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getaddrinfo(3) Linux Programmer's Manual getaddrinfo(3)
NAME
getaddrinfo, freeaddrinfo, gai_strerror - network address and service
translation
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int getaddrinfo(const char *node, const char *service,
const struct addrinfo *hints,
struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
const char *gai_strerror(int errcode);
DESCRIPTION
The getaddrinfo(3) function combines the functionality provided by the
getipnodebyname(3), getipnodebyaddr(3), getservbyname(3), and get-
servbyport(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(2) and connect(2) system calls to create a
client or a server socket.
The getaddrinfo(3) function is not limited to creating IPv4 socket
address structures; IPv6 socket address structures can be created if
IPv6 support is available. These socket address structures can be used
directly by bind(2) or connect(2), 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-allocated linked list
of addrinfo structures, linked by the ai_next member. There are sev-
eral reasons why the linked list may have more than one addrinfo struc-
ture, 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 members ai_family, ai_socktype, and ai_protocol have the same mean-
ing as the corresponding parameters in the socket(2) system call. The
getaddrinfo(3) function returns socket addresses in either IPv4 or IPv6
address family, (ai_family will be set to either AF_INET or AF_INET6).
The hints parameter specifies the preferred socket type, or protocol.
A NULL hints specifies that any network address or protocol is accept-
able. If this parameter is not NULL it points to an addrinfo structure
whose ai_family, ai_socktype, and ai_protocol members specify the pre-
ferred socket type. AF_UNSPEC in ai_family specifies any protocol
family (either IPv4 or IPv6, for example). 0 in ai_socktype or ai_pro-
tocol specifies that any socket type or protocol is acceptable as well.
The ai_flags member specifies additional options, defined below. Mul-
tiple 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 speci-
fies 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 hints.ai_flags contains the
AI_NUMERICHOST flag then the node parameter must be a numerical network
address. The AI_NUMERICHOST flag suppresses any potentially lengthy
network host address lookups.
The getaddrinfo(3) function creates a linked list of addrinfo struc-
tures, one for each network address subject to any restrictions imposed
by the hints parameter. The ai_canonname field of the first of these
addrinfo structures is set to point to the official name of the host,
if hints.ai_flags includes the AI_CANONNAME flag. ai_family, ai_sock-
type, 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
member.
If node is NULL, the network address in each socket structure is ini-
tialized according to the AI_PASSIVE flag, which is set in
hints.ai_flags. 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 connections 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.
If hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses
are returned in the list pointed to by result only if the local system
has at least one IPv4 address configured, and IPv6 addresses are only
returned if the local system has at least one IPv6 address configured.
If hint.ai_flags specifies the AI_V4MAPPED flag, and hints.ai_family
was specified as AF_INET6, and no matching IPv6 addresses could be
found, then return IPv4-mapped IPv6 addresses in the list pointed to by
result. If both AI_V4MAPPED and AI_ALL are specified in hints.ai_fam-
ily, then return both IPv6 and IPv4-mapped IPv6 addresses in the list
pointed to by result. AI_ALL is ignored if AI_V4MAPPED is not also
specified.
service sets the port number in the network address of each socket
structure. If service is NULL the port number will be left uninitial-
ized. If AI_NUMERICSERV is specified in hints.ai_flags and service is
not NULL, then service must point to a string containing a numeric port
number. This flag is used to inhibit the invocation of a name resolu-
tion service in cases where it is known not to be required.
The freeaddrinfo(3) function frees the memory that was allocated for
the dynamically allocated linked list res.
RETURN VALUE
getaddrinfo(3) returns 0 if it succeeds, or one of the following non-
zero error codes:
EAI_ADDRFAMILY
The specified network host does not have any network addresses
in the requested address family.
EAI_AGAIN
The name server returned a temporary failure indication. Try
again later.
EAI_BADFLAGS
ai_flags contains invalid flags.
EAI_FAIL
The name server returned a permanent failure indication.
EAI_FAMILY
The requested address family is not supported at all.
EAI_MEMORY
Out of memory.
EAI_NODATA
The specified network host exists, but does not have any network
addresses defined.
EAI_NONAME
The node or service is not known; or both node and service are
NULL; or AI_NUMERICSERV was specified in hints.ai_flags and ser-
vice was not a numeric port-number string.
EAI_SERVICE
The requested service is not available for the requested socket
type. It may be available through another socket type.
EAI_SOCKTYPE
The requested socket type is not supported at all.
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.
CONFORMING TO
POSIX.1-2001. The getaddrinfo() function is documented in RFC 2553.
NOTES
AI_ADDRCONFIG, AI_ALL, and AI_V4MAPPED are available since glibc 2.3.3.
AI_NUMERICSERV is available since glibc 2.3.4.
SEE ALSO
getipnodebyaddr(3), getipnodebyname(3)
Linux Man Page 2000-12-18 getaddrinfo(3)
Man(1) output converted with
man2html and wrapped by fishsponge
This page was generated on Sat Sep 8 16:37:35 GMT 2007
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