Notion

Notion is a thin wrapper around :telemetry that defines functions that dispatch telemetry events, documentation, and specs for your applications events.

Installation

The package can be installed by adding notion to your list of dependencies in mix.exs:

def deps do
  [
    {:notion, "~> 0.2.0"}
  ]
end

Usage

Add an Instrumentation module and use Notion.

Specify an app :name to be prepended to all events dispatched to telemetry. Optionally you can set metadata that will be the defaults and merged with lower precendence for all events.

defmodule MyApp.Instrumentation do
  use Notion, name: :my_app, metadata: %{env: "prod"}

  @doc "Processed an HTTP request"
  # Generate a default typespec of http_request(map, map) :: :ok
  defevent [:http, :request]

  @doc "Docs for my [:my_app, :cc_charge, :succeeded] event"
  # Override a typespec
  @spec cc_charge_succeeded(integer, map) :: :ok
  defevent [:cc_charge, :succeeded]

  @doc "Docs for my [:my_app, :cc_charge, :failed] event"
  defevent [:cc_charge, :failed]
end

Generated @moduledoc

A default @moduledoc will be generated for your module. To override it, simple re-define @moduledoc. Four "variables" exist that can be interpolated into your docs:

• MODULE_NAME - The name of the module using Notion
• NOTION_NAME - will be the value name in use Notion, name: :foo
• NOTION_EVENTS - a markdown formatted unordered list of emitted events
• NOTION_DEFAULT_METADATA the default metadata added to events, if set.

Generated Event Functions

Notion will create two functions for each event, described below. In additiona any @doc provided before the defevent call will be associated to that event.

The following default typespec will be added for each function.

@spec function_name(map(), map()) :: ok

1 arity event function form

When using the 1 arity telemetry will receive the provided measurements and the default metadata.

MyApp.Instrumentation.cc_charge_succeeded(%{"latency" => 300})
MyApp.Instrumentation.cc_charge_failed(%{"latency" => 300})

2 arity event function form

When using the 2 arity telemetry will receive the provided measurements and will merge the provided metadata with the defaults.

MyApp.Instrumentation.cc_charge_succeeded(%{"latency" => 300}, %{"cc_type" => "visa"})
MyApp.Instrumentation.cc_charge_failed(%{"latency" => 300}, %{"cc_type" => "visa"})

Overriding the default typespec for an event

To override the default typespec of map(), map() simple define a @spec before calling defevent/0. Note, the return type will always be :ok.

defmodule MyApp.Telemetry do
  @spec foo(integer, %{my_label: binary}) :: :ok
  defevent :foo
end

Attaching all events to a handler

Notion provides a events/0 function that provides all the event names telemetry receives. This is handy for binding handlers to

def MyApp.InstrumentationHandler do
  def setup() do
    :telemetry.attach_many("my-app-handler", MyApp.Instrumentation.events(), &handle_event/4, nil)
  end

  def handle_event(event, measurements, _metadata, _config) do
    IO.puts("Dispatched: #{inspect(event)} -> #{inspect(measurements)}")
  end
end

Documentation can be be found at https://hexdocs.pm/notion.

Etc

Credo: Modules should have a @moduledoc tag.

There is currently an issue open on credo to add support for checking if a used module adds a @moduledoc.

In the meantime if you want to mute the error, you can add @moduledoc false to the top of your instrumenter and docs will still be generated.

defmodule Bar.Instrumenter do
  @moduledoc false
  use Notion, ...
end