R/Middleware.R

In RestRserve: A Framework for Building HTTP API

#' @title Creates middleware object
#'
#' @description
#' Creates Middleware object.
#'
#' Middleware is a very useful concept which allows to perform
#' preprocessing of requests and post-processing of responses. Middleware has
#' an access to both `request` and  `response` objects and can modify them.
#' This way each request can be checked/modified before passing handler and
#' response can be post processed (for example this way we developer can set up
#' custom error messages).
#'
#' @export
#'
#' @seealso [Request] [Response] [Application]
#'
Middleware = R6::R6Class(
  classname = "Middleware",
  public = list(
    #' @field process_request Function which takes 2 arguments - `request` and
    #'   `response` objects (class  [Request] and [Response] correspondingly) and
    #'   modify `request` and `response` or throw exception using [HTTPError] helper.\cr
    #'   Function is called before request is routed to handler.\cr
    #'   Usually `process_request` is used to perform logging, check authorization, etc.
    process_request = NULL,
    #' @field process_response Function which takes 2 arguments - `request` and
    #'   `response` objects (class [Request] and [Response] correspondingly) and
    #'   modify `request` and `response` or throw exception using [HTTPError] helper.\cr
    #'   Function is called after request is processed by handler.
    #'   Usually `process_response` is used to perform logging, custom error handling, etc.
    process_response = NULL,
    #' @field id Middleware id.
    id = NULL,
    #' @description
    #' Creates middleware object
    #' @param process_request Modify `request` or `response` objects or  throw
    #'   exception using `[HTTPError]` helper. This function evaluate before
    #'   router handler called.
    #' @param process_response Modify `request` or `response` objects or  throw
    #'   exception using `[HTTPError]` helper. This function evaluate after
    #'   router handler called.
    #' @param id Middleware id.
    initialize = function(
      process_request  = function(request, response) TRUE,
      process_response = function(request, response) TRUE,
      id = "Middleware") {

        checkmate::assert_function(process_request, nargs = 2L)
        checkmate::assert_function(process_response, nargs = 2L)
        checkmate::assert_string(id)

        self$process_request  = process_request
        self$process_response = process_response
        self$id = id
    }
  )
)