[Android] Use prebuilts; add instructions for using them (pytorch#469)

* [Android] Use prebuilts; add instructions for using them

* Use persistent S3

docs/Android.md

@@ -1,5 +1,7 @@
 # Executing LLM models on Android
 
+## Option 1: Use ExecuTorch LLAMA Demo App
+
 Check out the [tutorial on how to build an Android app running your
 PyTorch models with
 ExecuTorch](https://pytorch.org/executorch/main/llm/llama-demo-android.html),
@@ -9,4 +11,43 @@ and give your torchchat models a spin.
 
 Detailed step by step in conjunction with ET Android build, to run on
 simulator for Android. `scripts/android_example.sh` for running a
-model on an Android simulator (on Mac)
+model on an Android simulator (on Mac)
+
+## Option 2: Integrate the Java API with your own app
+
+We provide a Java library for you to integrate LLM runner to your own app.
+See [this file](https://github.com/pytorch/executorch/blob/main/extension/android/src/main/java/org/pytorch/executorch/LlamaModule.java)
+for Java APIs.
+
+To add the Java library to your app, use helper functions `download_jar_library`
+and `download_jni_library` from `scripts/android_example.sh` to download the
+prebuilt libraries.
+
+```bash
+# my_build_script.sh
+source scripts/android_example.sh
+download_jar_library
+download_jni_library
+```
+
+In your app working directory (for example executorch/examples/demo-apps/android/LlamaDemo),
+copy the jar to your app libs:
+```bash
+mkdir -p app/libs
+cp ${TORCHCHAT_ROOT}/build/android/executorch.jar app/libs/executorch.jar
+```
+
+In your Java app, add the jar file path to your gradle build rule.
+```
+# app/build.grardle.kts
+dependencies {
+    implementation(files("libs/executorch.jar"))
+}
+```
+
+Then copy the corresponding JNI library to your app:
+
+```bash
+mkdir -p app/src/main/jniLibs/arm64-v8a
+cp ${TORCHCHAT_ROOT}/build/android/arm64-v8a/libexecutorch_llama_jni.so app/src/main/jniLibs/arm64-v8a
+```

scripts/android_example.sh

@@ -5,7 +5,7 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
-set -eu
+set -eux
 
 cd ${TORCHCHAT_ROOT}
 echo "Inside: $TORCHCHAT_ROOT"
@@ -25,6 +25,10 @@ else
   exit -1
 fi
 
+LLAMA_JNI_ARM64_URL="https://ossci-android.s3.us-west-1.amazonaws.com/executorch/release/0.2/arm64-v8a/libexecutorch_llama_jni.so"
+LLAMA_JNI_X86_64_URL="https://ossci-android.s3.us-west-1.amazonaws.com/executorch/release/0.2/x86_64/libexecutorch_llama_jni.so"
+LLAMA_JAR_URL="https://ossci-android.s3.us-west-1.amazonaws.com/executorch/release/0.2/executorch.jar"
+
 mkdir -p ${TORCHCHAT_ROOT}/build/android
 
 setup_java() {
@@ -64,30 +68,50 @@ setup_android_sdk_manager() {
 setup_android_sdk() {
   sdkmanager "platforms;android-34"
   sdkmanager "platform-tools"
-  sdkmanager "emulator"
-  sdkmanager "system-images;android-34;google_apis;${ANDROID_ABI}"
 }
 
 setup_android_ndk() {
   sdkmanager "ndk;25.0.8775105"
   export ANDROID_NDK="$ANDROID_HOME/ndk/25.0.8775105"
 }
 
+download_jar_library() {
+  mkdir -p ${TORCHCHAT_ROOT}/build/android
+  curl "${LLAMA_JAR_URL}" -o ${TORCHCHAT_ROOT}/build/android/executorch.jar
+}
+
+download_jni_library() {
+  mkdir -p ${TORCHCHAT_ROOT}/build/android/arm64-v8a
+  mkdir -p ${TORCHCHAT_ROOT}/build/android/x86_64
+  if [ ! -f ${TORCHCHAT_ROOT}/build/android/arm64-v8a/libexecutorch_llama_jni.so ]; then
+    curl "${LLAMA_JNI_ARM64_URL}" -o ${TORCHCHAT_ROOT}/build/android/arm64-v8a/libexecutorch_llama_jni.so
+  fi
+  if [ ! -f ${TORCHCHAT_ROOT}/build/android/x86_64/libexecutorch_llama_jni.so ]; then
+    curl "${LLAMA_JNI_X86_64_URL}" -o ${TORCHCHAT_ROOT}/build/android/x86_64/libexecutorch_llama_jni.so
+  fi
+}
+
 build_app() {
   pushd build/src/executorch/examples/demo-apps/android/LlamaDemo
-  ./gradlew :app:setup
+  mkdir -p app/src/main/jniLibs/arm64-v8a
+  mkdir -p app/src/main/jniLibs/x86_64
+  cp ${TORCHCHAT_ROOT}/build/android/arm64-v8a/libexecutorch_llama_jni.so app/src/main/jniLibs/arm64-v8a
+  cp ${TORCHCHAT_ROOT}/build/android/x86_64/libexecutorch_llama_jni.so app/src/main/jniLibs/x86_64
   ./gradlew :app:build
   popd
 }
 
 setup_avd() {
+  sdkmanager "emulator"
+  sdkmanager "system-images;android-34;google_apis;${ANDROID_ABI}"
+
   avdmanager create avd --name "torchchat" --package "system-images;android-34;google_apis;${ANDROID_ABI}"
   sdk/emulator/emulator @torchchat &
 }
 
 push_files_to_android() {
   adb wait-for-device
-  adb shell mkdir /data/local/tmp/llama
+  adb shell mkdir -p /data/local/tmp/llama
   adb push stories15M.pte /data/local/tmp/llama
   adb push checkpoints/stories15M/tokenizer.bin /data/local/tmp/llama
   adb install -t build/src/executorch/examples/demo-apps/android/LlamaDemo/app/build/outputs/apk/debug/app-debug.apk
@@ -98,7 +122,8 @@ if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
   setup_android_sdk_manager
   setup_android_sdk
   setup_android_ndk
-  build_app
   setup_avd
+  download_jni_library
+  build_app
   push_files_to_android
 fi