fix(android): use app cache dir for saveToTempFile

packages/react-native-executorch/android/src/main/cpp/ETInstallerModule.cpp

@@ -35,7 +35,9 @@ void ETInstallerModule::registerNatives() {
   });
 }
 
-void ETInstallerModule::injectJSIBindings() {
+void ETInstallerModule::injectJSIBindings(
+    jni::alias_ref<jstring> cacheDirPath) {
+  auto cacheDir = cacheDirPath->toStdString();
   // Grab a function for fetching images via URL from Java
   auto fetchDataByUrl = [](std::string url) {
     // Attaching Current Thread to JVM
@@ -68,8 +70,8 @@ void ETInstallerModule::injectJSIBindings() {
 
   auto _isEmulator = isEmulator();
 
-  RnExecutorchInstaller::injectJSIBindings(jsiRuntime_, jsCallInvoker_,
-                                           fetchDataByUrl, _isEmulator);
+  RnExecutorchInstaller::injectJSIBindings(
+      jsiRuntime_, jsCallInvoker_, fetchDataByUrl, cacheDir, _isEmulator);
 }
 } // namespace rnexecutorch
 

packages/react-native-executorch/android/src/main/cpp/ETInstallerModule.h

@@ -24,7 +24,7 @@ class ETInstallerModule : public jni::HybridClass<ETInstallerModule> {
 
   static void registerNatives();
 
-  void injectJSIBindings();
+  void injectJSIBindings(jni::alias_ref<jstring> cacheDirPath);
 
 private:
   friend HybridBase;

packages/react-native-executorch/android/src/main/java/com/swmansion/rnexecutorch/ETInstaller.kt

@@ -45,7 +45,7 @@ class ETInstaller(
     callInvoker: CallInvokerHolderImpl,
   ): HybridData
 
-  private external fun injectJSIBindings()
+  private external fun injectJSIBindings(cacheDirPath: String)
 
   init {
     try {
@@ -60,7 +60,7 @@ class ETInstaller(
 
   @ReactMethod(isBlockingSynchronousMethod = true)
   override fun install(): Boolean {
-    injectJSIBindings()
+    injectJSIBindings(reactApplicationContext.cacheDir.absolutePath)
     return true
   }
 }

packages/react-native-executorch/common/rnexecutorch/RnExecutorchInstaller.cpp

@@ -34,10 +34,19 @@ namespace rnexecutorch {
 // SSL intricacies manually, as it is done automagically in ObjC++/Kotlin.
 FetchUrlFunc_t fetchUrlFunc;
 
+// App-private writable directory provided by the platform layer. Android
+// passes reactApplicationContext.cacheDir; iOS passes NSTemporaryDirectory().
+// std::filesystem::temp_directory_path() resolves to /data/local/tmp on
+// Android <13, which is not writable by app processes — so we pipe the
+// platform-provided path through explicitly.
+std::string cacheDir;
+
 void RnExecutorchInstaller::injectJSIBindings(
     jsi::Runtime *jsiRuntime, std::shared_ptr<react::CallInvoker> jsCallInvoker,
-    FetchUrlFunc_t fetchDataFromUrl, bool isEmulator) {
+    FetchUrlFunc_t fetchDataFromUrl, const std::string &cacheDirPath,
+    bool isEmulator) {
   fetchUrlFunc = fetchDataFromUrl;
+  cacheDir = cacheDirPath;
 
   jsiRuntime->global().setProperty(*jsiRuntime, "__rne_isEmulator",
                                    jsi::Value(isEmulator));

packages/react-native-executorch/common/rnexecutorch/RnExecutorchInstaller.h

@@ -17,14 +17,16 @@ namespace rnexecutorch {
 
 using FetchUrlFunc_t = std::function<std::vector<std::byte>(std::string)>;
 extern FetchUrlFunc_t fetchUrlFunc;
+extern std::string cacheDir;
 using namespace facebook;
 
 class RnExecutorchInstaller {
 public:
   static void
   injectJSIBindings(jsi::Runtime *jsiRuntime,
                     std::shared_ptr<react::CallInvoker> jsCallInvoker,
-                    FetchUrlFunc_t fetchDataFromUrl, bool isEmulator);
+                    FetchUrlFunc_t fetchDataFromUrl,
+                    const std::string &cacheDirPath, bool isEmulator);
 
 private:
   template <typename ModelT>

packages/react-native-executorch/common/rnexecutorch/data_processing/ImageProcessing.cpp

@@ -14,6 +14,11 @@ namespace rnexecutorch {
 // to this variable. It's done to not handle SSL intricacies manually, as it is
 // done automagically in ObjC++/Kotlin.
 extern FetchUrlFunc_t fetchUrlFunc;
+// App-private writable directory bound by the platform layer (see
+// RnExecutorchInstaller.cpp). Used in place of std::filesystem::
+// temp_directory_path() because the latter points to /data/local/tmp on
+// Android <13, which is not writable by app processes.
+extern std::string cacheDir;
 namespace image_processing {
 std::vector<float> colorMatToVector(const cv::Mat &mat) {
   return colorMatToVector(mat, cv::Scalar(0.0, 0.0, 0.0),
@@ -64,8 +69,7 @@ cv::Mat bufferToColorMat(const std::span<const float> &buffer,
 std::string saveToTempFile(const cv::Mat &image) {
   std::string filename = "rn_executorch_" + file_utils::getTimeID() + ".png";
 
-  std::filesystem::path tempDir = std::filesystem::temp_directory_path();
-  std::filesystem::path filePath = tempDir / filename;
+  std::filesystem::path filePath = std::filesystem::path(cacheDir) / filename;
 
   if (!cv::imwrite(filePath.string(), image)) {
     throw RnExecutorchError(RnExecutorchErrorCode::FileWriteFailed,

packages/react-native-executorch/ios/RnExecutorch/ETInstaller.mm

@@ -43,8 +43,9 @@ @implementation ETInstaller
     }
   };
   bool isEmulator = TARGET_OS_SIMULATOR;
+  std::string cacheDir = [NSTemporaryDirectory() UTF8String];
   rnexecutorch::RnExecutorchInstaller::injectJSIBindings(
-      jsiRuntime, jsCallInvoker, fetchUrl, isEmulator);
+      jsiRuntime, jsCallInvoker, fetchUrl, cacheDir, isEmulator);
 
   NSLog(@"Successfully installed JSI bindings for react-native-executorch!");
   return @true;