fix(@angular-devkit/build-angular): ensure correct dev server path with public host option

If a custom path is provided the webpack dev server client drops the sockjs-node segment. This adds it back so that behavior is consistent when using a custom URL path.

Fixes #13627

Author: clydin

packages/angular_devkit/build_angular/src/dev-server/index.ts

@@ -144,15 +144,14 @@ export function serveWebpackBrowser(
       options.port = port;
 
       // Resolve public host and client address.
-      let clientAddress = `${options.ssl ? 'https' : 'http'}://0.0.0.0:0`;
+      let clientAddress = url.parse(`${options.ssl ? 'https' : 'http'}://0.0.0.0:0`);
       if (options.publicHost) {
         let publicHost = options.publicHost;
         if (!/^\w+:\/\//.test(publicHost)) {
           publicHost = `${options.ssl ? 'https' : 'http'}://${publicHost}`;
         }
-        const clientUrl = url.parse(publicHost);
-        options.publicHost = clientUrl.host;
-        clientAddress = url.format(clientUrl);
+        clientAddress = url.parse(publicHost);
+        options.publicHost = clientAddress.host;
       }
 
       // Resolve serve address.
@@ -338,7 +337,7 @@ function _addLiveReload(
   options: DevServerBuilderSchema,
   browserOptions: BrowserBuilderSchema,
   webpackConfig: webpack.Configuration,
-  clientAddress: string,
+  clientAddress: url.UrlWithStringQuery,
   logger: logging.LoggerApi,
 ) {
   if (webpackConfig.plugins === undefined) {
@@ -353,7 +352,14 @@ function _addLiveReload(
   } catch {
     throw new Error('The "webpack-dev-server" package could not be found.');
   }
-  const entryPoints = [`${webpackDevServerPath}?${clientAddress}`];
+
+  // If a custom path is provided the webpack dev server client drops the sockjs-node segment.
+  // This adds it back so that behavior is consistent when using a custom URL path
+  if (clientAddress.pathname) {
+    clientAddress.pathname = path.posix.join(clientAddress.pathname, 'sockjs-node');
+  }
+
+  const entryPoints = [`${webpackDevServerPath}?${url.format(clientAddress)}`];
   if (options.hmr) {
     const webpackHmrLink = 'https://webpack.js.org/guides/hot-module-replacement';