fix possible dhcp bounce

src/core/network.cpp

@@ -522,6 +522,22 @@ void Network::startWIFI() {
 #endif
 }
 
+#if CONFIG_IDF_TARGET_ESP32 && !defined(EMSESP_STANDALONE)
+// Unlike WiFi, which stamps the hostname onto the STA netif as it is created, the Arduino ETH class
+// leaves it unset, so lwIP falls back to CONFIG_LWIP_LOCAL_HOSTNAME ("tasmota" in the SDK we build
+// against). esp_eth_start() polls the PHY synchronously, so on a warm reboot where the link never
+// dropped the DHCP DISCOVER can go out before ETH.begin() has even returned. This handler is
+// registered ahead of the esp_netif glue and therefore runs first, applying the hostname before the
+// netif is handed to lwIP.
+static char eth_hostname[33] = {0};
+
+static void ethApplyHostname(void * /*arg*/, esp_event_base_t /*base*/, int32_t /*event_id*/, void * /*event_data*/) {
+    if (eth_hostname[0] != '\0' && ETH.netif() != nullptr) {
+        esp_netif_set_hostname(ETH.netif(), eth_hostname);
+    }
+}
+#endif
+
 // Ethernet management
 // Brings up the ETH driver / netif exactly once. After ETH.begin() returns true the driver
 // continues to run autonomously (link negotiation, DHCP, etc)
@@ -577,16 +593,44 @@ void Network::startEthernet() {
     eth_phy_type_t type = (phy_type_ == PHY_type::PHY_TYPE_LAN8720)  ? ETH_PHY_LAN8720
                           : (phy_type_ == PHY_type::PHY_TYPE_TLK110) ? ETH_PHY_TLK110
                                                                      : ETH_PHY_RTL8201; // Type of the Ethernet PHY (LAN8720 or TLK110)
+
+    // must be in place before ETH.begin() so it beats the esp_netif glue to the START event
+    strlcpy(eth_hostname, hostname_.c_str(), sizeof(eth_hostname));
+    if (!eth_hostname_handler_registered_ && esp_event_handler_register(ETH_EVENT, ETHERNET_EVENT_START, ethApplyHostname, nullptr) == ESP_OK) {
+        eth_hostname_handler_registered_ = true;
+    }
+
     if (ETH.begin(type, eth_phy_addr_, 23, 18, eth_power_, (eth_clock_mode_t)eth_clock_mode_)) {
-        LOG_DEBUG("Ethernet module found - starting");
+        LOG_DEBUG("Ethernet found - starting");
         ethernet_connect_pending_ = true;
-        ETH.setHostname(hostname_.c_str()); // Push hostname to the ETH netif immediately after it's created
+
+        // check whether DHCP already announced us under lwIP's default hostname, before we correct it
+        esp_netif_t * eth_netif    = ETH.netif();
+        const char *  old_hostname = nullptr;
+        bool          stale_dhcp   = false;
+        if (eth_netif != nullptr && !staticIPConfig_) {
+            esp_netif_dhcp_status_t dhcp_status = ESP_NETIF_DHCP_INIT;
+            stale_dhcp = esp_netif_get_hostname(eth_netif, &old_hostname) == ESP_OK && old_hostname != nullptr && hostname_ != old_hostname
+                         && esp_netif_dhcpc_get_status(eth_netif, &dhcp_status) == ESP_OK && dhcp_status == ESP_NETIF_DHCP_STARTED;
+        }
+
+        if (!ETH.setHostname(hostname_.c_str())) {
+            LOG_WARNING("Failed to set Ethernet hostname to %s", hostname_.c_str());
+        }
+
+        // the DHCP server has already been given the wrong name, so re-run the client to re-announce
+        if (stale_dhcp) {
+            LOG_DEBUG("Restarting Ethernet DHCP client to announce hostname %s", hostname_.c_str());
+            esp_netif_dhcpc_stop(eth_netif);
+            esp_netif_dhcpc_start(eth_netif);
+        }
+
         ETH.enableIPv6(true);
         if (staticIPConfig_) {
             ETH.config(localIP_, gatewayIP_, subnetMask_, dnsIP1_, dnsIP2_);
         }
     } else {
-        LOG_ERROR("Failed to start Ethernet module");
+        LOG_ERROR("Failed to start Ethernet");
     }
 #endif
 #endif

src/core/network.h

@@ -205,9 +205,10 @@ class Network {
 
     NetPhase phase_ = NetPhase::ETHERNET;
 
-    bool wifi_events_registered_  = false; // ensure WiFi.onEvent() handlers are registered only once across begin()/reconnect() cycles
+    bool wifi_events_registered_          = false; // ensure WiFi.onEvent() handlers are registered only once across begin()/reconnect() cycles
-    bool wifi_ever_connected_     = false; // set true once we've successfully obtained an IP
+    bool eth_hostname_handler_registered_ = false; // for the ETHERNET_EVENT_START hostname handler
-    bool ethernet_ever_connected_ = false; // set true once we've successfully obtained an IP
+    bool wifi_ever_connected_             = false; // set true once we've successfully obtained an IP
+    bool ethernet_ever_connected_         = false; // set true once we've successfully obtained an IP
 
     // Network and AP settings
     bool      enableMDNS_;