d9fad5273b
Notably, unlike in OpenBSD, which the man page was copied from, ai_canonname and ai_addr come in different order. PR: 225880 MFC after: 1 week
521 lines
12 KiB
Groff
521 lines
12 KiB
Groff
.\" $KAME: getaddrinfo.3,v 1.36 2005/01/05 03:23:05 itojun Exp $
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.\" $OpenBSD: getaddrinfo.3,v 1.35 2004/12/21 03:40:31 jaredy Exp $
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.\"
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.\" Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC")
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.\" Copyright (C) 2000, 2001 Internet Software Consortium.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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.\" REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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.\" AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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.\" INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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.\" LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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.\" OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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.\" PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 10, 2019
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.Dt GETADDRINFO 3
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.Os
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.Sh NAME
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.Nm getaddrinfo ,
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.Nm freeaddrinfo
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.Nd socket address structure to host and service name
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netdb.h
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.Ft int
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.Fo getaddrinfo
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.Fa "const char *hostname" "const char *servname"
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.Fa "const struct addrinfo *hints" "struct addrinfo **res"
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.Fc
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.Ft void
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.Fn freeaddrinfo "struct addrinfo *ai"
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.Sh DESCRIPTION
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The
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.Fn getaddrinfo
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function is used to get a list of
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addresses and port numbers for host
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.Fa hostname
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and service
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.Fa servname .
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It is a replacement for and provides more flexibility than the
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.Xr gethostbyname 3
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and
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.Xr getservbyname 3
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functions.
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.Pp
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The
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.Fa hostname
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and
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.Fa servname
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arguments are either pointers to NUL-terminated strings or the null pointer.
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An acceptable value for
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.Fa hostname
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is either a valid host name or a numeric host address string consisting
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of a dotted decimal IPv4 address,
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an IPv6 address,
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or a UNIX-domain address.
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The
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.Fa servname
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is either a decimal port number or a service name listed in
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.Xr services 5 .
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At least one of
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.Fa hostname
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and
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.Fa servname
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must be non-null.
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.Pp
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.Fa hints
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is an optional pointer to a
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.Li struct addrinfo ,
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as defined by
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.Aq Pa netdb.h :
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.Bd -literal
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struct addrinfo {
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int ai_flags; /* AI_PASSIVE, AI_CANONNAME, .. */
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int ai_family; /* AF_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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socklen_t ai_addrlen; /* length of ai_addr */
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char *ai_canonname; /* canonical name for hostname */
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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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This structure can be used to provide hints concerning the type of socket
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that the caller supports or wishes to use.
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The caller can supply the following structure elements in
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.Fa hints :
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.Bl -tag -width "ai_socktypeXX"
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.It Fa ai_family
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The address family that should be used.
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When
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.Fa ai_family
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is set to
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.Dv AF_UNSPEC ,
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it means the caller will accept any address family supported by the
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operating system.
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.It Fa ai_socktype
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Denotes the type of socket that is wanted:
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.Dv SOCK_STREAM ,
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.Dv SOCK_DGRAM ,
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.Dv SOCK_SEQPACKET ,
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or
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.Dv SOCK_RAW .
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When
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.Fa ai_socktype
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is zero the caller will accept any socket type.
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.It Fa ai_protocol
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Indicates which transport protocol is desired,
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.Dv IPPROTO_UDP ,
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.Dv IPPROTO_TCP ,
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.Dv IPPROTO_SCTP ,
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or
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.Dv IPPROTO_UDPLITE .
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If
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.Fa ai_protocol
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is zero the caller will accept any protocol.
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.It Fa ai_flags
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The
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.Fa ai_flags
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field to which the
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.Fa hints
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parameter points shall be set to zero
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or be the bitwise-inclusive OR of one or more of the values
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.Dv AI_ADDRCONFIG ,
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.Dv AI_ALL ,
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.Dv AI_CANONNAME ,
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.Dv AI_NUMERICHOST ,
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.Dv AI_NUMERICSERV ,
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.Dv AI_PASSIVE
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and
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.Dv AI_V4MAPPED .
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For a UNIX-domain address,
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.Fa ai_flags
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is ignored.
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.Bl -tag -width "AI_CANONNAMEXX"
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.It Dv AI_ADDRCONFIG
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If the
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.Dv AI_ADDRCONFIG
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bit is set, IPv4 addresses shall be returned only if
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an IPv4 address is configured on the local system,
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and IPv6 addresses shall be returned only if
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an IPv6 address is configured on the local system.
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.It Dv AI_ALL
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If the
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.Dv AI_ALL
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flag is used with the
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.Dv AI_V4MAPPED
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flag, then
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.Fn getaddrinfo
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shall return all matching IPv6 and IPv4 addresses.
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.Pp
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For example, when using the DNS, queries are made for both AAAA records and A records, and
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.Fn getaddrinfo
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returns the combined results of both queries.
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Any IPv4 addresses found are returned as IPv4-mapped IPv6 addresses.
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.Pp
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The
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.Dv AI_ALL
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flag without the
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.Dv AI_V4MAPPED
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flag is ignored.
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.It Dv AI_CANONNAME
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If the
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.Dv AI_CANONNAME
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bit is set, a successful call to
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.Fn getaddrinfo
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will return a NUL-terminated string containing the canonical name
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of the specified hostname in the
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.Fa ai_canonname
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element of the first
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.Li addrinfo
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structure returned.
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.It Dv AI_NUMERICHOST
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If the
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.Dv AI_NUMERICHOST
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bit is set, it indicates that
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.Fa hostname
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should be treated as a numeric string defining an IPv4 or IPv6 address
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and no name resolution should be attempted.
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.It Dv AI_NUMERICSERV
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If the
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.Dv AI_NUMERICSERV
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bit is set,
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then a non-null
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.Fa servname
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string supplied shall be a numeric port string.
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Otherwise, an
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.Dv EAI_NONAME
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error shall be returned.
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This bit shall prevent any type of name resolution service
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(for example, NIS+) from being invoked.
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.It Dv AI_PASSIVE
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If the
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.Dv AI_PASSIVE
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bit is set it indicates that the returned socket address structure
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is intended for use in a call to
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.Xr bind 2 .
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In this case, if the
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.Fa hostname
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argument is the null pointer, then the IP address portion of the
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socket 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, the returned socket address structure will be ready
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for use in a call to
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.Xr connect 2
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for a connection-oriented protocol or
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.Xr connect 2 ,
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.Xr sendto 2 ,
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or
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.Xr sendmsg 2
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if a connectionless protocol was chosen.
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The
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.Tn IP
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address portion of the socket address structure will be set to the
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loopback address if
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.Fa hostname
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is the null pointer and
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.Dv AI_PASSIVE
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is not set.
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.It Dv AI_V4MAPPED
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If the
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.Dv AI_V4MAPPED
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flag is specified along with an ai_family of
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.Dv AF_INET6 ,
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then
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.Fn getaddrinfo
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shall return IPv4-mapped IPv6 addresses on finding no matching IPv6 addresses (
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.Fa ai_addrlen
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shall be 16).
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.Pp
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For example, when using the DNS, if no AAAA records are found then a query is made for A records and any found are returned as IPv4-mapped IPv6 addresses.
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.Pp
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The
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.Dv AI_V4MAPPED
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flag shall be ignored unless
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.Fa ai_family
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equals
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.Dv AF_INET6 .
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.El
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.El
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.Pp
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All other elements of the
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.Li addrinfo
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structure passed via
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.Fa hints
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must be zero or the null pointer.
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.Pp
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If
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.Fa hints
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is the null pointer,
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.Fn getaddrinfo
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behaves as if the caller provided a
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.Li struct addrinfo
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with
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.Fa ai_family
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set to
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.Dv AF_UNSPEC
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and all other elements set to zero or
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.Dv NULL .
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.Pp
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After a successful call to
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.Fn getaddrinfo ,
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.Fa *res
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is a pointer to a linked list of one or more
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.Li addrinfo
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structures.
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The list can be traversed by following the
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.Fa ai_next
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pointer in each
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.Li addrinfo
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structure until a null pointer is encountered.
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Each returned
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.Li addrinfo
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structure contains three members that are suitable for a call to
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.Xr socket 2 :
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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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For each
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.Li addrinfo
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structure in the list, the
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.Fa ai_addr
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member points to a filled-in socket address structure of length
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.Fa ai_addrlen .
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.Pp
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This implementation of
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.Fn getaddrinfo
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allows numeric IPv6 address notation with scope identifier,
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as documented in chapter 11 of RFC 4007.
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By appending the percent character and scope identifier to addresses,
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one can fill the
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.Li sin6_scope_id
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field for addresses.
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This would make management of scoped addresses easier
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and allows cut-and-paste input of scoped addresses.
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.Pp
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At this moment the code supports only link-local addresses with the format.
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The scope identifier is hardcoded to the name of the hardware interface
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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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An example is
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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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The current implementation assumes a one-to-one relationship between
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the interface and link, which is not necessarily true from the specification.
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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: the
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.Li addrinfo
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structures themselves as well as the socket address structures and
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the canonical host name strings included in the
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.Li addrinfo
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structures.
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.Pp
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Memory allocated for the dynamically allocated structures created by
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a successful call to
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.Fn getaddrinfo
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is released by the
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.Fn freeaddrinfo
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function.
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The
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.Fa ai
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pointer should be a
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.Li addrinfo
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structure created by a call to
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.Fn getaddrinfo .
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.Sh IMPLEMENTATION NOTES
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The behavior of
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.Li freeadrinfo(NULL)
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is left unspecified by both
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.St -susv4
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and
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.Dv "RFC 3493" .
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The current implementation ignores a
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.Dv NULL
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argument for compatibility with programs that rely on the implementation
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details of other operating systems.
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.Sh RETURN VALUES
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.Fn getaddrinfo
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returns zero on success or one of the error codes listed in
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.Xr gai_strerror 3
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if an error occurs.
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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 a stream socket.
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It loops through all the addresses available, regardless of 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 a 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 = AF_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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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, "%s", 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 = AF_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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(void) listen(s[nsock], 5);
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nsock++;
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}
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if (nsock == 0) {
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err(1, "%s", 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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.Sh SEE ALSO
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.Xr bind 2 ,
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.Xr connect 2 ,
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.Xr send 2 ,
|
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.Xr socket 2 ,
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.Xr gai_strerror 3 ,
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.Xr gethostbyname 3 ,
|
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.Xr getnameinfo 3 ,
|
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.Xr getservbyname 3 ,
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.Xr resolver 3 ,
|
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.Xr inet 4 ,
|
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.Xr inet6 4 ,
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.Xr unix 4 ,
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.Xr hosts 5 ,
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.Xr resolv.conf 5 ,
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.Xr services 5 ,
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.Xr hostname 7 ,
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.Xr named 8
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.Rs
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.%A R. Gilligan
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.%A S. Thomson
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.%A J. Bound
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.%A J. McCann
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.%A W. Stevens
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.%T Basic Socket Interface Extensions for IPv6
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.%R RFC 3493
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.%D February 2003
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.Re
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.Rs
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.%A S. Deering
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.%A B. Haberman
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.%A T. Jinmei
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.%A E. Nordmark
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.%A B. Zill
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.%T "IPv6 Scoped Address Architecture"
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.%R RFC 4007
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.%D March 2005
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.Re
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.Rs
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.%A Craig Metz
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.%T Protocol Independence Using the Sockets API
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.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
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.%D June 2000
|
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.Re
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.Sh STANDARDS
|
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The
|
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.Fn getaddrinfo
|
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function is defined by the
|
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.St -p1003.1-2004
|
|
specification and documented in
|
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.Dv "RFC 3493" ,
|
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.Dq Basic Socket Interface Extensions for IPv6 .
|