NetBSD/lib/libc/sys/getsockname.2

.\"	$NetBSD: getsockname.2,v 1.23 2003/08/07 16:43:59 agc Exp $
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.\"     @(#)getsockname.2	8.1 (Berkeley) 6/4/93
.\"
.Dd August 11, 2002
.Dt GETSOCKNAME 2
.Os
.Sh NAME
.Nm getsockname
.Nd get socket name
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn getsockname "int s" "struct sockaddr * restrict name" "socklen_t * restrict 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
The call succeeds unless:
.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 EINVAL
The socket has been shut down.
.It Bq Er ENOBUFS
Insufficient resources were available in the system to perform the operation.
.It Bq Er EFAULT
The
.Fa name
parameter points to memory not in a valid part of the process address space.
.El
.Sh SEE ALSO
.Xr bind 2 ,
.Xr socket 2
.Sh HISTORY
The
.Fn getsockname
function call appeared in
.Bx 4.2 .
.Sh BUGS
Names bound to sockets in the
.Ux
domain are inaccessible;
.Fn getsockname
returns a zero length name.