qt6 twice (host + Android target), then PyQt6, then the python recipes, then packaging. Subsequent builds are much faster (cached).
• The msgfmt ... fatal errors during the locale step are non-fatal warnings; the build sails past them.

Remaining for a release build (polish, not blockers):

1. Branding — installs as "Electrum"; set APP_PACKAGE_NAME=Electrum-Bitmark (+ icon) in make_apk.sh.
2. Release signing — ./build.sh qml arm64-v8a release with a release keystore (debug uses the auto-generated android_debug.keystore).
3. Default server — bake electrum.bitmark.rocks:50002 into the QML network defaults so it auto-connects.
4. More archs — ./build.sh qml all release adds armeabi-v7a (older phones) + x86_64 (emulator).

Pipeline is proven; what's left is branding + signing + distribution.

[melvincarvalho]

✅ Branded release build also works

Built a release-signed, branded APK — and since it reuses the cached Qt6/PyQt6 from the debug build, it took ~7 min (not 2h):

cd contrib/android
./build.sh qml arm64-v8a release <keystore-password>

Tweaks (all reuse the build cache — no clean rebuild needed):

• contrib/android/buildozer_qml.spec: title = Electrum-Bitmark (launcher display name)
• electrum/chains/mainnet/servers.json: default server → electrum.bitmark.rocks ("s":"50002","t":"50001")
• release keystore at ~/.keystore (alias electrum)

Verified on the output APK:

• application-label: 'Electrum-Bitmark'
• signed by CN=Electrum-Bitmark, O=Project Bitmark (the release key, not the debug key)
• default server electrum.bitmark.rocks baked in (auto-connects on first run)
• legacy b... addresses (the SegWit fix from Safety bug: wallet can create SegWit (btm1...) addresses — unsafe on pre-SegWit Bitmark; force legacy-only #4)

Result: dist/Electrum-4.7.2-arm64-v8a-release.apk (~189 MB), installable.

Still open for a public store release:

• Distinct package id (e.g. rocks.bitmark.electrum; currently org.electrum.electrum) — ⚠️ changing package.name/package.domain forces a clean .buildozer rebuild (~2h), so do it when cutting the real release.
• Bitmark icon — replace icon.filename in the spec (currently the default electrum icon; needs a 192×192 PNG).
• More archs — ./build.sh qml all release adds armeabi-v7a + x86_64.