Behaviour for procedure middleware.

A middleware transforms a %RpcElixir.Resolution{} and returns one. The chain runs in order, before input validation and the handler. A middleware can halt, but it cannot see the handler's result. See call/2.

Declaring middleware

procedure "users.update", &Hello.Users.update/2,
  middleware: [
    MyApp.Middleware.RequireUser,
    {RpcElixir.Middleware.Assign, source: :api}
  ]

Each entry is a module or a {module, opts} tuple. Bare modules receive [].

Field ownership

Middleware must not write to :result. The dispatcher owns that field. Use Resolution.halt/2 to short-circuit with an error.

Implementing a middleware

Pass an %RpcElixir.RpcError{} to RpcElixir.Resolution.halt/2 when the code matters. A bare term becomes :middleware_halted at status 500, and the term lands under details.reason.

defmodule MyApp.Middleware.RequireUser do
  @behaviour RpcElixir.Middleware

  @impl true
  def call(%RpcElixir.Resolution{} = res, _opts) do
    case res.ctx.assigns[:current_user] do
      nil ->
        RpcElixir.Resolution.halt(res, %RpcElixir.RpcError{code: :unauthorized})

      _user ->
        res
    end
  end

  @impl true
  def rpc_error_codes(_opts), do: [:unauthorized]
end