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