Are there getters for meta keys in LUA?

[TomiReiman]

Does there exist a function to get the value of a specific meta key when writing LUA parsers for log content? My use case is the following:

I want to perform some additional processing on the url meta when it is registered but only in the case where the device.type associated with the log event is A. If the device.type is, say, B instead, I do not want to do anything. I.e.:

if meta 'url' is registered and 'device.type' equals 'A' then

   call function parseURL

end

Or if that is not possible, then:

if meta 'url' is registered then

   call function parseURL

   if 'device.type' is not nil and 'device.type' equals 'A' then

      ...do something...

   end

end

To put it short, I am kind of looking for the opposite of "nwlanguage.create" - something like 'nwlanguage.get("metaKey")'. I suppose this could be done by simply looking for a string in the payload, but that seems like unnecessarily heavy if such a getter exists.

[WilliamMotley1]

You can use a meta key as a callback.

A caveat, because you're talking about logs:  meta-callbacks from log parsers occur in no particular order.  You can't assume that device.type will be registered before url, or that url will be registered before device.type.

So I'd suggest something like this:

function myParser.onBegin()
    deviceType = nil
    url = nil
end
function myParser:doStuff()
    if deviceType and url then
        ...
    end
end
function myParser:onURL(idx, vlu)
    url = vlu
    self:doStuff()
end
function myParser:onDeviceType(idx, vlu)
    deviceType = vlu
    self:doStuff()
end
myParser:setCallbacks({
    [nwevents.OnSessionBegin] = myParser.onBegin,
    [nwlanguagekey.create("url")] = myParser.onURL,
    [nwlanguagekey.create("device.type")] = myParser.onDeviceType
})