1 files changed, 15 insertions, 3 deletions
diff --git a/libgo/go/net/lookup.go b/libgo/go/net/lookup.go
index 9008322..7aa111b 100644
--- a/libgo/go/net/lookup.go
+++ b/libgo/go/net/lookup.go
@@ -123,10 +123,22 @@ func lookupIPDeadline(host string, deadline time.Time) (addrs []IPAddr, err erro
 
 // LookupPort looks up the port for the given network and service.
 func LookupPort(network, service string) (port int, err error) {
-	if n, i, ok := dtoi(service, 0); ok && i == len(service) {
-		return n, nil
+	if service == "" {
+		// Lock in the legacy behavior that an empty string
+		// means port 0. See Issue 13610.
+		return 0, nil
 	}
-	return lookupPort(network, service)
+	port, _, ok := dtoi(service, 0)
+	if !ok && port != big && port != -big {
+		port, err = lookupPort(network, service)
+		if err != nil {
+			return 0, err
+		}
+	}
+	if 0 > port || port > 65535 {
+		return 0, &AddrError{Err: "invalid port", Addr: service}
+	}
+	return port, nil
 }
 
 // LookupCNAME returns the canonical DNS host for the given name.