Behaviour for pluggable components in the Gno.Commit.Processor pipeline.

The processor calls handle_state/3 on each middleware at every state transition (see the state machine in Gno.Commit.Processor). The callback receives the new state atom, the middleware struct, and the processor, and must return {:ok, processor} (optionally with an updated middleware) or an error tuple to abort. On failure, rollback/2 is called on all middlewares that were already invoked.

The :state field on the middleware struct tracks the last state it was called with, managed automatically by the processor.

Defining a Middleware

Use def_middleware/2 to define a Grax schema subclassing this module:

defmodule MyMiddleware do
  use Gno.CommitMiddleware

  def_middleware MyNS.MyMiddleware do
    property :my_option, type: :string
  end

  @impl true
  def handle_state(:initialized, middleware, processor) do
    # custom logic
    {:ok, processor}
  end
end

Middlewares are configured in the Gno.CommitOperation of a Gno.Service. See Gno.CommitLogger for a built-in example.