624 lines
14 KiB
Groff
624 lines
14 KiB
Groff
.\" $FreeBSD$
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.\" $KAME: getaddrinfo.3,v 1.22 2000/08/09 21:16:17 itojun Exp $
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.\"
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.\" Copyright (c) 1983, 1987, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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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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.\" 3. All advertising materials mentioning features or use of this software
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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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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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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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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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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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.\"
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.\" From: @(#)gethostbyname.3 8.4 (Berkeley) 5/25/95
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.\"
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.Dd May 25, 1995
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.Dt GETADDRINFO 3
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.Os
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.\"
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.Sh NAME
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.Nm getaddrinfo ,
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.Nm freeaddrinfo ,
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.Nm gai_strerror
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.Nd nodename-to-address translation in protocol-independent manner
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.\"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/socket.h>
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.Fd #include <netdb.h>
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.Ft int
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.Fn getaddrinfo "const char *nodename" "const char *servname" \
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"const struct addrinfo *hints" "struct addrinfo **res"
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.Ft void
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.Fn freeaddrinfo "struct addrinfo *ai"
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.Ft "char *"
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.Fn gai_strerror "int ecode"
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.\"
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.Sh DESCRIPTION
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The
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.Fn getaddrinfo
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function is defined for protocol-independent nodename-to-address translation.
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It performs the functionality of
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.Xr gethostbyname 3
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and
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.Xr getservbyname 3 ,
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but in a more sophisticated manner.
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.Pp
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The
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.Li addrinfo
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structure is defined as a result of including the
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.Aq Pa netdb.h
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header:
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.Bd -literal -offset
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struct addrinfo {
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int ai_flags; /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
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int ai_family; /* PF_xxx */
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int ai_socktype; /* SOCK_xxx */
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int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
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size_t ai_addrlen; /* length of ai_addr */
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char *ai_canonname; /* canonical name for nodename */
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struct sockaddr *ai_addr; /* binary address */
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struct addrinfo *ai_next; /* next structure in linked list */
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};
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.Ed
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.Pp
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The
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.Fa nodename
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and
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.Fa servname
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arguments are pointers to null-terminated strings or
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.Dv NULL .
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One or both of these two arguments must be a
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.Pf non Dv -NULL
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pointer.
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In the normal client scenario, both the
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.Fa nodename
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and
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.Fa servname
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are specified.
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In the normal server scenario, only the
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.Fa servname
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is specified.
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A
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.Pf non Dv -NULL
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.Fa nodename
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string can be either a node name or a numeric host address string
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.Po
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i.e., a dotted-decimal IPv4 address or an IPv6 hex address
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.Pc .
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A
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.Pf non Dv -NULL
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.Fa servname
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string can be either a service name or a decimal port number.
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.Pp
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The caller can optionally pass an
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.Li addrinfo
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structure, pointed to by the third argument,
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to provide hints concerning the type of socket that the caller supports.
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In this
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.Fa hints
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structure all members other than
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.Fa ai_flags ,
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.Fa ai_family ,
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.Fa ai_socktype ,
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and
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.Fa ai_protocol
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must be zero or a
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.Dv NULL
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pointer.
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A value of
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.Dv PF_UNSPEC
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for
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.Fa ai_family
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means the caller will accept any protocol family.
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A value of 0 for
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.Fa ai_socktype
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means the caller will accept any socket type.
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A value of 0 for
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.Fa ai_protocol
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means the caller will accept any protocol.
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For example, if the caller handles only TCP and not UDP, then the
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.Fa ai_socktype
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member of the hints structure should be set to
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.Dv SOCK_STREAM
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when
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.Fn getaddrinfo
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is called.
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If the caller handles only IPv4 and not IPv6, then the
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.Fa ai_family
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member of the
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.Fa hints
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structure should be set to
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.Dv PF_INET
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when
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.Fn getaddrinfo
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is called.
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If the third argument to
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.Fn getaddrinfo
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is a
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.Dv NULL
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pointer, this is the same as if the caller had filled in an
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.Li addrinfo
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structure initialized to zero with
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.Fa ai_family
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set to
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.Dv PF_UNSPEC .
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.Pp
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Upon successful return a pointer to a linked list of one or more
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.Li addrinfo
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structures is returned through the final argument.
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The caller can process each
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.Li addrinfo
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structure in this list by following the
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.Fa ai_next
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pointer, until a
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.Dv NULL
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pointer is encountered.
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In each returned
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.Li addrinfo
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structure the three members
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.Fa ai_family ,
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.Fa ai_socktype ,
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and
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.Fa ai_protocol
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are the corresponding arguments for a call to the
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.Fn socket
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function.
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In each
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.Li addrinfo
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structure the
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.Fa ai_addr
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member points to a filled-in socket address structure whose length is
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specified by the
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.Fa ai_addrlen
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member.
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.Pp
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If the
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.Dv AI_PASSIVE
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bit is set in the
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.Fa ai_flags
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member of the
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.Fa hints
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structure, then the caller plans to use the returned socket address
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structure in a call to
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.Fn bind .
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In this case, if the
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.Fa nodename
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argument is a
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.Dv NULL
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pointer, then the IP address portion of the socket
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address structure will be set to
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.Dv INADDR_ANY
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for an IPv4 address or
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.Dv IN6ADDR_ANY_INIT
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for an IPv6 address.
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.Pp
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If the
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.Dv AI_PASSIVE
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bit is not set in the
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.Fa ai_flags
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member of the
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.Fa hints
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structure, then the returned socket address structure will be ready for a
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call to
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.Fn connect
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.Pq for a connection-oriented protocol
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or either
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.Fn connect ,
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.Fn sendto ,
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or
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.Fn sendmsg
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.Pq for a connectionless protocol .
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In this case, if the
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.Fa nodename
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argument is a
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.Dv NULL
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pointer, then the IP address portion of the
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socket address structure will be set to the loopback address.
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.Pp
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If the
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.Dv AI_CANONNAME
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bit is set in the
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.Fa ai_flags
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member of the
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.Fa hints
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structure, then upon successful return the
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.Fa ai_canonname
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member of the first
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.Li addrinfo
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structure in the linked list will point to a null-terminated string
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containing the canonical name of the specified
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.Fa nodename .
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.Pp
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If the
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.Dv AI_NUMERICHOST
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bit is set in the
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.Fa ai_flags
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member of the
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.Fa hints
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structure, then a
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.Pf non Dv -NULL
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.Fa nodename
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string must be a numeric host address string.
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Otherwise an error of
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.Dv EAI_NONAME
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is returned.
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This flag prevents any type of name resolution service (e.g., the DNS)
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from being called.
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.Pp
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The arguments to
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.Fn getaddrinfo
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must be sufficiently consistent and unambiguous.
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Here are some problem cases you may encounter:
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.Bl -bullet
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.It
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.Fn getaddrinfo
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will fail if the members in the
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.Fa hints
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structure are not consistent.
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For example, for internet address families,
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.Fn getaddrinfo
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will fail if you specify
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.Dv SOCK_STREAM
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to
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.Fa ai_socktype
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while you specify
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.Dv IPPROTO_UDP
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to
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.Fa ai_protocol .
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.It
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If you specify a
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.Fa servname
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which is defined only for certain
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.Fa ai_socktype ,
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.Fn getaddrinfo
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will fail because the arguments are not consistent.
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For example,
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.Fn getaddrinfo
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will return an error if you ask for
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.Dq Li tftp
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service on
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.Dv SOCK_STREAM .
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.It
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For internet address families, if you specify
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.Fa servname
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while you set
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.Fa ai_socktype
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to
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.Dv SOCK_RAW ,
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.Fn getaddrinfo
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will fail, because service names are not defined for the internet
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.Dv SOCK_RAW
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space.
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.It
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If you specify numeric
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.Fa servname ,
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while leaving
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.Fa ai_socktype
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and
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.Fa ai_protocol
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unspecified,
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.Fn getaddrinfo
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will fail.
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This is because the numeric
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.Fa servname
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does not identify any socket type, and
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.Fn getaddrinfo
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is not allowed to glob the argument in such case.
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.El
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.Pp
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All of the information returned by
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.Fn getaddrinfo
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is dynamically allocated:
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the
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.Li addrinfo
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structures, the socket address structures, and canonical node name
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strings pointed to by the addrinfo structures.
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To return this information to the system the function
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.Fn freeaddrinfo
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is called.
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The
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.Fa addrinfo
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structure pointed to by the
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.Fa ai argument
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is freed, along with any dynamic storage pointed to by the structure.
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This operation is repeated until a
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.Dv NULL
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.Fa ai_next
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pointer is encountered.
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.Pp
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To aid applications in printing error messages based on the
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.Dv EAI_xxx
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codes returned by
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.Fn getaddrinfo ,
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.Fn gai_strerror
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is defined.
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The argument is one of the
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.Dv EAI_xxx
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values defined earlier and the return value points to a string describing
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the error.
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If the argument is not one of the
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.Dv EAI_xxx
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values, the function still returns a pointer to a string whose contents
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indicate an unknown error.
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.\"
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.Sh EXTENSIONS
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This implementation supports numeric IPv6 address notation with the
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experimental scope identifier.
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By appending a percent sign and scope identifier to the address, you
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can specify the value of the
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.Li sin6_scope_id
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field of the socket address.
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This makes management of scoped address easier,
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and allows cut-and-paste input of scoped addresses.
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.Pp
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At the moment the code supports only link-local addresses in this format.
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The scope identifier is hardcoded to name of hardware interface associated
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with the link,
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.Po
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such as
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.Li ne0
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.Pc .
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For example,
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.Dq Li fe80::1%ne0 ,
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which means
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.Do
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.Li fe80::1
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on the link associated with the
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.Li ne0
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interface
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.Dc .
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.Pp
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This implementation is still very experimental and non-standard.
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The current implementation assumes a one-to-one relationship between
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interfaces and links, which is not necessarily true according to the
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specification.
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.\"
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.Sh EXAMPLES
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The following code tries to connect to
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.Dq Li www.kame.net
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service
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.Dq Li http .
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via stream socket.
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It loops through all the addresses available, regardless of the address family.
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If the destination resolves to an IPv4 address, it will use an
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.Dv AF_INET
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socket.
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Similarly, if it resolves to IPv6, an
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.Dv AF_INET6
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socket is used.
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Observe that there is no hardcoded reference to particular address family.
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The code works even if
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.Fn getaddrinfo
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returns addresses that are not IPv4/v6.
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.Bd -literal -offset indent
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struct addrinfo hints, *res, *res0;
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int error;
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int s;
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const char *cause = NULL;
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memset(&hints, 0, sizeof(hints));
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hints.ai_family = PF_UNSPEC;
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hints.ai_socktype = SOCK_STREAM;
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error = getaddrinfo("www.kame.net", "http", &hints, &res0);
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if (error) {
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errx(1, "%s", gai_strerror(error));
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/*NOTREACHED*/
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}
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s = -1;
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cause = "no addresses";
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errno = EADDRNOTAVAIL;
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for (res = res0; res; res = res->ai_next) {
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s = socket(res->ai_family, res->ai_socktype,
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res->ai_protocol);
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if (s < 0) {
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cause = "socket";
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continue;
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}
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if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
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cause = "connect";
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close(s);
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s = -1;
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continue;
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}
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break; /* okay we got one */
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}
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if (s < 0) {
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err(1, cause);
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/*NOTREACHED*/
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}
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freeaddrinfo(res0);
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.Ed
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.Pp
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The following example tries to open a wildcard listening socket onto service
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.Dq Li http ,
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for all the address families available.
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.Bd -literal -offset indent
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struct addrinfo hints, *res, *res0;
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int error;
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int s[MAXSOCK];
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int nsock;
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const char *cause = NULL;
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memset(&hints, 0, sizeof(hints));
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hints.ai_family = PF_UNSPEC;
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hints.ai_socktype = SOCK_STREAM;
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hints.ai_flags = AI_PASSIVE;
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error = getaddrinfo(NULL, "http", &hints, &res0);
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if (error) {
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errx(1, "%s", gai_strerror(error));
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/*NOTREACHED*/
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}
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nsock = 0;
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for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
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s[nsock] = socket(res->ai_family, res->ai_socktype,
|
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res->ai_protocol);
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if (s[nsock] < 0) {
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cause = "socket";
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continue;
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}
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if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
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cause = "bind";
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close(s[nsock]);
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continue;
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}
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|
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if (listen(s[nsock], SOMAXCONN) < 0) {
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cause = "listen";
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close(s[nsock]);
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continue;
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}
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nsock++;
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}
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if (nsock == 0) {
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err(1, cause);
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/*NOTREACHED*/
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}
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freeaddrinfo(res0);
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.Ed
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.\"
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.Sh FILES
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|
.Bl -tag -width /etc/nsswitch.conf -compact
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.It Pa /etc/hosts
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.It Pa /etc/nsswitch.conf
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.It Pa /etc/resolv.conf
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.El
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.\"
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.Sh DIAGNOSTICS
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|
Error return status from
|
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.Fn getaddrinfo
|
|
is zero on success and non-zero on errors.
|
|
Non-zero error codes are defined in
|
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.Aq Pa netdb.h ,
|
|
and as follows:
|
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.Pp
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.Bl -tag -width EAI_ADDRFAMILY -compact
|
|
.It Dv EAI_ADDRFAMILY
|
|
Address family for
|
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.Fa nodename
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not supported.
|
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.It Dv EAI_AGAIN
|
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Temporary failure in name resolution.
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.It Dv EAI_BADFLAGS
|
|
Invalid value for
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.Fa ai_flags .
|
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.It Dv EAI_FAIL
|
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Non-recoverable failure in name resolution.
|
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.It Dv EAI_FAMILY
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.Fa ai_family
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not supported.
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.It Dv EAI_MEMORY
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Memory allocation failure.
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.It Dv EAI_NODATA
|
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No address associated with
|
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.Fa nodename .
|
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.It Dv EAI_NONAME
|
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.Fa nodename
|
|
nor
|
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.Fa servname
|
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provided, or not known.
|
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.It Dv EAI_SERVICE
|
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.Fa servname
|
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not supported for
|
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.Fa ai_socktype .
|
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.It Dv EAI_SOCKTYPE
|
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.Fa ai_socktype
|
|
not supported.
|
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.It Dv EAI_SYSTEM
|
|
System error returned in
|
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.Va errno .
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.It Dv EAI_BADHINTS
|
|
Invalid value for
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.Fa hints .
|
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.It Dv EAI_PROTOCOL
|
|
Resolved protocol is unknown.
|
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.It Dv EAI_MAX
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|
Unknown error.
|
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.El
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|
.Pp
|
|
If called with an appropriate argument,
|
|
.Fn gai_strerror
|
|
returns a pointer to a string describing the given error code.
|
|
If the argument is not one of the
|
|
.Dv EAI_xxx
|
|
values, the function still returns a pointer to a string whose contents
|
|
indicate an unknown error.
|
|
.\"
|
|
.Sh SEE ALSO
|
|
.Xr getnameinfo 3 ,
|
|
.Xr gethostbyname 3 ,
|
|
.Xr getservbyname 3 ,
|
|
.Xr hosts 5 ,
|
|
.Xr services 5 ,
|
|
.Xr hostname 7 ,
|
|
.Xr named 8
|
|
.Pp
|
|
.Rs
|
|
.%A R. Gilligan
|
|
.%A S. Thomson
|
|
.%A J. Bound
|
|
.%A W. Stevens
|
|
.%T Basic Socket Interface Extensions for IPv6
|
|
.%R RFC2553
|
|
.%D March 1999
|
|
.Re
|
|
.Rs
|
|
.%A Tatsuya Jinmei
|
|
.%A Atsushi Onoe
|
|
.%T "An Extension of Format for IPv6 Scoped Addresses"
|
|
.%R internet draft
|
|
.%N draft-ietf-ipngwg-scopedaddr-format-02.txt
|
|
.%O work in progress material
|
|
.Re
|
|
.Rs
|
|
.%A Craig Metz
|
|
.%T Protocol Independence Using the Sockets API
|
|
.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
|
|
.%D June 2000
|
|
.Re
|
|
.\"
|
|
.Sh HISTORY
|
|
The implementation first appeared in WIDE Hydrangea IPv6 protocol stack kit.
|
|
.\"
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn getaddrinfo
|
|
function is defined in
|
|
.St -p1003.1g-2000 ,
|
|
and documented in
|
|
.Dq Basic Socket Interface Extensions for IPv6
|
|
.Pq RFC2553 .
|
|
.\"
|
|
.Sh BUGS
|
|
The current implementation is not thread-safe.
|
|
.Pp
|
|
The text was shamelessly copied from RFC2553.
|