Pull request 1927: 6006-use-address-processor

Updates #6006.

Squashed commit of the following:

commit ac27db95c12858b6ef182a0bd4acebab67a23993
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jul 18 15:47:17 2023 +0300

    all: imp code

commit 3936288512bfc2d44902ead6ab1bb5711f92b73c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Jul 17 19:23:46 2023 +0300

    all: imp client resolving

internal/dnsforward/dialcontext.go

@@ -0,0 +1,57 @@
+package dnsforward
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/AdguardTeam/golibs/errors"
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// DialContext is a [whois.DialContextFunc] that uses s to resolve hostnames.
+func (s *Server) DialContext(ctx context.Context, network, addr string) (conn net.Conn, err error) {
+	log.Debug("dnsforward: dialing %q for network %q", addr, network)
+
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	dialer := &net.Dialer{
+		// TODO(a.garipov): Consider making configurable.
+		Timeout: time.Minute * 5,
+	}
+
+	if net.ParseIP(host) != nil {
+		return dialer.DialContext(ctx, network, addr)
+	}
+
+	addrs, err := s.Resolve(host)
+	if err != nil {
+		return nil, fmt.Errorf("resolving %q: %w", host, err)
+	}
+
+	log.Debug("dnsforward: resolving %q: %v", host, addrs)
+
+	if len(addrs) == 0 {
+		return nil, fmt.Errorf("no addresses for host %q", host)
+	}
+
+	var dialErrs []error
+	for _, a := range addrs {
+		addr = net.JoinHostPort(a.String(), port)
+		conn, err = dialer.DialContext(ctx, network, addr)
+		if err != nil {
+			dialErrs = append(dialErrs, err)
+
+			continue
+		}
+
+		return conn, err
+	}
+
+	// TODO(a.garipov): Use errors.Join in Go 1.20.
+	return nil, errors.List(fmt.Sprintf("dialing %q", addr), dialErrs...)
+}