ARES_GETNAMEINFO(3) Library Functions Manual ARES_GETNAMEINFO(3)

ares_getnameinfo - Address-to-nodename translation in protocol-independent manner

#include <ares.h>
typedef void (*ares_nameinfo_callback)(void *arg, int status,
                                       int timeouts, char *node,
                                       char *service)
void ares_getnameinfo(ares_channel_t *channel, const struct sockaddr *sa,
                      ares_socklen_t salen, int flags,
                      ares_nameinfo_callback callback, void *arg)

The ares_getnameinfo function is defined for protocol-independent address translation. The function is a combination of ares_gethostbyaddr(3) and getservbyport(3). The function will translate the address either by executing a host query on the name service channel identified by channel or it will attempt to resolve it locally if possible. The parameters sa and len give the address as a sockaddr structure, and flags gives the options that the function will use. Valid flags are listed below:

Only the nodename portion of the FQDN is returned for local hosts.
The numeric form of the hostname is returned rather than the name.
An error is returned if the hostname cannot be found in the DNS.
The numeric form of the service is returned rather than the name.
The service name is to be looked up for the TCP protocol.
The service name is to be looked up for the UDP protocol.
The service name is to be looked up for the SCTP protocol.
The service name is to be looked up for the DCCP protocol.
The numeric form of the scope ID is returned rather than the name.
A hostname lookup is being requested.
A service name lookup is being requested.

When the query is complete or has failed, the ares library will invoke callback. Completion or failure of the query may happen immediately, or may happen during a later call to ares_process(3), ares_destroy(3) or ares_cancel(3).

When the associated callback is called, it is called with a channel lock so care must be taken to ensure any processing is minimal to prevent DNS channel stalls.

The callback may be triggered from a different thread than the one which called ares_getnameinfo(3).

For integrators running their own event loops and not using ARES_OPT_EVENT_THREAD, care needs to be taken to ensure any file descriptor lists are updated immediately within the eventloop when notified.

The callback argument arg is copied from the ares_getnameinfo argument arg. The callback argument status indicates whether the query succeeded and, if not, how it failed. It may have any of the following values:

The host lookup completed successfully.
The ares library does not know how to look up addresses of type family.
The address addr was not found.
Memory was exhausted.
The query was cancelled.
The name service channel channel is being destroyed; the query will not be completed.
The flags parameter contains an illegal value.

The callback argument timeouts reports how many times a query timed out during the execution of the given request.

On successful completion of the query, the callback argument node contains a string representing the hostname (assuming ARES_NI_LOOKUPHOST was specified). Additionally, service contains a string representing the service name (assuming ARES_NI_LOOKUPSERVICE was specified). If the query did not complete successfully, or one of the values was not requested, node or service will be NULL.

ares_process(3),

Dominick Meglio
Copyright 2005 by Dominick Meglio.

1 May 2009