The purpose of this library is to provide an easy way to capture basic timing metrics from your application and surface them via the Server-Timing header (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Server-Timing).

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

def deps do
  [
    {:server_timing_plug, "~> 0.1.0"}
  ]
end

To use ServerTimingPlug in your application, open up your endpoint.ex file and add the following entry (shown with default configuration):

plug ServerTimingPlug, header_unit: :millisecond, enabled: true

Once that entry has been added to you endpoint.ex file, you can simple call ServerTimingPlug.capture_timing/3 and ServerTimingPlug.capture_timing/3 throughout your code in order to capture timings. The captured timings will be flushed when the response goes out. It is important to note that timings will only be available if the call to ServerTimingPlug.capture_timing is made in the same process as the process that is handling the request. A sample timing capture could look something like this:

def index(conn, params) do
  start_time = System.monotonic_time()
  #
  # Something expensive is done here
  #
  duration = System.monotonic_time() - start_time
  ServerTimingPlug.capture_timing("expensive-thing", duration, "This timing captures the expensive operation")
  json(conn, %{message: "All is well!"})
end

The design of this lib draws inspiration from https://github.com/hauleth/plug_telemetry_server_timing, but makes some slightly different design decisions. Whereas plug_telemetry_server_timing attaches :telemetry handlers to events and automatically aggregates the results of timings, this library allows you to time arbitrary events and does not infer timing label names based on telemetry events. There are other Server-Timing libraries on hex as well; Which one you choose depends on your specific needs :).