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diff --git a/ares_init.3 b/ares_init.3 new file mode 100644 index 0000000..14be75f --- /dev/null +++ b/ares_init.3 @@ -0,0 +1,199 @@ +.\" $Id: ares_init.3,v 1.8 2009-11-23 00:57:51 yangtse Exp $ +.\" +.\" Copyright 1998 by the Massachusetts Institute of Technology. +.\" Copyright (C) 2004-2009 by Daniel Stenberg +.\" +.\" 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 "26 May 2009" +.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 *\fIchannelptr\fP) +.B int ares_init_options(ares_channel *\fIchannelptr\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 \fIchannelptr\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. This option is being deprecated by +\fIARES_OPT_TIMEOUTMS\fP starting in c-ares 1.5.2. +.TP 18 +.B ARES_OPT_TIMEOUTMS +.B int \fItimeout\fP; +.br +The number of milliseconds 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. Note that this option is specified with the same +struct field as the former \fIARES_OPT_TIMEOUT\fP, it is but the option bits +that tell c-ares how to interpret the number. This option was added in c-ares +1.5.2. +.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. +.TP 18 +.B ARES_OPT_SOCK_STATE_CB +.B void (*\fIsock_state_cb\fP)(void *data, int s, int read, int write); +.br +.B void *\fIsock_state_cb_data\fP; +.br +A callback function to be invoked when a socket changes state. +.I s +will be passed the socket whose state has changed; +.I read +will be set to true if the socket should listen for read events, and +.I write +will be set to true if the socket should listen for write events. +The value of +.I sock_state_cb_data +will be passed as the +.I data +argument. +.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 communications 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. +.TP 14 +.B ARES_ENOTINITIALIZED +c-ares library initialization not yet performed. +.SH SEE ALSO +.BR ares_destroy(3), +.BR ares_dup(3), +.BR ares_library_init(3) +.SH AUTHOR +Greg Hudson, MIT Information Systems +.br +Copyright 1998 by the Massachusetts Institute of Technology. +.br +Copyright (C) 2004-2009 by Daniel Stenberg. |