execute: args => {
      const current = getCurrent(args);

      if (!current) {
        return;
      }

      const notebookPath = URLExt.encodeParts(current.context.path);
      const url = URLExt.join(
        services.serverSettings.baseUrl,
        'nbconvert',
        (args['format']) as string,
        notebookPath
      ) + '?download=true';
      const child = window.open('', '_blank');
      const { context } = current;

      if (context.model.dirty && !context.model.readOnly) {
        return context.save().then(() => { child.location.assign(url); });
      }

      return new Promise<void>((resolve) => {
        child.location.assign(url);
        resolve(undefined);
      });
    },

 export function makeSettings(
   options: Partial<ServerConnection.ISettings> = {}
 ): ServerConnection.ISettings {
   let extra: Partial<ServerConnection.ISettings> = {};
   if (options.baseUrl && !options.wsUrl) {
     // Setting baseUrl to https://host... sets wsUrl to wss://host...
     let baseUrl = options.baseUrl;
     if (baseUrl.indexOf('http') !== 0) {
       if (typeof location !== 'undefined') {
         baseUrl = URLExt.join(location.origin, baseUrl);
       } else {
         // TODO: Why are we hardcoding localhost and 8888? That doesn't seem
         // good. See https://github.com/jupyterlab/jupyterlab/issues/4761
         baseUrl = URLExt.join('http://localhost:8888/', baseUrl);
       }
     }
     extra = {
       wsUrl: 'ws' + baseUrl.slice(4)
     };
   }
   return {
     ...ServerConnection.defaultSettings,
     ...options,
     ...extra
   };
 }

    execute: args => {
      let current = getCurrent(args);
      if (!current) {
        return;
      }

      let notebookPath = URLExt.encodeParts(current.context.path);
      let url = URLExt.join(
        services.serverSettings.baseUrl,
        'nbconvert',
        (args['format']) as string,
        notebookPath
      ) + '?download=true';

      let w = window.open('', '_blank');
      if (current.context.model.dirty && !current.context.model.readOnly) {
        return current.context.save().then(() => {
          w.location.assign(url);
        });
      } else {
        return new Promise((resolve, reject) => {
          w.location.assign(url);
        });
      }
    },

      execute: (args: IRouter.ILocation) => {
        const { hash, path, search } = args;
        const query = URLExt.queryStringToObject(search || '');
        const reset = 'reset' in query;

        if (!reset) {
          return;
        }

        // If the state database has already been resolved, resetting is
        // impossible without reloading.
        if (resolved) {
          return document.location.reload();
        }

        // Empty the state database.
        resolved = true;
        transform.resolve({ type: 'clear', contents: null });

        // Maintain the query string parameters but remove `reset`.
        delete query['reset'];

        const url = path + URLExt.objectToQueryString(query) + hash;
        const cleared = commands.execute(CommandIDs.recoverState)
          .then(() => router.stop); // Stop routing before new route navigation.

        // After the state has been reset, navigate to the URL.
        cleared.then(() => { router.navigate(url, { silent: true }); });

        return cleared;
      }

 it('should test whether the url is a local url', () => {
   expect(URLExt.isLocal('https://foo/bar.txt')).to.equal(false);
   expect(URLExt.isLocal('http://foo/bar.txt')).to.equal(false);
   expect(URLExt.isLocal('//foo/bar.txt')).to.equal(false);
   expect(URLExt.isLocal('../foo/bar.txt')).to.equal(true);
   expect(URLExt.isLocal('./foo/bar.txt')).to.equal(true);
   expect(URLExt.isLocal('/foo/bar.txt')).to.equal(true);
   expect(URLExt.isLocal('foo/bar.txt')).to.equal(true);
   expect(URLExt.isLocal('bar.txt')).to.equal(true);
   expect(URLExt.isLocal('file://foo/bar.txt')).to.equal(false);
   expect(URLExt.isLocal('data:text/plain,123ABC')).to.equal(false);
 });

  activate: async (
    _: JupyterFrontEnd,
    paths: JupyterFrontEnd.IPaths,
    router: IRouter
  ) => {
    const { hash, path, search } = router.current;
    const query = URLExt.queryStringToObject(search || '');
    const solver = new WindowResolver();
    const match = path.match(new RegExp(`^${paths.urls.workspaces}([^?\/]+)`));
    const workspace = (match && decodeURIComponent(match[1])) || '';
    const candidate = Private.candidate(paths, workspace);

    try {
      await solver.resolve(candidate);
    } catch (error) {
      // Window resolution has failed so the URL must change. Return a promise
      // that never resolves to prevent the application from loading plugins
      // that rely on `IWindowResolver`.
      return new Promise<IWindowResolver>(() => {
        // If the user has requested workspace resolution create a new one.
        if (WORKSPACE_RESOLVE in query) {
          const { base, workspaces } = paths.urls;
          const pool =
            'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
          const random = pool[Math.floor(Math.random() * pool.length)];
          const path = URLExt.join(base, workspaces, `auto-${random}`);

          // Clone the originally requested workspace after redirecting.
          query['clone'] = workspace;

          // Change the URL and trigger a hard reload to re-route.
          const url = path + URLExt.objectToQueryString(query) + (hash || '');
          router.navigate(url, { hard: true, silent: true });
          return;
        }

        // Launch a dialog to ask the user for a new workspace name.
        console.warn('Window resolution failed:', error);
        return Private.redirect(router, paths, workspace);
      });
    }

    // If the user has requested workspace resolution remove the query param.
    if (WORKSPACE_RESOLVE in query) {
      delete query[WORKSPACE_RESOLVE];

      // Silently scrub the URL.
      const url = path + URLExt.objectToQueryString(query) + (hash || '');
      router.navigate(url, { silent: true });
    }

    return solver;
  }

      return new Promise<IWindowResolver>(() => {
        const { base, workspaces } = paths.urls;
        const pool =
          'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
        const random = pool[Math.floor(Math.random() * pool.length)];
        const path = URLExt.join(base, workspaces, `auto-${random}`) + rest;

        // Clone the originally requested workspace after redirecting.
        query['clone'] = workspace;

        // Change the URL and trigger a hard reload to re-route.
        const url = path + URLExt.objectToQueryString(query) + (hash || '');
        router.navigate(url, { hard: true, silent: true });
      });

      execute: (args: IRouter.ILocation) => {
        const { hash, path, search } = args;
        const query = URLExt.queryStringToObject(search || '');
        const reset = 'reset' in query;
        const clone = 'clone' in query;

        if (!reset) {
          return;
        }

        // If a splash provider exists, launch the splash screen.
        const loading = splash
          ? splash.show()
          : new DisposableDelegate(() => undefined);

        // If the state database has already been resolved, resetting is
        // impossible without reloading.
        if (resolved) {
          return router.reload();
        }

        // Empty the state database.
        resolved = true;
        transform.resolve({ type: 'clear', contents: null });

        // Maintain the query string parameters but remove `reset`.
        delete query['reset'];

        const silent = true;
        const hard = true;
        const url = path + URLExt.objectToQueryString(query) + hash;
        const cleared = commands
          .execute(CommandIDs.recoverState)
          .then(() => router.stop); // Stop routing before new route navigation.

        // After the state has been reset, navigate to the URL.
        if (clone) {
          void cleared.then(() => {
            router.navigate(url, { silent, hard });
          });
        } else {
          void cleared.then(() => {
            router.navigate(url, { silent });
            loading.dispose();
          });
        }

        return cleared;
      }

  export async function redirect(
    router: IRouter,
    paths: JupyterFrontEnd.IPaths,
    workspace: string,
    warn = false
  ): Promise<void> {
    const form = createRedirectForm(warn);
    const dialog = new Dialog({
      title: 'Please use a different workspace.',
      body: form,
      focusNodeSelector: 'input',
      buttons: [Dialog.okButton({ label: 'Switch Workspace' })]
    });
    const result = await dialog.launch();

    dialog.dispose();
    if (!result.value) {
      return redirect(router, paths, workspace, true);
    }

    // Navigate to a new workspace URL and abandon this session altogether.
    const page = paths.urls.page;
    const workspaces = paths.urls.workspaces;
    const prefix = (workspace ? workspaces : page).length + workspace.length;
    const rest = router.current.request.substring(prefix);
    const url = URLExt.join(workspaces, result.value, rest);

    router.navigate(url, { hard: true, silent: true });

    // This promise will never resolve because the application navigates
    // away to a new location. It only exists to satisfy the return type
    // of the `redirect` function.
    return new Promise<void>(() => undefined);
  }

 it('should return a serialized object string suitable for a query', () => {
   const obj = {
     name: 'foo',
     id: 'baz'
   };
   expect(URLExt.objectToQueryString(obj)).to.equal('?name=foo&id=baz');
 });