Add support for custom DNS resolvers

network/v2/dns.go

@@ -0,0 +1,53 @@
+package network
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/url"
+	"time"
+
+	"github.com/ncruces/go-dns"
+)
+
+var dnsCacheOptions = []dns.CacheOption{
+	dns.MaxCacheEntries(dns.DefaultMaxCacheEntries),
+	dns.MaxCacheTTL(time.Hour),
+	dns.NegativeCache(false),
+}
+
+func GetDNS(u *url.URL) (*net.Resolver, error) {
+	if u == nil {
+		return dns.NewCachingResolver(nil, dnsCacheOptions...), nil
+	}
+
+	switch u.Scheme {
+	case "tls":
+		return dns.NewDoTResolver(u.Host, dns.DoTCache(dnsCacheOptions...))
+	case "https":
+		if u.Path == "" {
+			u.Path = "/dns-query"
+		}
+
+		return dns.NewDoHResolver(u.String(), dns.DoHCache(dnsCacheOptions...))
+	case "udp", "":
+	default:
+		return nil, fmt.Errorf("unsupported DNS %v", u)
+	}
+
+	port := u.Port()
+	if port == "" {
+		port = "53"
+	}
+
+	hostport := net.JoinHostPort(u.Hostname(), port)
+	dialer := &net.Dialer{}
+	resolver := &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+			return dialer.DialContext(ctx, "udp", hostport)
+		},
+	}
+
+	return dns.NewCachingResolver(resolver, dnsCacheOptions...), nil
+}