Use tsurlfilter's DNS engine

[mjethani]

This patch uses the DNS engine in @adguard/tsurlfilter for hosts-only mode.

[mjethani]

@ameshkov FYI

Hosts-only mode is for testing blocking at the host level only. The DnsEngine object is perfect for this.

In actual DNS mode there would be no URL from which to extract the hostname, but the extractHostname() function is extremely fast and I don't think it makes any significant difference to the benchmark results.

[mjethani]

Something worth noting is that the DNS engine also supports whitelisting rules. This is also true of other content blockers like uBlock Origin. But we have no whitelisting rules in our hosts.txt file here.

[ameshkov]

Well, it also supports a little different subset of rules & modifiers, the syntax is explained here:
https://github.com/AdguardTeam/AdGuardHome/wiki/Hosts-Blocklists

Although, tsurlfilter is only capable of basic matching since it is only used for simple rules validation by different automation scripts. AdGuard DNS and AdGuard Home use another content blocking library.

[mjethani]

@ameshkov thanks for helping with the integration.

The only thing left now is serialization and deserialization. I could not find anything in the README.md file for this. I see there's a RuleStorage object, but I'm not sure how to use it.

Since the library is under development, it's not so important to implement this now.

In the future, when an API is available, we'll have to implement the following two functions in blockers/tsurlfilter.js in this repo:

class TSUrlFilter {
  async serialize() {
    // return data in serialized format
  }

  async deserialize(serialized) {
    // initialize engine with given data in serialized format
  }
}