Cypress doesn't work when there is no internet connection, testing to localhost

Current behavior:

Cypress will not load tests to localhost server when there is no internet connection. This happens in both GUI (cypress open) and command line (cypress run).

I’m experiencing something similar to https://github.com/cypress-io/cypress/issues/4235, but the differences are:

• It only doesn’t work when there is no internet connection.
• When there’s no connection, issue happens with both Chrome and Electron

In the console, I see this:

I’m not in a corporate proxy server.

Desired behavior:

The tests should still run, since I’m only testing a local server.

Steps to reproduce:

1. Clone this repo, then npm install. This repo is just create-react-app with a cypress test that visits the home page.
2. Disconnect internet connection.
3. npm start to start server. http://localhost:3000 should display the default page for create-react-app.
4. npm run cypress:open to start Cypress. Then run home.spec.js. You’ll see that the test doesn’t load.

I also included my logs in the repo. See log.txt.

Versions

Cypress 3.4.0, Windows 10, Chrome 75 and Electron 61

[flotwig]

The root issue appears to be nodejs/node#11320… Node on Windows cannot resolve localhost when there is no active network interface besides ‘loopback’.

A fix landed in Node 8.10: nodejs/node#17662, we’re on 8.9.3.

An interim fix is to intercept calls to dns.lookup and use os.networkInterfaces() to detect if this problem is going to occur, and if so, strip the problematic flag from dns.lookup. Submitted a PR to fix this (#4774) while we work on upgrading the bundled Node (#3568)

[brian-mann]

Cypress should most definitely work offline, @flotwig can you take a look at this?