path: root/lib/libc/net/getaddrinfo.3

.\"	$OpenBSD: getaddrinfo.3,v 1.31 2004/12/20 21:13:00 millert Exp $
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.Dd December 20, 2004
.Dt GETADDRINFO 3
.Os
.Sh NAME
.Nm getaddrinfo ,
.Nm freeaddrinfo
.Nd socket address structure to host and service name
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fd #include <netdb.h>
.Ft int
.Fn getaddrinfo "const char *hostname" "const char *servname" "const struct addrinfo *hints" "struct addrinfo **res"
.Ft void
.Fn freeaddrinfo "struct addrinfo *ai"
.Sh DESCRIPTION
.Fn getaddrinfo
is used to get a list of
.Dv IP
addresses and port numbers for host
.Fa hostname
and service
.Fa servname .
It is a replacement for and provides more flexibility than the
.Xr gethostbyname 3
and
.Xr getservbyname 3
functions.
.Pp
.Fa hostname
and
.Fa servname
are either pointers to NUL-terminated strings or the null pointer.
An acceptable value for
.Fa hostname
is either a host name or a numeric host address string consisting
of a dotted decimal IPv4 address or an IPv6 address.
The
.Fa servname
is either a decimal port number or a service name listed in
.Xr services 5 .
At least one of
.Fa hostname
and
.Fa servname
must be non-null.
.Pp
.Fa hints
is an optional pointer to a
.Li struct addrinfo ,
as defined by
.Aq Pa netdb.h :
.Bd -literal
struct addrinfo {
	int ai_flags;		/* input flags */
	int ai_family;		/* protocol family for socket */
	int ai_socktype;	/* socket type */
	int ai_protocol;	/* protocol for socket */
	socklen_t ai_addrlen;	/* length of socket-address */
	struct sockaddr *ai_addr; /* socket-address for socket */
	char *ai_canonname;	/* canonical name for service location */
	struct addrinfo *ai_next; /* pointer to next in list */
};
.Ed
.Pp
This structure can be used to provide hints concerning the type of socket
that the caller supports or wishes to use.
The caller can supply the following structure elements in
.Fa hints :
.Bl -tag -width "ai_socktypeXX"
.It Fa ai_family
The protocol family that should be used.
When
.Fa ai_family
is set to
.Dv PF_UNSPEC ,
it means the caller will accept any protocol family supported by the
operating system.
.It Fa ai_socktype
Denotes the type of socket that is wanted:
.Dv SOCK_STREAM ,
.Dv SOCK_DGRAM
or
.Dv SOCK_RAW .
When
.Fa ai_socktype
is zero the caller will accept any socket type.
.It Fa ai_protocol
Indicates which transport protocol is desired,
.Dv IPPROTO_UDP
or
.Dv IPPROTO_TCP .
If
.Fa ai_protocol
is zero the caller will accept any protocol.
.It Fa ai_flags
Flag bits.
.Bl -tag -width "AI_CANONNAMEXX"
.It Dv AI_CANONNAME
If the
.Dv AI_CANONNAME
bit is set, a successful call to
.Fn getaddrinfo
will return a NUL-terminated string containing the canonical name
of the specified hostname in the
.Fa ai_canonname
element of the first
.Li addrinfo
structure returned.
.It Dv AI_NUMERICHOST
If the
.Dv AI_NUMERICHOST
bit is set, it indicates that
.Fa hostname
should be treated as a numeric string defining an IPv4 or IPv6 address
and no name resolution should be attempted.
.It Dv AI_PASSIVE
If the
.Dv AI_PASSIVE
bit is set it indicates that the returned socket address structure
is intended for used in a call to
.Xr bind 2 .
In this case, if the
.Fa hostname
argument is a the null pointer, then the IP address portion of the
socket address structure will be set to
.Dv INADDR_ANY
for an IPv4 address or
.Dv IN6ADDR_ANY_INIT
for an IPv6 address.
.Pp
If the
.Dv AI_PASSIVE
bit is not set, the returned socket address structure will be ready
for use in a call to
.Xr connect 2
for a connection-oriented protocol or
.Xr connect 2 ,
.Xr sendto 2
or
.Xr sendmsg 2
if a connectionless protocol was chosen.
The
.Dv IP
address portion of the socket address structure will be set to the
loopback address if
.Fa hostname
is the null pointer and the
.Dv AI_PASSIVE
is not set.
.El
.El
.Pp
All other elements of the
.Li addrinfo
structure passed via
.Fa hints
must be zero or the null pointer.
.Pp
If
.Fa hints
is the null pointer,
.Fn getaddrinfo
behaves as if the caller provided a
.Li struct addrinfo
initialized to zero and with
.Fa ai_family
set to
.Dv PF_UNSPEC .
.Pp
After a successful call to
.Fn getaddrinfo ,
.Fa *res
is a pointer to a linked list of one or more
.Li addrinfo
structures.
The list can be traversed by following the
.Fa ai_next
pointer in each
.Li addrinfo
structure until a null pointer is encountered.
The three members,
.Fa ai_family,
.Fa ai_socktype,
and
.Fa ai_protocol
in each returned
.Li addrinfo
structure are suitable for a call to
.Xr socket 2 .
For each
.Li addrinfo
structure in the list, the
.Fa ai_addr
member points to a filled-in socket address structure of length
.Fa ai_addrlen .
.Pp
All of the information returned by
.Fn getaddrinfo
is dynamically allocated: the
.Li addrinfo
structures themselves as well as the socket address structures and
the canonical host name strings included in the
.Li addrinfo
structures.
.Pp
Memory allocated for the dynamically allocated structures created by
a successful call to
.Fn getaddrinfo
is released by the
.Fn freeaddrinfo
function.
The
.Fa ai
pointer should be a
.Li addrinfo
structure created by a call to
.Fn getaddrinfo .
.Sh RETURN VALUES
.Fn getaddrinfo
returns zero on success or one of the error codes listed in
.Xr gai_strerror 3
if an error occurs.
If both
.Fa hostname
and
.Fa servname
are
.Dv NULL ,
.Fn getaddrinfo
returns
.Dv EAI_NONAME .
.Sh SEE ALSO
.Xr bind 2 ,
.Xr connect 2 ,
.Xr send 2 ,
.Xr socket 2 ,
.Xr gai_strerror 3 ,
.Xr gethostbyname 3 ,
.Xr getnameinfo 3 ,
.Xr getservbyname 3 ,
.Xr resolver 3 ,
.Xr hosts 5 ,
.Xr resolv.conf 5 ,
.Xr services 5 ,
.Xr hostname 7 ,
.Xr named 8
.Rs
.%A R. Gilligan
.%A S. Thomson
.%A J. Bound
.%A J. McCann
.%A W. Stevens
.%T Basic Socket Interface Extensions for IPv6
.%R RFC 3493
.%D February 2003
.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 STANDARDS
The
.Fn getaddrinfo
function is defined by the
.St -p1003.1g-2000
draft specification and documented in
.Dv "RFC 3493" ,
.Dq Basic Socket Interface Extensions for IPv6 .
.Sh BUGS
Due to the use of dynamic allocation,
.Fn getaddrinfo
is not thread-safe.