Get the file descriptor of a socket file. C vs Python. Post: 302204431

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Top Forums Programming Get the file descriptor of a socket file. C vs Python. Post 302204431 by goon12 on Wednesday 11th of June 2008 03:02:40 PM

06-11-2008

Registered User

Get the file descriptor of a socket file. C vs Python.

Hi,

I want to validate that a file is a socket file on Linux. I know I can do this using the S_ISSOCK macro, but I am not sure how to get the file descriptor for the socket file.

For example, I know that /tmp/mapping-foo is a socket file. In Python I can do something like this:

Code:

>>> import os
>>> import stat
>>> sb = os.stat('/tmp/mapping-foo')
>>> print stat.S_ISSOCK(sb.st_mode)
True
>>>

How ever in C, I am unable to get the file descriptor for the file /tmp/mapping-foo. I tried using open, fopen and fileno as follows:

Code:

        file_des = open("/tmp/mapping-foo", O_RDONLY);
        if( file_des == -1 ) {
                perror("open(2)");
                if((file = fopen("/tmp/mapping-foo", "r")) == NULL ) {
                        perror("fopen()");
                } else {
                        file_des = fileno(file);
                        if (file_des == -1 ) {
                                perror("fileno()");
                        }
                }
                if( file_des == -1 )
                        exit(1);
        }

But, I am getting this error message:

Code:

$ ls -l /tmp/mapping-foo
srwxrwxr-x 1 joe joe 0 Jun  9 09:53 /tmp/mapping-foo
$ file /tmp/mapping-foo
/tmp/mapping-foo: socket
$ ./pc /tmp/mapping-foo
Stat file /tmp/mapping-foo
open(2): No such device or address
fopen(): No such device or address

I am trying to load the correct file.

Thanks,
Joe

goon12

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LEARN ABOUT OSF1

sockatmark

sockatmark(3)						     Library Functions Manual						     sockatmark(3)

NAME

       sockatmark - Tests whether a socket is at the out-of-band mark

LIBRARY

       Standard C Library: (libc.so, libc.a)

SYNOPSIS

       #include <sys/socket.h>

       int sockatmark (int socket);

STANDARDS

       The sockatmark function also supports POSIX.1g Draft 6.6.

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS

       Specifies the file descriptor associated with a socket.

DESCRIPTION

       The sockatmark() function enables applications to determine which received data precede the out-of-band data and which data follow the out-
       of-band data.  The function uses the file descriptor for the socket to locate the data.	Applications typically use this  function  between
       receive operations.

       The sockatmark() function does not remove the mark from the stream.

RETURN VALUES

       Upon  successful completion, the sockatmark() function returns 1 if the protocol has marked the data stream and all data preceding the mark
       have been read, or 0 (zero) if there is no mark or if data precede the mark in the receive queue.

       If the sockatmark() function fails, a value of -1 is returned and errno is set to indicate the error.

ERRORS

       If the sockatmark() function fails, errno may be set to one of the following values: The socket parameter is not a valid  file  descriptor.
       The socket parameter does not specify a descriptor for a socket.

RELATED INFORMATION

       Functions: recv(2), recvmsg(2).

       Standards: standards(5).  delim off

																     sockatmark(3)

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