ares_init_options.3 - third_party/c-ares - Git at Google

 .\"
 .\" Copyright 1998 by the Massachusetts Institute of Technology.
 .\" Copyright (C) 2004-2010 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 "5 March 2010"
 .SH NAME
 ares_init_options \- Initialize a resolver channel
 .SH SYNOPSIS
 .nf
 #include <ares.h>

 struct ares_options {
   int flags;
   int timeout; /* in seconds or milliseconds, depending on options */
   int tries;
   int ndots;
   unsigned short udp_port;
   unsigned short tcp_port;
   int socket_send_buffer_size;
   int socket_receive_buffer_size;
   struct in_addr *servers;
   int nservers;
   char **domains;
   int ndomains;
   char *lookups;
   ares_sock_state_cb sock_state_cb;
   void *sock_state_cb_data;
   struct apattern *sortlist;
   int nsort;
   int ednspsz;
 };

 int ares_init_options(ares_channel *\fIchannelptr\fP,
                       struct ares_options *\fIoptions\fP,
                       int \fIoptmask\fP)
 .fi
 .SH DESCRIPTION
 The \fBares_init_options(3)\fP function initializes a communications channel
 for name service lookups.  If it returns successfully,
 \fBares_init_options(3)\fP will set the variable pointed to by
 \fIchannelptr\fP to a handle used to identify the name service channel.  The
 caller should invoke \fIares_destroy(3)\fP on the handle when the channel is
 no longer needed.

 The \fIoptmask\fP parameter generally 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_UDP_PORT
 .B unsigned short \fIudp_port\fP;
 .br
 The port to use for queries over UDP, in network byte order.
 The default value is 53 (in network byte order), the standard name
 service port.
 .TP 18
 .B ARES_OPT_TCP_PORT
 .B unsigned short \fItcp_port\fP;
 .br
 The port to use for queries over TCP, 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 IPv4 servers to contact, instead of the servers specified in
 resolv.conf or the local named. In order to allow specification of either
 IPv4 or IPv6 name servers, the
 .BR ares_set_servers(3)
 function must be used instead.
 .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.
 .TP 18
 .B ARES_OPT_SORTLIST
 .B struct apattern *\fIsortlist\fP;
 .br
 .B int \fInsort\fP;
 .br
 A list of IP address ranges that specifies the order of preference that
 results from \fIares_gethostbyname\fP should be returned in.  Note that
 this can only be used with a sortlist retrieved via
 \fBares_save_options(3)\fP (because
 .B struct apattern
 is opaque); to set a fresh sort list, use \fBares_set_sortlist(3)\fP.
 .TP 18
 .B ARES_OPT_SOCK_SNDBUF
 .B int \fIsocket_send_buffer_size\fP;
 .br
 The send buffer size to set for the socket.
 .TP 18
 .B ARES_OPT_SOCK_RCVBUF
 .B int \fIsocket_receive_buffer_size\fP;
 .br
 The receive buffer size to set for the socket.
 .TP 18
 .B ARES_OPT_EDNSPSZ
 .B int \fIednspsz\fP;
 .br
 The message size to be advertized in EDNS; only takes effect if the
 .B ARES_FLAG_EDNS
 flag is set.
 .br
 .PP
 The \fIoptmask\fP parameter also includes options without a corresponding
 field in the
 .B ares_options
 structure, as follows:
 .TP 23
 .B ARES_OPT_ROTATE
 Perform round-robin selection of the nameservers configured for the channel
 for each resolution.
 .TP 23
 .B ARES_OPT_NOROTATE
 Do not perform round-robin nameserver selection; always use the list of
 nameservers in the same order.
 .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.
 .TP 23
 .B ARES_FLAG_EDNS
 Include an EDNS pseudo-resource record (RFC 2671) in generated requests.
 .SH RETURN VALUES
 \fBares_init_options(3)\fP 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 NOTES
 When initializing from
 .B /etc/resolv.conf,
 \fBares_init_options(3)\fP reads the \fIdomain\fP and \fIsearch\fP directives
 to allow lookups of short names relative to the domains specified. The
 \fIdomain\fP and \fIsearch\fP directives override one another. If more that
 one instance of either \fIdomain\fP or \fIsearch\fP directives is specified,
 the last occurrence wins. For more information, please see the
 .BR resolv.conf (5)
 manual page.
 .SH SEE ALSO
 .BR ares_init(3),
 .BR ares_destroy(3),
 .BR ares_dup(3),
 .BR ares_library_init(3),
 .BR ares_save_options(3),
 .BR ares_set_servers(3),
 .BR ares_set_sortlist(3)
 .SH AUTHOR
 Greg Hudson, MIT Information Systems
 .br
 Copyright 1998 by the Massachusetts Institute of Technology.
 .br
 Copyright (C) 2004-2010 by Daniel Stenberg.
	.\"
	.\" Copyright 1998 by the Massachusetts Institute of Technology.
	.\" Copyright (C) 2004-2010 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 "5 March 2010"
	.SH NAME
	ares_init_options \- Initialize a resolver channel
	.SH SYNOPSIS
	.nf
	#include <ares.h>

	struct ares_options {
	int flags;
	int timeout; /* in seconds or milliseconds, depending on options */
	int tries;
	int ndots;
	unsigned short udp_port;
	unsigned short tcp_port;
	int socket_send_buffer_size;
	int socket_receive_buffer_size;
	struct in_addr *servers;
	int nservers;
	char **domains;
	int ndomains;
	char *lookups;
	ares_sock_state_cb sock_state_cb;
	void *sock_state_cb_data;
	struct apattern *sortlist;
	int nsort;
	int ednspsz;
	};

	int ares_init_options(ares_channel *\fIchannelptr\fP,
	struct ares_options *\fIoptions\fP,
	int \fIoptmask\fP)
	.fi
	.SH DESCRIPTION
	The \fBares_init_options(3)\fP function initializes a communications channel
	for name service lookups. If it returns successfully,
	\fBares_init_options(3)\fP will set the variable pointed to by
	\fIchannelptr\fP to a handle used to identify the name service channel. The
	caller should invoke \fIares_destroy(3)\fP on the handle when the channel is
	no longer needed.

	The \fIoptmask\fP parameter generally 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_UDP_PORT
	.B unsigned short \fIudp_port\fP;
	.br
	The port to use for queries over UDP, in network byte order.
	The default value is 53 (in network byte order), the standard name
	service port.
	.TP 18
	.B ARES_OPT_TCP_PORT
	.B unsigned short \fItcp_port\fP;
	.br
	The port to use for queries over TCP, 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 IPv4 servers to contact, instead of the servers specified in
	resolv.conf or the local named. In order to allow specification of either
	IPv4 or IPv6 name servers, the
	.BR ares_set_servers(3)
	function must be used instead.
	.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.
	.TP 18
	.B ARES_OPT_SORTLIST
	.B struct apattern *\fIsortlist\fP;
	.br
	.B int \fInsort\fP;
	.br
	A list of IP address ranges that specifies the order of preference that
	results from \fIares_gethostbyname\fP should be returned in. Note that
	this can only be used with a sortlist retrieved via
	\fBares_save_options(3)\fP (because
	.B struct apattern
	is opaque); to set a fresh sort list, use \fBares_set_sortlist(3)\fP.
	.TP 18
	.B ARES_OPT_SOCK_SNDBUF
	.B int \fIsocket_send_buffer_size\fP;
	.br
	The send buffer size to set for the socket.
	.TP 18
	.B ARES_OPT_SOCK_RCVBUF
	.B int \fIsocket_receive_buffer_size\fP;
	.br
	The receive buffer size to set for the socket.
	.TP 18
	.B ARES_OPT_EDNSPSZ
	.B int \fIednspsz\fP;
	.br
	The message size to be advertized in EDNS; only takes effect if the
	.B ARES_FLAG_EDNS
	flag is set.
	.br
	.PP
	The \fIoptmask\fP parameter also includes options without a corresponding
	field in the
	.B ares_options
	structure, as follows:
	.TP 23
	.B ARES_OPT_ROTATE
	Perform round-robin selection of the nameservers configured for the channel
	for each resolution.
	.TP 23
	.B ARES_OPT_NOROTATE
	Do not perform round-robin nameserver selection; always use the list of
	nameservers in the same order.
	.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.
	.TP 23
	.B ARES_FLAG_EDNS
	Include an EDNS pseudo-resource record (RFC 2671) in generated requests.
	.SH RETURN VALUES
	\fBares_init_options(3)\fP 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 NOTES
	When initializing from
	.B /etc/resolv.conf,
	\fBares_init_options(3)\fP reads the \fIdomain\fP and \fIsearch\fP directives
	to allow lookups of short names relative to the domains specified. The
	\fIdomain\fP and \fIsearch\fP directives override one another. If more that
	one instance of either \fIdomain\fP or \fIsearch\fP directives is specified,
	the last occurrence wins. For more information, please see the
	.BR resolv.conf (5)
	manual page.
	.SH SEE ALSO
	.BR ares_init(3),
	.BR ares_destroy(3),
	.BR ares_dup(3),
	.BR ares_library_init(3),
	.BR ares_save_options(3),
	.BR ares_set_servers(3),
	.BR ares_set_sortlist(3)
	.SH AUTHOR
	Greg Hudson, MIT Information Systems
	.br
	Copyright 1998 by the Massachusetts Institute of Technology.
	.br
	Copyright (C) 2004-2010 by Daniel Stenberg.