Custom Middleware Source

telem.middleware.custom (
  handler: fun(collection: MetricCollection): MetricCollection
)

This middleware wraps a user-provided function for custom middleware implementations. Need to calculate the ratio between two metrics? Count the total number of items from an adapter? Measure a metric relative to an in-game day? Anything is possible!

Name	Type	Default
handler	fun(collection: MetricCollection): MetricCollection	nil
Function executed when processing this middleware. The returned collection can be a new collection or a reference to the input collection.

Usage

local telem = require 'telem'
local mw = telem.middleware

local fluent = require('telem.vendor').fluent

local backplane = telem.backplane()
  :addInput('elements', telem.input.custom(function ()
    return {
      fire = 111,
      water = 222,
      earth = 333,
      air = 444,
    }
  end))

  :addInput('rare_elements', telem.input.custom(function ()
    return {
      gold = 777,
      silver = 888,
      platinum = 999,
    }
  end))

  -- calculate the sum of all metrics from the rare_elements adapter
  :middleware(mw.custom(function (collection)
    local sum = 0
    
    for _, metric in ipairs(collection) do
      if metric.adapter == 'rare_elements' then
        sum = sum + metric.value
      end
    end

    collection:insert(telem.metric{
      name = 'rare_elements_total',
      value = sum,
      source = 'middleware'
    })

    return collection
  end))
  :cycleEvery(1)()

This will result in the following collection:

Name	Value	Unit	Adapter	Source
fire	111		elements
water	222		elements
earth	333		elements
air	444		elements
gold	777		rare_elements
silver	888		rare_elements
platinum	999		rare_elements
rare_elements_total	2664			middleware