Use a different address than 255.255.255.0 for netprobes

Windows doesn't seem to like this address.

Also default to the fallback resolver IP if there is one and
no netprobe_address option in the configuration file.

Fix netprobe_timeout = -1 by the way

dnscrypt-proxy/config.go

@@ -22,6 +22,7 @@ import (
 
 const (
 	MaxTimeout             = 3600
+	DefaultNetprobeAddress = "9.9.9.9:53"
 )
 
 type Config struct {
@@ -112,7 +113,6 @@ func newConfig() Config {
 		LogMaxBackups:            1,
 		TLSDisableSessionTickets: false,
 		TLSCipherSuite:           nil,
-		NetprobeAddress:          "255.255.255.0:53",
 		NetprobeTimeout:          60,
 		OfflineMode:              false,
 		RefusedCodeInResponses:   false,
@@ -425,7 +425,13 @@ func ConfigLoad(proxy *Proxy, svcFlag *string) error {
 			netprobeTimeout = *netprobeTimeoutOverride
 		}
 	})
-	NetProbe(config.NetprobeAddress, netprobeTimeout)
+	netprobeAddress := DefaultNetprobeAddress
+	if len(config.NetprobeAddress) > 0 {
+		netprobeAddress = config.NetprobeAddress
+	} else if len(config.FallbackResolver) > 0 {
+		netprobeAddress = config.FallbackResolver
+	}
+	NetProbe(netprobeAddress, netprobeTimeout)
 	if !config.OfflineMode {
 		if err := config.loadSources(proxy); err != nil {
 			return err

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -217,7 +217,7 @@ netprobe_timeout = 60
 ## On other operating systems, the connection will be initialized
 ## but nothing will be sent at all.
 
-netprobe_address = "255.255.255.0:53"
+netprobe_address = "9.9.9.9:53"
 
 
 ## Offline mode - Do not use any remote encrypted servers.

dnscrypt-proxy/netprobe_windows.go

@@ -9,7 +9,7 @@ import (
 )
 
 func NetProbe(address string, timeout int) error {
-	if len(address) <= 0 || timeout <= 0 {
+	if len(address) <= 0 || timeout == 0 {
 		return nil
 	}
 	remoteUDPAddr, err := net.ResolveUDPAddr("udp", address)