Resolve mDNS address for MQTT broker

[schildbach]

When connecting to an MQTT broker, please allow putting an mDNS domain into the "broker" field. Currently (on version 0.15.1.beta2) it seems only IP addresses and regular DNS names are supported.

[blazoncek]

MQTT broker is considered a "server" and as such should have a static IP address.
Adding ability to enter FQDN (or at least hotname) adds to complexity and increases code size.

[schildbach]

Just for reference, both mDNS and DNS can point to static IP addresses as well.

DNS is already supported in the field.

Tasmota can resolve both mDNS and DNS as well.

[Jason2866]

Agree that servers have in general a static IP. Nevertheless even in my LAN i don't put an IP address in any config. My mqtt broker has mqtt.lan as DNS name for example. Don't agree that it puts a lot of code to resolve the DNS name in an IP address. It makes it a lot easier to maintain stuff. If the IP address changes of a server it is a lot of "fun" to change all the addresses in all devices. Imho it is a no go not to support DNS name resolution.
A lot of flash space can be saved to drop support for the crappy mDNS which brings as "benefit" a lot of issues when used with an esp8266 / esp32.
Tasmota does not support mDNS

[blazoncek]

I did not say it won't or shouldn't be implemented. 😄

[schildbach]

Tasmota does not support mDNS

I think it does: arendst/Tasmota#6866 (comment)

[Jason2866]

@schildbach I am a member of Tasmota dev core crew. The post ist really old you linked. I convinced Theo to remove mDNS support in all precompiled binaries one or two years later ;-)

[blazoncek]

As an Apple user I have yet to find an issue with mDNS. My experience is that incorrectly set up networks may exhibit issues with mDNS. And once those are resolved it is up to devices to support it.

That being said, I fully understand the benefits of DNS (or mDNS) resolution. Unfortunately the issue #4586 will add headeaches if only DNS is used, and I have no idea on how to resolve that.

As for WLED to support DNS/mDNS resolution, plenty of UI fields would need to be updated adding code (JS/HTML) as well as backend validation and DNS resolution. If someone finds the time and will to comb through all of it I will be more than happy to help.

[blazoncek]

Anyone interested may want to try adding this in mqtt.cpp to initMqtt() function:

...
    #ifdef ARDUINO_ARCH_ESP32
    if (strlen(cmDNS) > 0 && strchr(mqttServer, '.') == nullptr) { // if mDNS is enabled and server does not have domain
      mqttIP = MDNS.queryHost(mqttServer);
      if (mqttIP != IPAddress()) // if MDNS resolved the hostname
        mqtt->setServer(mqttIP, mqttPort);
      else
        mqtt->setServer(mqttServer, mqttPort);
    } else
    #endif
...

in the elseportion of if (mqttIP.fromString(mqttServer).

And then, please, report back.