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On success, the ''error'' variable is assigned to 0 and ''result'' is pointed to | On success, the ''error'' variable is assigned to 0 and ''result'' is pointed to | ||
a linked list of one or more result objects. | a linked list of ''one or more'' result objects. | ||
'''Warning: Never assume that getaddrinfo() returns just one result! Never assume | |||
that the first result of getaddrinfo() actually works!''' | |||
Revision as of 21:00, 21 November 2012
Domain Name System
Resolving using getaddrinfo() in applications
The getaddrinfo() function is a dualstack-friendly API to name
resolution. It is used by applications to translate host and
service names to a linked list of struct addrinfo
objects.
And example of getaddrinfo() call:
const char *node = "www.fedoraproject.org";
const char *service = "http";
struct addrinfo hints = {
.ai_family = AF_UNSPEC,
.ai_socktype = SOCK_DGRAM,
.ai_flags = 0,
.ai_protocol = 0,
.ai_canonname = NULL,
.ai_addr = NULL,
.ai_next = NULL
};
struct addrinfo *result;
int error;
error = getaddrinfo(node, service, &hints, &result);
The input of getaddrinfo() consists of node specification, service specification and further hints.
- node: literal IPv4 or IPv6 address, or a hostname to be resolved
- service: numeric port number or a symbolic service name
- hints.ai_family: enable dualprotocol, IPv4-only or IPv6-only queries
- hints.ai_socktype: select socket type (and thus protocol family)
getaddrinfo() can be futher tweaked with the hints.ai_flags. Other
attributes are either not needed (ai_protocol) or not supposed
to be set in hints (ai_canonname, ai_addr and ai_next).
On success, the error variable is assigned to 0 and result is pointed to a linked list of one or more result objects.
Warning: Never assume that getaddrinfo() returns just one result! Never assume that the first result of getaddrinfo() actually works!