DragonFly On-Line Manual Pages
GETADDRINFO(3) DragonFly Library Functions Manual GETADDRINFO(3)
NAME
getaddrinfo, freeaddrinfo -- socket address structure to host and service
name
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#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);
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
decimal 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
accept any protocol.
ai_flags The ai_flags field to which the hints parameter points
shall be set to zero or be the bitwise-inclusive OR of one
or more of the values AI_ADDRCONFIG, AI_CANONNAME,
AI_NUMERICHOST, AI_NUMERICSERV and AI_PASSIVE.
AI_ADDRCONFIG If the AI_ADDRCONFIG bit is set, IPv4
addresses shall be returned only if an
IPv4 address is configured on the local
system, and IPv6 addresses shall be
returned only if an IPv6 address is
configured on the local system.
AI_CANONNAME If the AI_CANONNAME bit is set, a
successful 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
indicates 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, then a
non-null servname string supplied shall be
a numeric port string. Otherwise, an
EAI_NONAME error shall be returned. This
bit shall prevent any type of name
resolution service (for example, NIS+)
from being invoked.
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
portion 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
provided 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
member 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
format. 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
allocated: 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()
function. 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
service ``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 = PF_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), 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 1003.1-2004
(``POSIX.1'') specification and documented in RFC 3493, ``Basic Socket
Interface Extensions for IPv6''.
DragonFly 5.1 February 22, 2018 DragonFly 5.1