# OpenTelemetryDecorator

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A function decorator for OpenTelemetry traces.

## Usage

    defmodule MyApp.Worker do
      use OpenTelemetryDecorator

      @decorate trace([:my_app, :worker, :do_work])
      def do_work(arg1, arg2) do
        ...doing work
        do_more_work(arg1)
      end

      @decorate trace([:my_app, :worker, :do_more_work])
      def do_more_work(arg1) do
        ...doing more work
      end
    end

We use `OpenTelemetry.Tracer.current_span_ctx()` to automatically link new spans to the current trace (if it exists and is in the same process). So the above example will link the `do_work` and `do_more_work` spans for you by default. 

You can provide span attributes by specifying a list of variable names as atoms.

This list can include...

Any variables (in the top level closure) available when the function exits:

    defmodule MyApp.Worker do
      use OpenTelemetryDecorator

      @decorate trace([:my_app, :worker, :do_work], [:arg1, :arg2, :thing1])
      def do_work(arg1, arg2) do
        thing1 = arg1.count + arg2.count
        {:ok, thing1}
      end
    end
    
    
The result of the function by including the atom `:result`:

    defmodule MyApp.Worker do
      use OpenTelemetryDecorator

      @decorate trace([:my_app, :worker, :do_work], [:result])
      def do_work(arg1, arg2) do
        thing1 = arg1.count + arg2.count
        {:ok, thing1}
      end
    end
    
    
Map/struct properties using nested lists of atoms:

    defmodule MyApp.Worker do
      use OpenTelemetryDecorator

      @decorate trace([:my_app, :worker, :do_work], [[:arg1, :count], [:arg2, :count]])
      def do_work(arg1, arg2) do
        thing1 = arg1.count + arg2.count
        {:ok, thing1}
      end
    end

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## Installation

Add `open_telemetry_decorator` to your list of dependencies in `mix.exs` and do a `mix deps.get`:

```elixir
def deps do
  [
    {:open_telemetry_decorator, "~> 0.1.0"}
  ]
end
```

## Development

`make check` before you commit! If you'd prefer to do it manually:

* `mix do deps.get, deps.unlock --unused, deps.clean --unused` if you change dependencies
* `mix compile --warnings-as-errors` for a stricter compile
* `mix coveralls.html` to check for test coverage
* `mix credo` to suggest more idiomatic style for your code
* `mix dialyzer` to find problems typing might reveal… albeit *slowly*
* `mix docs` to generate documentation