fix(core): IPC fallback hanging when sending responses, closes #10327 (#10582)

The IPC fallback system kicks in when the custom protocol implementation cannot be used (e.g. CORS issues).
The fallback uses the postMessage mechanism, which by default uses channels to send large responses. If the custom protocol implementation cannot be used, we should not use channels, but eval the response directly.

.changes/fix-ipc-fallback.md

@@ -0,0 +1,5 @@
+---
+"tauri": patch:bug
+---
+
+Fix IPC fallback (postMessage implementation when custom protocol fails) hanging when sending responses.

core/tauri/scripts/ipc-protocol.js

@@ -62,7 +62,11 @@
             )
           }
         })
-        .catch(() => {
+        .catch((e) => {
+          console.warn(
+            'IPC custom protocol failed, Tauri will now use the postMessage interface instead',
+            e
+          )
           // failed to use the custom protocol IPC (either the webview blocked a custom protocol or it was a CSP error)
           // so we need to fallback to the postMessage interface
           customProtocolIpcFailed = true
@@ -74,7 +78,10 @@
         cmd,
         callback,
         error,
-        options,
+        options: {
+          ...options,
+          customProtocolIpcBlocked: customProtocolIpcFailed
+        },
         payload,
         __TAURI_INVOKE_KEY__
       })

core/tauri/src/ipc/protocol.rs

@@ -174,6 +174,7 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
 
     use serde::{Deserialize, Deserializer};
 
+    #[derive(Default)]
     pub(crate) struct HeaderMap(http::HeaderMap);
 
     impl<'de> Deserialize<'de> for HeaderMap {
@@ -199,9 +200,13 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
       }
     }
 
-    #[derive(Deserialize)]
+    #[derive(Deserialize, Default)]
+    #[serde(rename_all = "camelCase")]
     struct RequestOptions {
+      #[serde(default)]
       headers: HeaderMap,
+      #[serde(default)]
+      custom_protocol_ipc_blocked: bool,
     }
 
     #[derive(Deserialize)]
@@ -260,13 +265,15 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
 
     match message {
       Ok(message) => {
+        let options = message.options.unwrap_or_default();
+
         let request = InvokeRequest {
           cmd: message.cmd,
           callback: message.callback,
           error: message.error,
           url: Url::parse(&request.uri().to_string()).expect("invalid IPC request URL"),
           body: message.payload.into(),
-          headers: message.options.map(|o| o.headers.0).unwrap_or_default(),
+          headers: options.headers.0,
           invoke_key: message.invoke_key,
         };
 
@@ -293,9 +300,7 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
             .entered();
 
             // the channel data command is the only command that uses a custom protocol on Linux
-            if webview.manager().webview.invoke_responder.is_none()
-              && cmd != crate::ipc::channel::FETCH_CHANNEL_DATA_COMMAND
-            {
+            if webview.manager().webview.invoke_responder.is_none() {
               fn responder_eval<R: Runtime>(
                 webview: &crate::Webview<R>,
                 js: crate::Result<String>,
@@ -310,6 +315,10 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
                 let _ = webview.eval(&eval_js);
               }
 
+              let can_use_channel_for_response = cmd
+                != crate::ipc::channel::FETCH_CHANNEL_DATA_COMMAND
+                && !options.custom_protocol_ipc_blocked;
+
               #[cfg(feature = "tracing")]
               let _response_span = tracing::trace_span!(
                 "ipc::request::response",
@@ -327,6 +336,7 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
                 InvokeResponse::Ok(InvokeBody::Json(v)) => {
                   if !(cfg!(target_os = "macos") || cfg!(target_os = "ios"))
                     && matches!(v, JsonValue::Object(_) | JsonValue::Array(_))
+                    && can_use_channel_for_response
                   {
                     let _ = Channel::from_callback_fn(webview, callback).send(v);
                   } else {
@@ -338,7 +348,10 @@ fn handle_ipc_message<R: Runtime>(request: Request<String>, manager: &AppManager
                   }
                 }
                 InvokeResponse::Ok(InvokeBody::Raw(v)) => {
-                  if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
+                  if cfg!(target_os = "macos")
+                    || cfg!(target_os = "ios")
+                    || !can_use_channel_for_response
+                  {
                     responder_eval(
                       &webview,
                       format_callback_result(Result::<_, ()>::Ok(v), callback, error),