Segmentation violation

#>
#ifndef MHTTPD_CHICKEN_INCLUDES
#define MHTTPD_CHICKEN_INCLUDES
#include <sys/types.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <microhttpd.h>
#include <unistd.h>
#endif
<#
(use r7rs)
(import scheme)
(import chicken)
(use posix)
(import foreign)
(require-extension srfi-18)

(define send-response
  (foreign-lambda* int
      ((c-pointer connection)
       (int status)
       (c-string page))
    "struct MHD_Response * response;
int ret;
response = MHD_create_response_from_buffer (strlen(page), (void*) page, MHD_RESPMEM_PERSISTENT);
ret = MHD_queue_response (connection, status, response);
C_return(ret);"))

(define http-daemon
  (foreign-safe-lambda* c-pointer
      (((function int (c-pointer c-pointer c-string c-string c-string c-string size_t c-pointer)) handler)
       (int port))
    "struct MHD_Daemon * daemon;
daemon = calloc(1, sizeof(daemon));
daemon = MHD_start_daemon (MHD_USE_SELECT_INTERNALLY, port, NULL, NULL, &handler, NULL, MHD_OPTION_END);
C_return(daemon);"))

(define kill-http-daemon
  (foreign-lambda* void
      ((c-pointer daemon))
    "MHD_stop_daemon (daemon);
free(daemon);"))

(define-external (answer_to_connection
		  (c-pointer cls)
		  (c-pointer connection)
		  (c-string url)
		  (c-string method)
		  (c-string version)
		  (c-string upload-data)
		  (size_t upload-data-size)
		  (c-pointer con-cls)) int
		  
		  (let ((page "<html><body>Hello Browser!</body></html>"))
		    (send-response connection (foreign-value "MHD_HTTP_OK" int) page)))

(http-daemon answer_to_connection 8080)
(sleep 20)


;; FOR REFERENCE: THE ERROR
Error: segmentation violation

	Call history:

	machine-byte-order	  
	##sys#require	  
	numbers.scm:267: ##sys#gc	  
	numbers.scm:1770: register-feature!	  
	microhttpd.scm:1: ##sys#require	  
	microhttpd.scm:1: ##sys#require	  
	microhttpd.scm:3: ##sys#provide	  
	microhttpd.lib.scm:11: ##sys#require	  
	microhttpd.lib.scm:57: http-daemon	  
	microhttpd.lib.scm:30: ##sys#gc	  
	microhttpd.lib.scm:30: g134	  
	microhttpd.lib.scm:58: sleep	  	<--