getaddrinfo - network address and service translation
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int rc=getaddrinfo(const char *node, const char *service,
const struct addrinfo *hints,
struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
char *gai_strerror(int errcode);
DESCRIPTION
The getaddrinfo(3) function combines the functionality
provided by the getipnodebyname(3), getipnodebyaddr(3),
getservbyname(3), and getservbyport(3) functions into a
single interface. The thread-safe getaddrinfo(3) function
creates one or more socket address structures that can be
used by the bind(3) and connect(3) function calls to cre
ate a client or a server socket.
The getaddrinfo(3) function is not limited to creating
IPv4 socket address structures; IPv6 socket address struc
tures can be created if IPv6 support is available. These
socket address structures can be used directly by bind(3)
or connect(3), to prepare a client or a server socket.
The addrinfo structure used by this function contains the
following members:
struct addrinfo {
int ai_flags;
int ai_family;
int ai_socktype;
int ai_protocol;
size_t ai_addrlen;
struct sockaddr *ai_addr;
char *ai_canonname;
struct addrinfo *ai_next;
};
getaddrinfo(3) sets res to point to a dynamically-allo
cated link list of addrinfo structures, linked by the
ai_next member. There are several reasons why the link
list may have more than one addrinfo structure, including:
if the network host is multi-homed; or if the same service
is available from multiple socket protocols (one
SOCK_STREAM address and another SOCK_DGRAM address, for
example).
the same meaning as the corresponding parameters in the
socket(3) function call. The getaddrinfo(3) function
returns socket addresses in either IPv4 or IPv6 address
family, (ai_family will be set to either PF_INET or
PF_INET6).
The hints parameter specifies the preferred socket type,
or protocol. A NULL hints specifies that any network
address or protocol is acceptable. If this parameter is
not NULL it points to an addrinfo structure whose ai_fam
ily, ai_socktype, and ai_protocol members specify the pre
ferred socket type. PF_UNSPEC in ai_family specifies any
protocol family (either IPv4 or IPv6, for example). 0 in
ai_socktype or ai_protocol specifies that any socket type
or protocol is acceptable as well. The ai_flags member
specifies additional options, defined below. Multiple
flags are specified by logically OR-ing them together.
All the other members in the hints parameter must contain
either 0, or a null pointer.
The node or service parameter, but not both, may be NULL.
node specifies either a numerical network address (dotted-
decimal format for IPv4, hexadecimal format for IPv6) or a
network hostname, whose network addresses are looked up
and resolved. If the ai_flags member in the hints parame
ter contains the AI_NUMERICHOST flag then the node parame
ter must be a numerical network address. The AI_NUMERI
CHOST flag suppresses any potentially lengthy network host
address lookups.
The getaddrinfo(3) function creates a link list of
addrinfo structures, one for each network address subject
to any restrictions imposed by the hints parameter.
ai_canonname is set to point to the official name of the
host, if ai_flags in hints includes the AI_CANONNAME flag.
ai_family, ai_socktype, and ai_protocol specify the socket
creation parameters. A pointer to the socket address is
placed in the ai_addr member, and the length of the socket
address, in bytes, is placed in the ai_addrlen structure.
If node is NULL, the network address in each socket struc
ture is initialized according to the AI_PASSIVE flag,
which is set in the ai_flags member of the hints parame
ter. The network address in each socket structure will be
left unspecified if AI_PASSIVE flag is set. This is used
by server applications, which intend to accept client con
nections on any network address. The network address will
be set to the loopback interface address if the AI_PASSIVE
flag is not set. This is used by client applications,
which intend to connect to a server running on the same
network host.
will be left uninitialized.
The freeaddrinfo(3) function frees the memory that was
allocated for the dynamically allocated link list res.
RETURN VALUES
getaddrinfo(3) returns 0 if it succeeds, or one of the
following non-zero error codes:
EAI_FAMILY The requested address family is not sup
ported at all.
EAI_SOCKTYPE The requested socket type is not supported
at all.
EAI_BADFLAGS ai_flags contains invalid flags.
EAI_NONAME The node or service is not known. This
error is also returned if both node and ser
vice are NULL.
EAI_SERVICE The requested service is not available for
the requested socket type. It may be avail
able through another socket type.
EAI_ADDRFAMILY
The specified network host does not have any
network addresses in the requested address
family.
EAI_NODATA The specified network host exists, but does
not have any network addresses defined.
EAI_MEMORY Out of memory.
EAI_FAIL The name server returned a permanent failure
indication.
EAI_AGAIN The name server returned a temporary failure
indication. Try again later.
EAI_SYSTEM Other system error, check errno for details.
The gai_strerror(3) function translates these error codes
to a human readable string, suitable for error reporting.
SEE ALSO
getipnodebyname(3), getipnodebyaddr(3)
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