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.\"     $OpenBSD: getpeername.2,v 1.16 2001/06/26 19:56:52 dugsong Exp $
.\"     $NetBSD: getpeername.2,v 1.6 1995/10/12 15:40:56 jtc Exp $
.\"
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.\"     @(#)getpeername.2       8.1 (Berkeley) 6/4/93
.\"
.Dd July 17, 1999
.Dt GETPEERNAME 2
.Os
.Sh NAME
.Nm getpeername
.Nd get name of connected peer
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Ft int
.Fn getpeername "int s" "struct sockaddr *name" "socklen_t *namelen"
.Sh DESCRIPTION
.Fn getpeername
returns the address information of the peer connected to socket
.Fa s .
One common use occurs when a process inherits an open socket, such as
TCP servers forked from
.Xr inetd 8 .
In this scenario,
.Fn getpeername
is used to determine the connecting client's IP address.
.Pp
.Fn getpeername
takes three parameters:
.Pp
.Fa s
Contains the file descriptor of the socket whose peer should be looked up.
.Pp
.Fa name
Points to a
.Li sockaddr
structure that will hold the address information for the connected peer.
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, especially with the newer protocol families, the new
.Li struct sockaddr_storage
should be used.
.Li sockaddr_storage
is large enough to hold any of the other sockaddr_* variants.
On return, it can be cast to the correct sockaddr type,
based the protocol family contained in its ss_family field.
.Pp
.Fa namelen
Indicates the amount of space pointed to by
.Fa name ,
in bytes.
.Pp
If address information for the local end of the socket is required, the
.Xr getsockname 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
If the call succeeds, a 0 is returned 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
On failure,
.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 ENOTCONN
The socket is not connected.
.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 getsockname 2 ,
.Xr getpeereid 2 ,
.Xr socket 2
.Sh HISTORY
The
.Fn getpeername
function call appeared in
.Bx 4.2 .