Pull request: * all: move internal Go packages to internal/

Merge in DNS/adguard-home from 2234-move-to-internal to master

Squashed commit of the following:

commit d26a288cabeac86f9483fab307677b1027c78524
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 12:44:18 2020 +0300

    * all: move internal Go packages to internal/

    Closes #2234.

internal/dnsforward/util.go

@@ -0,0 +1,102 @@
+package dnsforward
+
+import (
+	"net"
+	"sort"
+	"strings"
+
+	"github.com/AdguardTeam/golibs/utils"
+)
+
+// GetIPString is a helper function that extracts IP address from net.Addr
+func GetIPString(addr net.Addr) string {
+	switch addr := addr.(type) {
+	case *net.UDPAddr:
+		return addr.IP.String()
+	case *net.TCPAddr:
+		return addr.IP.String()
+	}
+	return ""
+}
+
+func stringArrayDup(a []string) []string {
+	a2 := make([]string, len(a))
+	copy(a2, a)
+	return a2
+}
+
+// Get IP address from net.Addr object
+// Note: we can't use net.SplitHostPort(a.String()) because of IPv6 zone:
+// https://github.com/AdguardTeam/AdGuardHome/internal/issues/1261
+func ipFromAddr(a net.Addr) string {
+	switch addr := a.(type) {
+	case *net.UDPAddr:
+		return addr.IP.String()
+	case *net.TCPAddr:
+		return addr.IP.String()
+	}
+	return ""
+}
+
+// Get IP address from net.Addr
+func getIP(addr net.Addr) net.IP {
+	switch addr := addr.(type) {
+	case *net.UDPAddr:
+		return addr.IP
+	case *net.TCPAddr:
+		return addr.IP
+	}
+	return nil
+}
+
+// Find value in a sorted array
+func findSorted(ar []string, val string) int {
+	i := sort.SearchStrings(ar, val)
+	if i == len(ar) || ar[i] != val {
+		return -1
+	}
+	return i
+}
+
+func isWildcard(host string) bool {
+	return len(host) >= 2 &&
+		host[0] == '*' && host[1] == '.'
+}
+
+// Return TRUE if host name matches a wildcard pattern
+func matchDomainWildcard(host, wildcard string) bool {
+	return isWildcard(wildcard) &&
+		strings.HasSuffix(host, wildcard[1:])
+}
+
+// Return TRUE if client's SNI value matches DNS names from certificate
+func matchDNSName(dnsNames []string, sni string) bool {
+	if utils.IsValidHostname(sni) != nil {
+		return false
+	}
+	if findSorted(dnsNames, sni) != -1 {
+		return true
+	}
+
+	for _, dn := range dnsNames {
+		if matchDomainWildcard(sni, dn) {
+			return true
+		}
+	}
+	return false
+}
+
+// Is not comment
+func isUpstream(line string) bool {
+	return !strings.HasPrefix(line, "#")
+}
+
+func filterOutComments(lines []string) []string {
+	var filtered []string
+	for _, l := range lines {
+		if isUpstream(l) {
+			filtered = append(filtered, l)
+		}
+	}
+	return filtered
+}