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Full Discussion: Get the file descriptor of a socket file. C vs Python.
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
Old 06-11-2008
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
 

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LEARN ABOUT REDHAT

bio_s_socket

BIO_s_socket(3) 						      OpenSSL							   BIO_s_socket(3)

NAME

       BIO_s_socket, BIO_new_socket - socket BIO

SYNOPSIS

	#include <openssl/bio.h>

	BIO_METHOD *BIO_s_socket(void);

	long BIO_set_fd(BIO *b, int fd, long close_flag);
	long BIO_get_fd(BIO *b, int *c);

	BIO *BIO_new_socket(int sock, int close_flag);

DESCRIPTION

       BIO_s_socket() returns the socket BIO method. This is a wrapper round the platform's socket routines.

       BIO_read() and BIO_write() read or write the underlying socket.	BIO_puts() is supported but BIO_gets() is not.

       If the close flag is set then the socket is shut down and closed when the BIO is freed.

       BIO_set_fd() sets the socket of BIO b to fd and the close flag to close_flag.

       BIO_get_fd() places the socket in c if it is not NULL, it also returns the socket. If c is not NULL it should be of type (int *).

       BIO_new_socket() returns a socket BIO using sock and close_flag.

NOTES

       Socket BIOs also support any relevant functionality of file descriptor BIOs.

       The reason for having separate file descriptor and socket BIOs is that on some platforms sockets are not file descriptors and use distinct
       I/O routines, Windows is one such platform. Any code mixing the two will not work on all platforms.

       BIO_set_fd() and BIO_get_fd() are macros.

RETURN VALUES

       BIO_s_socket() returns the socket BIO method.

       BIO_set_fd() always returns 1.

       BIO_get_fd() returns the socket or -1 if the BIO has not been initialized.

       BIO_new_socket() returns the newly allocated BIO or NULL is an error occurred.

SEE ALSO

       TBA

0.9.7a								    2000-10-19							   BIO_s_socket(3)
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