Pull request 1964: AG-23599 use hostsfile

Merge in DNS/adguard-home from AG-23599-use-hostsfile to master

Squashed commit of the following:

commit 4766e67a9d5faa4bc89a2a935d187ce4829f7214
Merge: 38369360b 762e5be97
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Aug 22 16:33:54 2023 +0300

    Merge branch 'master' into AG-23599-use-hostsfile

commit 38369360b7d0e5c9ec373c5a06bac8792ca9cd69
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Aug 21 18:09:15 2023 +0300

    filtering: imp tests

commit 1c4d4a9f9639f048173e1c949f39f9ecb6ed0347
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Aug 21 14:00:10 2023 +0300

    filtering: imp cognit, cyclo

commit c50c33d7240c2812a715759fabf140e02184b729
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Aug 21 12:57:31 2023 +0300

    filtering: imp code

commit 92203b16719a717a2946c0401e166b1b38ddb7bc
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Aug 18 17:39:11 2023 +0300

    all: imp code, docs

commit 523e8cd50f9136feede657385b7274fa6ba64131
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 17 15:14:02 2023 +0300

    all: fix ipv6

commit 6ce4537132615cbdc34a0b1f326fedd2b63c355d
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 17 14:17:27 2023 +0300

    all: rm urlfilter from hosts

commit d6666e851680c7e586325ea5970e0356ab919074
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 16 15:09:52 2023 +0300

    WIP

commit 4a2732960558bef6636d3c428bad4c7c830016ca
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 16 14:47:13 2023 +0300

    all: use hostsfile

internal/filtering/dnsrewrite.go

@@ -1,6 +1,10 @@
 package filtering
 
 import (
+	"net"
+
+	"github.com/AdguardTeam/golibs/hostsfile"
+	"github.com/AdguardTeam/urlfilter"
 	"github.com/AdguardTeam/urlfilter/rules"
 	"github.com/miekg/dns"
 )
@@ -73,3 +77,59 @@ func (d *DNSFilter) processDNSRewrites(dnsr []*rules.NetworkRule) (res Result) {
 		Reason:           RewrittenRule,
 	}
 }
+
+// processDNSResultRewrites returns an empty Result if there are no dnsrewrite
+// rules in dnsres.  Otherwise, it returns the processed Result.
+func (d *DNSFilter) processDNSResultRewrites(
+	dnsres *urlfilter.DNSResult,
+	host string,
+) (dnsRWRes Result) {
+	dnsr := dnsres.DNSRewrites()
+	if len(dnsr) == 0 {
+		return Result{}
+	}
+
+	res := d.processDNSRewrites(dnsr)
+	if res.Reason == RewrittenRule && res.CanonName == host {
+		// A rewrite of a host to itself.  Go on and try matching other things.
+		return Result{}
+	}
+
+	return res
+}
+
+// appendRewriteResultFromHost appends the rewrite result from rec to vals and
+// resRules.
+func appendRewriteResultFromHost(
+	vals []rules.RRValue,
+	resRules []*ResultRule,
+	rec *hostsfile.Record,
+	qtype uint16,
+) (updatedVals []rules.RRValue, updatedRules []*ResultRule) {
+	switch qtype {
+	case dns.TypeA:
+		if !rec.Addr.Is4() {
+			return vals, resRules
+		}
+
+		vals = append(vals, net.IP(rec.Addr.AsSlice()))
+	case dns.TypeAAAA:
+		if !rec.Addr.Is6() {
+			return vals, resRules
+		}
+
+		vals = append(vals, net.IP(rec.Addr.AsSlice()))
+	case dns.TypePTR:
+		for _, name := range rec.Names {
+			vals = append(vals, name)
+		}
+	}
+
+	recText, _ := rec.MarshalText()
+	resRules = append(resRules, &ResultRule{
+		FilterListID: SysHostsListID,
+		Text:         string(recText),
+	})
+
+	return vals, resRules
+}