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.\"     $OpenBSD: getsockname.2,v 1.16 2001/08/06 10:42:26 mpech Exp $

.\"     $NetBSD: getsockname.2,v 1.6 1995/10/12 15:41:00 jtc Exp $

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.\"     @(#)getsockname.2       8.1 (Berkeley) 6/4/93

.\"

.Dd July 17, 1999

.Dt GETSOCKNAME 2

.Os

.Sh NAME

.Nm getsockname

.Nd get socket name

.Sh SYNOPSIS

.Fd #include 

.Fd #include 

.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 desriptor 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

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 getpeername 2 ,

.Xr getpeereid 2 ,

.Xr socket 2

.Sh BUGS

Names bound to sockets in the UNIX domain are inaccessible;

.Nm getsockname

returns a zero length name.

.Sh HISTORY

The

.Fn getsockname

function call appeared in

.Bx 4.2 .