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.\" $OpenBSD: getsockname.2,v 1.24 2007/05/31 19:19:32 jmc Exp $
.\" $NetBSD: getsockname.2,v 1.6 1995/10/12 15:41:00 jtc Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)getsockname.2 8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt GETSOCKNAME 2
.Os
.Sh NAME
.Nm getsockname
.Nd get socket name
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Ft int
.Fn getsockname "int s" "struct sockaddr *name" "socklen_t *namelen"
.Sh DESCRIPTION
.Fn getsockname
returns the locally bound address information for a specified socket.
.Pp
Common uses of this function are as follows:
.Bl -bullet
.It
When
.Xr bind 2
is called with a port number of 0 (indicating the kernel should pick
an ephemeral port)
.Fn getsockname
is used to retrieve the kernel-assigned port number.
.It
When a process calls
.Xr bind 2
on a wildcard IP address,
.Fn getsockname
is used to retrieve the local IP address for the connection.
.It
When a function wishes to know the address family of a socket,
.Fn getsockname
can be used.
.El
.Pp
.Fn getsockname
takes three parameters:
.Pp
.Fa s
contains the file descriptor for the socket to be looked up.
.Pp
.Fa name
points to a
.Li 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
.Li sockaddr_in
(IPv4) or
.Li sockaddr_in6
(IPv6), cast to a (struct sockaddr *).
.Pp
For greater portability (such as newer protocol families) the new
structure sockaddr_storage exists.
.Li 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.
.Pp
.Fa namelen
indicates the amount of space pointed to by
.Fa name ,
in bytes.
Upon return,
.Fa namelen
is set to the actual size of the returned address information.
.Pp
If the address of the destination socket for a given socket connection is
needed, the
.Xr getpeername 2
function should be used instead.
.Pp
If
.Fa name
does not point to enough space to hold the entire socket address, the
result will be truncated to
.Fa namelen
bytes.
.Sh RETURN VALUES
On success,
.Fn getsockname
returns a 0, and
.Fa namelen
is set to the actual size of the socket address returned in
.Fa name .
Otherwise,
.Va errno
is set, and a value of \-1 is returned.
.Sh ERRORS
If
.Fn getsockname
fails,
.Va errno
is set to one of the following:
.Bl -tag -width Er
.It Bq Er EBADF
The argument
.Fa s
is not a valid descriptor.
.It Bq Er ENOTSOCK
The argument
.Fa s
is a file, not a socket.
.It Bq Er ENOBUFS
Insufficient resources were available in the system
to perform the operation.
.It Bq Er EFAULT
The
.Fa name
or
.Fa namelen
parameter points to memory not in a valid part of the
process address space.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr bind 2 ,
.Xr getpeereid 2 ,
.Xr getpeername 2 ,
.Xr socket 2
.Sh HISTORY
The
.Fn getsockname
function call appeared in
.Bx 4.2 .
.Sh BUGS
Names bound to sockets in the UNIX domain are inaccessible;
.Nm getsockname
returns a zero length name.
|
