Function to generate MAC addresses

[giorgiga]

Please add a function that allows generating MAC addresses based on some value (similar to ansible's community.general.random_mac when used with a seed)

[hairyhenderson]

This seems like a reasonably decent idea. Until I (or someone else!) can implement this, one option is to define a template that calls random.Number a bunch of times and formats it as hex:

mac.t:

{{ define "hex" -}}
  {{ random.Number 0 255 | printf "%02x" -}}
{{ end -}}
{{ define "mac" -}}
  {{ template "hex" -}}
  {{ range (seq 5) }}:{{ template "hex" }}{{ end -}}
{{end -}}

then you can include that as a nested template:

$ gomplate -t mac=mac.t -i 'mac is {{ template "mac" }}{{"\n"}}'
mac is 3b:c2:aa:86:b2:b9

[giorgiga]

Random MACs are good but IMHO the killer feature of ansible's community.general.random_mac is that you can use any string as a seed.

This allows writing things like:

mac: "{{ 'AA:BB' | community.general.random_mac( seed= hostname + '/' + nic ) }}")

to get a (consistently reproducible) MAC based on hostname and nic (or on whatever else you please).

The above is ansible's syntax; personally I think that it would be better to have two separate functions, one (say prefix | net.CompleteRandomMAC) that generates a random MAC based on an optional prefix and another (say seed | net.ToMAC prefix) that "converts" any string to a mac address.

[hairyhenderson]

Ah, thanks for the followup - this makes sense.

BTW, two functions aren't necessary - a single function can behave differently given different inputs. For example:

• net.GenerateMAC (no args) - could create a random MAC address
• net.GenerateMAC "AA:BB" (1 arg) - could create a random MAC address with a fixed prefix
• net.GenerateMAC "AA:BB" "seed" (2 args) - could create a predictably-random MAC with a fixed prefix - the prefix could be "" for none (to preserve the 2-arg signature)

The concept of allowing a user-provided seed is interesting - this may be useful to add into the random functions too 🤔

I can't promise that I'll be able to write this function any time soon - I have limited time to work on gomplate, and most of my gomplate-time is currently being used to get the v4.0 release ready... But if you're interested in contributing I would accept a PR for a function like this!

[giorgiga]

TIA about the U/L bit in MAC addresses, which I think might be relevant for implementing this feature: https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local_(U/L_bit)

I doubt this would matter much in any practical scenario, but I think the new net.GenerateMAC should generate locally administered addresses when the user doesn't specify a prefix.

[hairyhenderson]

huh, good callout, TIL 😂

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[hairyhenderson]

Reopening as I still think this is useful, but can't commit to this for v4