*scratch*.el

(defun test-filter (process string)
  (with-current-buffer (process-buffer process)
    (insert "Filter: " string)))
(defun test-sentinel (process event)
  (with-current-buffer (process-buffer process)
    (insert "Sentinel: " event)))

(let ((buf (get-buffer-create "*Test*")))
  (make-network-process :name "*Test*"
                        :buffer buf
                        :host "localhost"
                        :service 12345
                        :coding 'raw-text-dos
                        :nowait t
                        :noquery t
                        :filter #'test-filter
                        :sentinel #'test-sentinel
                        :keepalive t)
  (display-buffer "*Test*"))