OTA subscription doesn't work if there is no active connection

[AndreKR]

The library remembers most subscriptions, for example this works fine:

void setup() {
  [...]
  if (!rpc.RPC_Subscribe(callbacks.cbegin(), callbacks.cend())) {
    Serial.println("Failed to subscribe for RPC");
  }

  if (!shared_update.Shared_Attributes_Subscribe(attr_update_callback)) {
    Serial.println("Failed to subscribe for shared attribute updates");
  }

  if (!tb.connect(THINGSBOARD_SERVER, TOKEN, THINGSBOARD_PORT)) {
    Serial.println("Failed to connect");
  }
}

Both the RPC subscription and the attributes subscription are remembered across the (re)connect and after the connection has been made, both RPC requests and attribute updates are processed.

However, if I add an OTA subscription:

void setup() {
  [...]
  if (!rpc.RPC_Subscribe(callbacks.cbegin(), callbacks.cend())) {
    Serial.println("Failed to subscribe for RPC");
  }

  if (!shared_update.Shared_Attributes_Subscribe(attr_update_callback)) {
    Serial.println("Failed to subscribe for shared attribute updates");
  }

  if (!ota.Subscribe_Firmware_Update(ota_callback)) {
    Serial.println("Failed to subscribe for OTA attribute updates");
  }

  if (!tb.connect(THINGSBOARD_SERVER, TOKEN, THINGSBOARD_PORT)) {
    Serial.println("Failed to connect");
  }
}

that one doesn't work.

I have to do this OTA subscription after the connection has been made, in other words every time that I reconnect.

Doing some subscriptions only once and others every time on-connect makes the code harder to read, I would prefer to have them all in one place.

I didn't want to move the other subscriptions (RPC and attributes) to on-connect because I'm not sure if doing them multiple times will cause issues.