Merge pull request #15 from ianthomas23/sync_get_stdin

Use blocking synchronous get_stdin for input_request

Author: ianthomas23

.github/workflows/main.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        emsdk: ["3.1.45", "latest"]
+        emsdk: ["3.1.73", "4.0.3"]
     steps:
       - uses: actions/checkout@v4
       - uses: docker-practice/actions-setup-docker@master

BuildWasmDockerfile

@@ -1,4 +1,4 @@
-ARG EMSCRIPTEN_VER=3.1.45
+ARG EMSCRIPTEN_VER=3.1.73
 FROM emscripten/emsdk:$EMSCRIPTEN_VER
 
 ARG USER_ID

src/xserver_emscripten.cpp

@@ -13,13 +13,22 @@ namespace ems = emscripten;
 
 namespace xeus
 {
-    EM_JS(ems::EM_VAL, get_stdin, (), {
-      return Asyncify.handleAsync(() => {
-        return globalThis.get_stdin().then(msg => {
-          return Emval.toHandle(msg);
-        });
-      });
-    });
+    // Get input from stdin by sending the input_request message and receiving back the
+    // input_reply.  This is blocking (synchronous) from the point of view of the lite
+    // kernel running in its WebWorker. The implementation in the main UI thread is async.
+    //
+    // It calls the globalThis.get_stdin defined in jupyterlite/xeus.
+    //
+    // Here implemented as a C function which is simpler than the equivalent EM_JS
+    // function:
+    //     EM_JS(ems::EM_VAL, get_stdin, (ems::EM_VAL input_request), {
+    //         return Emval.toHandle(globalThis.get_stdin(Emval.toValue(input_request)));
+    //     });
+    // and the EM_JS function fails at runtime as it lacks an autogenerated signature.
+    inline ems::val get_stdin(ems::val input_request)
+    {
+      return emscripten::val::global("self").call<ems::val>("get_stdin", input_request);
+    }
 
     // we use this instead of EM_JS since this is more robust.
     // EM_JS functions where somewhat undefined  / buggy when
@@ -94,11 +103,20 @@ namespace xeus
 
     void xserver_emscripten::send_stdin_impl(xmessage message) 
     {
-        post_kernel_message("stdin", js_message_from_xmessage(message, true));
         // Block until a response to the input request is received.
-        ems::val js_message = ems::val::take_ownership(get_stdin());
+        // input_request messages are sent via get_stdin rather than post_kernel_message.
+        ems::val msg = js_message_from_xmessage(message, true);
+        msg.set("channel", emscripten::val("stdin"));
+        ems::val js_message = get_stdin(msg);
+
         try
         {
+            if (js_message.hasOwnProperty("error"))
+            {
+                std::string error_msg = js_message["error"].as<std::string>();
+                throw std::runtime_error(error_msg);
+            }
+
             auto reply = xmessage_from_js_message(js_message);
             xserver::notify_stdin_listener(std::move(reply));
         }