Normandy.Guardrails.Guard behaviour (normandy v0.6.0)

Behaviour for guardrails that inspect agent input or output.

A guard is a module that implements check/2. It is called with a runtime value (either the agent's validated input or its validated output) and the guard's options. It must return :ok to allow the value through, or {:error, [violation]} to reject it.

Violations use the same %{path, message, constraint} shape as Normandy.Agents.ValidationMiddleware, with an additional :guard key identifying the module that produced the violation. This means Normandy.Agents.ValidationMiddleware.error_message/1 renders guardrail violations without modification.

Example

defmodule MyApp.NoShouting do
  @behaviour Normandy.Guardrails.Guard

  @impl true
  def check(value, _opts) when is_binary(value) do
    if value == String.upcase(value) and String.length(value) > 3 do
      {:error,
       [
         %{
           guard: __MODULE__,
           path: [],
           message: "must not be all caps",
           constraint: :no_shouting
         }
       ]}
    else
      :ok
    end
  end

  def check(_value, _opts), do: :ok
end

Summary

Types

violation()

Callbacks

check(value, opts)

Types

violation()

@type violation() :: %{
  :guard => module(),
  :path => [atom()],
  :message => String.t(),
  :constraint => atom(),
  optional(atom()) => term()
}

Callbacks

check(value, opts)

@callback check(value :: term(), opts :: keyword()) :: :ok | {:error, [violation()]}