Feat/android port

.cargo/config.toml

@@ -0,0 +1,7 @@
+# Android link paths, relative to the repo root (cargo's rustc cwd):
+#  - NDK r23+ dropped libgcc but rustc's aarch64-linux-android spec still emits
+#    `-lgcc`; android/scripts/build.sh writes the stub that satisfies it.
+#  - jniLibs holds the libSDL2.so the linker needs for `-lSDL2`.
+# Here rather than in RUSTFLAGS: a changing RUSTFLAGS invalidates every crate.
+[target.aarch64-linux-android]
+rustflags = ["-L", "target/ndk-libgcc-stub", "-L", "android/app/src/main/jniLibs/arm64-v8a"]

.github/workflows/build-android.yml

@@ -0,0 +1,125 @@
+name: Android
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - "main"
+  release:
+    types: [published]
+
+permissions:
+  contents: write
+
+env:
+  NDK_VERSION: "27.2.12479018" # r27c
+  ANDROID_API: "24"
+  ABI: "arm64-v8a"
+  RUST_TARGET: "aarch64-linux-android"
+
+jobs:
+  build-android:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up JDK
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "17"
+
+      - name: Set up Android SDK + NDK
+        uses: android-actions/setup-android@v3
+
+      - name: Install NDK + platform + build-tools
+        run: |
+          set -eux
+          sdkmanager --install "ndk;${NDK_VERSION}" "platforms;android-34" "build-tools;34.0.0"
+          echo "ANDROID_NDK_HOME=${ANDROID_SDK_ROOT}/ndk/${NDK_VERSION}" >> "$GITHUB_ENV"
+
+      - name: Rust toolchain
+        run: |
+          set -eux
+          # rust-toolchain.toml pins the channel; rustup honors it.
+          rustup show
+          rustup target add "${RUST_TARGET}"
+
+      - name: Install cargo-ndk
+        run: cargo install cargo-ndk --locked
+
+      # sync-sdl.sh needs the sdl2-sys source for the Java glue and libSDL2.so.
+      - name: Fetch crates
+        run: cargo fetch
+
+      - name: Sync SDL glue + build libSDL2.so
+        run: bash android/scripts/sync-sdl.sh
+
+      - name: Build Rust cdylib
+        env:
+          # CI performance build, kept out of Cargo.toml so local release builds
+          # stay fast to compile.
+          CARGO_PROFILE_RELEASE_LTO: "fat"
+          CARGO_PROFILE_RELEASE_CODEGEN_UNITS: "1"
+        run: |
+          set -eux
+          # NDK r23+ dropped libgcc but rustc still emits -lgcc; stub it to
+          # libunwind. The -L paths are in .cargo/config.toml.
+          mkdir -p target/ndk-libgcc-stub
+          echo "INPUT(-lunwind)" > target/ndk-libgcc-stub/libgcc.a
+          cargo ndk -t "${ABI}" -P "${ANDROID_API}" \
+            -o android/app/src/main/jniLibs build --release
+
+      # A stable key keeps `adb install -r` updating in place across releases.
+      # Without the secret (a fork) fall back to an ephemeral one so the build
+      # still runs. No `set -x` here: keep the base64 out of the logs.
+      - name: Restore signing keystore
+        env:
+          KS_B64: ${{ secrets.RETSEND_KEYSTORE_BASE64 }}
+        run: |
+          set -eu
+          if [ -n "${KS_B64:-}" ]; then
+            echo "$KS_B64" | base64 -d > android/app/release.keystore
+            echo "Using keystore from RETSEND_KEYSTORE_BASE64 (stable signature)."
+          else
+            keytool -genkeypair -v -keystore android/app/release.keystore \
+              -storepass android -keypass android -alias androiddebugkey \
+              -keyalg RSA -keysize 2048 -validity 10000 \
+              -dname "CN=retsend,O=retsend,C=US"
+            echo "::warning::RETSEND_KEYSTORE_BASE64 not set; using an ephemeral key (APKs won't update in place)."
+          fi
+
+      - name: Assemble release APK
+        env:
+          RETSEND_KEYSTORE: release.keystore
+          RETSEND_KEYSTORE_PASS: ${{ secrets.RETSEND_KEYSTORE_PASS || 'android' }}
+          RETSEND_KEY_ALIAS: ${{ secrets.RETSEND_KEY_ALIAS || 'androiddebugkey' }}
+          RETSEND_KEY_PASS: ${{ secrets.RETSEND_KEY_PASS || 'android' }}
+        run: |
+          set -eux
+          cd android
+          ./gradlew --no-daemon assembleRelease
+          ls -la app/build/outputs/apk/release/
+
+      - name: Stage the APK
+        run: |
+          set -eux
+          cp android/app/build/outputs/apk/release/app-release.apk retsend-android-arm64.apk
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: retsend-android-arm64
+          path: retsend-android-arm64.apk
+
+      - name: Upload to GitHub Release
+        if: github.event_name == 'release'
+        run: sha256sum retsend-android-arm64.apk > retsend-android-arm64.apk.sha256
+
+      - name: Attach APK to release
+        if: github.event_name == 'release'
+        uses: softprops/action-gh-release@v2
+        with:
+          files: |
+            retsend-android-arm64.apk
+            retsend-android-arm64.apk.sha256

CHANGELOG.md

@@ -9,13 +9,32 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **An Android build**, `retsend-android-arm64.apk`. SDL2's Android port loads
+  the Rust code as a cdylib and enters it through `SDL_main`, so windowing, the
+  GLES path, gamepad input and the whole net stack are the ones the handhelds
+  run — what is Android's alone is packaging, storage and the Back button, all of
+  it behind `cfg(target_os = "android")` or additive Cargo entries. The system
+  Back button is B and quits at the top level, and the activity holds a
+  `MulticastLock` so the Wi-Fi driver stops filtering out the announces discovery
+  is built on. It runs landscape, which is both the UI it already had and one
+  less relayout to get wrong. The app asks for all-files access before starting:
+  granted, received files land in `Download/` where an emulator can find them;
+  denied, it keeps to its own external folder, which file managers can't open on
+  Android 11+. Built with
+  `android/scripts/build.sh`; the port is written up in
+  [android/README.md](android/README.md).
 - **Touch and mouse input**, which the UI had never read: it is painted from a
   cursor that only a pad or the keyboard moved, so on a phone there was nothing
   to press. A tap now becomes the same `AppCommand` a button emits — on a row it
   places the cursor there and confirms, so tapping a device sends to it and
   tapping a file picks it, and each slot of the footer hint bar *is* the button
   it names, which is what makes Start/Select/X/Y reachable without a pad. The
   same applies to a desktop mouse, where clicking used to do nothing.
+- `RETSEND_BROWSER_ROOTS` (`:`-separated) adds file-browser roots a launcher
+  knows and no built-in candidate could name, and `RETSEND_ALIAS` seeds the
+  device name where there is no hostname to read. The Android activity passes
+  its storage volumes and `Build.MODEL` through them.
+
 ## [0.5.5] - 2026-08-18
 
 ### Changed

Cargo.toml

@@ -7,6 +7,12 @@ license = "GPL-3.0"
 description = "LocalSend client for retro handhelds (SDL2 + egui)"
 repository = "https://github.com/mxmgorin/retsend"
 
+# `cdylib` is the `libretsend.so` SDL's Android shell loads (named in
+# RetsendActivity.getLibraries()); `lib` keeps `src/main.rs` and the tests linkable.
+[lib]
+name = "retsend"
+crate-type = ["lib", "cdylib"]
+
 [features]
 default = ["software-render"]
 sdl2-bundled = ["sdl2/bundled"]
@@ -58,3 +64,8 @@ socket2 = { version = "0.6", features = ["all"] }
 # Random session ids / tokens / fingerprint; a hex helper in net::protocol is
 # all we need on top, so no uuid/rand.
 getrandom = "0.4"
+
+# Android: SDL loads our cdylib and calls the C `SDL_main` we export. There is no
+# stderr to mirror to a file, so `log` goes to logcat via android_logger.
+[target.'cfg(target_os = "android")'.dependencies]
+android_logger = "0.15"

README.md

@@ -8,14 +8,15 @@
   <a href="https://github.com/mxmgorin/retsend/actions/workflows/ci.yml"><img src="https://github.com/mxmgorin/retsend/actions/workflows/ci.yml/badge.svg" alt="CI"></a>
   <a href="https://github.com/mxmgorin/retsend/actions/workflows/build-linux-arm.yml"><img src="https://github.com/mxmgorin/retsend/actions/workflows/build-linux-arm.yml/badge.svg" alt="Linux ARM"></a>
   <a href="https://github.com/mxmgorin/retsend/actions/workflows/build-linux.yml"><img src="https://github.com/mxmgorin/retsend/actions/workflows/build-linux.yml/badge.svg" alt="Linux"></a>
+  <a href="https://github.com/mxmgorin/retsend/actions/workflows/build-android.yml"><img src="https://github.com/mxmgorin/retsend/actions/workflows/build-android.yml/badge.svg" alt="Android"></a>
   <a href="https://deps.rs/repo/github/mxmgorin/retsend"><img src="https://deps.rs/repo/github/mxmgorin/retsend/status.svg" alt="Dependencies"></a>
 </div>
 
 `retsend` (**ret**ro + **send**ing) is a Rust [LocalSend](https://localsend.org)
 client for retro handhelds: send and receive files with your phone
 or PC over Wi-Fi, no cable or SSH. Compatible with the official LocalSend apps.
 
-It targets [PortMaster-compatible](https://portmaster.games/supported-devices.html) Linux handhelds and the Miyoo Mini Plus and Flip running OnionOS, both of which are gamepad-only systems without a compositor. It also runs on regular desktop Linux too.
+It targets [PortMaster-compatible](https://portmaster.games/supported-devices.html) Linux handhelds and the Miyoo Mini Plus and Flip running OnionOS, both of which are gamepad-only systems without a compositor. It also runs on regular desktop Linux and on Android handhelds and phones too.
 
 | Receive | Request | Save | Transfer |
 |:---:|:---:|:---:|:---:|
@@ -60,6 +61,18 @@ The zip carries an SDL2 built for the Miyoo's panel and a launcher that asks for
 the software renderer, since the SSD202D has no GPU at all. What ships inside it,
 in full: [onionos/App/Retsend/lib/README.md](onionos/App/Retsend/lib/README.md).
 
+## Install (Android)
+
+Grab `retsend-android-arm64.apk` from
+[Releases](https://github.com/mxmgorin/retsend/releases) and sideload it. Same
+app, driven by touch or by a pad, with the system Back button as B: tap a device
+to send to it, a file to pick it, a row to open it, and the button hints along
+the bottom are themselves the buttons.
+
+Grant **All files access** when it asks and received files land in `Download/`,
+where an emulator or file manager can reach them; deny it and the app is confined
+to its own folder. See [android/README.md](android/README.md).
+
 ## Building & running (desktop)
 
 System SDL2 is the only native dependency. On Debian/Ubuntu:
@@ -86,6 +99,20 @@ Tests are headless (no SDL, no network setup needed):
 cargo test
 ```
 
+### Building the APK
+
+With the Android SDK and an NDK installed:
+
+```sh
+rustup target add aarch64-linux-android
+cargo install cargo-ndk --locked
+./android/scripts/build.sh release   # android/app/build/outputs/apk/release/app-release.apk
+```
+
+It builds `libSDL2.so` on the first run, cross-compiles the Rust cdylib SDL loads,
+and assembles the APK — see [android/README.md](android/README.md) for how the
+port fits together.
+
 ## Controls
 
 Touch works too, where there is a touchscreen: tap a row to act on it, or tap a
@@ -114,10 +141,10 @@ Settings screen edits everything in it except:
 - `[transfer] pinned_paths`, `last_send_dir` — written by Y and by sending
 
 Environment variables override paths and control logging at launch:
-`RETSEND_DATA_DIR`, `RETSEND_CONFIG`, `RETSEND_SAVE_DIR`, `RETSEND_SCALE`,
-`RETSEND_GLES=0|1`, `RETSEND_SOFTWARE=1`, `RETSEND_BLIT=1`,
-`RETSEND_KEYMAP=miyoo|desktop`, `RETSEND_LOG_LEVEL`, `RETSEND_LOG_FILE`,
-`RETSEND_PANIC_FILE`.
+`RETSEND_DATA_DIR`, `RETSEND_CONFIG`, `RETSEND_SAVE_DIR`, `RETSEND_BROWSER_ROOTS`
+(`:`-separated), `RETSEND_ALIAS`, `RETSEND_SCALE`, `RETSEND_GLES=0|1`,
+`RETSEND_SOFTWARE=1`, `RETSEND_BLIT=1`, `RETSEND_KEYMAP=miyoo|desktop`,
+`RETSEND_LOG_LEVEL`, `RETSEND_LOG_FILE`, `RETSEND_PANIC_FILE`.
 
 `RETSEND_BLIT=1` rasterizes the UI offscreen and presents it as a single texture
 copy per frame, for drivers that show nothing else — the Miyoo Mini's panel driver

android/.gitignore

@@ -0,0 +1,14 @@
+# Generated by android/scripts/sync-sdl.sh (copied from sdl2-sys, or built):
+app/src/main/java/org/libsdl/app/
+app/src/main/jniLibs/
+app/src/main/res/mipmap-*/
+gradle/wrapper/gradle-wrapper.jar
+gradlew
+gradlew.bat
+
+# Gradle / build output:
+.gradle/
+build/
+app/build/
+local.properties
+*.keystore