CGI/FastCGI app in C/C++ (socket programming question)

Question

I am developing my first C/C++ fastCGI app, using the FastCGI Developers Kit.

I have successfully built one of the sample programs (snippet shown below):

int main (void)
{
    int count = 0;
    long pid = getpid();

    streambuf * cin_streambuf  = cin.rdbuf();
    streambuf * cout_streambuf = cout.rdbuf();
    streambuf * cerr_streambuf = cerr.rdbuf();

    FCGX_Request request;

    FCGX_Init();
    FCGX_InitRequest(&request, 0, 0);

    while (FCGX_Accept_r(&request) == 0)
    {
       /* Handle request */
    }

    return 0;
}

However, when I run the example above, it simply terminates. Upon debugging, I realized that FCGX_Accept_r was returning an error code. Upon further investigation, I realized that the accept() method call was failing.

The actual line that fails is:

 socket = accept(listen_sock, (struct sockaddr *)&sa, &len);

The arguments passed to the function are:

listen_sock: 0
len: 112
sa:

{un = {sun_family = 0, sun_path = "\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\000\\020\\"'\\000\\000\\032\\356m\\000\\000\\000\\000\\377\\377\\377\\377\\364\\277\\022\\000\\310\\366\\377\\277\\001\\000\\000\\000\\000\\000\\000\\000X\\366\\377\\277\\343\\276\\004\\b\\377\\377\\377\\377\\001\\000\\000\\000\\001\\000\\000\\000\\000\\000\\000\\000\\001\\000\\000\\000\\310\\366\\377\\277\\210\\366\\377\\277F\\277\\004\\b\\310\\366\\377\\277\\001\\000\\000\\000\\000"}, in = {sin_family = 0, sin_port = 0, sin_addr = {s_addr = 0}, sin_zero = "\\000\\000\\000\\000\\000\\000\\000"}}

I am new to socket programming, so I am need some assistance in being able to diagnose what is causing accept() to fail.

Given the information above, can anyone see why the call to accept() would fail?

I am developing on Ubuntu 10.x

See my answer to http://stackoverflow.com/questions/9223007/spawn-fastcgi-apps-on-windows/11900263#11900263 — Alexey Vassiliev, Aug 10 '12 at 11:01

score 4 · Answer 1 · answered Jan 03 '11 at 12:36

4

Don't know much about this SDK, however a cursory glance through their headers reveals that you need to create a socket first to accept an incoming request, and pass this into the FCGX_InitRequest method.

http://www.fastcgi.com/devkit/include/fcgiapp.h

reveals a method: int FCGX_OpenSocket(const char *path, int backlog); which I would assume you call to create the socket, and then call FCGX_InitRequest with this socket as the second parameter...

Hence why your code fails, you pass in a 0 for socket, which is invalid!

answered Jan 03 '11 at 12:36

Nim

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Yes, passing a socket (fd) value of 0, seemed pretty suspect to me. Thanks for the tip. I will investigate and let you know. As an aside, the code I built is a verbatim copy from the kit. So it is rather worrying that it has such a rudimentary error in it... – skyeagle Jan 03 '11 at 12:45
`0` is valid as a socket; it's STDIN and is the default in the fcgi library. To use a UNIX domain or TCP socket, first call `FCGX_OpenSocket`. Then pass the file number return value to `FCGX_InitRequest`. – Clint Pachl Nov 08 '20 at 12:16

CGI/FastCGI app in C/C++ (socket programming question)

1 Answers1