ESP32 Wi-Fi reconnect: handle disconnect events instead of hoping

Symptom

The device works for hours or days, then goes silent after a router reboot, a DHCP hiccup or a short outage, and only comes back after a power cycle.

Why

In ESP-IDF, the Wi-Fi driver does not reconnect on its own. The documentation states it is the application's responsibility; the recommended strategy is to call esp_wifi_connect() when WIFI_EVENT_STA_DISCONNECTED arrives. If the disconnect came from your own esp_wifi_disconnect(), you may choose not to reconnect.

ESP-IDF pattern

static void on_wifi_event(void *arg, esp_event_base_t base, int32_t id, void *data) {
    if (base == WIFI_EVENT && id == WIFI_EVENT_STA_START) {
        esp_wifi_connect();
    } else if (base == WIFI_EVENT && id == WIFI_EVENT_STA_DISCONNECTED) {
        // Optionally inspect ((wifi_event_sta_disconnected_t *)data)->reason
        esp_wifi_connect();   // recommended by ESP-IDF; add backoff if you also scan
    }
}

If your application also calls esp_wifi_scan_start() at arbitrary times, a naive reconnect-on-every-disconnect loop can block scanning; use a state machine or a timer-based retry instead.

Arduino pattern

#include <WiFi.h>

void onWiFiEvent(WiFiEvent_t event) {
  // Runs on a separate thread: keep it short, set flags, don't block.
  if (event == ARDUINO_EVENT_WIFI_STA_DISCONNECTED) {
    Serial.println("Wi-Fi lost");
  } else if (event == ARDUINO_EVENT_WIFI_STA_GOT_IP) {
    Serial.println("Wi-Fi back, IP: " + WiFi.localIP().toString());
  }
}

void setup() {
  Serial.begin(115200);
  WiFi.onEvent(onWiFiEvent);
  WiFi.setAutoReconnect(true);
  WiFi.begin("your-ssid", "your-password");
}

void loop() {
  // Application-level health check: MQTT/HTTP clients need their own reconnect logic,
  // even when Wi-Fi itself has reconnected.
}

Checklist

• Treat "Wi-Fi connected" and "got IP" as different events; only start network clients after an IP is assigned.
• Reconnect your protocol clients (MQTT, WebSocket, HTTP keep-alive) after Wi-Fi returns; they don't recover automatically in most libraries.
• Add backoff between attempts so a dead access point doesn't keep the radio busy (and the battery drained).
• Consider a last-resort restart (esp_restart()) after a long period offline, and log why.
• Don't hard-code credentials in published code; store them in NVS/Preferences.