Test: etharp_gratuitous (#1877)

* test: etharp_gratuitous

* proper checks before calling etharp_gratuitous, move includes

* disable at runtime

* ms values

* reload

* debug

* reword

* filter by ifnum instead of checking for AP mode

* drop station_if check

2.3.0/lwip1 builds netif->num increments on for each sta or ap
lwip2 keeps those constant, but that seems like a implementation detail
might break in the future anyways...

code/espurna/config/general.h

@@ -554,6 +554,25 @@
 #define WIFI_PROPAGATION_CONST      4           // This is typically something between 2.7 to 4.3 (free space is 2)
 #endif
 
+// ref: https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/kconfig.html#config-lwip-esp-gratuitous-arp
+// ref: https://github.com/xoseperez/espurna/pull/1877#issuecomment-525612546 
+//
+// Broadcast gratuitous ARP periodically to update ARP tables on the AP and all devices on the same network.
+// Helps to solve compatibility issues when ESP fails to timely reply to ARP requests, causing the device's ARP table entry to expire.
+
+#ifndef WIFI_GRATUITOUS_ARP_SUPPORT
+#define WIFI_GRATUITOUS_ARP_SUPPORT              1
+#endif
+
+// Interval is randomized on each boot in range from ..._MIN to ..._MAX (ms)
+#ifndef WIFI_GRATUITOUS_ARP_INTERVAL_MIN
+#define WIFI_GRATUITOUS_ARP_INTERVAL_MIN         15000
+#endif
+
+#ifndef WIFI_GRATUITOUS_ARP_INTERVAL_MAX
+#define WIFI_GRATUITOUS_ARP_INTERVAL_MAX         30000
+#endif
+
 // -----------------------------------------------------------------------------
 // WEB
 // -----------------------------------------------------------------------------

code/espurna/config/prototypes.h

@@ -367,6 +367,12 @@ using wifi_callback_f = std::function<void(justwifi_messages_t code, char * para
 void wifiRegister(wifi_callback_f callback);
 bool wifiConnected();
 
+#if LWIP_VERSION_MAJOR == 1
+#include <netif/etharp.h>
+#else // LWIP_VERSION_MAJOR >= 2
+#include <lwip/etharp.h>
+#endif
+
 // -----------------------------------------------------------------------------
 // THERMOSTAT
 // -----------------------------------------------------------------------------

code/espurna/wifi.ino

@@ -15,6 +15,11 @@ bool _wifi_smartconfig_running = false;
 bool _wifi_smartconfig_initial = false;
 uint8_t _wifi_ap_mode = WIFI_AP_FALLBACK;
 
+#if WIFI_GRATUITOUS_ARP_SUPPORT
+unsigned long _wifi_gratuitous_arp_interval = 0;
+unsigned long _wifi_gratuitous_arp_last = 0;
+#endif
+
 // -----------------------------------------------------------------------------
 // PRIVATE
 // -----------------------------------------------------------------------------
@@ -91,6 +96,14 @@ void _wifiConfigure() {
     sleep_mode = constrain(sleep_mode, 0, 2);
 
     WiFi.setSleepMode(static_cast<WiFiSleepType_t>(sleep_mode));
+
+    #if WIFI_GRATUITOUS_ARP_SUPPORT
+        _wifi_gratuitous_arp_last = millis();
+        _wifi_gratuitous_arp_interval = getSetting("wifiGarpIntvl", secureRandom(
+            WIFI_GRATUITOUS_ARP_INTERVAL_MIN, WIFI_GRATUITOUS_ARP_INTERVAL_MAX
+        )).toInt();
+    #endif
+
 }
 
 void _wifiScan(uint32_t client_id = 0) {
@@ -504,6 +517,47 @@ void _wifiWebSocketOnAction(uint32_t client_id, const char * action, JsonObject&
 
 #endif
 
+// -----------------------------------------------------------------------------
+// SUPPORT
+// -----------------------------------------------------------------------------
+
+#if WIFI_GRATUITOUS_ARP_SUPPORT
+
+// ref: lwip src/core/netif.c netif_issue_reports(...)
+// ref: esp-lwip/core/ipv4/etharp.c garp_tmr()
+// TODO: only for ipv4, need (?) a different method with ipv6
+bool _wifiSendGratuitousArp() {
+
+    bool result = false;
+    for (netif* interface = netif_list; interface != nullptr; interface = interface->next) {
+        if (
+            (interface->flags & NETIF_FLAG_ETHARP)
+            && (interface->hwaddr_len == ETHARP_HWADDR_LEN)
+        #if LWIP_VERSION_MAJOR == 1
+            && (!ip_addr_isany(&interface->ip_addr))
+        #else
+            && (!ip4_addr_isany_val(*netif_ip4_addr(interface)))
+        #endif
+            && (interface->flags & NETIF_FLAG_LINK_UP)
+            && (interface->flags & NETIF_FLAG_UP)
+        ) {
+            etharp_gratuitous(interface);
+            result = true;
+        }
+    }
+
+    return result;
+}
+
+void _wifiSendGratuitousArp(unsigned long interval) {
+    if (millis() - _wifi_gratuitous_arp_last > interval) {
+        _wifi_gratuitous_arp_last = millis();
+        _wifiSendGratuitousArp();
+    }
+}
+
+#endif // WIFI_GRATUITOUS_ARP_SUPPORT
+
 // -----------------------------------------------------------------------------
 // INFO
 // -----------------------------------------------------------------------------
@@ -730,4 +784,11 @@ void wifiLoop() {
         _wifiCheckAP();
     }
 
+    #if WIFI_GRATUITOUS_ARP_SUPPORT
+        // Only send out gra arp when in STA mode
+        if (_wifi_gratuitous_arp_interval) {
+            _wifiSendGratuitousArp(_wifi_gratuitous_arp_interval);
+        }
+    #endif
+
 }