feat: android support

Author: jaoleal

.github/workflows/ci.yml

@@ -212,26 +212,45 @@ jobs:
       run: cargo test -vv
 
 
-  android-nix-cross-check:
-    name: Cross-Compile (${{ matrix.check }}) building using nix
+  android-cross-compile:
+    name: Cross-Compile for Android (${{ matrix.target }})
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        check:
-          - android-aarch64
-          - android-armv7
-          - android-x86_64
+        target:
+          - aarch64-linux-android
+          - armv7-linux-androideabi
+          - x86_64-linux-android
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v3
 
-    - uses: cachix/install-nix-action@v27
+    - name: Install Rust toolchain
+      uses: actions-rs/toolchain@v1
       with:
-        extra_nix_config: |
-          accept-flake-config = true
+        profile: minimal
+        toolchain: stable
+        override: true
+        target: ${{ matrix.target }}
+
+    - name: Cache dependencies
+      uses: Swatinem/rust-cache@v2
 
-    - name: Build check
-      run: nix build .#checks.x86_64-linux.${{ matrix.check }} -L
+    - name: Install Boost library
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y libboost-all-dev
+
+    - name: Set up Android NDK
+      uses: nttld/setup-ndk@v1
+      id: setup-ndk
+      with:
+        ndk-version: r27c
+
+    - name: Build
+      env:
+        ANDROID_NDK_HOME: ${{ steps.setup-ndk.outputs.ndk-path }}
+      run: cargo build -p libbitcoinkernel-sys --target ${{ matrix.target }} -vv
 
   fuzz-corpus:
     name: Verify Fuzz Corpus

flake.nix

@@ -64,71 +64,6 @@
 					}).rust-std
 				];
 
-				# -- Source filtering --
-				src = pkgs.lib.cleanSourceWith {
-					src = self;
-					filter = path: type:
-						!(builtins.any (suffix: pkgs.lib.hasSuffix suffix path) [
-							"/target"
-							"/.git"
-							"/result"
-						]);
-				};
-
-				# -- Stable Rust for checks (MSRV is too old for some vendored crate manifests) --
-				rustStable = fenix.packages.${system}.stable;
-				mkAndroidCheck = { name, rustTarget }:
-					let
-						androidStableToolchain = fenix.packages.${system}.combine [
-							rustStable.rustc
-							rustStable.cargo
-							rustStable.rust-src
-							rustStable.rust-std
-							fenix.packages.${system}.targets.${rustTarget}.stable.rust-std
-						];
-						androidRustPlatform = pkgs.makeRustPlatform {
-							cargo = androidStableToolchain;
-							rustc = androidStableToolchain;
-						};
-					in
-					androidRustPlatform.buildRustPackage {
-						pname = "rust-bitcoinkernel-android-${name}";
-						version = "0.2.0";
-						inherit src;
-
-						cargoLock.lockFile = self + "/Cargo-recent.lock";
-
-						nativeBuildInputs = [
-							pkgs.cmake
-							pkgs.pkg-config
-							pkgs.python3
-							androidSdk
-						];
-
-						buildInputs = [
-							pkgs.boost.dev
-						];
-
-						LIBCLANG_PATH = "${pkgs.llvmPackages.clang-unwrapped.lib}/lib/";
-						ANDROID_HOME = "${androidSdk}/libexec/android-sdk";
-						ANDROID_NDK_HOME = androidNdk;
-						ANDROID_NDK_ROOT = androidNdk;
-						CARGO_BUILD_TARGET = rustTarget;
-
-						buildPhase = ''
-							runHook preBuild
-							cargo build --target ${rustTarget} --release -p libbitcoinkernel-sys
-							runHook postBuild
-						'';
-						doCheck = false;
-
-						installPhase = ''
-							touch $out
-						'';
-
-						dontFixup = true;
-					};
-
 				rustfilt = rustPlatformNightly.buildRustPackage rec {
 					pname = "rustfilt";
 					version = "0.2.1";
@@ -192,26 +127,6 @@
 					ANDROID_NDK_ROOT = androidNdk;
 				};
 
-				# Verify Android cross-compilation. Run with:
-				#   nix build .#checks.x86_64-linux.android-aarch64 -L
-				#   nix build .#checks.x86_64-linux.android-armv7 -L
-				#   nix build .#checks.x86_64-linux.android-x86_64 -L
-				checks = {
-					android-aarch64 = mkAndroidCheck {
-						name = "aarch64";
-						rustTarget = "aarch64-linux-android";
-					};
-
-					android-armv7 = mkAndroidCheck {
-						name = "armv7";
-						rustTarget = "armv7-linux-androideabi";
-					};
-
-					android-x86_64 = mkAndroidCheck {
-						name = "x86_64";
-						rustTarget = "x86_64-linux-android";
-					};
-				};
 			}
 		);
 }

libbitcoinkernel-sys/CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+
 - New `btck_ConsensusParams` opaque type for holding consensus parameters
 - New `btck_chain_parameters_get_consensus_params` for extracting consensus params from `btck_ChainParameters` (lifetime-bound to the chain parameters object)
 - New `btck_block_check` for context-free block validation (size limits, coinbase structure, sigop limits, with optional POW and merkle-root checks via `btck_BlockCheckFlags`)
@@ -18,14 +19,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - New `btck_block_header_to_bytes` for serializing a block header to its 80-byte consensus encoding
 
 ### Changed
+
 - Replaced bindgen-generated bindings with hand-written FFI bindings
+- Added Android cross-compilation support in `build.rs` (aarch64, armv7, x86_64)
+- Made compile-time layout assertions pointer-width aware for 32-bit target support
 - `btck_chain_get_by_height` `block_height` parameter type changed from `int` to `int32_t`
 - `btck_chain_get_height` return type changed from `int` to `int32_t`
 - `btck_block_validation_state_destroy` now accepts a null pointer (removed `NONNULL` annotation)
 
 ## [0.2.0] - 2026-01-26
 
 ### Added
+
 - New `btck_block_tree_entry_equals` function for comparing BlockTreeEntry objects (096924d39d64)
 - New `btck_PrecomputedTransactionData` object for holding transaction hashes required when validating scripts (eb0594e23f0c)
 - New `btck_BlockHeader` object for holding block headers (9a9d797ef6ed)
@@ -36,11 +41,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - New `btck_block_validation_state_*` functions for managing an owned block validation state, that may be used for processing block headers (9a9d797ef6ed)
 
 ### Changed
+
 - `data_directory` and `blocks_directory` parameters in `btck_chainstate_manager_options_create` now allow null values to represent empty paths (6657bcbdb4d0)
 - `btck_script_pubkey_verify` now takes a `btck_PrecomputedTransactionData` instead of an array of outputs for verifying taproot outputs (eb0594e23f0c)
 
 ## [0.1.1] - 2025-24-11
 
 ### Fixed
+
 - Precise package excludes to ensure the test/fuzz directory is included
   in the packaged crate correctly.

libbitcoinkernel-sys/build.rs

@@ -2,6 +2,35 @@ use std::env;
 use std::path::Path;
 use std::process::Command;
 
+/// Maps Rust target triples to Android ABI names used by the NDK.
+fn android_abi(target: &str) -> Option<&'static str> {
+    match target {
+        t if t.contains("aarch64") => Some("arm64-v8a"),
+        t if t.contains("armv7") => Some("armeabi-v7a"),
+        t if t.contains("x86_64") => Some("x86_64"),
+        t if t.contains("i686") => Some("x86"),
+        _ => None,
+    }
+}
+
+/// Maps Rust target triples to the NDK sysroot directory names.
+/// These differ from Rust triples for armv7 targets.
+fn android_sysroot_triple(target: &str) -> &str {
+    if target.starts_with("armv7") {
+        "arm-linux-androideabi"
+    } else {
+        target
+    }
+}
+
+/// Detect whether we are cross-compiling for Android and return the NDK home path if so.
+fn android_ndk_home() -> Option<String> {
+    env::var("ANDROID_NDK_HOME")
+        .or_else(|_| env::var("ANDROID_NDK_ROOT"))
+        .or_else(|_| env::var("NDK_HOME"))
+        .ok()
+}
+
 fn main() {
     let bitcoin_dir = Path::new("bitcoin");
     let out_dir = env::var("OUT_DIR").unwrap();
@@ -15,7 +44,12 @@ fn main() {
 
     let build_config = "RelWithDebInfo";
 
-    Command::new("cmake")
+    let target = env::var("TARGET").unwrap();
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
+    let is_android = target_os == "android";
+
+    let mut cmake_configure = Command::new("cmake");
+    cmake_configure
         .arg("-B")
         .arg(&build_dir)
         .arg("-S")
@@ -38,9 +72,33 @@ fn main() {
         .arg("-DBUILD_SHARED_LIBS=OFF")
         .arg("-DCMAKE_INSTALL_LIBDIR=lib")
         .arg("-DENABLE_IPC=OFF")
-        .arg(format!("-DCMAKE_INSTALL_PREFIX={}", install_dir.display()))
-        .status()
-        .expect("cmake should be installed and available in PATH");
+        .arg(format!("-DCMAKE_INSTALL_PREFIX={}", install_dir.display()));
+
+    if is_android {
+        let ndk =
+            android_ndk_home().expect("Android target detected but ANDROID_NDK_HOME is not set");
+        let toolchain_file = format!("{ndk}/build/cmake/android.toolchain.cmake");
+        let abi =
+            android_abi(&target).unwrap_or_else(|| panic!("unsupported Android target: {target}"));
+        // API level 24+ is required because Bitcoin Core uses getifaddrs
+        // which was introduced in Android API 24 (Nougat).
+        let api_level = env::var("ANDROID_API_LEVEL").unwrap_or_else(|_| "24".to_string());
+
+        cmake_configure
+            .arg(format!("-DCMAKE_TOOLCHAIN_FILE={toolchain_file}"))
+            .arg(format!("-DANDROID_ABI={abi}"))
+            .arg(format!("-DANDROID_PLATFORM=android-{api_level}"))
+            .arg("-DCMAKE_SYSTEM_NAME=Android")
+            .arg(format!("-DCMAKE_ANDROID_ARCH_ABI={abi}"))
+            .arg(format!("-DCMAKE_SYSTEM_VERSION={api_level}"))
+            .arg(format!("-DCMAKE_ANDROID_NDK={ndk}"))
+            // The Android NDK toolchain sets CMAKE_FIND_ROOT_PATH_MODE_PACKAGE
+            // to ONLY, which prevents cmake from finding host packages via
+            // CMAKE_PREFIX_PATH. Override it so Boost headers can be located.
+            .arg("-DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=BOTH");
+    }
+
+    cmake_configure.status().unwrap();
 
     let num_jobs = env::var("NUM_JOBS")
         .ok()
@@ -75,14 +133,27 @@ fn main() {
     println!("cargo:rustc-link-lib=static=bitcoinkernel");
 
     let compiler = cc::Build::new().get_compiler();
-    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();
 
     if target_os == "windows" {
         println!("cargo:rustc-link-lib=bcrypt");
         println!("cargo:rustc-link-lib=shell32");
-    }
-
-    if compiler.is_like_clang() {
+    } else if is_android {
+        // Android NDK ships libc++_static.a and libc++abi.a in the
+        // per-architecture sysroot directory (not the API-level subdirectory).
+        if let Some(ndk) = android_ndk_home() {
+            let ndk_triple = android_sysroot_triple(&target);
+            let host_tag = if cfg!(target_os = "macos") {
+                "darwin-x86_64"
+            } else {
+                "linux-x86_64"
+            };
+            let ndk_lib_dir =
+                format!("{ndk}/toolchains/llvm/prebuilt/{host_tag}/sysroot/usr/lib/{ndk_triple}");
+            println!("cargo:rustc-link-search=native={ndk_lib_dir}");
+        }
+        println!("cargo:rustc-link-lib=static=c++_static");
+        println!("cargo:rustc-link-lib=static=c++abi");
+    } else if compiler.is_like_clang() {
         if target_os == "macos" {
             println!("cargo:rustc-link-lib=dylib=c++");
         } else {

libbitcoinkernel-sys/src/lib.rs

@@ -324,10 +324,22 @@ pub struct btck_ValidationInterfaceCallbacks {
 const _: () = {
     assert!(core::mem::size_of::<btck_LoggingOptions>() == 20);
     assert!(core::mem::align_of::<btck_LoggingOptions>() == 4);
-    assert!(core::mem::size_of::<btck_NotificationInterfaceCallbacks>() == 72);
-    assert!(core::mem::align_of::<btck_NotificationInterfaceCallbacks>() == 8);
-    assert!(core::mem::size_of::<btck_ValidationInterfaceCallbacks>() == 48);
-    assert!(core::mem::align_of::<btck_ValidationInterfaceCallbacks>() == 8);
+    assert!(
+        core::mem::size_of::<btck_NotificationInterfaceCallbacks>()
+            == 9 * core::mem::size_of::<*const ()>()
+    );
+    assert!(
+        core::mem::align_of::<btck_NotificationInterfaceCallbacks>()
+            == core::mem::align_of::<*const ()>()
+    );
+    assert!(
+        core::mem::size_of::<btck_ValidationInterfaceCallbacks>()
+            == 6 * core::mem::size_of::<*const ()>()
+    );
+    assert!(
+        core::mem::align_of::<btck_ValidationInterfaceCallbacks>()
+            == core::mem::align_of::<*const ()>()
+    );
 };
 
 // extern "C" declarations - grouped by type