fix(android): drop MainPipe on activity destroy (#1415)

fixes a memory leak when the activity is destroyed but the app is opened in the foreground

ref tauri-apps/tauri#11609

Author: lucasfernog

src/android/binding.rs

@@ -32,6 +32,8 @@ macro_rules! android_binding {
   ($domain:ident, $package:ident, $wry:path) => {{
     use $wry::{android_setup as _, prelude::*};
 
+    android_fn!($domain, $package, WryActivity, onActivityDestroy, [JObject]);
+
     android_fn!(
       $domain,
       $package,
@@ -258,6 +260,11 @@ fn handle_request(
   Ok(*JObject::null())
 }
 
+#[allow(non_snake_case)]
+pub unsafe fn onActivityDestroy(_: JNIEnv, _: JClass, _: JObject) {
+  super::MainPipe::send(super::WebViewMessage::OnDestroy);
+}
+
 #[allow(non_snake_case)]
 pub unsafe fn handleRequest(
   mut env: JNIEnv,

src/android/kotlin/WryActivity.kt

@@ -93,6 +93,7 @@ abstract class WryActivity : AppCompatActivity() {
     override fun onDestroy() {
         super.onDestroy()
         destroy()
+        onActivityDestroy()
     }
 
     override fun onLowMemory() {
@@ -125,6 +126,7 @@ abstract class WryActivity : AppCompatActivity() {
     private external fun stop()
     private external fun save()
     private external fun destroy()
+    private external fun onActivityDestroy()
     private external fun memory()
     private external fun focus(focus: Boolean)
 

src/android/main_pipe.rs

@@ -21,6 +21,11 @@ pub static MAIN_PIPE: Lazy<[OwnedFd; 2]> = Lazy::new(|| {
   unsafe { pipe.map(|fd| OwnedFd::from_raw_fd(fd)) }
 });
 
+pub enum MainPipeState {
+  Alive,
+  Destroyed,
+}
+
 pub struct MainPipe<'a> {
   pub env: JNIEnv<'a>,
   pub activity: GlobalRef,
@@ -42,7 +47,7 @@ impl<'a> MainPipe<'a> {
     }
   }
 
-  pub fn recv(&mut self) -> JniResult<()> {
+  pub fn recv(&mut self) -> JniResult<MainPipeState> {
     let activity = self.activity.as_obj();
     if let Ok(message) = CHANNEL.1.recv() {
       match message {
@@ -341,9 +346,12 @@ impl<'a> MainPipe<'a> {
             .unwrap();
           }
         }
+        WebViewMessage::OnDestroy => {
+          return Ok(MainPipeState::Destroyed);
+        }
       }
     }
-    Ok(())
+    Ok(MainPipeState::Alive)
   }
 }
 
@@ -413,6 +421,7 @@ pub(crate) enum WebViewMessage {
   LoadUrl(String, Option<http::HeaderMap>),
   LoadHtml(String),
   ClearAllBrowsingData,
+  OnDestroy,
 }
 
 pub(crate) struct CreateWebViewAttributes {

src/android/mod.rs

@@ -27,15 +27,17 @@ use std::{
   collections::HashMap,
   os::fd::{AsFd as _, AsRawFd as _},
   sync::{mpsc::channel, Mutex},
+  time::Duration,
 };
 
 pub(crate) mod binding;
 mod main_pipe;
-use main_pipe::{CreateWebViewAttributes, MainPipe, WebViewMessage, MAIN_PIPE};
+use main_pipe::{CreateWebViewAttributes, MainPipe, MainPipeState, WebViewMessage, MAIN_PIPE};
 
 use crate::util::Counter;
 
 static COUNTER: Counter = Counter::new();
+const MAIN_PIPE_TIMEOUT: Duration = Duration::from_secs(10);
 
 pub struct Context<'a, 'b> {
   pub env: &'a mut JNIEnv<'b>,
@@ -133,8 +135,11 @@ pub unsafe fn android_setup(
       let size = std::mem::size_of::<bool>();
       let mut wake = false;
       if libc::read(fd.as_raw_fd(), &mut wake as *mut _ as *mut _, size) == size as libc::ssize_t {
-        main_pipe.recv().is_ok()
+        let res = main_pipe.recv();
+        // unregister itself on errors or destroy event
+        matches!(res, Ok(MainPipeState::Alive))
       } else {
+        // unregister itself
         false
       }
     })
@@ -300,7 +305,7 @@ impl InnerWebView {
               });
 
             (custom_protocol.1)(webview_id, request, RequestAsyncResponder { responder });
-            return Some(rx.recv().unwrap());
+            return Some(rx.recv_timeout(MAIN_PIPE_TIMEOUT).unwrap());
           }
           None
         },
@@ -337,7 +342,7 @@ impl InnerWebView {
   pub fn url(&self) -> crate::Result<String> {
     let (tx, rx) = bounded(1);
     MainPipe::send(WebViewMessage::GetUrl(tx));
-    rx.recv().map_err(Into::into)
+    rx.recv_timeout(MAIN_PIPE_TIMEOUT).map_err(Into::into)
   }
 
   pub fn eval(&self, js: &str, callback: Option<impl Fn(String) + Send + 'static>) -> Result<()> {
@@ -391,7 +396,7 @@ impl InnerWebView {
   pub fn cookies_for_url(&self, url: &str) -> Result<Vec<cookie::Cookie<'static>>> {
     let (tx, rx) = bounded(1);
     MainPipe::send(WebViewMessage::GetCookies(tx, url.to_string()));
-    rx.recv().map_err(Into::into)
+    rx.recv_timeout(MAIN_PIPE_TIMEOUT).map_err(Into::into)
   }
 
   pub fn cookies(&self) -> Result<Vec<cookie::Cookie<'static>>> {
@@ -440,7 +445,7 @@ impl JniHandle {
 pub fn platform_webview_version() -> Result<String> {
   let (tx, rx) = bounded(1);
   MainPipe::send(WebViewMessage::GetWebViewVersion(tx));
-  rx.recv().unwrap()
+  rx.recv_timeout(MAIN_PIPE_TIMEOUT).unwrap()
 }
 
 fn with_html_head<F: FnOnce(&NodeRef)>(document: &mut NodeRef, f: F) {

src/error.rs

@@ -28,6 +28,9 @@ pub enum Error {
   NulError(#[from] std::ffi::NulError),
   #[error(transparent)]
   ReceiverError(#[from] std::sync::mpsc::RecvError),
+  #[cfg(target_os = "android")]
+  #[error(transparent)]
+  ReceiverTimeoutError(#[from] crossbeam_channel::RecvTimeoutError),
   #[error(transparent)]
   SenderError(#[from] std::sync::mpsc::SendError<String>),
   #[error("Failed to send the message")]