NAME

getsockname — get socket name

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/socket.h>

int
getsockname(int s, struct sockaddr * restrict name, socklen_t * restrict namelen);

DESCRIPTION

getsockname() returns the locally bound address information for a specified socket.

Common uses of this function are as follows:

• When bind(2) is called with a port number of 0 (indicating the kernel should pick an ephemeral port) getsockname() is used to retrieve the kernel-assigned port number.
• When a process calls bind(2) on a wildcard IP address, getsockname() is used to retrieve the local IP address for the connection.
• When a function wishes to know the address family of a socket, getsockname() can be used.

getsockname() takes three parameters:

s, Contains the file descriptor for the socket to be looked up.

name points to a sockaddr structure which will hold the resulting address information. Normal use requires one to use a structure specific to the protocol family in use, such as sockaddr_in (IPv4) or sockaddr_in6 (IPv6), cast to a (struct sockaddr *).

For greater portability (such as newer protocol families) the new structure sockaddr_storage exists. sockaddr_storage is large enough to hold any of the other sockaddr_* variants. On return, it should be cast to the correct sockaddr type, according to the current protocol family.

namelen indicates the amount of space pointed to by name, in bytes. Upon return, namelen is set to the actual size of the returned address information.

If the address of the destination socket for a given socket connection is needed, the getpeername(2) function should be used instead.

If name does not point to enough space to hold the entire socket address, the result will be truncated to namelen bytes.

RETURN VALUES

On success, getsockname() returns a 0, and namelen is set to the actual size of the socket address returned in name. Otherwise, errno is set, and a value of -1 is returned.

ERRORS

The call succeeds unless:

[EBADF]

The argument s is not a valid descriptor.

[ENOTSOCK]

The argument s is a file, not a socket.

[EINVAL]

The socket has been shut down.

[ENOBUFS]

Insufficient resources were available in the system to perform the operation.

[EFAULT]

The name parameter points to memory not in a valid part of the process address space.

SEE ALSO

bind(2), socket(2)

HISTORY

The getsockname() function call appeared in 4.2BSD.

BUGS

Names bound to sockets in the UNIX domain are inaccessible; getsockname() returns a zero length name.