Automatically watches the metro configuration file

Reviewed By: BYK

Differential Revision: D6408358

fbshipit-source-id: d167534c9c51c3c079148d982ef4ab44c8be0d75

packages/metro-bundler/src/cli-utils.js

@@ -19,12 +19,20 @@ import type {ConfigT} from './Config';
 
 const METRO_CONFIG_FILENAME = 'metro.config.js';
 
-exports.findMetroConfig = async function(
+exports.watchFile = async function(
-  filename: ?string,
+  filename: string,
-): Promise<$Shape<ConfigT>> {
+  callback: () => *,
+): Promise<void> {
+  fs.watchFile(filename, () => {
+    callback();
+  });
+
+  await callback();
+};
+
+exports.findMetroConfig = async function(filename: ?string): Promise<?string> {
   if (filename) {
-    // $FlowFixMe: We want this require to be dynamic
+    return path.resolve(process.cwd(), filename);
-    return require(path.resolve(process.cwd(), filename));
   } else {
     let previous;
     let current = process.cwd();
@@ -33,14 +41,25 @@ exports.findMetroConfig = async function(
       const filename = path.join(current, METRO_CONFIG_FILENAME);
 
       if (fs.existsSync(filename)) {
-        // $FlowFixMe: We want this require to be dynamic
+        return filename;
-        return require(filename);
       }
 
       previous = current;
       current = path.dirname(current);
     } while (previous !== current);
 
+    return null;
+  }
+};
+
+exports.fetchMetroConfig = async function(
+  filename: ?string,
+): Promise<$Shape<ConfigT>> {
+  const location = await exports.findMetroConfig(filename);
+  if (location) {
+    // $FlowFixMe: We want this require to be dynamic
+    return require(location);
+  } else {
     return {};
   }
 };

packages/metro-bundler/src/commands/build.js

@@ -16,7 +16,7 @@ const MetroApi = require('..');
 
 const os = require('os');
 
-const {findMetroConfig, makeAsyncCommand} = require('../cli-utils');
+const {fetchMetroConfig, makeAsyncCommand} = require('../cli-utils');
 
 import typeof Yargs from 'yargs';
 
@@ -52,6 +52,6 @@ exports.builder = (yargs: Yargs) => {
 
 // eslint-disable-next-line no-unclear-flowtypes
 exports.handler = makeAsyncCommand(async (argv: any) => {
-  argv.config = await findMetroConfig(argv.config);
+  const config = await fetchMetroConfig(argv.config);
-  await MetroApi.runBuild(argv);
+  await MetroApi.runBuild({...argv, config});
 });

packages/metro-bundler/src/commands/serve.js

@@ -16,7 +16,13 @@ const MetroApi = require('..');
 
 const os = require('os');
 
-const {findMetroConfig, makeAsyncCommand} = require('../cli-utils');
+const {
+  findMetroConfig,
+  fetchMetroConfig,
+  watchFile,
+  makeAsyncCommand,
+} = require('../cli-utils');
+const {promisify} = require('util');
 
 import typeof Yargs from 'yargs';
 
@@ -49,15 +55,44 @@ exports.builder = (yargs: Yargs) => {
 
 // eslint-disable-next-line no-unclear-flowtypes
 exports.handler = makeAsyncCommand(async (argv: any) => {
-  argv.config = await findMetroConfig(argv.config);
+  let server = null;
+  let restarting = false;
 
-  await MetroApi.runServer({
+  async function restart() {
+    if (restarting) {
+      return;
+    } else {
+      restarting = true;
+    }
+
+    if (server) {
+      console.log('Configuration changed... restarting the server...');
+      await promisify(server.close).call(server);
+    }
+
+    const config = await fetchMetroConfig(argv.config);
+
+    server = await MetroApi.runServer({
       ...argv,
-    onReady(server) {
+      config,
+      onReady,
+    });
+
+    restarting = false;
+  }
+
+  function onReady(server) {
     console.log(
       `The HTTP server is ready to accept requests on ${server.address()
         .address}:${server.address().port}`,
     );
-    },
+  }
-  });
+
+  const metroConfigLocation = await findMetroConfig(argv.config);
+
+  if (metroConfigLocation) {
+    await watchFile(metroConfigLocation, restart);
+  } else {
+    await restart();
+  }
 });

packages/metro-bundler/src/index.js

@@ -145,8 +145,13 @@ exports.createConnectMiddleware = async function(
     watch: true,
   });
 
-  return (req: IncomingMessage, res: ServerResponse) => {
+  return {
+    middleware(req: IncomingMessage, res: ServerResponse) {
       return metroServer.processRequest(req, res);
+    },
+    end() {
+      metroServer.end();
+    },
   };
 };
 
@@ -163,13 +168,13 @@ type RunServerOptions = {|
 exports.runServer = async (options: RunServerOptions) => {
   const serverApp = connect();
 
-  const metroMiddleware = exports.createConnectMiddleware({
+  const {middleware, end} = await exports.createConnectMiddleware({
     config: options.config,
     maxWorkers: options.maxWorkers,
     projectRoots: options.projectRoots,
   });
 
-  serverApp.use(metroMiddleware);
+  serverApp.use(middleware);
 
   let httpServer;
 
@@ -185,7 +190,6 @@ exports.runServer = async (options: RunServerOptions) => {
     httpServer = Http.createServer(serverApp);
   }
 
-  // $FlowFixMe: The port parameter IS optional
   httpServer.listen(options.port, options.host, () => {
     options.onReady && options.onReady(httpServer);
   });
@@ -195,15 +199,15 @@ exports.runServer = async (options: RunServerOptions) => {
   // timeout of 120 seconds to respond to a request.
   httpServer.timeout = 0;
 
-  return new Promise((resolve, reject) => {
   httpServer.on('error', error => {
-      reject(error);
+    end();
   });
 
   httpServer.on('close', () => {
-      resolve();
+    end();
-    });
   });
+
+  return httpServer;
 };
 
 type RunBuildOptions = {|