feat: support reconnecting websocket

Instead of asking a user to refresh the browser, we let the websocket
reconnect and try to restore the page session.

 * Fixes #254
 * Fixes #161

packages/solara-widget-manager/src/manager.ts

@@ -78,11 +78,15 @@ export class WidgetManager extends JupyterLabManager {
     );
     this._registerWidgets();
     this._loader = requireLoader;
-    const commId = base.uuid();
     const kernel = context.sessionContext?.session?.kernel;
+    this.connectControlComm();
     if (!kernel) {
       throw new Error('No current kernel');
     }
+  }
+  async connectControlComm() {
+    const commId = base.uuid();
+    const kernel = this.context.sessionContext?.session?.kernel;
     this.controlComm = kernel.createComm('solara.control', commId);
     this.controlCommHandler = {
       onMsg: (msg) => {
@@ -107,31 +111,40 @@ export class WidgetManager extends JupyterLabManager {
   }
   async check() {
     // checks if app is still valid (e.g. server restarted and lost the widget state)
-    const okPromise = new Promise((resolve, reject) => {
-      this.controlCommHandler = {
-        onMsg: (msg) => {
+    // if we are connected to the same kernel, we'll get a reply instantly
+    // however, if we are connected to a new kernel, we rely on the timeout
+    // so every time we create a new comm.
+
+    const kernel = this.context.sessionContext?.session?.kernel;
+    const commId = base.uuid();
+    const controlComm = kernel.createComm('solara.control', commId);
+    controlComm.open({}, {}, [])
+    try {
+      return await new Promise((resolve, reject) => {
+        controlComm.onMsg = (msg) => {
           const data = msg['content']['data'];
-          if (data.method === 'finished') {
-            resolve(data.ok);
+          if (data.method === 'check') {
+            if (data.ok === true) {
+              resolve({ ok: true, message: data.message });
+            } else {
+              resolve({ ok: false, message: data.message });
+            }
           }
           else {
-            reject(data.error);
+            reject({ ok: false, message: "unexpected message" });
           }
-        },
-        onClose: () => {
+        }
+        controlComm.onClose = () => {
           console.error("closed solara control comm")
-          reject()
+          reject({ ok: false, message: "closed solara control comm" });
         }
-      };
-      setTimeout(() => {
-        reject('timeout');
-      }, CONTROL_COMM_TIMEOUT);
-    });
-    this.controlComm.send({ method: 'check' });
-    try {
-      return await okPromise;
+        setTimeout(() => {
+          reject('timeout');
+        }, CONTROL_COMM_TIMEOUT);
+        controlComm.send({ method: 'check' });
+      });
     } catch (e) {
-      return false;
+      return { ok: false, message: e };
     }
   }
 

solara/server/app.py

@@ -352,13 +352,23 @@ def on_msg(msg):
             comm.send({"method": "finished", "widget_id": context.container._model_id})
         elif method == "check":
             context = kernel_context.get_current_context()
+            # if there is no container, we never ran the app
+            if context.container is not None:
+                logger.info("Reconnect check: %s is ok", context.id)
+                comm.send({"method": "check", "ok": True, "message": "All fine"})
+            else:
+                logger.info("Reconnect check: %s is not ok", context.id)
+                comm.send({"method": "check", "ok": False, "message": "Not reconnected"})
+
         elif method == "reload":
             assert app is not None
             context = kernel_context.get_current_context()
             path = data.get("path", "")
             with context:
                 load_app_widget(context.state, app, path)
                 comm.send({"method": "finished"})
+        else:
+            logger.error("Unknown comm method called on solara.control comm: %s", method)
 
     comm.on_msg(on_msg)
 

solara/server/static/main-vuetify.js

@@ -158,10 +158,16 @@ async function solaraInit(mountId, appName) {
         }
         if (s.connectionStatus == 'connected' && !skipReconnectedCheck) {
             (async () => {
-                let ok = await widgetManager.check()
-                if (!ok) {
+                if (app.$data.needsRefresh) {
+                    // give up
+                    return;
+                }
+                const msg = await widgetManager.check()
+                if (!msg.ok) {
                     app.$data.needsRefresh = true;
                     await solara.shutdownKernel(kernel);
+                } else {
+                    await widgetManager.fetchAll();
                 }
             })();
         }

tests/integration/reconnect_test.py

@@ -0,0 +1,101 @@
+from pathlib import Path
+from typing import Optional
+
+import playwright.sync_api
+
+import solara
+import solara.server.kernel_context
+
+HERE = Path(__file__).parent
+
+
+set_value = None
+context: Optional["solara.server.kernel_context.VirtualKernelContext"] = None
+
+
+@solara.component
+def Page():
+    global set_value, app_context
+    value, set_value = solara.use_state(0)
+    assert set_value is not None
+    context = solara.server.kernel_context.get_current_context()
+    assert context is not None
+    solara.Text(f"Value {value}")
+
+    def disconnect():
+        assert len(context.kernel.session.websockets) == 1
+        list(context.kernel.session.websockets)[0].close()
+
+    solara.Button("Disconnect", on_click=disconnect)
+    solara.Button("Increment", on_click=lambda: set_value(value + 1))
+
+    def disconnect_and_change():
+        assert len(context.kernel.session.websockets) == 1
+        list(context.kernel.session.websockets)[0].close()
+        set_value(100)
+
+    solara.Button("Disconnect and change", on_click=disconnect_and_change)
+
+
+def test_reconnect_simple(browser: playwright.sync_api.Browser, page_session: playwright.sync_api.Page, solara_server, solara_app, extra_include_path):
+    with extra_include_path(HERE), solara_app("reconnect_test:Page"):
+        page_session.goto(solara_server.base_url)
+        page_session.locator("text=Value 0").wait_for()
+        page_session.locator("text=Increment").click()
+        page_session.locator("text=Value 1").wait_for()
+        assert len(solara.server.kernel_context.contexts) == 1
+        context = list(solara.server.kernel_context.contexts.values())[0]
+        assert len(context.kernel.session.websockets) == 1
+        ws = list(context.kernel.session.websockets)[0]
+        page_session.locator("text=Disconnect").nth(0).click()
+        n = 0
+        # we wait till the current websocket is not connected anymore, and a different one is connected
+        while not (ws not in context.kernel.session.websockets and len(context.kernel.session.websockets) == 1):
+            page_session.wait_for_timeout(100)
+            n += 1
+            if n > 50:
+                raise RuntimeError("Timeout waiting for reconnected websocket")
+        page_session.locator("text=Value 1").wait_for()
+        page_session.locator("text=Increment").click()
+        page_session.locator("text=Value 2").wait_for()
+        # we should not have created a new context
+        assert len(solara.server.kernel_context.contexts) == 1
+
+
+def test_reconnect_fail(browser: playwright.sync_api.Browser, page_session: playwright.sync_api.Page, solara_server, solara_app, extra_include_path):
+    with extra_include_path(HERE), solara_app("reconnect_test:Page"):
+        # import reconnect_test as module
+
+        page_session.goto(solara_server.base_url)
+        page_session.locator("text=Value 0").wait_for()
+        page_session.locator("text=Increment").click()
+        page_session.locator("text=Value 1").wait_for()
+        cull_timeout_previous = solara.server.settings.kernel.cull_timeout
+        try:
+            solara.server.settings.kernel.cull_timeout = "0s"
+            assert len(solara.server.kernel_context.contexts) == 1
+            context = list(solara.server.kernel_context.contexts.values())[0]
+            assert len(context.kernel.session.websockets) == 1
+            page_session.locator("text=Disconnect").nth(0).click()
+            page_session.locator("text=Could not restore session").wait_for()
+            n = 0
+            # we wait till the all contexts are closed
+            while len(solara.server.kernel_context.contexts):
+                page_session.wait_for_timeout(100)
+                n += 1
+                if n > 50:
+                    raise RuntimeError("Timeout waiting for kernel shutdown")
+
+        finally:
+            solara.server.settings.kernel.cull_timeout = cull_timeout_previous
+
+
+def test_reconnect_and_update(browser: playwright.sync_api.Browser, page_session: playwright.sync_api.Page, solara_server, solara_app, extra_include_path):
+    with extra_include_path(HERE), solara_app("reconnect_test:Page"):
+        page_session.goto(solara_server.base_url)
+        page_session.locator("text=Value 0").wait_for()
+        page_session.locator("text=Increment").click()
+        page_session.locator("text=Value 1").wait_for()
+        # this will disconnect, and aftwards change something so the websocket queue feature is used
+        page_session.locator("text=Disconnect and change").click()
+        page_session.locator("text=Value 100").wait_for()