Middlewares

Middlewares are used to "hook" into Marten's request/response lifecycle. They can be used to alter or implement logic based on incoming HTTP requests and the resulting HTTP responses. These hooks take an HTTP request as their input and they output an HTTP response; in the process, they can implement whatever logic they deem necessary to perform actions based on the incoming request and/or the associated response.

How middlewares work

Middlewares are subclasses of the Marten::Middleware abstract class. They must implement a #call method that takes a request object (instance of Marten::HTTP::Request) and a get_response proc (allowing to get the final response) as arguments, and that returns a Marten::HTTP::Response object:

class TestMiddleware < Marten::Middleware
  def call(request : Marten::HTTP::Request, get_response : Proc(Marten::HTTP::Response)) : Marten::HTTP::Response
    # Do something with the request object.

    response = get_response.call

    # Do something with the response object.

    response
  end
end

The get_response proc will either call the next middleware in the chain of middlewares, or the handler processing the request and returning the response. Which of these is actually called is a detail that is hidden by the get_response proc, and this does not matter at an individual middleware level.

Activating middlewares

In order to be used, middleware classes need to be specified in the middleware setting. This setting is an array of middleware classes that defines the "chain" of middlewares that will be "hooked" into Marten's request/response lifecycle.

For example:

config.middleware = [
  Marten::Middleware::Session,
  Marten::Middleware::I18n,
  Marten::Middleware::GZip,
]

It should be noted that the order of middlewares is important. For example, if one of your middleware depends on a session value, you will want to ensure that it appears after the Marten::Middleware::Session class in the middleware setting.

Available middlewares

All the available middlewares are listed in the dedicated reference section.