mirror of https://github.com/mkerrisk/man-pages
146 lines
4.7 KiB
Groff
146 lines
4.7 KiB
Groff
.\" Copyright (c) 1983, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" %%%LICENSE_END
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.\"
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.\" @(#)getpeername.2 6.5 (Berkeley) 3/10/91
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.\"
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.\" Modified Sat Jul 24 16:37:50 1993 by Rik Faith <faith@cs.unc.edu>
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.\" Modified Thu Jul 30 14:37:50 1993 by Martin Schulze <joey@debian.org>
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.\" Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 17 Jul 2002, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added 'socket' to NAME, so that "man -k socket" will show this page.
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.\"
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.TH GETPEERNAME 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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getpeername \- get name of connected peer socket
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.SH SYNOPSIS
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.nf
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.B #include <sys/socket.h>
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.PP
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.BI "int getpeername(int " sockfd ", struct sockaddr *restrict " addr ,
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.BI " socklen_t *restrict " addrlen );
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.fi
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.SH DESCRIPTION
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.BR getpeername ()
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returns the address of the peer connected to the socket
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.IR sockfd ,
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in the buffer pointed to by
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.IR addr .
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The
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.I addrlen
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argument should be initialized to indicate the amount of space pointed to
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by
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.IR addr .
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On return it contains the actual size of the name returned (in bytes).
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The name is truncated if the buffer provided is too small.
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.PP
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The returned address is truncated if the buffer provided is too small;
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in this case,
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.I addrlen
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will return a value greater than was supplied to the call.
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.SH RETURN VALUE
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EBADF
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The argument
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.I sockfd
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is not a valid file descriptor.
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.TP
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.B EFAULT
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The
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.I addr
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argument points to memory not in a valid part of the
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process address space.
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.TP
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.B EINVAL
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.I addrlen
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is invalid (e.g., is negative).
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.TP
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.B ENOBUFS
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Insufficient resources were available in the system
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to perform the operation.
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.TP
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.B ENOTCONN
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The socket is not connected.
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.TP
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.B ENOTSOCK
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The file descriptor
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.I sockfd
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does not refer to a socket.
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD
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.RB ( getpeername ()
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first appeared in 4.2BSD).
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.SH NOTES
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For background on the
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.I socklen_t
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type, see
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.BR accept (2).
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.PP
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For stream sockets, once a
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.BR connect (2)
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has been performed, either socket can call
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.BR getpeername ()
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to obtain the address of the peer socket.
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On the other hand, datagram sockets are connectionless.
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Calling
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.BR connect (2)
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on a datagram socket merely sets the peer address for outgoing
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datagrams sent with
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.BR write (2)
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or
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.BR recv (2).
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The caller of
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.BR connect (2)
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can use
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.BR getpeername ()
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to obtain the peer address that it earlier set for the socket.
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However, the peer socket is unaware of this information, and calling
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.BR getpeername ()
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on the peer socket will return no useful information (unless a
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.BR connect (2)
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call was also executed on the peer).
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Note also that the receiver of a datagram can obtain
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the address of the sender when using
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.BR recvfrom (2).
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.SH SEE ALSO
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.BR accept (2),
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.BR bind (2),
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.BR getsockname (2),
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.BR ip (7),
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.BR socket (7),
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.BR unix (7)
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