1.\" $OpenBSD: getpeername.2,v 1.27 2022/09/11 06:38:11 jmc Exp $ 2.\" $NetBSD: getpeername.2,v 1.6 1995/10/12 15:40:56 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)getpeername.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: September 11 2022 $ 34.Dt GETPEERNAME 2 35.Os 36.Sh NAME 37.Nm getpeername 38.Nd get name of connected peer 39.Sh SYNOPSIS 40.In sys/socket.h 41.Ft int 42.Fn getpeername "int s" "struct sockaddr *name" "socklen_t *namelen" 43.Sh DESCRIPTION 44.Fn getpeername 45returns the address information of the peer connected to socket 46.Fa s . 47One common use occurs when a process inherits an open socket, such as 48TCP servers forked from 49.Xr inetd 8 . 50In this scenario, 51.Fn getpeername 52is used to determine the connecting client's IP address. 53.Pp 54.Fn getpeername 55takes three parameters: 56.Pp 57.Fa s 58contains the file descriptor of the socket whose peer should be looked up. 59.Pp 60.Fa name 61points to a 62.Vt sockaddr 63structure that will hold the address information for the connected peer. 64Normal use requires one to use a structure 65specific to the protocol family in use, such as 66.Vt sockaddr_in 67(IPv4) or 68.Vt sockaddr_in6 69(IPv6), cast to a (struct sockaddr *). 70.Pp 71For greater portability, especially with the newer protocol families, the new 72.Vt struct sockaddr_storage 73should be used. 74.Vt sockaddr_storage 75is large enough to hold any of the other sockaddr_* variants. 76On return, it can be cast to the correct sockaddr type, 77based on the protocol family contained in its ss_family field. 78.Pp 79.Fa namelen 80indicates the amount of space pointed to by 81.Fa name , 82in bytes. 83.Pp 84If address information for the local end of the socket is required, the 85.Xr getsockname 2 86function should be used instead. 87.Pp 88If 89.Fa name 90does not point to enough space to hold the entire socket address, the 91result will be truncated to 92.Fa namelen 93bytes. 94.Sh RETURN VALUES 95If the call succeeds, a 0 is returned and 96.Fa namelen 97is set to the actual size of the socket address returned in 98.Fa name . 99Otherwise, 100.Va errno 101is set and a value of \-1 is returned. 102.Sh ERRORS 103On failure, 104.Va errno 105is set to one of the following: 106.Bl -tag -width Er 107.It Bq Er EBADF 108The argument 109.Fa s 110is not a valid descriptor. 111.It Bq Er ENOTSOCK 112The argument 113.Fa s 114is a file, not a socket. 115.It Bq Er ENOTCONN 116The socket is not connected. 117.It Bq Er ENOBUFS 118Insufficient resources were available in the system 119to perform the operation. 120.It Bq Er EFAULT 121The 122.Fa name 123or 124.Fa namelen 125parameter points to memory not in a valid part of the 126process address space. 127.El 128.Sh SEE ALSO 129.Xr accept 2 , 130.Xr bind 2 , 131.Xr getsockname 2 , 132.Xr socket 2 , 133.Xr getpeereid 3 134.Sh STANDARDS 135The 136.Fn getpeername 137function conforms to 138.St -p1003.1-2008 . 139.Sh HISTORY 140The 141.Fn getpeername 142function call appeared in 143.Bx 4.2 . 144