Provided by: libc-ares-dev_1.7.5-1_amd64 bug


       ares_init, ares_init_options - Initialize a resolver channel


       #include <ares.h>

       int ares_init(ares_channel *channelptr)
       int ares_init_options(ares_channel *channelptr,
            struct ares_options *options, int optmask)

       cc file.c -lcares


       The  ares_init function initializes a communications channel for name service lookups.  If
       it returns successfully, ares_init will set the variable pointed to  by  channelptr  to  a
       handle   used   to   identify   the  name  service  channel.   The  caller  should  invoke
       ares_destroy(3) on the handle when the channel is no longer needed.

       The ares_init_options function also initializes a name service  channel,  with  additional
       options  useful  for  applications requiring more control over name service configuration.
       The optmask parameter specifies which fields in the structure pointed to  by  options  are
       set, as follows:

       ARES_OPT_FLAGS    int flags;
                         Flags  controlling  the  behavior  of  the  resolver.   See  below for a
                         description of possible flag values.

       ARES_OPT_TIMEOUT  int timeout;
                         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  timeout.)   The
                         default   is   five   seconds.   This  option  is  being  deprecated  by
                         ARES_OPT_TIMEOUTMS starting in c-ares 1.5.2.

                         int timeout;
                         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
                         timeout.)   The  default  is  five  seconds.  Note  that  this option is
                         specified with the same struct field as the former ARES_OPT_TIMEOUT,  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.

       ARES_OPT_TRIES    int tries;
                         The number of tries the resolver will try contacting  each  name  server
                         before giving up.  The default is four tries.

       ARES_OPT_NDOTS    int ndots;
                         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.

       ARES_OPT_PORT     unsigned short port;
                         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.

       ARES_OPT_SERVERS  struct in_addr *servers;
                         int nservers;
                         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 ares_set_servers(3) function  must
                         be used instead.

       ARES_OPT_DOMAINS  char **domains;
                         int ndomains;
                         The  domains  to search, instead of the domains specified in resolv.conf
                         or the domain derived from the kernel hostname variable.

       ARES_OPT_LOOKUPS  char *lookups;
                         The lookups to perform for host queries.  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.

                         void (*sock_state_cb)(void *data, int s, int read, int write);
                         void *sock_state_cb_data;
                         A callback function to be invoked when a socket changes state.   s  will
                         be  passed  the socket whose state has changed; read will be set to true
                         if the socket should listen for read events, and write will  be  set  to
                         true  if  the  socket  should  listen  for  write  events.  The value of
                         sock_state_cb_data will be passed as the data argument.

       The flags field should be the bitwise or of some subset of the following values:

       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.

       ARES_FLAG_PRIMARY      Only query the first server in the list of servers to query.

       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.

       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 ARES_FLAG_NORECURSE is

       ARES_FLAG_STAYOPEN     Do not close communications  sockets  when  the  number  of  active
                              queries drops to zero.

       ARES_FLAG_NOSEARCH     Do  not  use the default search domains; only query hostnames as-is
                              or as aliases.

       ARES_FLAG_NOALIASES    Do not honor the HOSTALIASES environment variable,  which  normally
                              specifies a file of hostname translations.

       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.


       ares_init or ares_init_options can return any of the following values:

       ARES_SUCCESS  Initialization succeeded.

       ARES_EFILE    A configuration file could not be read.

       ARES_ENOMEM   The process's available memory was exhausted.

                     c-ares library initialization not yet performed.


       When  initializing  from  /etc/resolv.conf,  ares_init(3)  reads  the  domain  and  search
       directives  to  allow lookups of short names relative to the domains specified. The domain
       and search directives override one another. If more that one instance of either domain  or
       search  directives is specified, the last occurence wins. For more information, please see
       the resolv.conf(5) manual page.


       ares_destroy(3), ares_dup(3), ares_library_init(3), ares_set_servers(3)


       Greg Hudson, MIT Information Systems
       Copyright 1998 by the Massachusetts Institute of Technology.
       Copyright (C) 2004-2010 by Daniel Stenberg.

                                           5 March 2010                              ARES_INIT(3)