fix(driver): stop sending protocol messages after disconnect (#4688)

When the client only closes the input pipe, we are still
sending protocol messages over the output pipe. This could
probably lead to some errors, e.g. write buffer being full.

src/driver.ts

@@ -50,15 +50,17 @@ export function runServer() {
 
   const dispatcherConnection = new DispatcherConnection();
   const transport = new Transport(process.stdout, process.stdin);
+  transport.onmessage = message => dispatcherConnection.dispatch(JSON.parse(message));
+  dispatcherConnection.onmessage = message => transport.send(JSON.stringify(message));
   transport.onclose = async () => {
+    // Drop any messages during shutdown on the floor.
+    dispatcherConnection.onmessage = () => {};
     // Force exit after 30 seconds.
     setTimeout(() => process.exit(0), 30000);
     // Meanwhile, try to gracefully close all browsers.
     await gracefullyCloseAll();
     process.exit(0);
   };
-  transport.onmessage = message => dispatcherConnection.dispatch(JSON.parse(message));
-  dispatcherConnection.onmessage = message => transport.send(JSON.stringify(message));
 
   const playwright = new Playwright(__dirname, require('../browsers.json')['browsers']);
   new PlaywrightDispatcher(dispatcherConnection.rootDispatcher(), playwright);

src/protocol/transport.ts

@@ -47,7 +47,11 @@ export class Transport {
     this._endian = endian;
     this._closeableStream = closeable;
     pipeRead.on('data', buffer => this._dispatch(buffer));
-    pipeRead.on('close', () => this.onclose && this.onclose());
+    pipeRead.on('close', () => {
+      this._closed = true;
+      if (this.onclose)
+        this.onclose();
+    });
     this.onmessage = undefined;
     this.onclose = undefined;
   }