Arduino v3.1.2 String crashes on serializeJson

[Tobi177]

Describe the bug
On the latest Arduino release v3.1.2 the function serializeJson does not work anymore and the app is crashing instantly. Within the Arduino release I see that some changes to the String objects were done: espressif/arduino-esp32#10938 Maybe, around this issue is the reason for the crashes, but that is just an assumption. Switching back to previous releases are working fine again. I rollback to Arduino v3.1.1 and the app is working fine again.

Environment
esp-idf v5.3 and Arduino v3.1.2 as a component
ArduinoJson v7.3.0
esp32, esp32c2

Reproduction

String getAvailableNetworks() {

  JsonDocument json_doc;
  JsonArray networks = json_doc.to<JsonArray>();

  int n = WiFi.scanNetworks(false, false);
  if (n) {
    for (int i = 0; i < n; ++i) {
      JsonObject networkObj = networks.add<JsonObject>();
      networkObj["ssid"] = WiFi.SSID(i);
      networkObj["rssi"] = WiFi.RSSI(i);
      networkObj["authmode"] = (WiFi.encryptionType(i) == WIFI_AUTH_OPEN) ? 0 : 1;
    }
  }

  String json_available_networks;
  serializeJson(json_doc, json_available_networks);  // CRASHES HERE

  return json_available_networks;

}

Only the String handling is affected! Once I use char arrays/pointers the serializeJson work fine on Arduino v3.1.2 as well. Only if strings are serialized the problem occurs. Please report back if any further information are needed. Thank you.

[bblanchon]

Hi @Tobi177,

Thank you for reporting this issue.

This issue was reported in espressif/arduino-esp32#10971 and fixed in espressif/arduino-esp32#10972.
Please confirm that this PR fixes the crash.

Best regards,
Benoit