.\" $Id$ .\" .\" Copyright 1998 by the Massachusetts Institute of Technology. .\" .\" Permission to use, copy, modify, and distribute this .\" software and its documentation for any purpose and without .\" fee is hereby granted, provided that the above copyright .\" notice appear in all copies and that both that copyright .\" notice and this permission notice appear in supporting .\" documentation, and that the name of M.I.T. not be used in .\" advertising or publicity pertaining to distribution of the .\" software without specific, written prior permission. .\" M.I.T. makes no representations about the suitability of .\" this software for any purpose. It is provided "as is" .\" without express or implied warranty. .\" .TH ARES_INIT 3 "7 December 2004" .SH NAME ares_init, ares_init_options \- Initialize a resolver channel .SH SYNOPSIS .nf .B #include <ares.h> .PP .B int ares_init(ares_channel *\fIchannel\fP) .B int ares_init_options(ares_channel *\fIchannel\fP, .B struct ares_options *\fIoptions\fP, int \fIoptmask\fP) .PP .B cc file.c -lcares .fi .SH DESCRIPTION The \fBares_init\fP function initializes a communications channel for name service lookups. If it returns successfully, \fBares_init\fP will set the variable pointed to by \fIchannel\fP to a handle used to identify the name service channel. The caller should invoke .BR ares_destroy (3) on the handle when the channel is no longer needed. .PP The \fBares_init_options\fP function also initializes a name service channel, with additional options useful for applications requiring more control over name service configuration. The \fIoptmask\fP parameter specifies which fields in the structure pointed to by \fIoptions\fP are set, as follows: .TP 18 .B ARES_OPT_FLAGS .B int \fIflags\fP; .br Flags controlling the behavior of the resolver. See below for a description of possible flag values. .TP 18 .B ARES_OPT_TIMEOUT .B int \fItimeout\fP; .br The number of seconds each name server is given to respond to a query on the first try. (After the first try, the timeout algorithm becomes more complicated, but scales linearly with the value of \fItimeout\fP.) The default is five seconds. .TP 18 .B ARES_OPT_TRIES .B int \fItries\fP; .br The number of tries the resolver will try contacting each name server before giving up. The default is four tries. .TP 18 .B ARES_OPT_NDOTS .B int \fIndots\fP; .br The number of dots which must be present in a domain name for it to be queried for "as is" prior to querying for it with the default domain extensions appended. The default value is 1 unless set otherwise by resolv.conf or the RES_OPTIONS environment variable. .TP 18 .B ARES_OPT_PORT .B unsigned short \fIport\fP; .br The port to use for queries (both TCP and UDP), in network byte order. The default value is 53 (in network byte order), the standard name service port. .TP 18 .B ARES_OPT_SERVERS .B struct in_addr *\fIservers\fP; .br .B int \fInservers\fP; .br The list of servers to contact, instead of the servers specified in resolv.conf or the local named. .TP 18 .B ARES_OPT_DOMAINS .B char **\fIdomains\fP; .br .B int \fIndomains\fP; .br The domains to search, instead of the domains specified in resolv.conf or the domain derived from the kernel hostname variable. .TP 18 .B ARES_OPT_LOOKUPS .B char *\fIlookups\fP; .br The lookups to perform for host queries. .I lookups should be set to a string of the characters "b" or "f", where "b" indicates a DNS lookup and "f" indicates a lookup in the hosts file. .PP The .I flags field should be the bitwise or of some subset of the following values: .TP 23 .B ARES_FLAG_USEVC Always use TCP queries (the "virtual circuit") instead of UDP queries. Normally, TCP is only used if a UDP query yields a truncated result. .TP 23 .B ARES_FLAG_PRIMARY Only query the first server in the list of servers to query. .TP 23 .B ARES_FLAG_IGNTC If a truncated response to a UDP query is received, do not fall back to TCP; simply continue on with the truncated response. .TP 23 .B ARES_FLAG_NORECURSE Do not set the "recursion desired" bit on outgoing queries, so that the name server being contacted will not try to fetch the answer from other servers if it doesn't know the answer locally. Be aware that ares will not do the recursion for you. Recursion must be handled by the application calling ares if \fIARES_FLAG_NORECURSE\fP is set. .TP 23 .B ARES_FLAG_STAYOPEN Do not close communciations sockets when the number of active queries drops to zero. .TP 23 .B ARES_FLAG_NOSEARCH Do not use the default search domains; only query hostnames as-is or as aliases. .TP 23 .B ARES_FLAG_NOALIASES Do not honor the HOSTALIASES environment variable, which normally specifies a file of hostname translations. .TP 23 .B ARES_FLAG_NOCHECKRESP Do not discard responses with the SERVFAIL, NOTIMP, or REFUSED response code or responses whose questions don't match the questions in the request. Primarily useful for writing clients which might be used to test or debug name servers. .SH RETURN VALUES .I ares_init or .I ares_init_options can return any of the following values: .TP 14 .B ARES_SUCCESS Initialization succeeded. .TP 14 .B ARES_EFILE A configuration file could not be read. .TP 14 .B ARES_ENOMEM The process's available memory was exhausted. .SH SEE ALSO .BR ares_destroy (3) .SH AUTHOR Greg Hudson, MIT Information Systems .br Copyright 1998 by the Massachusetts Institute of Technology.