Use ensure_async to shut down kernel

share/jupyter/voila/templates/base/static/main.js

@@ -52,7 +52,7 @@ require([window.voila_js_url || 'static/voila'], function(voila) {
             // it seems if we attach this to early, it will not be called
             const matches = document.cookie.match('\\b_xsrf=([^;]*)\\b');
             const xsrfToken = (matches && matches[1]) || '';
-            const  configData = JSON.parse(document.getElementById('jupyter-config-data').textContent);
+            const configData = JSON.parse(document.getElementById('jupyter-config-data').textContent);
             const baseUrl = configData.baseUrl;
             window.addEventListener('beforeunload', function (e) {
                 const data = new FormData();

tests/app/shutdown_kernel_test.py

@@ -0,0 +1,12 @@
+import re
+
+
+async def test_shutdown_handler(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
+    html_text = response.body.decode('utf-8')
+    pattern = r"""kernelId": ["']([0-9a-zA-Z-]+)["']"""
+    groups = re.findall(pattern, html_text)
+    kernel_id = groups[0]
+    shutdown_url = f'{base_url}voila/api/shutdown/{kernel_id}'
+    shutdown_response = await http_server_client.fetch(shutdown_url, method='POST', body=b'')
+    assert shutdown_response.code == 204

voila/shutdown_kernel_handler.py

@@ -1,5 +1,6 @@
 import tornado
 from jupyter_server.base.handlers import APIHandler
+from nbclient.util import ensure_async
 
 
 class VoilaShutdownKernelHandler(APIHandler):
@@ -8,6 +9,6 @@ class VoilaShutdownKernelHandler(APIHandler):
 
     @tornado.web.authenticated
     async def post(self, kernel_id):
-        await self.kernel_manager.shutdown_kernel(kernel_id)
+        await ensure_async(self.kernel_manager.shutdown_kernel(kernel_id))
         self.set_status(204)
         self.finish()