fix(unix): race condition on script eval (#815)

* fix(linux): race condition on script eval

When evaluating scripts immediately after creating a webview on Linux, the script runs before the page is ready, so it gets lost or fails to execute. This commit changes it to be similar to other platforms, where the evaluated scripts are executed after the initialization scripts. This issue was raised in tauri-apps/tauri#5615

* do the same on macOS

.changes/eval-race-condition.md

@@ -0,0 +1,5 @@
+---
+"wry": patch
+---
+
+Evaluate scripts after the page load starts on Linux and macOS.

src/webview/webkitgtk/mod.rs

@@ -15,11 +15,12 @@ use std::{
   collections::hash_map::DefaultHasher,
   hash::{Hash, Hasher},
   rc::Rc,
+  sync::Mutex,
 };
 use url::Url;
 use webkit2gtk::{
-  traits::*, NavigationPolicyDecision, PolicyDecisionType, UserContentInjectedFrames, UserScript,
-  UserScriptInjectionTime, WebView, WebViewBuilder,
+  traits::*, LoadEvent, NavigationPolicyDecision, PolicyDecisionType, UserContentInjectedFrames,
+  UserScript, UserScriptInjectionTime, WebView, WebViewBuilder,
 };
 use webkit2gtk_sys::{
   webkit_get_major_version, webkit_get_micro_version, webkit_get_minor_version,
@@ -42,6 +43,7 @@ pub(crate) struct InnerWebView {
   pub webview: Rc<WebView>,
   #[cfg(any(debug_assertions, feature = "devtools"))]
   is_inspector_open: Arc<AtomicBool>,
+  pending_scripts: Arc<Mutex<Option<Vec<String>>>>,
 }
 
 impl InnerWebView {
@@ -323,6 +325,7 @@ impl InnerWebView {
       webview,
       #[cfg(any(debug_assertions, feature = "devtools"))]
       is_inspector_open,
+      pending_scripts: Arc::new(Mutex::new(Some(Vec::new()))),
     };
 
     // Initialize message handler
@@ -355,6 +358,20 @@ impl InnerWebView {
       w.webview.load_html(&html, Some("http://localhost"));
     }
 
+    let pending_scripts = w.pending_scripts.clone();
+    w.webview.connect_load_changed(move |webview, event| {
+      if let LoadEvent::Committed = event {
+        let mut pending_scripts_ = pending_scripts.lock().unwrap();
+        if let Some(pending_scripts) = &*pending_scripts_ {
+          let cancellable: Option<&Cancellable> = None;
+          for script in pending_scripts {
+            webview.run_javascript(script, cancellable, |_| ());
+          }
+          *pending_scripts_ = None;
+        }
+      }
+    });
+
     Ok(w)
   }
 
@@ -369,8 +386,12 @@ impl InnerWebView {
   }
 
   pub fn eval(&self, js: &str) -> Result<()> {
-    let cancellable: Option<&Cancellable> = None;
-    self.webview.run_javascript(js, cancellable, |_| ());
+    if let Some(pending_scripts) = &mut *self.pending_scripts.lock().unwrap() {
+      pending_scripts.push(js.into());
+    } else {
+      let cancellable: Option<&Cancellable> = None;
+      self.webview.run_javascript(js, cancellable, |_| ());
+    }
     Ok(())
   }
 

src/webview/wkwebview/mod.rs

@@ -24,6 +24,7 @@ use std::{
   ptr::{null, null_mut},
   rc::Rc,
   slice, str,
+  sync::{Arc, Mutex},
 };
 
 use core_graphics::geometry::CGRect;
@@ -71,6 +72,7 @@ pub(crate) struct InnerWebView {
   #[cfg(target_os = "macos")]
   pub ns_window: id,
   pub manager: id,
+  pending_scripts: Arc<Mutex<Option<Vec<String>>>>,
   // Note that if following functions signatures are changed in the future,
   // all functions pointer declarations in objc callbacks below all need to get updated.
   ipc_handler_ptr: *mut (Box<dyn Fn(&Window, String)>, Rc<Window>),
@@ -402,20 +404,21 @@ impl InnerWebView {
               let has_download_handler = &mut *(*has_download_handler as *mut Box<bool>);
               if **has_download_handler {
                 (*handler).call((2,));
+              } else {
+                (*handler).call((0,));
               }
+            } else {
+              (*handler).call((0,));
             }
           } else {
-            let function = this.get_ivar::<*mut c_void>("function");
+            let function = this.get_ivar::<*mut c_void>("navigation_policy_function");
             if !function.is_null() {
               let function = &mut *(*function as *mut Box<dyn for<'s> Fn(String, bool) -> bool>);
               match (function)(url.to_str().to_string(), is_main_frame) {
                 true => (*handler).call((1,)),
                 false => (*handler).call((0,)),
               };
             } else {
-              log::warn!(
-                "WebView instance is dropped! This navigation handler shouldn't be called."
-              );
               (*handler).call((1,));
             }
           }
@@ -449,31 +452,58 @@ impl InnerWebView {
         }
       }
 
+      extern "C" fn did_commit_navigation(this: &Object, _: Sel, webview: id, _navigation: id) {
+        unsafe {
+          let pending_scripts_ptr: *mut c_void = *this.get_ivar("pending_scripts");
+          let pending_scripts = &(*(pending_scripts_ptr as *mut Arc<Mutex<Option<Vec<String>>>>));
+          let mut pending_scripts_ = pending_scripts.lock().unwrap();
+          if let Some(pending_scripts) = &*pending_scripts_ {
+            for script in pending_scripts {
+              let _: id = msg_send![webview, evaluateJavaScript:NSString::new(script) completionHandler:null::<*const c_void>()];
+            }
+            *pending_scripts_ = None;
+          }
+        }
+      }
+
+      let pending_scripts = Arc::new(Mutex::new(Some(Vec::new())));
+
+      let navigation_delegate_cls = match ClassDecl::new("UIViewController", class!(NSObject)) {
+        Some(mut cls) => {
+          cls.add_ivar::<*mut c_void>("pending_scripts");
+          cls.add_ivar::<*mut c_void>("navigation_policy_function");
+          cls.add_ivar::<*mut c_void>("HasDownloadHandler");
+          cls.add_method(
+            sel!(webView:decidePolicyForNavigationAction:decisionHandler:),
+            navigation_policy as extern "C" fn(&Object, Sel, id, id, id),
+          );
+          cls.add_method(
+            sel!(webView:decidePolicyForNavigationResponse:decisionHandler:),
+            navigation_policy_response as extern "C" fn(&Object, Sel, id, id, id),
+          );
+          cls.add_method(
+            sel!(webView:didCommitNavigation:),
+            did_commit_navigation as extern "C" fn(&Object, Sel, id, id),
+          );
+          add_download_methods(&mut cls);
+          cls.register()
+        }
+        None => class!(UIViewController),
+      };
+
+      let navigation_policy_handler: id = msg_send![navigation_delegate_cls, new];
+
+      (*navigation_policy_handler).set_ivar(
+        "pending_scripts",
+        Box::into_raw(Box::new(pending_scripts.clone())) as *mut c_void,
+      );
+
       let (navigation_decide_policy_ptr, download_delegate) = if attributes
         .navigation_handler
         .is_some()
         || attributes.new_window_req_handler.is_some()
         || attributes.download_started_handler.is_some()
       {
-        let cls = match ClassDecl::new("UIViewController", class!(NSObject)) {
-          Some(mut cls) => {
-            cls.add_ivar::<*mut c_void>("function");
-            cls.add_ivar::<*mut c_void>("HasDownloadHandler");
-            cls.add_method(
-              sel!(webView:decidePolicyForNavigationAction:decisionHandler:),
-              navigation_policy as extern "C" fn(&Object, Sel, id, id, id),
-            );
-            cls.add_method(
-              sel!(webView:decidePolicyForNavigationResponse:decisionHandler:),
-              navigation_policy_response as extern "C" fn(&Object, Sel, id, id, id),
-            );
-            add_download_methods(&mut cls);
-            cls.register()
-          }
-          None => class!(UIViewController),
-        };
-
-        let handler: id = msg_send![cls, new];
         let function_ptr = {
           let navigation_handler = attributes.navigation_handler;
           let new_window_req_handler = attributes.new_window_req_handler;
@@ -491,16 +521,18 @@ impl InnerWebView {
             }) as Box<dyn Fn(String, bool) -> bool>,
           ))
         };
-        (*handler).set_ivar("function", function_ptr as *mut _ as *mut c_void);
+        (*navigation_policy_handler).set_ivar(
+          "navigation_policy_function",
+          function_ptr as *mut _ as *mut c_void,
+        );
 
         let has_download_handler = Box::into_raw(Box::new(Box::new(
           attributes.download_started_handler.is_some(),
         )));
-        (*handler).set_ivar(
+        (*navigation_policy_handler).set_ivar(
           "HasDownloadHandler",
           has_download_handler as *mut _ as *mut c_void,
         );
-        let _: () = msg_send![webview, setNavigationDelegate: handler];
 
         // Download handler
         let download_delegate = if attributes.download_started_handler.is_some()
@@ -538,9 +570,9 @@ impl InnerWebView {
               .set_ivar("completed", download_completed_ptr as *mut _ as *mut c_void);
           }
 
-          set_download_delegate(handler, download_delegate);
+          set_download_delegate(navigation_policy_handler, download_delegate);
 
-          handler
+          navigation_policy_handler
         } else {
           null_mut()
         };
@@ -550,6 +582,8 @@ impl InnerWebView {
         (null_mut(), null_mut())
       };
 
+      let _: () = msg_send![webview, setNavigationDelegate: navigation_policy_handler];
+
       // File upload panel handler
       extern "C" fn run_file_upload_panel(
         _this: &Object,
@@ -647,6 +681,7 @@ impl InnerWebView {
         #[cfg(target_os = "macos")]
         ns_window,
         manager,
+        pending_scripts,
         ipc_handler_ptr,
         navigation_decide_policy_ptr,
         #[cfg(target_os = "macos")]
@@ -753,9 +788,13 @@ r#"Object.defineProperty(window, 'ipc', {
   }
 
   pub fn eval(&self, js: &str) -> Result<()> {
-    // Safety: objc runtime calls are unsafe
-    unsafe {
-      let _: id = msg_send![self.webview, evaluateJavaScript:NSString::new(js) completionHandler:null::<*const c_void>()];
+    if let Some(scripts) = &mut *self.pending_scripts.lock().unwrap() {
+      scripts.push(js.into());
+    } else {
+      // Safety: objc runtime calls are unsafe
+      unsafe {
+        let _: id = msg_send![self.webview, evaluateJavaScript:NSString::new(js) completionHandler:null::<*const c_void>()];
+      }
     }
     Ok(())
   }