JSON validation for Cowboy REST API, Mimic Celebrate Joi in Elixir

Thi is a Elixir Cowboy Plug module for incomming json validation. Use schema definition, trying to mimic a (minimal) functionality of Celebrate Joi.

Validate the presence of key, their data type and their stored value.

Has programers we want to write the minimal possible lines of code. Bassically reduce all to a schema definition and then apply in our route.

Schema:

photo_book_schema = [
                      qty: {:number, 1, 200},
                      hardcover: {:boolean},
                      colors: {:options, ["bw", "color", "sepia"]},
                      client_name: {:string, 6, 20},
                      client_phone: {:string, 8, 25, ~r/^[\d\-()\s]+$/}
                    ]

Route:

plug(:match)
plug(Plug.RouterValidatorschema, on_error: &__MODULE__.on_error_fn/2)
plug(:dispatch)

post "/create/", private: %{validate: photo_book_schema} do
  status = Orders.create(conn.body_params)
  {:ok, str} = Jason.encode(%{status: status})
  send_resp(conn |> put_resp_content_type("application/json"), str)
end

def on_error_fn(conn, errors, status \\ 422) do
  IO.inspect(errors, label: "errors")
  {:ok, str} = Jason.encode(%{status: "fail", errors: errors})
  send_resp(conn |> put_resp_content_type("application/json"), str) |> halt()
end

For more complex validations is recommended to use Ecto.Changests https://hexdocs.pm/ecto/Ecto.Changeset.html

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