Provided by: libc-ares-dev_1.15.0-1build1_amd64 bug


       ares_init_options - Initialize a resolver channel


       #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;
         char *resolvconf_path;

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


       The  ares_init_options(3)  function  initializes a communications channel for name service
       lookups.  If it returns successfully, ares_init_options(3) 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 optmask parameter generally 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_UDP_PORT unsigned short udp_port;
                         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

       ARES_OPT_TCP_PORT unsigned short tcp_port;
                         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

       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, ares_socket_t socket_fd, int readable,
                         int writable);
                         void *sock_state_cb_data;
                         A  callback  function  to  be  invoked  when  a  socket  changes  state.
                         socket_fd will be passed the socket whose state  has  changed;  readable
                         will  be  set  to  true if the socket should listen for read events, and
                         writable 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

       ARES_OPT_SORTLIST struct apattern *sortlist;
                         int nsort;
                         A list of IP address ranges that specifies the order of preference  that
                         results  from  ares_gethostbyname should be returned in.  Note that this
                         can only be used with  a  sortlist  retrieved  via  ares_save_options(3)
                         (because  struct  apattern  is  opaque);  to  set a fresh sort list, use

                         int socket_send_buffer_size;
                         The send buffer size to set for the socket.

                         int socket_receive_buffer_size;
                         The receive buffer size to set for the socket.

       ARES_OPT_EDNSPSZ  int ednspsz;

                         char *resolvconf_path; The path to use for reading the resolv.conf file.
                         The resolvconf_path should be set to a path string, and will be honoured
                         on *nix like systems. The default is /etc/resolv.conf
                         The message size to be advertized in EDNS;  only  takes  effect  if  the
                         ARES_FLAG_EDNS flag is set.

       The  optmask  parameter  also  includes  options  without  a  corresponding  field  in the
       ares_options structure, as follows:

       ARES_OPT_ROTATE        Perform round-robin selection of the nameservers configured for the
                              channel for each resolution.

       ARES_OPT_NOROTATE      Do  not  perform  round-robin  nameserver selection; always use the
                              list of nameservers in the same order.

       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_FLAG_EDNS         Include an EDNS pseudo-resource  record  (RFC  2671)  in  generated


       ares_init_options(3) 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,  (or,  alternatively  when  specified  by  the
       resolvconf_path path location) ares_init_options(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 occurrence wins. For more information, please see the
       resolv.conf(5) manual page.


       ares_init(3), ares_destroy(3),  ares_dup(3),  ares_library_init(3),  ares_save_options(3),
       ares_set_servers(3), ares_set_sortlist(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)