[Question] Is it possible to define host resolution rules per browser instance?

[southp]

In my daily work, I often have to tweak the /etc/hosts file for routing production site URLs to the development sites for testing.
Is it possible to launch a browser instance with a set of customized host resolution rules? For example,

const browser = await chromium.launch( {
    hosts: {
        'example.com': '127.0.0.1',  // all the request to example.com will then be routed to my local machine.
    }
} );

I believe it's possible by dockerizing my playwright testing program, but would like to see if there is a lightweight solution for this.

Thanks :)

[shirshak55]

i think it is better if u edit manually or use proxies? And I create dns myself and u can also do that ?

[pavelfeldman]

No way to do this for all the browsers atm. Let's open it to collecting feedback.

You can pass host rules via args to Chromium, but other browsers don't support it:

https://stackoverflow.com/questions/14605636/host-rules-google-chrome-adding-configuration

[pavelfeldman]

Posting an investigation note for myself, network.dns.forceResolve does most of the job for Firefox, so can be passed using firefoxUserPrefs. Discussion: https://bugzilla.mozilla.org/show_bug.cgi?id=1523367

[southp]

Thanks for finding those, @pavelfeldman . I haven't been able to make it work since I don't have enough time today, but it indeed looks promising.

Even though it's not yet supported by all the browsers, my two cents go to abstract it to the Playwright level, e.g.

browser.launch( {
    hostResolutionRules: [ ... ],
} );

or

browser.addHostResolutionRules( '...' );

If the browser instance being used doesn't support it, throwing an exception to terminate further attempts could be a good first step.

I'll circle back after I've done more testing.

[Quo0]

No way to do this for all the browsers atm. Let's open it to collecting feedback.

You can pass host rules via args to Chromium, but other browsers don't support it:

https://stackoverflow.com/questions/14605636/host-rules-google-chrome-adding-configuration

Hi Pavel!
Looks like Chrome headless doesn't see local etc/hosts.
(Windows 10, Playwright 1.1.1)

I keep getting 404 at page navigation when headless but don't have any issues when run script headfull.
The most bizarre thing is that if I will debug headless by using --remote-debugging-port
and navigate manually through the chrome://inspect to the desired URL
I will not get any errors!

Can you recommend something?

My hosts file is
127.0.0.1 dev.mysite

const browserOptions = {
  ignoreHTTPSErrors: true,

  args: [
    '--no-sandbox',
    '--remote-debugging-port=9222',
    '--host-rules="MAP 127.0.0.1 dev.mysite'
  ],
}

[southp]

I am experiencing the same as @Quo0 described above, but am not sure if it's a Chromium issue or a Playwright one. Fwiw, according to the latest command line list, --host-rules should be replaced by --host-resolver-rules.

[Quo0]

Tried both variants, but still an issue with Chrome:

args: [
    // '--host-rules="MAP 127.0.0.1 dev.smthg'
    '--host-resolver-rules="MAP 127.0.0.1 dev.smthg'
]

I have Github Actions workflow and inside it I'm updating the etc/hosts file manually.
Firefox is working fine, but looks like Chrome doesn't see this file at all...
The same happens locally with Windows 10

[Quo0]

Sorry, @southp , did you overcome this issue with this additional args ???

[Quo0]

Found this Chromium issue: https://bugs.chromium.org/p/chromium/issues/detail?id=798793

[Gotterbild]

Same bug in Puppeteer: puppeteer/puppeteer#1701

[southp]

@Quo0 Hey, sorry for the late response. After rerunning my test code, I can confirm that the issue is still there. I thought I had seen the additional flag work for me previously, but can't confirm if it was just me being mistaken or it really had worked once.

[pavelfeldman]

Now that Playwright supports proxies, we consider this being outside of the Playwright scope. Closing this as a part of the triage, please feel free to file a new issue with additional details. Given the limited resource and a lot of requests, we need to fulfill most popular requests and at the same time keep our issue database manageable.

[PiotrCzapla]

Tried both variants, but still an issue with Chrome:

args: [
    // '--host-rules="MAP 127.0.0.1 dev.smthg'
    '--host-resolver-rules="MAP 127.0.0.1 dev.smthg'
]

I have Github Actions workflow and inside it I'm updating the etc/hosts file manually.
Firefox is working fine, but looks like Chrome doesn't see this file at all...
The same happens locally with Windows 10

I think the code doesn't work due to additional quote inside of the rule.

 args: [ '--host-resolver-rules="MAP 127.0.0.1 dev.smthg"' ]  // the double quote cause the issue

This argument should looks as follows in playwright:

args: [ '--host-resolver-rules=MAP 127.0.0.1 dev.smthg' ]