Add string checks for IPv4, IPv6

[NeQuissimus]

Uses java.net.Inet{,4,6}Address to determine whether a String is a valid IPv4/IPv6.

[NeQuissimus]

What should I do about the MiMa errors about 2.11 and 2.10?
I was not expecting additions to cause binary compatibility issues...

[fthomas]

@NeQuissimus In principle these predicates would be a welcome addition but I'm afraid we can't use java.net.InetAddress.getByName in the Validate instances because of their side-effecting nature. It seems that this method performs a DNS lookup if the given string is a hostname and only checks the validity of the address format if a literal IP address is provided. This means that code like

val x: String Refined IPv4 = "github.com"

would perform a DNS lookup at compile-time and therefore compilation would be dependent on the network. This should be avoided.

As far as I can see java.net.InetAddress has no function that just checks the format of literal IP addresses. Fortunately there is a refined-guava module by @derekmorr that provides IPv4 and IPv6 predicates (besides others) which uses Guava's com.google.common.net.InetAddresses.forString function which deliberately avoids all DNS lookups.

[NeQuissimus]

@fthomas Oooh, I did not know about refined-guava! It does exactly what I need then :)
I realized just today that it would allow DNS lookups, so I was already planning to update this PR... I'll just close it now.

[fthomas]

Out of curiosity, is there an easy way to implement these predicates without adding additional dependencies?

[NeQuissimus]

Well, you could create Regex' to match them but then you'll end up with giant regular expressions :)
I mean, look at this: https://stackoverflow.com/questions/53497/regular-expression-that-matches-valid-ipv6-addresses/17871737

All the JDK stuff makes DNS calls as far as I know.

[NeQuissimus]

Actually, we could boolean a very simple regex on top of this PR to avoid DNS lookups...

[derekmorr]

I can look into published refined-guava. That was based on some work I did that also needed IP address parsing, but I didn't want to side-effect. Unfortunately, guava is a big dependency for that.

@fthomas Would you want this as a module for refined, or would you prefer it as a separate project?

[NeQuissimus]

@fthomas @derekmorr Or, we could use apache/commons-validator, which is much smaller, and would allow us to add a bunch of stuff. (think credit card numbers, email address...)
I'd be more than willing to help out with this (since I will be using it :D)

[fthomas]

I don't have any experience with commons-validator but if it is more suitable than Guava, go for it. However, one downside of Java dependencies is that we won't be able to cross-compile it for Scala.js and Scala Native.
A new module in refined for these predicates is fine with me.