getaddrinfo(3)
- NetBSD Manual Pages
GETADDRINFO(3) NetBSD Library Functions Manual GETADDRINFO(3)
NAME
getaddrinfo, freeaddrinfo, allocaddrinfo -- host and service name to
socket address structure
SYNOPSIS
#include <netdb.h>
int
getaddrinfo(const char * restrict hostname,
const char * restrict servname,
const struct addrinfo * restrict hints,
struct addrinfo ** restrict res);
void
freeaddrinfo(struct addrinfo *ai);
struct addrinfo *
allocaddrinfo(socklen_t len);
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; /* address 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 address (and protocol) family that should be used.
When ai_family is set to AF_UNSPEC, it means the caller
will accept any address family supported by the operating
system. Note that while address families (AF_*) and pro-
tocol families (PF_*) are theoretically distinct, in prac-
tice the distinction has been lost. RFC 3493 defines
getaddrinfo() in terms of the address family constants
AF_* even though ai_family is to be passed as a protocol
family to socket(2).
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
accept any protocol.
ai_flags ai_flags is formed by OR'ing the following values:
AI_CANONNAME If the AI_CANONNAME bit is set, a success-
ful call to getaddrinfo() will return a
NUL-terminated string containing the
canonical name of the specified hostname
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_NUMERICSERV If the AI_NUMERICSERV bit is set, it indi-
cates that the servname string contains a
numeric port number. This is used to pre-
vent service name resolution.
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.
AI_SRV Perform SRV (RFC 2782) record lookups
first. This is a non-portable extension.
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 AF_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.
By default IPv6 address entries are ordered before IPv4 ones, but the
order of the entries in the list can be controlled using ip6addrctl(8).
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
interface and link, which is not necessarily true from the specification.
All of the information returned by getaddrinfo() is dynamically allo-
cated: the addrinfo structures themselves as well as the socket address
structures and the canonical host name strings included in the addrinfo
structures.
Memory allocated for the dynamically allocated structures created by a
successful call to getaddrinfo() is released by the freeaddrinfo() func-
tion. The ai pointer should be an addrinfo structure created by a call
to getaddrinfo() or allocaddrinfo(). The allocaddrinfo() function is
intended primarily for authors of nsdispatch(3) plugins implementing
getaddrinfo() backends. allocaddrinfo() allocates a struct addrinfo in a
way that is compatible with being returned from getaddrinfo() and being
ultimately freed by freeaddrinfo(). The returned structure is zeroed,
except for the ai_addr field, which will point to len bytes of memory for
storage of a socket address. It is safe to allocate memory separately
for ai_canonname with malloc(3), or in any other way that is compatible
with deallocation by free(3).
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 = AF_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;
int error;
int s[MAXSOCK];
int nsock;
const char *cause = NULL;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
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), ip6addrctl(8),
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, USENIX
Association,
http://www.usenix.org/events/usenix2000/freenix/metzprotocol/metzprotocol.pdf,
99-108, June 18-23, 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''.
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