From 4195d7c2eec2d93781d5f88fd71f5c7e1ee1ff20 Mon Sep 17 00:00:00 2001
From: Michael Balzer <balzer@expeedo.de>
Date: Tue, 17 Dec 2019 21:16:36 +0100
Subject: [PATCH] LWIP DHCP server: fix disabling DNS offer
MIME-Version: 1.0
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Applying tcpip_adapter_dhcps_option(TCPIP_ADAPTER_OP_SET,
TCPIP_ADAPTER_DOMAIN_NAME_SERVER, …) with option value 0 now disables
the DNS offer. It previously would only switch the DNS offer to sending
the interface IP address instead of the DNS set. If enabled now with an
unset DNS IP (0.0.0.0) it will fallback to the interface IP.
---
 components/lwip/apps/dhcpserver/dhcpserver.c | 30 +++++++++++---------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/components/lwip/apps/dhcpserver/dhcpserver.c b/components/lwip/apps/dhcpserver/dhcpserver.c
index 5e0c1a678..7997eb419 100644
--- a/components/lwip/apps/dhcpserver/dhcpserver.c
+++ b/components/lwip/apps/dhcpserver/dhcpserver.c
@@ -341,18 +341,20 @@ static u8_t *add_offer_options(u8_t *optptr)
         }
     }
 
-    *optptr++ = DHCP_OPTION_DNS_SERVER;
-    *optptr++ = 4;
     if (dhcps_dns_enabled(dhcps_dns)) {
-        *optptr++ = ip4_addr1(&dns_server);
-        *optptr++ = ip4_addr2(&dns_server);
-        *optptr++ = ip4_addr3(&dns_server);
-        *optptr++ = ip4_addr4(&dns_server);
-    }else {
-        *optptr++ = ip4_addr1(&ipadd);
-        *optptr++ = ip4_addr2(&ipadd);
-        *optptr++ = ip4_addr3(&ipadd);
-        *optptr++ = ip4_addr4(&ipadd);
+        *optptr++ = DHCP_OPTION_DNS_SERVER;
+        *optptr++ = 4;
+        if (dns_server.addr != IPADDR_ANY) {
+            *optptr++ = ip4_addr1(&dns_server);
+            *optptr++ = ip4_addr2(&dns_server);
+            *optptr++ = ip4_addr3(&dns_server);
+            *optptr++ = ip4_addr4(&dns_server);
+        } else {
+            *optptr++ = ip4_addr1(&ipadd);
+            *optptr++ = ip4_addr2(&ipadd);
+            *optptr++ = ip4_addr3(&ipadd);
+            *optptr++ = ip4_addr4(&ipadd);
+        }
     }
 
 #ifdef CLASS_B_NET
@@ -1110,7 +1112,7 @@ static void dhcps_poll_set(u32_t ip)
 
 /******************************************************************************
  * FunctionName : dhcps_set_new_lease_cb
- * Description  : set callback for dhcp server when it assign an IP 
+ * Description  : set callback for dhcp server when it assign an IP
  *                to the connected dhcp client
  * Parameters   : cb -- callback for dhcp server
  * Returns      : none
@@ -1306,7 +1308,7 @@ dhcps_dns_setserver(const ip_addr_t *dnsserver)
         dns_server = *(ip_2_ip4(dnsserver));
     } else {
         dns_server = *(ip_2_ip4(IP_ADDR_ANY));
-    } 
+    }
 }
 
 /******************************************************************************
@@ -1315,7 +1317,7 @@ dhcps_dns_setserver(const ip_addr_t *dnsserver)
  * Parameters   : none
  * Returns      : ip4_addr_t
 *******************************************************************************/
-ip4_addr_t 
+ip4_addr_t
 dhcps_dns_getserver()
 {
     return dns_server;