GETADDRINFO(3) | Library Functions Manual | GETADDRINFO(3) |
getaddrinfo
, freeaddrinfo
,
allocaddrinfo
—
#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);
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; /* 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:
AF_UNSPEC
, it means the caller will accept any
address family supported by the operating system. Note that while address
families (AF_*
) and protocol families
(PF_*
) are theoretically distinct, in practice 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).SOCK_STREAM
, SOCK_DGRAM
,
or SOCK_RAW
. When
ai_socktype is zero the caller will accept any
socket type.IPPROTO_UDP
or
IPPROTO_TCP
. If ai_protocol
is zero the caller will accept any protocol.AI_CANONNAME
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
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
AI_NUMERICSERV
bit is set, it indicates
that the servname string contains a numeric port
number. This is used to prevent service name resolution.AI_PASSIVE
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.
AI_SRV
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 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 member 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 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 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).
getaddrinfo
() returns zero on success or one of the
error codes listed in
gai_strerror(3) if an
error occurs.
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 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 = 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);
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.
getaddrinfo
() function is defined by the
IEEE Std 1003.1g-2000 (“POSIX.1g”) draft
specification and documented in RFC 3493
,
“Basic Socket Interface Extensions for IPv6”.
December 13, 2015 | NetBSD 9.0 |