increase the default UDP buffer

Author: ameshkov

server.go

@@ -18,6 +18,10 @@ const defaultReadTimeout = 2 * time.Second
 // then we start using defaultTCPIdleTimeout
 const defaultTCPIdleTimeout = 8 * time.Second
 
+// defaultUDPSize is the size of the UDP read buffer. Using 1252 by default,
+// see here: https://github.com/AdguardTeam/AdGuardDNS/issues/188
+const defaultUDPSize = 1252
+
 // helper struct that is used in several SetReadDeadline calls
 var longTimeAgo = time.Unix(1, 0)
 
@@ -49,7 +53,7 @@ type Server struct {
 	ResolverCert *Cert
 
 	// UDPSize is the default buffer size to use to read incoming UDP messages.
-	// If not set it defaults to dns.MinMsgSize (512 B).
+	// If not set it defaults to defaultUDPSize (1252 B).
 	UDPSize int
 
 	// Handler to invoke. If nil, uses DefaultHandler.
@@ -154,7 +158,7 @@ func (s *Server) init() {
 	s.tcpListeners = map[net.Listener]struct{}{}
 
 	if s.UDPSize == 0 {
-		s.UDPSize = dns.MinMsgSize
+		s.UDPSize = defaultUDPSize
 	}
 }