myapp/node_modules/react-scripts/config/webpackDevServer.config.js

// @remove-on-eject-begin
/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
// @remove-on-eject-end
'use strict';

const fs = require('fs');
const errorOverlayMiddleware = require('react-dev-utils/errorOverlayMiddleware');
const evalSourceMapMiddleware = require('react-dev-utils/evalSourceMapMiddleware');
const noopServiceWorkerMiddleware = require('react-dev-utils/noopServiceWorkerMiddleware');
const ignoredFiles = require('react-dev-utils/ignoredFiles');
const redirectServedPath = require('react-dev-utils/redirectServedPathMiddleware');
const paths = require('./paths');
const getHttpsConfig = require('./getHttpsConfig');

const host = process.env.HOST || '0.0.0.0';
const sockHost = process.env.WDS_SOCKET_HOST;
const sockPath = process.env.WDS_SOCKET_PATH; // default: '/sockjs-node'
const sockPort = process.env.WDS_SOCKET_PORT;

module.exports = function(proxy, allowedHost) {
  return {
    // WebpackDevServer 2.4.3 introduced a security fix that prevents remote
    // websites from potentially accessing local content through DNS rebinding:
    // https://github.com/webpack/webpack-dev-server/issues/887
    // https://medium.com/webpack/webpack-dev-server-middleware-security-issues-1489d950874a
    // However, it made several existing use cases such as development in cloud
    // environment or subdomains in development significantly more complicated:
    // https://github.com/facebook/create-react-app/issues/2271
    // https://github.com/facebook/create-react-app/issues/2233
    // While we're investigating better solutions, for now we will take a
    // compromise. Since our WDS configuration only serves files in the `public`
    // folder we won't consider accessing them a vulnerability. However, if you
    // use the `proxy` feature, it gets more dangerous because it can expose
    // remote code execution vulnerabilities in backends like Django and Rails.
    // So we will disable the host check normally, but enable it if you have
    // specified the `proxy` setting. Finally, we let you override it if you
    // really know what you're doing with a special environment variable.
    disableHostCheck:
      !proxy || process.env.DANGEROUSLY_DISABLE_HOST_CHECK === 'true',
    // Enable gzip compression of generated files.
    compress: true,
    // Silence WebpackDevServer's own logs since they're generally not useful.
    // It will still show compile warnings and errors with this setting.
    clientLogLevel: 'none',
    // By default WebpackDevServer serves physical files from current directory
    // in addition to all the virtual build products that it serves from memory.
    // This is confusing because those files won’t automatically be available in
    // production build folder unless we copy them. However, copying the whole
    // project directory is dangerous because we may expose sensitive files.
    // Instead, we establish a convention that only files in `public` directory
    // get served. Our build script will copy `public` into the `build` folder.
    // In `index.html`, you can get URL of `public` folder with %PUBLIC_URL%:
    // <link rel="icon" href="%PUBLIC_URL%/favicon.ico">
    // In JavaScript code, you can access it with `process.env.PUBLIC_URL`.
    // Note that we only recommend to use `public` folder as an escape hatch
    // for files like `favicon.ico`, `manifest.json`, and libraries that are
    // for some reason broken when imported through webpack. If you just want to
    // use an image, put it in `src` and `import` it from JavaScript instead.
    contentBase: paths.appPublic,
    contentBasePublicPath: paths.publicUrlOrPath,
    // By default files from `contentBase` will not trigger a page reload.
    watchContentBase: true,
    // Enable hot reloading server. It will provide WDS_SOCKET_PATH endpoint
    // for the WebpackDevServer client so it can learn when the files were
    // updated. The WebpackDevServer client is included as an entry point
    // in the webpack development configuration. Note that only changes
    // to CSS are currently hot reloaded. JS changes will refresh the browser.
    hot: true,
    // Use 'ws' instead of 'sockjs-node' on server since we're using native
    // websockets in `webpackHotDevClient`.
    transportMode: 'ws',
    // Prevent a WS client from getting injected as we're already including
    // `webpackHotDevClient`.
    injectClient: false,
    // Enable custom sockjs pathname for websocket connection to hot reloading server.
    // Enable custom sockjs hostname, pathname and port for websocket connection
    // to hot reloading server.
    sockHost,
    sockPath,
    sockPort,
    // It is important to tell WebpackDevServer to use the same "publicPath" path as
    // we specified in the webpack config. When homepage is '.', default to serving
    // from the root.
    // remove last slash so user can land on `/test` instead of `/test/`
    publicPath: paths.publicUrlOrPath.slice(0, -1),
    // WebpackDevServer is noisy by default so we emit custom message instead
    // by listening to the compiler events with `compiler.hooks[...].tap` calls above.
    quiet: true,
    // Reportedly, this avoids CPU overload on some systems.
    // https://github.com/facebook/create-react-app/issues/293
    // src/node_modules is not ignored to support absolute imports
    // https://github.com/facebook/create-react-app/issues/1065
    watchOptions: {
      ignored: ignoredFiles(paths.appSrc),
    },
    https: getHttpsConfig(),
    host,
    overlay: false,
    historyApiFallback: {
      // Paths with dots should still use the history fallback.
      // See https://github.com/facebook/create-react-app/issues/387.
      disableDotRule: true,
      index: paths.publicUrlOrPath,
    },
    public: allowedHost,
    // `proxy` is run between `before` and `after` `webpack-dev-server` hooks
    proxy,
    before(app, server) {
      // Keep `evalSourceMapMiddleware` and `errorOverlayMiddleware`
      // middlewares before `redirectServedPath` otherwise will not have any effect
      // This lets us fetch source contents from webpack for the error overlay
      app.use(evalSourceMapMiddleware(server));
      // This lets us open files from the runtime error overlay.
      app.use(errorOverlayMiddleware());

      if (fs.existsSync(paths.proxySetup)) {
        // This registers user provided middleware for proxy reasons
        require(paths.proxySetup)(app);
      }
    },
    after(app) {
      // Redirect to `PUBLIC_URL` or `homepage` from `package.json` if url not match
      app.use(redirectServedPath(paths.publicUrlOrPath));

      // This service worker file is effectively a 'no-op' that will reset any
      // previous service worker registered for the same host:port combination.
      // We do this in development to avoid hitting the production cache if
      // it used the same host and port.
      // https://github.com/facebook/create-react-app/issues/2272#issuecomment-302832432
      app.use(noopServiceWorkerMiddleware(paths.publicUrlOrPath));
    },
  };
};