fix: live reload port fallback if port is used (#899)

* Move start reload server into separate module

* Find an unused port when starting the live reload server

* Move findUnusedPort into module

* Add tests for findUnusedPort module

* Refactor findUnusedPort

* Move starting of servers into separate module and add tests

* Remove unused constants.js

* Zap extra line breaks

* Add tests for liveReloadServer

* Rename serverController to start

* Move start into lib/server

* Add portfinder package

* Replace findUnusedPort with portfinder

* nits

lib/server/__tests__/start.test.js

@@ -0,0 +1,138 @@
+/**
+ * Copyright (c) 2017-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.
+ */
+
+const program = require('commander');
+const openBrowser = require('react-dev-utils/openBrowser');
+const portFinder = require('portfinder');
+const liveReloadServer = require('../liveReloadServer.js');
+const server = require('../server.js');
+
+const siteConfig = require(`${process.cwd()}/siteConfig.js`);
+
+// When running Jest the siteConfig import fails because siteConfig doesn't exist
+// relative to the cwd of the tests. Rather than mocking out cwd just mock
+// siteConfig virtually.
+jest.mock(`${process.cwd()}/siteConfig.js`, () => jest.fn(), {virtual: true});
+
+jest.mock('commander');
+jest.mock('react-dev-utils/openBrowser');
+jest.mock('portfinder');
+jest.mock('../liveReloadServer.js');
+jest.mock('../server.js');
+jest.mock('process');
+
+console.log = jest.fn();
+
+const start = require('../start.js');
+
+beforeEach(() => jest.resetAllMocks());
+
+describe('start live reload', () => {
+  test('uses inital port 35729', () => {
+    portFinder.getPortPromise.mockResolvedValue();
+    start.startLiveReloadServer();
+    expect(portFinder.getPortPromise).toHaveBeenCalledWith({port: 35729});
+  });
+
+  test('when an unused port is found, starts the live reload server on that port', () => {
+    expect.assertions(1);
+    const unusedPort = 1234;
+    portFinder.getPortPromise.mockResolvedValue(unusedPort);
+    return start.startLiveReloadServer().then(() => {
+      expect(liveReloadServer.start).toHaveBeenCalledWith(unusedPort);
+    });
+  });
+
+  test('when no unused port found, returns error', () => {
+    expect.assertions(1);
+    const unusedPortError = new Error('no unused port');
+    portFinder.getPortPromise.mockRejectedValue(unusedPortError);
+    return expect(start.startLiveReloadServer()).rejects.toEqual(
+      unusedPortError
+    );
+  });
+});
+
+describe('start server', () => {
+  test('when custom port provided as parameter, uses as inital port', () => {
+    const customPort = 1234;
+    program.port = customPort;
+    portFinder.getPortPromise.mockResolvedValue();
+    start.startServer();
+    expect(portFinder.getPortPromise).toBeCalledWith({port: customPort});
+    delete program.port;
+  });
+
+  test('when port environment variable set and no custom port, used as inital port', () => {
+    const customPort = '4321';
+    process.env.PORT = customPort;
+    portFinder.getPortPromise.mockResolvedValue();
+    start.startServer();
+    expect(portFinder.getPortPromise).toBeCalledWith({port: customPort});
+    delete process.env.PORT;
+  });
+
+  test('when no custom port specified, uses port 3000', () => {
+    portFinder.getPortPromise.mockResolvedValue();
+    start.startServer();
+    expect(portFinder.getPortPromise).toBeCalledWith({port: 3000});
+  });
+
+  test('when unused port found, starts server on that port', () => {
+    expect.assertions(1);
+    const port = 1357;
+    portFinder.getPortPromise.mockResolvedValue(port);
+    return start.startServer().then(() => {
+      expect(server).toHaveBeenCalledWith(port);
+    });
+  });
+
+  test('when unused port found, opens browser to server address', () => {
+    expect.assertions(1);
+    const baseUrl = '/base_url';
+    siteConfig.baseUrl = baseUrl;
+    const port = 2468;
+    portFinder.getPortPromise.mockResolvedValue(port);
+    const expectedServerAddress = `http://localhost:${port}${baseUrl}`;
+    return start.startServer().then(() => {
+      expect(openBrowser).toHaveBeenCalledWith(expectedServerAddress);
+    });
+  });
+});
+
+describe('start docusaurus', () => {
+  test('when watch enabled, starts live reload server', () => {
+    expect.assertions(1);
+    program.watch = true;
+    portFinder.getPortPromise.mockResolvedValue();
+    return start.startDocusaurus().then(() => {
+      expect(liveReloadServer.start).toBeCalled();
+    });
+  });
+
+  test('when live reload fails to start, server still started', () => {
+    expect.assertions(1);
+    program.watch = true;
+    console.warn = jest.fn();
+    portFinder.getPortPromise
+      .mockRejectedValueOnce('could not find live reload port')
+      .mockResolvedValueOnce();
+    return start.startDocusaurus().then(() => {
+      expect(server).toBeCalled();
+    });
+  });
+
+  test('live reload disabled, only starts docusarus server', () => {
+    expect.assertions(2);
+    program.watch = false;
+    portFinder.getPortPromise.mockResolvedValue();
+    return start.startDocusaurus().then(() => {
+      expect(liveReloadServer.start).not.toBeCalled();
+      expect(server).toBeCalled();
+    });
+  });
+});