Handle disconnection events whilst executing requests

Summary:
If there's a device client disconnect during request execution, no response is ever given back to the client (flipperd).

This change effectively subscribes to client disconnect events and notifies flipperd of any disconnection during request processing.

Reviewed By: passy

Differential Revision: D37787986

fbshipit-source-id: 31737a50b83b0cbe4141ce814064aebef7e09bfc

desktop/flipper-server-companion/src/companion.tsx

@@ -378,7 +378,23 @@ export class FlipperServerCompanion {
         );
       }
 
-      return pluginInstance.companionApi[api](...(params ?? []));
+      return new Promise(async (resolve, reject) => {
+        const closeHandle = () => {
+          reject(new Error('Client disconnected whilst executing request'));
+        };
+        client.once('close', closeHandle);
+
+        try {
+          const response = await pluginInstance.companionApi[api](
+            ...(params ?? []),
+          );
+          resolve(response);
+        } catch (error) {
+          reject(error);
+        } finally {
+          client.off('close', closeHandle);
+        }
+      });
     },
     'companion-plugin-subscribe': async (clientId, pluginId, api) => {
       const client = this.clients.get(clientId);