Example of basic libevent http server in Racket using FFI

racket-libevent-webserver-example.rkt

#lang racket
(require ffi/unsafe
         ffi/unsafe/define)

(define-ffi-definer define-libevent (ffi-lib "libevent"))

; Event Base
(define evbase-ptr (_cpointer 'evbase))
(define-libevent event_base_new (_fun -> evbase-ptr))
(define-libevent event_base_dispatch (_fun evbase-ptr -> _void))
(define-libevent event_base_free (_fun evbase-ptr -> _void))

; evbuffer
(define evbuffer-ptr (_cpointer 'evbuffer))
(define-libevent evbuffer_new (_fun -> evbuffer-ptr))
(define-libevent evbuffer_add (_fun evbuffer-ptr _string _intptr -> _int))
(define-libevent evbuffer_free (_fun evbuffer-ptr -> _void))

; evhttp
(define evhttp-ptr (_cpointer 'evhttp))
(define-libevent evhttp_new (_fun evbase-ptr -> evhttp-ptr))
(define-libevent evhttp_bind_socket (_fun evhttp-ptr _string _ushort -> _int))
(define-libevent evhttp_free (_fun evhttp-ptr -> _void))
(define evkeyvalq-ptr (_cpointer 'evkeyvalq))
(define-libevent evhttp_add_header (_fun evkeyvalq-ptr _string _string -> _int))

; evhttp requests
(define evhttp-request-ptr (_cpointer 'evhttp_request))
(define-libevent evhttp_send_reply (_fun evhttp-request-ptr _int _string evbuffer-ptr -> _void))
(define-libevent evhttp_request_get_input_headers (_fun evhttp-request-ptr -> evkeyvalq-ptr))
(define-libevent evhttp_request_get_output_headers (_fun evhttp-request-ptr -> evkeyvalq-ptr))
(define _evhttp_callback (_fun evhttp-request-ptr _gcpointer -> _void))
(define-libevent evhttp_set_cb (_fun evhttp-ptr _string _evhttp_callback _pointer -> _int))
  
(define (http-handler request arg)
  (void
   (evhttp_add_header (evhttp_request_get_output_headers request) "Content-Type" "text/plain")
   (let ([buffer (evbuffer_new)])
     (evbuffer_add buffer "Hello" 5)
     (evhttp_send_reply request 200 "OK" buffer)
     (evbuffer_free buffer))))

(define (main)
  (let ([base (event_base_new)])
    (let ([httpd (evhttp_new base)])
      (evhttp_bind_socket httpd "localhost" 8093)
      (evhttp_set_cb httpd "/" http-handler #f)
      (event_base_dispatch base)
      (evhttp_free httpd)
      (event_base_free base))))

(main)