FreeBSD Man Pagesgetaddrinfo(3)
NAME
getaddrinfo, freeaddrinfo -- socket address structure to host and service
name
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int
getaddrinfo(const char *hostname, const char *servname,
const struct addrinfo *hints, struct addrinfo **res);
void
freeaddrinfo(struct addrinfo *ai);
DESCRIPTION
The getaddrinfo() function is used to get a list of IP addresses and port
numbers for host hostname and service servname. It is a replacement for
and provides more flexibility than the gethostbyname(3) and
getservbyname(3) functions.
The hostname and servname arguments are either pointers to NUL-terminated
strings or the null pointer. An acceptable value for hostname is either
a valid host name or a numeric host address string consisting of a dotted
decimal IPv4 address or an IPv6 address. The servname is either a deci-
mal port number or a service name listed in services(5). At least one of
hostname and servname must be non-null.
hints is an optional pointer to a struct addrinfo, as defined by
<netdb.h>:
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 */
};
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 hints:
ai_family The protocol family that should be used. When ai_family
is set to PF_UNSPEC, it means the caller will accept any
protocol family supported by the operating system.
ai_socktype Denotes the type of socket that is wanted: SOCK_STREAM,
SOCK_DGRAM, or SOCK_RAW. When ai_socktype is zero the
caller will accept any socket type.
ai_protocol Indicates which transport protocol is desired, IPPROTO_UDP
or IPPROTO_TCP. If ai_protocol is zero the caller will
in the ai_canonname element of the first
addrinfo structure returned.
AI_NUMERICHOST If the AI_NUMERICHOST bit is set, it indi-
cates that hostname should be treated as a
numeric string defining an IPv4 or IPv6
address and no name resolution should be
attempted.
AI_PASSIVE If the AI_PASSIVE bit is set it indicates
that the returned socket address structure
is intended for use in a call to bind(2).
In this case, if the hostname argument is
the null pointer, then the IP address por-
tion of the socket address structure will
be set to INADDR_ANY for an IPv4 address
or IN6ADDR_ANY_INIT for an IPv6 address.
If the AI_PASSIVE bit is not set, the
returned socket address structure will be
ready for use in a call to connect(2) for
a connection-oriented protocol or
connect(2), sendto(2), or sendmsg(2) if a
connectionless protocol was chosen. The
IP address portion of the socket address
structure will be set to the loopback
address if hostname is the null pointer
and AI_PASSIVE is not set.
All other elements of the addrinfo structure passed via hints must be
zero or the null pointer.
If hints is the null pointer, getaddrinfo() behaves as if the caller pro-
vided a struct addrinfo with ai_family set to PF_UNSPEC and all other
elements set to zero or NULL.
After a successful call to getaddrinfo(), *res is a pointer to a linked
list of one or more addrinfo structures. The list can be traversed by
following the ai_next pointer in each addrinfo structure until a null
pointer is encountered. The three members ai_family, ai_socktype, and
ai_protocol in each returned addrinfo structure are suitable for a call
to socket(2). For each addrinfo structure in the list, the ai_addr mem-
ber points to a filled-in socket address structure of length ai_addrlen.
This implementation of getaddrinfo() allows numeric IPv6 address notation
with scope identifier, as documented in chapter 11 of draft-ietf-
ipv6-scoping-arch-02.txt. By appending the percent character and scope
identifier to addresses, one can fill the sin6_scope_id field for
addresses. This would make management of scoped addresses easier and
allows cut-and-paste input of scoped addresses.
At this moment the code supports only link-local addresses with the for-
mat. The scope identifier is hardcoded to the name of the hardware
interface associated with the link (such as ne0). An example is
``fe80::1%ne0'', which means ``fe80::1 on the link associated with the
ne0 interface''.
The current implementation assumes a one-to-one relationship between the
successful call to getaddrinfo() is released by the freeaddrinfo() func-
tion. The ai pointer should be a addrinfo structure created by a call to
getaddrinfo().
RETURN VALUES
getaddrinfo() returns zero on success or one of the error codes listed in
gai_strerror(3) if an error occurs.
EXAMPLES
The following code tries to connect to ``www.kame.net'' service ``http''
via a stream socket. It loops through all the addresses available,
regardless of address family. If the destination resolves to an IPv4
address, it will use an AF_INET socket. Similarly, if it resolves to
IPv6, an AF_INET6 socket is used. Observe that there is no hardcoded
reference to a particular address family. The code works even if
getaddrinfo() returns addresses that are not IPv4/v6.
struct addrinfo hints, *res, *res0;
int error;
int s;
const char *cause = NULL;
memset(&hints, 0, sizeof(hints));
hints.ai_family = PF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
error = getaddrinfo("www.kame.net", "http", &hints, &res0);
if (error) {
errx(1, "%s", gai_strerror(error));
/*NOTREACHED*/
}
s = -1;
for (res = res0; res; res = res->ai_next) {
s = socket(res->ai_family, res->ai_socktype,
res->ai_protocol);
if (s < 0) {
cause = "socket";
continue;
}
if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
cause = "connect";
close(s);
s = -1;
continue;
}
break; /* okay we got one */
}
if (s < 0) {
err(1, "%s", cause);
/*NOTREACHED*/
}
freeaddrinfo(res0);
The following example tries to open a wildcard listening socket onto ser-
vice ``http'', for all the address families available.
struct addrinfo hints, *res, *res0;
hints.ai_flags = AI_PASSIVE;
error = getaddrinfo(NULL, "http", &hints, &res0);
if (error) {
errx(1, "%s", gai_strerror(error));
/*NOTREACHED*/
}
nsock = 0;
for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
s[nsock] = socket(res->ai_family, res->ai_socktype,
res->ai_protocol);
if (s[nsock] < 0) {
cause = "socket";
continue;
}
if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
cause = "bind";
close(s[nsock]);
continue;
}
(void) listen(s[nsock], 5);
nsock++;
}
if (nsock == 0) {
err(1, "%s", cause);
/*NOTREACHED*/
}
freeaddrinfo(res0);
SEE ALSO
bind(2), connect(2), send(2), socket(2), gai_strerror(3),
gethostbyname(3), getnameinfo(3), getservbyname(3), resolver(3),
hosts(5), resolv.conf(5), services(5), hostname(7), named(8)
R. Gilligan, S. Thomson, J. Bound, J. McCann, and W. Stevens, Basic
Socket Interface Extensions for IPv6, RFC 3493, February 2003.
S. Deering, B. Haberman, T. Jinmei, E. Nordmark, and B. Zill, IPv6 Scoped
Address Architecture, internet draft, draft-ietf-ipv6-scoping-
arch-02.txt, work in progress material.
Craig Metz, "Protocol Independence Using the Sockets API", Proceedings of
the freenix track: 2000 USENIX annual technical conference, June 2000.
STANDARDS
The getaddrinfo() function is defined by the IEEE Std 1003.1g-2000
(``POSIX.1'') draft specification and documented in RFC 3493, ``Basic
Socket Interface Extensions for IPv6''.
BUGS
The implementation of getaddrinfo() is not thread-safe.
FreeBSD 5.4 December 20, 2004 FreeBSD 5.4
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