Servers updater (#232)

* Support for all VPN providers
* Update all VPN providers servers information
* Remove old tooling binaries

internal/updater/resolver.go

@@ -0,0 +1,41 @@
+package updater
+
+import (
+	"context"
+	"net"
+)
+
+func newResolver(resolverAddress string) *net.Resolver {
+	return &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+			d := net.Dialer{}
+			return d.DialContext(ctx, "udp", net.JoinHostPort(resolverAddress, "53"))
+		},
+	}
+}
+
+func newLookupIP(r *net.Resolver) lookupIPFunc {
+	return func(ctx context.Context, host string) (ips []net.IP, err error) {
+		addresses, err := r.LookupIPAddr(ctx, host)
+		if err != nil {
+			return nil, err
+		}
+		ips = make([]net.IP, len(addresses))
+		for i := range addresses {
+			ips[i] = addresses[i].IP
+		}
+		return ips, nil
+	}
+}
+
+func resolveRepeat(ctx context.Context, lookupIP lookupIPFunc, host string, n int) (ips []net.IP, err error) {
+	for i := 0; i < n; i++ {
+		newIPs, err := lookupIP(ctx, host)
+		if err != nil {
+			return nil, err
+		}
+		ips = append(ips, newIPs...)
+	}
+	return uniqueSortedIPs(ips), nil
+}