rsend: push phone folders to a home SSH host over rsync

A small Android app for one-way folder backup, a KISS alternative to
Syncthing. It bundles rsync (built from pinned source via the NDK) and
a pure-Go SSH transport, both shipped in the APK as lib*.so and run from
the native library directory.

rsend pins the host key, stores the ed25519 identity Keystore-encrypted,
pushes each folder additively or as a mirror, and runs on demand or on a
WiFi-only schedule. The build is self-contained and reproducible: make
setup provisions the toolchain, make builds rsync, rsh, and the APK.

1 files changed, 88 insertions, 0 deletions

diff --git a/app/build.gradle b/app/build.gradle
new file mode 100644
index 0000000..56036ab
--- /dev/null
+++ b/app/build.gradle
@@ -0,0 +1,88 @@
+plugins {
+    id 'com.android.application'
+    id 'org.jetbrains.kotlin.android'
+}
+
+// Release signing is configured only if a local keystore.properties exists
+// (gitignored). Otherwise the release build is unsigned, which is what F-Droid
+// and reproducible-build verification want.
+def keystoreProps = rootProject.file('keystore.properties')
+
+android {
+    namespace 'invalid.lena.rsend'
+    compileSdk 35
+
+    defaultConfig {
+        applicationId 'invalid.lena.rsend'
+        minSdk 30
+        targetSdk 35
+        versionCode 1
+        versionName '0.1.0'
+        // Ship only the ABIs we build native libs for.
+        ndk { abiFilters 'arm64-v8a', 'x86_64' }
+    }
+
+    signingConfigs {
+        if (keystoreProps.exists()) {
+            def props = new Properties()
+            keystoreProps.withInputStream { props.load(it) }
+            release {
+                storeFile rootProject.file(props['storeFile'])
+                storePassword props['storePassword']
+                keyAlias props['keyAlias']
+                keyPassword props['keyPassword']
+                // Include v1 (JAR) signing too; some sideload installers
+                // (Samsung One UI on Android 11/12) reject v2-only APKs with
+                // "problem parsing the package".
+                enableV1Signing true
+                enableV2Signing true
+                enableV3Signing true
+            }
+        }
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            if (keystoreProps.exists()) {
+                signingConfig signingConfigs.release
+            }
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_17
+        targetCompatibility JavaVersion.VERSION_17
+    }
+    kotlinOptions {
+        jvmTarget = '17'
+    }
+
+    buildFeatures {
+        buildConfig true
+    }
+
+    // Native executables ship as lib*.so and must be extracted so we can exec
+    // them from nativeLibraryDir (useLegacyPackaging => extractNativeLibs=true).
+    packaging {
+        jniLibs {
+            useLegacyPackaging true
+        }
+    }
+
+    // Reproducible / F-Droid: do not embed the Google dependency metadata block.
+    dependenciesInfo {
+        includeInApk false
+        includeInBundle false
+    }
+}
+
+dependencies {
+    implementation 'androidx.core:core-ktx:1.13.1'
+    implementation 'androidx.appcompat:appcompat:1.7.0'
+    implementation 'androidx.work:work-runtime-ktx:2.10.0'
+
+    // The real org.json shadows the android.jar stub so JSON tests run on the JVM.
+    testImplementation 'junit:junit:4.13.2'
+    testImplementation 'org.json:json:20240303'
+}