fix(android): Fix JNI signature mismatch causing SIGSEGV on Android 11+

- Fixed initialize() function to return jstring instead of void to match Java signature
- Changed jstring_to_string() to return Option<String> instead of panicking on error
- Updated all call sites to handle the Option return type safely

This resolves the crash on newer Android versions where JNI signature mismatch was causing segmentation faults during app initialization.

Author: 0xbrayo

aw-server/src/android/mod.rs

@@ -82,9 +82,10 @@ pub mod android {
         output.into_raw()
     }
 
-    unsafe fn jstring_to_string(env: &JNIEnv, string: JString) -> String {
-        let c_str = CStr::from_ptr(env.get_string(string).expect("invalid string").as_ptr());
-        String::from(c_str.to_str().unwrap())
+    unsafe fn jstring_to_string(env: &JNIEnv, string: JString) -> Option<String> {
+        let java_str = env.get_string(string).ok()?;
+        let c_str = CStr::from_ptr(java_str.as_ptr());
+        c_str.to_str().ok().map(String::from)
     }
 
     unsafe fn string_to_jstring(env: &JNIEnv, string: String) -> jstring {
@@ -136,7 +137,7 @@ pub mod android {
     pub unsafe extern "C" fn Java_net_activitywatch_android_RustInterface_initialize(
         env: JNIEnv,
         _: JClass,
-    ) {
+    ) -> jstring {
         if !INITIALIZED {
             android_logger::init_once(
                 Config::default()
@@ -154,9 +155,8 @@ pub mod android {
         }
         INITIALIZED = true;
 
-        // Without this it might not work due to weird error probably arising from Rust optimizing away the JNIEnv:
-        //  JNI DETECTED ERROR IN APPLICATION: use of deleted weak global reference
-        string_to_jstring(&env, "test".to_string());
+        // Return a string as expected by Java
+        string_to_jstring(&env, "initialized".to_string())
     }
 
     #[no_mangle]
@@ -165,9 +165,16 @@ pub mod android {
         _: JClass,
         java_dir: JString,
     ) {
-        let path = &jstring_to_string(&env, java_dir);
-        debug!("Setting android data dir as {}", path);
-        dirs::set_android_data_dir(path);
+        match jstring_to_string(&env, java_dir) {
+            Some(path) => {
+                debug!("Setting android data dir as {}", path);
+                dirs::set_android_data_dir(&path);
+            }
+            None => {
+                // Failed to convert string - do nothing and return
+                return;
+            }
+        }
     }
 
     #[no_mangle]
@@ -185,7 +192,10 @@ pub mod android {
         _: JClass,
         java_bucket: JString,
     ) -> jstring {
-        let bucket = jstring_to_string(&env, java_bucket);
+        let bucket = match jstring_to_string(&env, java_bucket) {
+            Some(s) => s,
+            None => return create_error_object(&env, "Failed to parse bucket string".to_string()),
+        };
         let bucket_json: Bucket = match serde_json::from_str(&bucket) {
             Ok(json) => json,
             Err(err) => return create_error_object(&env, err.to_string()),
@@ -207,8 +217,16 @@ pub mod android {
         java_event: JString,
         java_pulsetime: jdouble,
     ) -> jstring {
-        let bucket_id = jstring_to_string(&env, java_bucket_id);
-        let event = jstring_to_string(&env, java_event);
+        let bucket_id = match jstring_to_string(&env, java_bucket_id) {
+            Some(s) => s,
+            None => {
+                return create_error_object(&env, "Failed to parse bucket_id string".to_string())
+            }
+        };
+        let event = match jstring_to_string(&env, java_event) {
+            Some(s) => s,
+            None => return create_error_object(&env, "Failed to parse event string".to_string()),
+        };
         let pulsetime = java_pulsetime as f64;
         let event_json: Event = match serde_json::from_str(&event) {
             Ok(json) => json,
@@ -233,7 +251,12 @@ pub mod android {
         java_bucket_id: JString,
         java_limit: jint,
     ) -> jstring {
-        let bucket_id = jstring_to_string(&env, java_bucket_id);
+        let bucket_id = match jstring_to_string(&env, java_bucket_id) {
+            Some(s) => s,
+            None => {
+                return create_error_object(&env, "Failed to parse bucket_id string".to_string())
+            }
+        };
         let limit = java_limit as u64;
         match openDatastore().get_events(&bucket_id, None, None, Some(limit)) {
             Ok(events) => string_to_jstring(&env, json!(events).to_string()),