Warn when localhost is not mapped to 127.0.0.1 and launch Cypress directly on that ip address

[brian-mann]

When users /etc/hosts file is nuked or has had the localhost -> 127.0.0.1 ip address mapping removed then Cypress will fail to spawn the browser correctly.

We can detect this and provide a warning to the user, and additionally could just launch the browser on 127.0.0.1 as opposed to localhost.

Related to: #1455 and #680

[punkosu]

I just ran into this, and spent a little bit of time debugging to figure it out. A warning message would be a nice to have

[brian-mann]

@flotwig hey see I'm not crazy it does happen. Maybe we can fix this - it should be fairly simple - but there may be a lot of hard coded localhost strings everywhere that we'd have to synchronize and update.

We likely need to pass around a defaultHostname configuration variable and then point to that everywhere - and let the server initially set this if baseUrl is not specified by testing to see that localhost is mapped to 127.0.0.1.

[flotwig]

Logging a warning if localhost !== 127.0.0.1 would be nice, as we do make that assumption in a lot of places. So would launching the test runner on 127.0.0.1 instead of localhost.

[khan-zia]

It's been 4 years, I ran into a similar issue today. @jennifer-shehane @brian-mann

[pm0u]

What is the fix for this? Everything in my org uses http-get://localhost:3333 to initiate cypress so I can't modify the URL... but it only works if I change the CLI params to http-get://127.0.0.1:3333

This is on MacOS Ventura

[MikeMcC399]

@pm0u

You may be running into a issue where your dev server is not responding on both IPv4 and IPv6 stacks. This is something which can be a problem with Node.js 18 and 20.

Depending on the network setup localhost may map to the IPv4 loopback address 127.0.0.1 or to the IPv6 loopback address ::1 or both.

You may want to open a separate issue so that you can provide full details, including which dev server you are using. There is a recent related issue where I gave some comments

• see IPv6 used for cypress backendUrl connection check #27962.

[pm0u]

Thanks @MikeMcC399 - not sure if this is the "best" fix but I did manage to get this working by commenting out the IPv6 localhost loopback that was in my hosts file

#::1 localhost

that line was last and previously not commented. We are running Node 18.16, maybe node found that IPv6 was available as a loopback and ignored the ipv4 binding? Not sure - it was particularly confusing as localhost worked in all browsers but maybe theres more magic in those environments to manage ipv4/6. I'll leave this here in case others run into the issue but if I am still having problems I'll make a new issue to track my particular case.

[MikeMcC399]

@pm0u

Good to hear that you've got things working! I wouldn't worry too much about whether this is the best workaround. There isn't a one-size-fits-all solution and if your workaround is doing the job, then just stick with it!