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Asked: 2026-05-27T01:01:21+00:00

I’ve got C++ backend application that interacts with webpage using fastcgi. Webpage uses jQuery

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I’ve got C++ backend application that interacts with webpage using fastcgi.
Webpage uses jQuery ‘get’ method to send request to this application but it can’t receive proper answer.
All this works on nginx.

Here is simplified source of C++ app (it uses FastCGI C++ library libfcgi.lib from http://www.fastcgi.com/drupal/node/5 ) 

#include <string>

#include "fcgi_stdio.h"

int main() {
    FCGX_Init();

    std::string port=":9000";
    int listenQueueBacklog = 400;

    int listen_socket = FCGX_OpenSocket(port.c_str(), listenQueueBacklog);

    FCGX_Request request;
    FCGX_InitRequest(&request, listen_socket, 0);

    while(FCGX_Accept_r(&request) == 0)
    {
         FCGX_FPrintF(request.out, "Content-type: text/html\r \n\r\n<TITLE>fastcgi</TITLE>\n<H1>Fastcgi: Hello world.</H1>\n");
         FCGX_Finish_r(&request);
    }

    return 0;
}

Here is source of webpage.

<html>
    <head>
        <script type="text/javascript" src="jquery-1.7.min.js"></script>
    </head>
    <body>
        <script type="text/javascript">
            $.get("http://localhost:8081", function(data, status, xhr) {  alert("Data=" + data + ";Status=" + status); });
        </script>
    </body>
</html>

And here is part of nginx configuration

server {
    listen       8080;
    server_name  localhost;

    location / {
        root   html;
        index  index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }
}

server {
    listen       8081;
    server_name  localhost;

    location / {
        fastcgi_pass   127.0.0.1:9000;
        include        fastcgi_params;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }
 }

I receive request in C++ app (stopping at breakpoint inside while loop) after opening webpage.
But after executing FCGX_Finish_r I see no alert, i.e. callback function is not called.
(When I used jQuery 1.4.2 instead of 1.7, callback function was called, but without data, and I saw ‘Data=;Status=success’ alert window,
so problem remained).

And one more thing – if I just open ‘http://localhost:8081&#8217; in browser, everything is correct, I see ‘Fastcgi: Hello world.’ in browser.

I’d be very grateful if anyone could point out what is the problem.

UPDATE:

I edited nginx configuration (removed server listening on 8081 and added fastcgi pass to folder)

server {
    listen       8080;
    server_name  localhost;

    location / {
        root   html;
        index  index.html index.htm;
    }

    location /foo {
        fastcgi_pass   127.0.0.1:9000;
        include        fastcgi_params;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   html;
    }
}

and webpage source code

$.get("http://localhost:8080/foo", function(data, status, xhr) { alert("Data=" + data + ";Status=" + status); });

according to omnosis’s advice and everything started working fine!

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1 Answer

  1. Editorial Team

    http://localhost:8081
    this cause the error, because it called from a different URL, athough this is only the port different, so this request is actually a cross domain request which is disabled by the browser.

    You should check out these topics:

    AJAX response not valid in C++ but Apache

    and the solution to use the apache proxy forwarding, as Byron Whitlock suggest:

    apache httpd extension help

    You should forward a folder to a port so instead of localhost:8081 you should use localhost:8080/foo or a different file like localhost:8080/foo.cgi, or use a subdomain like foo.localhost:8080

    I dont know how to configure maybe this is good

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