From ca94b4a2a27f942147a75a5ffd53af8db583d677 Mon Sep 17 00:00:00 2001
From: Juraj Andrassy <juraj.andrassy@gmail.com>
Date: Sun, 11 Oct 2020 14:40:02 +0200
Subject: [PATCH] EthernetUdp - prevent filtering of received messages by IP
 and port of sent message

---
 src/Ethernet.cpp    |  2 +-
 src/EthernetUdp.cpp | 16 ++++++++++++++--
 src/EthernetUdp.h   |  2 +-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/Ethernet.cpp b/src/Ethernet.cpp
index 44863b1..919003d 100644
--- a/src/Ethernet.cpp
+++ b/src/Ethernet.cpp
@@ -262,7 +262,7 @@ UIPEthernetClass::tick()
           // uip_len is set to a value > 0. */
           if (uip_len > 0)
             {
-              EthernetUDP::_send((uip_udp_userdata_t *)(uip_udp_conns[i].appstate));
+              EthernetUDP::_send(&uip_udp_conns[i]);
             }
         }
 #endif /* UIP_UDP */
diff --git a/src/EthernetUdp.cpp b/src/EthernetUdp.cpp
index b03cd7d..bbfd2ae 100644
--- a/src/EthernetUdp.cpp
+++ b/src/EthernetUdp.cpp
@@ -90,6 +90,9 @@ UIPUDP::beginPacket(IPAddress ip, uint16_t port)
 #endif
       if (_uip_udp_conn)
         {
+          // [J.A]: for UDP server, setting ripaddr and rport causes in uIP filtering
+          // of incoming messages. it would be better to store the IP and port in fields
+          // and set them only in endPacket().
           _uip_udp_conn->rport = htons(port);
           uip_ipaddr_copy(_uip_udp_conn->ripaddr, &ripaddr);
         }
@@ -170,7 +173,7 @@ UIPUDP::endPacket()
       uip_udp_periodic_conn(_uip_udp_conn);
       if (uip_len > 0)
         {
-          _send(&appdata);
+          _send(_uip_udp_conn);
           return 1;
         }
     }
@@ -359,7 +362,8 @@ uipudp_appcall(void) {
 }
 
 void
-UIPUDP::_send(uip_udp_userdata_t *data) {
+UIPUDP::_send(struct uip_udp_conn *uip_udp_conn) {
+
   uip_arp_out(); //add arp
   if (uip_len == UIP_ARPHDRSIZE)
     {
@@ -373,9 +377,17 @@ UIPUDP::_send(uip_udp_userdata_t *data) {
   else
   //arp found ethaddr for ip (otherwise packet is replaced by arp-request)
     {
+      uip_udp_userdata_t* data = (uip_udp_userdata_t *)(uip_udp_conn->appstate);
       UIPEthernetClass::network_send();
       data->send = false;
       data->packet_out = NOBLOCK;
+
+      // [J.A] a listening UDP port in uIP filters received messages
+      // if rport and ripaddr are set. so we better clear them
+      uip_udp_conn->rport = 0;
+      uip_udp_conn->ripaddr[0] = 0;
+      uip_udp_conn->ripaddr[1] = 0;
+
 #ifdef UIPETHERNET_DEBUG_UDP
       Serial.print(F("udp, uip_packet to send: "));
       Serial.println(UIPEthernetClass::uip_packet);
diff --git a/src/EthernetUdp.h b/src/EthernetUdp.h
index df7d4bc..43d27ca 100644
--- a/src/EthernetUdp.h
+++ b/src/EthernetUdp.h
@@ -129,7 +129,7 @@ class EthernetUDP : public UDP
   friend void uipudp_appcall(void);
 
   friend class UIPEthernetClass;
-  static void _send(uip_udp_userdata_t *data);
+  static void _send(struct uip_udp_conn *uip_udp_conn);
 
   static uint8_t _newBlock(uip_udp_msg_rec_t* blocks);
   static void _moveBlocks(uip_udp_msg_rec_t* blocks);