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ARES_QUERY

Section: C Library Functions (3)
Updated: 24 July 1998
Index

NAME

ares_query - Initiate a single-question DNS query

SYNOPSIS

#include <ares.h>typedef void (*ares_callback)(void *arg, int status,void ares_query(ares_channel channel, const char *name,int dnsclass, int type, ares_callback callback,

DESCRIPTION

Theares_queryfunction initiates a single-question DNS query on the name servicechannel identified bychannel.The parameternamegives the query name as a NUL-terminated C string of period-separatedlabels optionally ending with a period; periods and backslashes withina label must be escaped with a backslash. The parametersdnsclassandtypegive the class and type of the query using the values defined in<arpa/nameser.h>.When the query is complete or has failed, the ares library will invokecallback.Completion or failure of the query may happen immediately, or mayhappen during a later call toares_process(3)orares_destroy(3).

The callback argumentargis copied from theares_queryargumentarg.The callback argumentstatusindicates whether the query succeeded and, if not, how it failed. Itmay have any of the following values:

ARES_SUCCESS: The query completed successfully.
ARES_ENODATA: The query completed but contains no answers.
ARES_EFORMERR: The query completed but the server claims that the query wasmalformatted.
ARES_ESERVFAIL: The query completed but the server claims to have experienced afailure. (This code can only occur if theARES_FLAG_NOCHECKRESPflag was specified at channel initialization time; otherwise, suchresponses are ignored at theares_send(3)level.)
ARES_ENOTFOUND: The query completed but the queried-for domain name was not found.
ARES_ENOTIMP: The query completed but the server does not implement the operationrequested by the query. (This code can only occur if theARES_FLAG_NOCHECKRESPflag was specified at channel initialization time; otherwise, suchresponses are ignored at theares_send(3)level.)
ARES_EREFUSED: The query completed but the server refused the query. (This code canonly occur if theARES_FLAG_NOCHECKRESPflag was specified at channel initialization time; otherwise, suchresponses are ignored at theares_send(3)level.)
ARES_EBADNAME: The query namenamecould not be encoded as a domain name, either because it contained azero-length label or because it contained a label of more than 63characters.
ARES_ETIMEOUT: No name servers responded within the timeout period.
ARES_ECONNREFUSED: No name servers could be contacted.
ARES_ENOMEM: Memory was exhausted.
ARES_EDESTRUCTION: The name service channelchannelis being destroyed; the query will not be completed.

If the query completed (even if there was something wrong with it, asindicated by some of the above error codes), the callback argumentabufpoints to a result buffer of lengthalen.If the query did not complete,abufwill be NULL andalenwill be 0.

AUTHOR

Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.

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