FallbackController

Bastion.FallbackController — catch-all error handler for controller actions.

When a controller action returns Controller.Error(status, message), the FallbackController converts it into an appropriate HTTP response. This mirrors the Phoenix fallback controller pattern, centralising error handling.

Usage:

-- Use the default fallback (renders ErrorView HTML pages):
fn show_handler(conn : Conn) : Conn do
  FallbackController.call(conn, show_action(conn))
end

-- Or create a custom fallback for API routes:
let api_fallback = FallbackController.new(fn (conn, result) ->
  match result do
  Controller.Ok(c) -> c
  Controller.Error(status, msg) ->
    Response.json(conn, status, "{\"error\":\"" ++ msg ++ "\"}")
  end
)

Functions

fncallcall(conn : Conn, result : ActionResult) : Conn#

Handle a Controller.ActionResult using the default error renderer.

If the result is Ok(conn), the conn is returned unchanged.
If the result is Error(status, message), an HTML error page is rendered
using ErrorView.

Example:
  FallbackController.call(conn, my_action(conn))

fncall_jsoncall_json(conn : Conn, result : ActionResult) : Conn#

Handle a Controller.ActionResult by rendering JSON error responses.

Useful for API endpoints where HTML error pages are not appropriate.

Example:
  FallbackController.call_json(conn, my_action(conn))

fnnewnew(handler : Conn -> ActionResult -> Conn) : Conn -> ActionResult -> Conn#

Create a custom fallback handler function.

The handler receives the original conn and the ActionResult, and must
return a Conn. This lets you define application-specific error rendering.

Example:
  let my_fallback = FallbackController.new(fn (conn, result) ->
    match result do
    Controller.ActionOk(c) -> c
    Controller.ActionError(status, msg) ->
      Response.text(conn, status, msg)
    end
  )

  -- Later, in a handler:
  my_fallback(conn, some_action(conn))