fix(app, app-shell, app-shell-odd): block initial HTTP request until …

…successful MQTT subscription (#15094)

Closes EXEC-429

Currently, the desktop app/ODD attempt to address the "missed update problem" in the following way: while we subscribe to a topic, we simultaneously GET whatever equivalent HTTP resource we just subscribed to. However, there's definitely a world (albeit a very small one) in which we receive the HTTP response, a server update occurs, the server publishes, and then we successfully subscribe to a topic. In this world, we've missed the update event.

Solve for this by simply refetching right after the client subscribe ACKs. We still keep the initial fetch on mount to keep latency low.

app-shell-odd/src/notifications/deserialize.ts

@@ -31,6 +31,10 @@ export function sendDeserialized(
   } catch {} // Prevents shell erroring during app shutdown event.
 }
 
+export function sendDeserializedRefetch(topic: NotifyTopic): void {
+  sendDeserialized(topic, { refetch: true })
+}
+
 export function sendDeserializedGenericError(topic: NotifyTopic): void {
   sendDeserialized(topic, FAILURE_STATUSES.ECONNFAILED)
 }

app-shell-odd/src/notifications/subscribe.ts

@@ -1,7 +1,11 @@
 import mqtt from 'mqtt'
 
 import { connectionStore } from './store'
-import { sendDeserialized, sendDeserializedGenericError } from './deserialize'
+import {
+  sendDeserialized,
+  sendDeserializedGenericError,
+  sendDeserializedRefetch,
+} from './deserialize'
 import { notifyLog } from './notifyLog'
 
 import type { NotifyTopic } from '@opentrons/app/src/redux/shell/types'
@@ -30,8 +34,8 @@ export function subscribe(topic: NotifyTopic): Promise<void> {
         if (client == null) {
           return Promise.reject(new Error('Expected hostData, received null.'))
         }
-
-        if (
+        // The first time the client wants to subscribe on a robot to a particular topic.
+        else if (
           !connectionStore.isActiveSub(topic) &&
           !connectionStore.isPendingSub(topic)
         ) {
@@ -44,13 +48,15 @@ export function subscribe(topic: NotifyTopic): Promise<void> {
                 })
             )
             .catch((error: Error) => notifyLog.debug(error.message))
-        } else {
-          void waitUntilActiveOrErrored('subscription', topic).catch(
-            (error: Error) => {
+        }
+        // The client is either already subscribed or the subscription is currently pending.
+        else {
+          void waitUntilActiveOrErrored('subscription', topic)
+            .then(() => sendDeserializedRefetch(topic))
+            .catch((error: Error) => {
               notifyLog.debug(error.message)
               sendDeserializedGenericError(topic)
-            }
-          )
+            })
         }
       })
       .catch((error: Error) => {
@@ -74,6 +80,8 @@ export function subscribe(topic: NotifyTopic): Promise<void> {
       connectionStore
         .setSubStatus(topic, 'subscribed')
         .catch((error: Error) => notifyLog.debug(error.message))
+
+      sendDeserializedRefetch(topic)
     }
   }
 }

app-shell/src/notifications/deserialize.ts

@@ -33,6 +33,14 @@ export function sendDeserialized({
   } catch {} // Prevents shell erroring during app shutdown event.
 }
 
+export function sendDeserializedRefetch(ip: string, topic: NotifyTopic): void {
+  sendDeserialized({
+    ip,
+    topic,
+    message: { refetch: true },
+  })
+}
+
 export function sendDeserializedGenericError(
   ip: string,
   topic: NotifyTopic

app-shell/src/notifications/subscribe.ts

@@ -1,7 +1,11 @@
 import mqtt from 'mqtt'
 
 import { connectionStore } from './store'
-import { sendDeserialized, sendDeserializedGenericError } from './deserialize'
+import {
+  sendDeserialized,
+  sendDeserializedGenericError,
+  sendDeserializedRefetch,
+} from './deserialize'
 import { notifyLog } from './notifyLog'
 
 import type { NotifyTopic } from '@opentrons/app/src/redux/shell/types'
@@ -36,8 +40,8 @@ export function subscribe(ip: string, topic: NotifyTopic): Promise<void> {
         if (client == null) {
           return Promise.reject(new Error('Expected hostData, received null.'))
         }
-
-        if (
+        // The first time the client wants to subscribe on a robot to a particular topic.
+        else if (
           !connectionStore.isActiveSub(robotName, topic) &&
           !connectionStore.isPendingSub(robotName, topic)
         ) {
@@ -50,16 +54,20 @@ export function subscribe(ip: string, topic: NotifyTopic): Promise<void> {
                 })
             )
             .catch((error: Error) => notifyLog.debug(error.message))
-        } else {
+        }
+        // The client is either already subscribed or the subscription is currently pending.
+        else {
           void waitUntilActiveOrErrored({
             connection: 'subscription',
             ip,
             robotName,
             topic,
-          }).catch((error: Error) => {
-            notifyLog.debug(error.message)
-            sendDeserializedGenericError(ip, topic)
           })
+            .then(() => sendDeserializedRefetch(ip, topic))
+            .catch((error: Error) => {
+              notifyLog.debug(error.message)
+              sendDeserializedGenericError(ip, topic)
+            })
         }
       })
       .catch((error: Error) => {
@@ -81,6 +89,8 @@ export function subscribe(ip: string, topic: NotifyTopic): Promise<void> {
       connectionStore
         .setSubStatus(ip, topic, 'subscribed')
         .catch((error: Error) => notifyLog.debug(error.message))
+
+      sendDeserializedRefetch(ip, topic)
     }
   }
 }

app/src/resources/useNotifyService.ts

@@ -56,7 +56,7 @@ export function useNotifyService<TData, TError = Error>({
 
   React.useEffect(() => {
     if (shouldUseNotifications) {
-      // Always fetch on initial mount.
+      // Always fetch on initial mount to keep latency as low as possible.
       setRefetch('once')
       appShellListener({
         hostname,