Discover device IP from domain name or ARP sniffing

[kevinms]

The IP address of a device may not be static (i.e. DHCP). For these, I can set any bogus IP and successfully wake my device as long as the MAC is correct. But, UpSnap always shows the device as offline and after waking shows the full 2 minute countdown and then offline again.

When I enter a domain name (i.e. foo.example.com or foo) as the device IP, logs show:

handlers.go:33: ip not a valid ipv4 address

Maybe domain names could be allowed in the IP field and UpSnap could discover the IP via DNS lookups?

Or, maybe IP could be completely optional and could sniff ARP traffic to discover the IP after sending the WoL packet?

[invario]

I'd be in favor of making UpSnap a bit more dynamic but I just want to point out that if you don't have a DNS server on the network, you can't look up a host if that host is powered down. (Even with mDNS)

But that should still be okay because the IP address isn't required for WOL unless you are doing WOL routed directly to that IP.

[invario]

@seriousm4x If you're open to it, I think I'd like to take a shot at working on this. I read through your comments in #583 about why an IP address is required and I believe I can still satisfy having the IP address. Workflow as follows:

1. Device form requires either a hostname or an IP using two separate form fields (so as to not break the RCE mitigation code you put in place.)
2. For PING, if an IP address was provided on the form, ping that IP. If no IP was provided on the form, attempt to resolve the hostname using DNS first, and then mDNS. Ping the IP address returned, or if it fails to resolve, return an error.
   • I would have to include https://github.com/hashicorp/mdns for mDNS resolution if that is okay with you.
3. For WOL, obtain the IP in the same way above. Determine the broadcast address based on that IP and then send 2 broadcast packets to that address (port 7/9), 2 to global broadcast (port 7/9), and send the additional 2 unicast packets only if the IP was originally provided. (for routed WOL)

[seriousm4x]

Sounds good to me 👍 I'm also open for dropping the IP requirement and using hostnames. Adding other dependencies is okay for me as long as they are supported and work cross platform.
https://github.com/hashicorp/mdns looks like it might have issues for some people on windows but not sure. There is also https://github.com/pion/mdns as an alternative.

I've created a new issue to have a combined place for this: #1753

[invario]

Agreed about hashicorp/mdns. I saw pion/mdns but was trying to stick with something with more stars. How about https://github.com/grandcat/zeroconf? That should work I think.

[seriousm4x]

zeroconf looks abondaned to me. Last commits from 3 years ago and last release from 6 years ago. Stars should not be a big factor in choosing a dependency (yes, 0 stars is bad) but I value active development and caring about the issues more. So I'd rather stick with hashicorp or pion. Which ever works better and is easier to work with.

[invario]

Gotcha. My mistake, I should've looked closer!