Add headless-demo plugin and its usage example

Summary:
Next steps:
1. Refactor it TS for consistency
2. Remove it in favor of tic-tac-toe integration

Reviewed By: mweststrate

Differential Revision: D36102002

fbshipit-source-id: 7dc930f67bed636159a2ec433d7405ab6ee09f97

desktop/examples/headless-demo/README.md

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+# headless-demo
+
+**Experimental feature!**
+
+Flipper can run plugins in a headless mode - expose their API over the wire. This is a simple example of how it might look like.
+
+## Quick start
+
+0. Run `yarn` from this repo to install dependencies
+0. Start Flipper Server: from `desktop` folder run `yarn flipper-server`
+0. Start an Android device
+0. Run `yarn start` from this repo
+
+## What happens under the hood
+
+0. This script connects to Flipper via WebSockets
+0. It fetches a list of devices
+0. It fetches a list of available headless plugins for the Android device
+0. It activates `headless-demo` plugin
+0. It sends `increment` command to the plugin

desktop/examples/headless-demo/index.js

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+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+const WebSocket = require('ws');
+
+class FlipperServerClient {
+  messageId = 0;
+  wsClient = new WebSocket('ws://localhost:52342?server_companion=true');
+  execReqs = new Map();
+
+  async init() {
+    await new Promise((resolve) => this.wsClient.on('open', resolve));
+
+    this.wsClient.on('message', (data) => {
+      const {event, payload} = JSON.parse(data);
+
+      switch (event) {
+        case 'exec-response':
+        case 'exec-response-error': {
+          const req = this.execReqs.get(payload.id);
+
+          if (!req) {
+            console.warn('Unknown exec request');
+            return;
+          }
+
+          this.execReqs.delete(payload.id);
+
+          if (event === 'exec-response') {
+            req.resolve(payload.data);
+          } else {
+            req.reject(payload.data);
+          }
+          return;
+        }
+      }
+    });
+  }
+
+  exec(command, args) {
+    return new Promise((resolve, reject) => {
+      const id = this.messageId++;
+
+      this.wsClient.send(
+        JSON.stringify({
+          event: 'exec',
+          payload: {
+            id,
+            command,
+            args,
+          },
+        }),
+      );
+
+      this.execReqs.set(id, {resolve, reject});
+    });
+  }
+}
+
+const main = async () => {
+  console.log('main');
+
+  const client = new FlipperServerClient();
+  await client.init();
+
+  console.log('Initialized client');
+
+  const devices = await client.exec('device-list', []);
+
+  console.log('Devices', JSON.stringify(devices));
+
+  const targetDevice = devices.find((device) => !!device.serial);
+
+  const availablePlugins = await client.exec('companion-device-plugin-list', [
+    targetDevice.serial,
+  ]);
+
+  console.log(
+    'Available plugins',
+    targetDevice.serial,
+    JSON.stringify(availablePlugins),
+  );
+
+  console.log('Activating headless-demo plugin for', targetDevice.serial);
+
+  await client.exec('companion-device-plugin-start', [
+    targetDevice.serial,
+    'headless-demo',
+  ]);
+
+  console.log('Activated headless-demo plugin');
+
+  console.log('Using increment api');
+
+  const res = await client.exec('companion-device-plugin-exec', [
+    targetDevice.serial,
+    'headless-demo',
+    'increment',
+    [3],
+  ]);
+
+  console.log('Received a response', JSON.stringify(res));
+};
+
+main().catch(console.error);

desktop/examples/headless-demo/package.json

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+{
+  "name": "headless-demo",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "scripts": {
+    "start": "node index.js"
+  },
+  "dependencies": {
+    "ws": "^8.6.0"
+  }
+}

desktop/examples/headless-demo/yarn.lock

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+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+ws@^8.6.0:
+  version "8.6.0"
+  resolved "https://registry.yarnpkg.com/ws/-/ws-8.6.0.tgz#e5e9f1d9e7ff88083d0c0dd8281ea662a42c9c23"
+  integrity sha512-AzmM3aH3gk0aX7/rZLYvjdvZooofDu3fFOzGqcSnQ1tOcTWwhM/o+q++E8mAyVVIyUdajrkzWUGftaVSDLn1bw==