Setting the servername to an empty string '' should disable sending the SNI extension.

[holgerkoser]

The option servername in tls.connect(options[, callback]) is the name of the host being connected to, and must be a host name, and not an IP address. If the server is not a multi-homed server and I want to connect with the IP address it is not possible to disable sending the SNI extension by setting the servername to empty string ''. This PR implements the defaulting of the servername in the same way as it is done in the node.

This PR is related to #1347 .

Example
In node v12 with the following code

new WebSocket('wss://127.0.0.1', {
  ca: fs.readFileSync('ssl/ca.pem'),
  servername: '',
})

I get the deprecation warning [DEP0123]

(node:71346) [DEP0123] DeprecationWarning: Setting the TLS ServerName to an IP address 
is not permitted by RFC 6066. This will be ignored in a future version.

[lpinca]

Can you add a test?

[holgerkoser]

Yes, of course. I already tried to add a test in the SSL but I not found an easy way to intercept the tls.connect call. I normally use proxyquire for this but don't wanted to add a new dependency for such a small change. I try to find an alternative simple solution for a test.

[lpinca]

I think you can "copy" the test included in nodejs/node@98e9de7.

[holgerkoser]

Thanks for the hint. I have seen it too late and already added a test. If you think it is better to "copy" the kind of test from node I will do that.

[lpinca]

Can you please mock tls.connect() here and remove the describe wrapper and the beforeEach() and afterEach() hook? We will add them if/when needed. Thank you.

[lpinca]

I prefer your test.

[lpinca]

Thank you.

[holgerkoser]

@lpinca Couldn't answer any more, because I had two days off and since today I'm back in office again. Many thanks for your fast reply and your help.

Wouldn't it be better to restore the original net.connect before the assert?

        tls.connect = original;
        assert.strictEqual(options.servername, '');

Or does the test runner stop all tests if the first test fails?