From f77a6c20e54d44405e95405497f28a62fec2c620 Mon Sep 17 00:00:00 2001
From: Ivan Grokhotkov <ivan@espressif.com>
Date: Thu, 28 Dec 2017 06:12:55 +0800
Subject: [PATCH] WiFiUDP: fix crash when calling destinationIP with no packet
 available

Fixes https://github.com/esp8266/Arduino/issues/3989.
---
 libraries/ESP8266WiFi/src/include/UdpContext.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libraries/ESP8266WiFi/src/include/UdpContext.h b/libraries/ESP8266WiFi/src/include/UdpContext.h
index 95f3420809..31fad1789a 100644
--- a/libraries/ESP8266WiFi/src/include/UdpContext.h
+++ b/libraries/ESP8266WiFi/src/include/UdpContext.h
@@ -163,6 +163,9 @@ class UdpContext
 
     uint32_t getDestAddress()
     {
+        if (!_rx_buf)
+            return 0;
+
         ip_hdr* iphdr = GET_IP_HDR(_rx_buf);
         return iphdr->dest.addr;
     }