Resolve trusted proxy host names to all available A/AAAA records

[ahus1]

Closes #42782

During my tests, I found that CNAMEs are resolved implicitly already, so no manual extra where necessary to handle those.

I might need some help for additional tests, as I don't know how to best mock a DNS.

[cescoffier]

LGTM, but yes, a bit more testing would be great.

Unfortunately, testing DNS is hard. @vietj how do you do that in Vert.x?

@ahus1 Look at https://github.com/eclipse-vertx/vert.x/blob/master/vertx-core/src/test/java/io/vertx/test/fakedns/FakeDNSServer.java.

[vietj]

You can look at the FakeDNSServer in vertx core tests (or reuse it) to do proper testing.

[michalvavrik]

Changes LGTM. +1 for test, I remember I didn't know how to make one.

[geoand]

@ahus1 do you plan to add a test like @cescoffier mentions?

[ahus1]

I had a look at FakeDNSServer. In commit 61f8329 I copied it over as I didn't find it available in a dependency, and used it in a first test which is green. A future commit might clear the bits that are not needed. As this is more like a PoC for a DNS based test, I kept it for now.

It still tests only part of the code, as it is not testing IPv6 as the caller is using IPv4 all the time. Also event.remoteAddress()).ipAddress() is always available, so no resolving of the remote address is necessary. It seems I need some help here to also test those code paths.