Feat: Android support by jaoleal · Pull Request #158 · sedited/rust-bitcoinkernel

jaoleal · 2026-04-10T17:49:36Z

This pr contain 3 commits:

an old version of Add MSRV Cargo-minimal.lock and Cargo-recent.lock files #150 to make CI work again flawlessly.
A patch to the projects flake adding a nix-shell that give us the necessary setup for the android build, which includes the android toolchain and some environment variables. The second commit also introduces a new job on the CI that executes the building for android.
Android building instructions for build.rs

This is just a PoC, the main commit is the third one and the CI job containing the android building at that point should run fine.
For more context read #156

sedited · 2026-04-23T08:02:59Z

This looks nice, can you rebase this?

jaoleal · 2026-04-30T20:33:49Z

Changelog:

Removed some PoC code
Included android native building in ci (whitout nix).
A fix regarding building on macos was included to.
Rebased on top of Chore: remove bindgen and replace with hand-rolled FFI bindings #163 and included a fix regarding pointer sizes.

jaoleal · 2026-05-06T20:08:49Z

I reduced a lot the code and i think this is the concise version to support android

alexanderwiederin · 2026-05-07T09:53:42Z

~~I don't think android is a supported target for libbitcoinkernel. Doesn't this require upstream work on bitcoin core first?~~

alexanderwiederin

From what I understand the ubuntu boost packages don't ship with the cmake config that core needs when cross-compiling.

Am I right that you got it working on nix locally? If so, can we stick with with only supporting the nix build for android?

jaoleal · 2026-05-07T20:55:29Z

Am I right that you got it working on nix locally? If so, can we stick with with only supporting the nix build for android?

Yes, i worked all this on nix but Im not sure about leaving android building exclusively for nix, this would make it a direct dependency of the project and its not something really special that only nix can do. Besides the dependency problem, nix can drift versions because of nixpkgs releases and that can raise problems only by itself.

~~Therefore, i still would like for CI to keep the runner as ubuntu. Its easier for the general developer audience to replicate the build on their machine if they need~~

Edit: see the comment below

jaoleal · 2026-05-07T22:11:57Z

Correction, I changed my mind... The idea is that the build.rs file is already bloated because of the android support additions, adding support for ubuntu bloated it even more... It looks like leaving to nix to cross-compile to android is actually a good choice, the changes stay minimal on build.rs side and it have broader support running on linux and macos machines... Ill make sure to document that somewhere and state how to make the android build.

jaoleal · 2026-05-08T00:37:47Z

Okay the android build being exclusive for nix made things easier for this PR, the changes on build.rs are minimal... I included some inline doc comments so the reviewer can follow why each line were added.

I added a section on the readme explaining the android build but its not that explanatory in a level that one can learn how to build this lib to android, do you guys think thats needed ?

I can extend the docs to include instructions for one to reproduce it on a downstream build.rs, just tell me where to put it.
AFAIK is trivial for those using Kotlin, as mandacaru is using, to pull an already compiled shared object during build time. Thats what ill do on floresta-nix for mandacaru, ideally the CI would also offer the compiled objects too for those who might need it.

alexanderwiederin

Great to see this working.

If we land the hand-written bindings PR (#163) first, the changes in build.rs should become simpler. I would suggest we wait for it.

sedited · 2026-05-20T16:07:40Z

@jaoleal I'm interested in getting this change through. Can you rebase it and address Alex' comments?

jaoleal · 2026-05-20T16:13:45Z

@jaoleal I'm interested in getting this change through. Can you rebase it and address Alex' comments?

Yes, sorry for taking long... I was waiting for the bindgen pr to be merged so we had sure what that would imply here without rebasing on a pr

jaoleal · 2026-05-23T14:43:09Z

Addressed suggestions @sedited @alexanderwiederin

sedited · 2026-05-25T15:25:22Z

 ## [0.2.1] 2026-05-20

 ### Added
+- Added Nix package outputs for Android with bundled NDK r27, Rust toolchains, Boost, and cmake.


This needs to go in a new ###Added entry in the unreleased section.

sedited · 2026-05-25T15:27:02Z

@jaoleal how are you testing the build artifacts? Are you running the tests in some emulated environment, or do you just link the kernel crate into an existing project and observe that there are no failures?

jaoleal · 2026-05-25T16:32:16Z

@jaoleal how are you testing the build artifacts? Are you running the tests in some emulated environment, or do you just link the kernel crate into an existing project and observe that there are no failures?

None of these, I got satisfied by the build succeeding since testing this can be tricky... Are you looking into CI tests for this ?

But youre correct, we should be testing the outputs.

Testing it using floresta will be hard but ill look into it.

sedited · 2026-05-25T16:34:55Z

Ah, I thought this was intended for eventual floresta integration. Or what was your motivation for working on it?

jaoleal · 2026-05-25T16:53:08Z

Ah, I thought this was intended for eventual floresta integration. Or what was your motivation for working on it?

Well, yes, im fixing a "floresta-issue" here but allow me to expose the whole picture.

Floresta uses bitcoin-kernel only for script validation, whitout the bitcoin-kernel feature, floresta just skips script validation.

Mandacaru, basically a port of floresta to android, needs floresta running on android, and is currently skipping script validation.

To test this using floresta i would need to: 1. Make floresta use this current android_support branch. 2. Build a binary and ship it to Mandacaru. 3. Build Mandacu, run it on android and perform full sync.

And this would not result in a satisfatory test because floresta would only exercise script validation. Too hard for basically useless results.

AFAIK the best solution to be sure that bitcoin-kernel is indeed working on android is by adding a test in CI running inside an emulated environment, ill push it and lets see how it goes

sedited · 2026-05-25T17:03:43Z

I'm also fine with just leaving it be for now and handling that in a follow-up pull request. Having something link is already a good assurance :)

Build instructions for targeting android expecting it to be executed in nix move internal changelog to unreleased

Outputs and environment setup for building android. move nix changelog to unreleased

This commit introduces preparation for testing in both Nix and CI. Testing android outputs is restricted to x86_64-linux machines for simplicity. QEMU user-mode emulation is configured as the Cargo test runner for cross-compiled Android targets. fix formatting

jaoleal · 2026-05-25T18:30:57Z

Ok, done.

32115fc Addressed suggestions:

Moved changelog edits to unreleased section.
Added tests for the android outputs.
fixed formatting on string literals

cc @sedited take a look on https://github.com/sedited/rust-bitcoinkernel/actions/runs/26413972282/job/77754301637#step:4:6483

jaoleal mentioned this pull request Apr 10, 2026

Android Support #156

Open

jaoleal mentioned this pull request Apr 30, 2026

Chore: remove bindgen and replace with hand-rolled FFI bindings #163

Merged

jaoleal force-pushed the android_support branch from 55272e4 to 378a3bc Compare April 30, 2026 20:31

jaoleal mentioned this pull request Apr 30, 2026

Android cross-compilation blocked by aws-lc-rs and bitcoinkernel getfloresta/Floresta#943

Open

jaoleal force-pushed the android_support branch 6 times, most recently from a2c959f to 0f3252f Compare May 6, 2026 20:07

jaoleal changed the title ~~POC: Android support~~ Feat: Android support May 6, 2026

jaoleal marked this pull request as ready for review May 6, 2026 20:08

alexanderwiederin reviewed May 7, 2026

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alexanderwiederin reviewed May 7, 2026

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Comment thread flake.nix Outdated

jaoleal force-pushed the android_support branch 5 times, most recently from 479401e to 30f44a8 Compare May 8, 2026 00:24

alexanderwiederin reviewed May 12, 2026

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alexanderwiederin linked an issue May 22, 2026 that may be closed by this pull request

ci: add cross-compilation job for 32-bit/Android targets #175

Open

jaoleal force-pushed the android_support branch 4 times, most recently from f1fed04 to 5387332 Compare May 23, 2026 14:40

jaoleal force-pushed the android_support branch from 5387332 to d898366 Compare May 23, 2026 21:24

sedited reviewed May 25, 2026

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Comment thread flake.nix Outdated

sedited reviewed May 25, 2026

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jaoleal added 3 commits May 25, 2026 14:08

feat: minimal android support

672657a

Build instructions for targeting android expecting it to be executed in nix move internal changelog to unreleased

feat(nix): android build outputs

460b4f1

Outputs and environment setup for building android. move nix changelog to unreleased

ci: add Android cross-compilation CI job

1eaca12

jaoleal force-pushed the android_support branch 2 times, most recently from 9eb3d5c to d5724e1 Compare May 25, 2026 17:28

jaoleal force-pushed the android_support branch from d5724e1 to 32115fc Compare May 25, 2026 18:14

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