mirror of https://github.com/c-ares/c-ares.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
100 lines
2.8 KiB
100 lines
2.8 KiB
.\" |
|
.\" Copyright 1998 by the Massachusetts Institute of Technology. |
|
.\" SPDX-License-Identifier: MIT |
|
.\" |
|
.TH ARES_GETHOSTBYADDR 3 "24 July 1998" |
|
.SH NAME |
|
ares_gethostbyaddr \- Initiate a host query by address |
|
.SH SYNOPSIS |
|
.nf |
|
#include <ares.h> |
|
|
|
typedef void (*ares_host_callback)(void *\fIarg\fP, int \fIstatus\fP, |
|
int \fItimeouts\fP, |
|
struct hostent *\fIhostent\fP) |
|
|
|
void ares_gethostbyaddr(ares_channel_t *\fIchannel\fP, const void *\fIaddr\fP, |
|
int \fIaddrlen\fP, int \fIfamily\fP, |
|
ares_host_callback \fIcallback\fP, void *\fIarg\fP) |
|
.fi |
|
.SH DESCRIPTION |
|
The |
|
.B ares_gethostbyaddr |
|
function initiates a host query by address on the name service channel |
|
identified by |
|
.IR channel . |
|
The parameters |
|
.I addr |
|
and |
|
.I addrlen |
|
give the address as a series of bytes, and |
|
.I family |
|
gives the type of address. When the query is complete or has failed, the ares |
|
library will invoke \fIcallback\fP. Completion or failure of the query may |
|
happen immediately, or may happen during a later call to |
|
\fIares_process(3)\fP, \fIares_destroy(3)\fP or \fIares_cancel(3)\fP. |
|
.PP |
|
The callback argument |
|
.I arg |
|
is copied from the |
|
.B ares_gethostbyaddr |
|
argument |
|
.IR arg . |
|
The callback argument |
|
.I status |
|
indicates whether the query succeeded and, if not, how it failed. It |
|
may have any of the following values: |
|
.TP 19 |
|
.B ARES_SUCCESS |
|
The host lookup completed successfully. |
|
.TP 19 |
|
.B ARES_ENOTIMP |
|
The ares library does not know how to look up addresses of type |
|
.IR family . |
|
.TP 19 |
|
.B ARES_ENOTFOUND |
|
The address |
|
.I addr |
|
was not found. |
|
.TP 19 |
|
.B ARES_ENOMEM |
|
Memory was exhausted. |
|
.TP 19 |
|
.B ARES_ECANCELLED |
|
The query was cancelled. |
|
.TP 19 |
|
.B ARES_EDESTRUCTION |
|
The name service channel |
|
.I channel |
|
is being destroyed; the query will not be completed. |
|
.PP |
|
The callback argument |
|
.I timeouts |
|
reports how many times a query timed out during the execution of the |
|
given request. |
|
.PP |
|
On successful completion of the query, the callback argument |
|
.I hostent |
|
points to a |
|
.B struct hostent |
|
containing the name of the host returned by the query. The callback |
|
need not and should not attempt to free the memory pointed to by |
|
.IR hostent ; |
|
the ares library will free it when the callback returns. If the query |
|
did not complete successfully, |
|
.I hostent |
|
will be |
|
.BR NULL . |
|
.PP |
|
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 \fIares_gethostbyaddr(3)\fP. |
|
|
|
For integrators running their own event loops and not using \fBARES_OPT_EVENT_THREAD\fP, |
|
care needs to be taken to ensure any file descriptor lists are updated immediately |
|
within the eventloop when notified. |
|
.SH SEE ALSO |
|
.BR ares_process (3), |
|
.BR ares_gethostbyname (3)
|
|
|