Attach connection handler earlier

Summary:
This change attaches our event handlers as soon as the ws is created.

As a consequence, we need to wait until the server has created any necessary instances required to process incoming requests.

To achieve this, I created a type called `Lazy`.

This type wraps around a value and a promise to that value. Callers can check if the value is set. If not, callers can wait for it.

Ultimately, the value can be set outside of the promise itself.

Reviewed By: passy

Differential Revision: D37284939

fbshipit-source-id: 17dec548d7155a3d65440c9584cec07cbb826c37

desktop/flipper-server-core/src/server/attachSocketServer.tsx

@@ -42,8 +42,8 @@ const safe = (f: () => void) => {
  * @param socket A ws socket on which to listen for events.
  */
 export function attachSocketServer(
-  flipperServer: FlipperServerImpl,
   socket: WebSocketServer,
+  server: FlipperServerImpl,
   companionEnv: FlipperServerCompanionEnv,
 ) {
   socket.on('connection', (client, req) => {
@@ -53,7 +53,6 @@ export function attachSocketServer(
       '';
 
     console.log('Client connected', clientAddress);
-
     let connected = true;
 
     let flipperServerCompanion: FlipperServerCompanion | undefined;
@@ -62,7 +61,7 @@ export function attachSocketServer(
 
       if (params.get('server_companion')) {
         flipperServerCompanion = new FlipperServerCompanion(
-          flipperServer,
+          server,
           getLogger(),
           companionEnv.pluginInitializer.initialPlugins,
         );
@@ -112,7 +111,7 @@ export function attachSocketServer(
       client.send(JSON.stringify(message));
     }
 
-    flipperServer.onAny(onServerEvent);
+    server.onAny(onServerEvent);
 
     async function onServerCompanionEvent(event: string, payload: any) {
       const message = {
@@ -167,7 +166,7 @@ export function attachSocketServer(
 
           const execRes = flipperServerCompanion?.canHandleCommand(command)
             ? flipperServerCompanion.exec(command, ...args)
-            : flipperServer.exec(command, ...args);
+            : server.exec(command, ...args);
 
           execRes
             .then((result: any) => {
@@ -229,7 +228,7 @@ export function attachSocketServer(
       }
 
       connected = false;
-      flipperServer.offAny(onServerEvent);
+      server.offAny(onServerEvent);
       flipperServerCompanion?.destroyAll();
     }
 

desktop/flipper-server-core/src/server/startServer.tsx

@@ -20,6 +20,9 @@ import {makeSocketPath, checkSocketInUse} from './utilities';
 
 import proxy from 'http-proxy';
 import exitHook from 'exit-hook';
+import {attachSocketServer} from './attachSocketServer';
+import {FlipperServerImpl} from '../FlipperServerImpl';
+import {FlipperServerCompanionEnv} from 'flipper-server-companion';
 
 type Config = {
   port: number;
@@ -27,6 +30,11 @@ type Config = {
   entry: string;
 };
 
+type ReadyForConnections = (
+  server: FlipperServerImpl,
+  companionEnv: FlipperServerCompanionEnv,
+) => Promise<void>;
+
 /**
  * Orchestrates the creation of the HTTP server, proxy, and web socket.
  * @param config Server configuration.
@@ -36,14 +44,9 @@ export async function startServer(config: Config): Promise<{
   app: Express;
   server: http.Server;
   socket: WebSocketServer;
+  readyForIncomingConnections: ReadyForConnections;
 }> {
-  const {app, server} = await startHTTPServer(config);
-  const socket = addWebsocket(server, config);
-  return {
-    app,
-    server,
-    socket,
-  };
+  return await startHTTPServer(config);
 }
 
 /**
@@ -52,9 +55,12 @@ export async function startServer(config: Config): Promise<{
  * @param config Server configuration.
  * @returns A promise to both app and HTTP server.
  */
-async function startHTTPServer(
-  config: Config,
-): Promise<{app: Express; server: http.Server}> {
+async function startHTTPServer(config: Config): Promise<{
+  app: Express;
+  server: http.Server;
+  socket: WebSocketServer;
+  readyForIncomingConnections: ReadyForConnections;
+}> {
   const app = express();
 
   app.use((_req, res, next) => {
@@ -89,8 +95,14 @@ async function startHTTPServer(
 async function startProxyServer(
   config: Config,
   app: Express,
-): Promise<{app: Express; server: http.Server}> {
+): Promise<{
+  app: Express;
+  server: http.Server;
+  socket: WebSocketServer;
+  readyForIncomingConnections: ReadyForConnections;
+}> {
   const server = http.createServer(app);
+  const socket = addWebsocket(server, config);
 
   // For now, we only support domain socket access on POSIX-like systems.
   // On Windows, a proxy is not created and the server starts
@@ -98,7 +110,12 @@ async function startProxyServer(
   if (os.platform() === 'win32') {
     return new Promise((resolve) => {
       console.log(`Starting server on http://localhost:${config.port}`);
-      server.listen(config.port, undefined, () => resolve({app, server}));
+      const readyForIncomingConnections = (): Promise<void> => {
+        return new Promise((resolve) => {
+          server.listen(config.port, undefined, () => resolve());
+        });
+      };
+      resolve({app, server, socket, readyForIncomingConnections});
     });
   }
 
@@ -140,8 +157,17 @@ async function startProxyServer(
   });
 
   return new Promise((resolve) => {
-    proxyServer.listen(config.port);
-    server.listen(socketPath, undefined, () => resolve({app, server}));
+    const readyForIncomingConnections = (
+      serverImpl: FlipperServerImpl,
+      companionEnv: FlipperServerCompanionEnv,
+    ): Promise<void> => {
+      attachSocketServer(socket, serverImpl, companionEnv);
+      return new Promise((resolve) => {
+        proxyServer.listen(config.port);
+        server.listen(socketPath, undefined, () => resolve());
+      });
+    };
+    resolve({app, server, socket, readyForIncomingConnections});
   });
 }