A new newbie -> use a pure socket for communictaion

Hi,

I try to connect a C++ application on a embedded device to the web
through fastcgi.

For the first test I reused the code by E. Bareev already published on
this list during August. (Thanks)

Instead of using a port, I want to use a unix Socket.
...........code............
#include <string>
#include "fcgi_stdio.h"
#include <stdlib.h>
#include <iostream>

void handle(FCGX_Request request){
        FCGX_FPrintF(request.out,
"Content-type:text/html\r\n\r\n<TITLE>fastcgi</TITLE>\n<H1>Fastcgi:
Hello world!</H1>\n");
}

int main(int argc, char* const argv[] )
{
    std::string port = "/var/run/fastcgitest.socket";
    int listenQueueBacklog = 400;
    FCGX_Stream *in, *out, *err;
    FCGX_ParamArray envp;

    if(FCGX_Init())    exit(1);

    int listen_socket = FCGX_OpenSocket(port.c_str(), listenQueueBacklog);
    if(listen_socket < 0)    exit(1);

    FCGX_Request request;
    if(FCGX_InitRequest(&request,  listen_socket, 0)) exit(1);

    int reqCounter = 0;
    while(FCGX_Accept_r(&request) == 0)
    {
        handle(request);
        reqCounter++;
        FCGX_FPrintF(request.out, "\n\r\n\r counter: %d", reqCounter);
        FCGX_Finish_r(&request);
    }
    return 0;
}
...........code............

I got a 500 internal Server Error. Since this is my first fastcgi
project using a socket, I don't really know the problem.

The lighttpd.error log says:
2009-09-08 22:34:45: (mod_fastcgi.c.1761) connect failed: Permission
denied on unix:/var/run/lighttpd/fastcgitest.socket
2009-09-08 22:34:45: (mod_fastcgi.c.2930) backend died; we'll disable it
for 5 seconds and send the request to another backend instead:
reconnects: 0 load: 1
2009-09-08 22:34:51: (mod_fastcgi.c.2743) fcgi-server re-enabled:
unix:/var/run/lighttpd/fastcgitest.socket

The lighttpd.conf looks like this:
fastcgi.debug = 1
fastcgi.server = (
  "/test.fcgi" =>
  ((
     "socket" => "/var/run/lighttpd/fastcgitest.socket",
     "check-local" => "disable"
  ))
)

If I start the fcgi-app the socket file
(/var/run/lighttpd/fastcgitest.socket) will be created.
The access rights are: srwxr-xr-x 1 root root 0 2009-09-08 22:34
fastcgitest.socket

Lighttpd runs as root, it should be able to access the socket.

What could be the problem?

Thanks for your support.

Maurus