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)
ARES_INIT(3) Library Functions Manual ARES_INIT(3) NAME ares_init_options - Initialize a resolver channel SYNOPSIS #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) DESCRIPTION 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 compli- cated, but scales linearly with the value of time- out.) The default is five seconds. This option is being deprecated by ARES_OPT_TIMEOUTMS starting in c- ares 1.5.2. ARES_OPT_TIMEOUTMS 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 compli- cated, but scales linearly with the value of time- out.) 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 query- ing for it with the default domain extensions appended. The default value is 1 unless set other- wise 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 port. 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 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 speci- fied 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" indi- cates a lookup in the hosts file. ARES_OPT_SOCK_STATE_CB 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 argu- ment. 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 ares_set_sortlist(3). ARES_OPT_SOCK_SNDBUF int socket_send_buffer_size; The send buffer size to set for the socket. ARES_OPT_SOCK_RCVBUF int socket_receive_buffer_size; The receive buffer size to set for the socket. ARES_OPT_EDNSPSZ int ednspsz; The message size to be advertized in EDNS; only takes effect if the ARES_FLAG_EDNS flag is set. ARES_OPT_RESOLVCONF 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 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 follow- ing 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 con- tinue on with the truncated response. ARES_FLAG_NORECURSE Do not set the "recursion desired" bit on outgo- ing queries, so that the name server being con- tacted 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_NORE- CURSE is set. 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 vari- able, which normally specifies a file of host- name 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 requests. RETURN VALUES 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. ARES_ENOTINITIALIZED c-ares library initialization not yet performed. ATTRIBUTES See attributes(7) for descriptions of the following attributes: +---------------+------------------+ |ATTRIBUTE TYPE | ATTRIBUTE VALUE | +---------------+------------------+ |Availability | library/libcares | +---------------+------------------+ |Stability | Volatile | +---------------+------------------+ NOTES When initializing from /etc/resolv.conf, (or, alternatively when speci- fied by the resolvconf_path path location) ares_init_options(3) reads the domain and search directives to allow lookups of short names rela- tive to the domains specified. The domain and search directives over- ride one another. If more that one instance of either domain or search directives is specified, the last occurrence wins. For more informa- tion, please see the resolv.conf(5) manual page. Source code for open source software components in Oracle Solaris can be found at https://www.oracle.com/downloads/opensource/solaris-source- code-downloads.html. This software was built from source available at https://github.com/oracle/solaris-userland. The original community source was downloaded from https://c-ares.haxx.se/download/c- ares-1.17.2.tar.gz. Further information about this software can be found on the open source community website at https://c-ares.haxx.se/. SEE ALSO 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) AUTHOR 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)