CI: cache Android SDK/NDK, Gradle, and npm across APK builds

Persist three Docker volumes into the build job (android-sdk, gradle home, npm
cache) and enable the Gradle build cache, so repeat builds skip the ~2GB NDK
download, Maven dependency resolution, and unchanged native/Kotlin compilation
— cutting builds from ~1h to a few minutes after the first run.

The runner must whitelist these volumes via config.yaml (container.valid_volumes);
deploy-runner.sh now writes that config, pre-creates the volumes, and starts the
daemon with --config. Requires re-running deploy-runner.sh on the runner host
before the next tag.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.forgejo/workflows/build-apk.yml

@@ -11,14 +11,27 @@ jobs:
     runs-on: docker
     container:
       image: node:22-bookworm
+      # Persistent caches across runs (Docker named volumes). These must be
+      # allowed in the runner's config.yaml `container.valid_volumes` — the
+      # deploy-runner.sh script sets that up. First run populates them (~1h);
+      # later runs reuse the SDK/NDK, Gradle deps + build cache, and npm cache,
+      # dropping the build to a few minutes.
+      volumes:
+        - camptickets-android-sdk:/opt/android-sdk
+        - camptickets-gradle:/root/.gradle
+        - camptickets-npm:/root/.npm
     env:
       ANDROID_HOME: /opt/android-sdk
       ANDROID_SDK_ROOT: /opt/android-sdk
+      GRADLE_USER_HOME: /root/.gradle
       # Force IPv4 for all JVMs (Gradle launcher, daemon, Kotlin/CMake workers).
       # The runner host has no working IPv6 route, so Maven Central (which has
       # AAAA records) was unreachable — this makes Java ignore AAAA and use IPv4.
       JAVA_TOOL_OPTIONS: -Djava.net.preferIPv4Stack=true
-      GRADLE_OPTS: -Dorg.gradle.jvmargs=-Xmx4g -Dorg.gradle.daemon=false
+      # org.gradle.caching enables the local build cache (persisted in
+      # GRADLE_USER_HOME), so unchanged native/Kotlin tasks are restored instead
+      # of recompiled.
+      GRADLE_OPTS: -Dorg.gradle.jvmargs=-Xmx4g -Dorg.gradle.daemon=false -Dorg.gradle.caching=true
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -36,16 +49,25 @@ jobs:
           apt-get install -y --no-install-recommends openjdk-17-jdk-headless unzip wget git
           echo "JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64" >> "$GITHUB_ENV"
 
-      - name: Install Android SDK
+      - name: Install Android SDK (cached)
         run: |
-          set -eux
+          set -eu
-          mkdir -p "$ANDROID_HOME/cmdline-tools"
+          # Skip the whole install when the cache volume already has the SDK.
-          cd /tmp
+          # (NDK + CMake are auto-installed by Gradle into the same volume on
-          wget -q https://dl.google.com/android/repository/commandlinetools-linux-11076708_latest.zip -O cmdtools.zip
+          # the first build, so they persist too.)
-          unzip -q cmdtools.zip -d "$ANDROID_HOME/cmdline-tools"
+          if [ ! -x "$ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager" ]; then
-          mv "$ANDROID_HOME/cmdline-tools/cmdline-tools" "$ANDROID_HOME/cmdline-tools/latest"
+            echo "Installing Android command-line tools..."
+            mkdir -p "$ANDROID_HOME/cmdline-tools"
+            cd /tmp
+            wget -q https://dl.google.com/android/repository/commandlinetools-linux-11076708_latest.zip -O cmdtools.zip
+            unzip -q cmdtools.zip -d "$ANDROID_HOME/cmdline-tools"
+            mv "$ANDROID_HOME/cmdline-tools/cmdline-tools" "$ANDROID_HOME/cmdline-tools/latest"
+          else
+            echo "Android SDK found in cache volume — skipping download."
+          fi
           export PATH="$ANDROID_HOME/cmdline-tools/latest/bin:$PATH"
-          yes | sdkmanager --licenses >/dev/null || true
+          yes | sdkmanager --licenses >/dev/null 2>&1 || true
+          # sdkmanager is a no-op for packages already present in the volume.
           sdkmanager --install "platform-tools" \
             "platforms;android-36" "platforms;android-35" \
             "build-tools;36.0.0" "build-tools;35.0.0" >/dev/null
@@ -73,7 +95,7 @@ jobs:
           CAMPSCAN_KEY_PASSWORD: ${{ secrets.ANDROID_KEY_PASSWORD }}
         run: |
           chmod +x ./gradlew
-          ./gradlew assembleRelease --init-script ../../ci/signing.gradle --no-daemon
+          ./gradlew assembleRelease --init-script ../../ci/signing.gradle --no-daemon --build-cache
           mkdir -p "$GITHUB_WORKSPACE/artifacts"
           cp app/build/outputs/apk/release/app-release.apk \
              "$GITHUB_WORKSPACE/artifacts/camp-scan-${{ steps.ver.outputs.tag }}.apk"

runner/README.md

@@ -30,6 +30,27 @@ The runner advertises the `docker` label; the build workflow (`.forgejo/workflow
 2. Push a tag: `git tag v0.1.0 && git push origin v0.1.0`.
 3. The runner builds `camp-scan-v0.1.0.apk` and attaches it to a Forgejo release; Obtainium picks it up.
 
+## Build caching (fast repeat builds)
+
+The first APK build takes ~1h (downloads Gradle + the ~2GB Android NDK, resolves
+all Maven deps, compiles native modules). After that it should drop to a few
+minutes because three persistent Docker volumes are reused across runs:
+
+| Volume | Holds |
+|---|---|
+| `camptickets-android-sdk` → `/opt/android-sdk` | SDK, NDK, CMake |
+| `camptickets-gradle` → `/root/.gradle` | Gradle dist, Maven deps, local build cache |
+| `camptickets-npm` → `/root/.npm` | npm download cache |
+
+For this to work the runner must **allow** these volumes via `config.yaml`
+(`container.valid_volumes`) — `deploy-runner.sh` writes that config, pre-creates
+the volumes, and starts the daemon with `--config /data/config.yaml`. If you set
+the runner up by hand, copy `config.yaml` next to the compose file and add
+`--config /data/config.yaml` to the daemon command.
+
+To force a clean rebuild, remove the volumes:
+`docker volume rm camptickets-android-sdk camptickets-gradle camptickets-npm`.
+
 ## Notes
 
 - The runner I initially registered on the app host has been removed. If Forgejo
@@ -37,3 +58,6 @@ The runner advertises the `docker` label; the build workflow (`.forgejo/workflow
   *Settings → Actions → Runners*.
 - `DOCKER_GID` must match the roomy server's docker socket group, or the runner
   can't reach the Docker daemon.
+- After updating to a caching-enabled runner, re-run `deploy-runner.sh` (or
+  `docker compose up -d` in the runner dir) so the new `config.yaml` + volumes
+  take effect, then push a fresh tag.

runner/config.yaml

@@ -0,0 +1,9 @@
+# Forgejo runner config. The important bit is valid_volumes: it whitelists the
+# named Docker volumes the build-apk workflow mounts as persistent caches
+# (Android SDK/NDK, Gradle home, npm cache). Without these listed, the runner
+# rejects the workflow's `volumes:` and the job fails.
+container:
+  valid_volumes:
+    - camptickets-android-sdk
+    - camptickets-gradle
+    - camptickets-npm

runner/docker-compose.yml

@@ -11,6 +11,9 @@ services:
       - "${DOCKER_GID:-988}"
     volumes:
       - ./data:/data
+      # config.yaml allows the build workflow to mount the persistent cache
+      # volumes (valid_volumes); without it those mounts are rejected.
+      - ./config.yaml:/data/config.yaml:ro
       # Runner spawns job containers via the host Docker daemon.
       - /var/run/docker.sock:/var/run/docker.sock
     env_file: .env
@@ -31,4 +34,4 @@ services:
             --name "${RUNNER_NAME:-camptickets-runner}" \
             --labels "docker:docker://node:22-bookworm"
         fi
-        exec forgejo-runner daemon
+        exec forgejo-runner daemon --config /data/config.yaml

scripts/deploy-runner.sh

@@ -61,6 +61,24 @@ mkdir -p "$INSTALL_DIR/data"
 # The runner image runs as uid/gid 1000 and must own its config dir.
 chown -R 1000:1000 "$INSTALL_DIR/data"
 
+# Runner config: allow the build workflow to mount the persistent cache volumes
+# (Android SDK/NDK, Gradle home, npm cache) so APK builds don't redownload and
+# recompile everything each run. Without valid_volumes listed, the runner
+# rejects the workflow's `volumes:` and the job fails.
+cat > "$INSTALL_DIR/config.yaml" <<'CONFIG'
+container:
+  valid_volumes:
+    - camptickets-android-sdk
+    - camptickets-gradle
+    - camptickets-npm
+CONFIG
+chown 1000:1000 "$INSTALL_DIR/config.yaml"
+
+# Pre-create the named cache volumes (idempotent).
+docker volume create camptickets-android-sdk >/dev/null
+docker volume create camptickets-gradle >/dev/null
+docker volume create camptickets-npm >/dev/null
+
 cat > "$INSTALL_DIR/docker-compose.yml" <<COMPOSE
 services:
   runner:
@@ -72,6 +90,7 @@ services:
       - "\${DOCKER_GID}"
     volumes:
       - ./data:/data
+      - ./config.yaml:/data/config.yaml:ro
       - /var/run/docker.sock:/var/run/docker.sock
     env_file: .env
     command:
@@ -86,7 +105,7 @@ services:
             --name "\${RUNNER_NAME}" \\
             --labels "${JOB_LABEL}"
         fi
-        exec forgejo-runner daemon
+        exec forgejo-runner daemon --config /data/config.yaml
 COMPOSE
 
 # Preserve an existing token line if re-running without a new token.