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evdns(3)                   Library Functions Manual                   evdns(3)



NAME
       evdns -

       Welcome, gentle reader.


SYNOPSIS
       #include <event2/dns.h>
       #include <event2/util.h>


   Macros
           #define DNS_ERR_CANCEL   69
           The request was canceled via a call to evdns_cancel_request.
           #define DNS_ERR_FORMAT   1
           The name server was unable to interpret the query.  #define
           DNS_ERR_NODATA   70
           There were no answers and no error condition in the DNS packet.
           #define DNS_ERR_NONE   0
           Error codes 0-5 are as described in RFC 1035.  #define
           DNS_ERR_NOTEXIST   3
           The domain name does not exist.  #define DNS_ERR_NOTIMPL   4
           The name server does not support the requested kind of query.
           #define DNS_ERR_REFUSED   5
           The name server refuses to reform the specified operation for
           policy reasons.  #define DNS_ERR_SERVERFAILED   2
           The name server was unable to process this query due to a problem
           with the name server.  #define DNS_ERR_SHUTDOWN   68
           The request was canceled because the DNS subsystem was shut down.
           #define DNS_ERR_TIMEOUT   67
           Communication with the server timed out.  #define DNS_ERR_TRUNCATED
           65
           The reply was truncated or ill-formatted.  #define DNS_ERR_UNKNOWN
           66
           An unknown error occurred.  #define DNS_IPv4_A   1
           #define DNS_IPv6_AAAA   3
           #define DNS_NO_SEARCH   DNS_QUERY_NO_SEARCH
           #define DNS_OPTION_HOSTSFILE   8
           #define DNS_OPTION_MISC   4
           #define DNS_OPTION_NAMESERVERS   2
           #define DNS_OPTION_SEARCH   1
           #define DNS_OPTIONS_ALL   15
           #define DNS_PTR   2
           #define DNS_QUERY_NO_SEARCH   1
           #define EVDNS_ADDITIONAL_SECTION   2
           #define EVDNS_ANSWER_SECTION   0
           #define EVDNS_AUTHORITY_SECTION   1
           #define EVDNS_CLASS_INET   1
           #define EVDNS_FLAGS_AA   0x400
           #define EVDNS_FLAGS_RD   0x080
           #define EVDNS_QTYPE_ALL   255
           #define EVDNS_QTYPE_AXFR   252
           #define EVDNS_TYPE_A   1
           #define EVDNS_TYPE_AAAA   28
           #define EVDNS_TYPE_CNAME   5
           #define EVDNS_TYPE_MX   15
           #define EVDNS_TYPE_NS   2
           #define EVDNS_TYPE_PTR   12
           #define EVDNS_TYPE_SOA   6
           #define EVDNS_TYPE_TXT   16

   Typedefs
           typedef void(* evdns_callback_type )(int result, char type, int
           count, int ttl, void *addresses, void *arg)
           The callback that contains the results from a lookup.  typedef
           void(* evdns_debug_log_fn_type )(int is_warning, const char *msg)
           A callback that is invoked when a log message is generated.
           typedef void(* evdns_getaddrinfo_cb )(int result, struct
           evutil_addrinfo *res, void *arg)
           Callback for evdns_getaddrinfo.  typedef void(*
           evdns_request_callback_fn_type )(struct evdns_server_request *,
           void *)
           A callback to implement a DNS server.

   Functions
           struct evdns_server_port * evdns_add_server_port_with_base (struct
           event_base *base, evutil_socket_t socket, int flags,
           evdns_request_callback_fn_type callback, void *user_data)
           Create a new DNS server port.  int
           evdns_base_clear_nameservers_and_suspend (struct evdns_base *base)
           Remove all configured nameservers, and suspend all pending
           resolves.  int evdns_base_count_nameservers (struct evdns_base
           *base)
           Get the number of configured nameservers.  void evdns_base_free
           (struct evdns_base *base, int fail_requests)
           Shut down the asynchronous DNS resolver and terminate all active
           requests.  int evdns_base_load_hosts (struct evdns_base *base,
           const char *hosts_fname)
           Load an /etc/hosts-style file from 'hosts_fname' into 'base'.  int
           evdns_base_nameserver_add (struct evdns_base *base, unsigned long
           int address)
           Add a nameserver.  int evdns_base_nameserver_ip_add (struct
           evdns_base *base, const char *ip_as_string)
           Add a nameserver by string address.  int
           evdns_base_nameserver_sockaddr_add (struct evdns_base *base, const
           struct sockaddr *sa, ev_socklen_t len, unsigned flags)
           Add a nameserver by sockaddr.  struct evdns_base * evdns_base_new
           (struct event_base *event_base, int initialize_nameservers)
           Initialize the asynchronous DNS library.  int
           evdns_base_resolv_conf_parse (struct evdns_base *base, int flags,
           const char *const filename)
           Parse a resolv.conf file.  struct evdns_request *
           evdns_base_resolve_ipv4 (struct evdns_base *base, const char *name,
           int flags, evdns_callback_type callback, void *ptr)
           Lookup an A record for a given name.  struct evdns_request *
           evdns_base_resolve_ipv6 (struct evdns_base *base, const char *name,
           int flags, evdns_callback_type callback, void *ptr)
           Lookup an AAAA record for a given name.  struct evdns_request *
           evdns_base_resolve_reverse (struct evdns_base *base, const struct
           in_addr *in, int flags, evdns_callback_type callback, void *ptr)
           Lookup a PTR record for a given IP address.  struct evdns_request *
           evdns_base_resolve_reverse_ipv6 (struct evdns_base *base, const
           struct in6_addr *in, int flags, evdns_callback_type callback, void
           *ptr)
           Lookup a PTR record for a given IPv6 address.  int
           evdns_base_resume (struct evdns_base *base)
           Resume normal operation and continue any suspended resolve
           requests.  void evdns_base_search_add (struct evdns_base *base,
           const char *domain)
           Add a domain to the list of search domains.  void
           evdns_base_search_clear (struct evdns_base *base)
           Obtain nameserver information using the Windows API.  void
           evdns_base_search_ndots_set (struct evdns_base *base, const int
           ndots)
           Set the 'ndots' parameter for searches.  int evdns_base_set_option
           (struct evdns_base *base, const char *option, const char *val)
           Set the value of a configuration option.  void evdns_cancel_request
           (struct evdns_base *base, struct evdns_request *req)
           Cancels a pending DNS resolution request.  void
           evdns_close_server_port (struct evdns_server_port *port)
           Close down a DNS server port, and free associated structures.
           const char * evdns_err_to_string (int err)
           Convert a DNS error code to a string.  struct
           evdns_getaddrinfo_request * evdns_getaddrinfo (struct evdns_base
           *dns_base, const char *nodename, const char *servname, const struct
           evutil_addrinfo *hints_in, evdns_getaddrinfo_cb cb, void *arg)
           Make a non-blocking getaddrinfo request using the dns_base in
           'dns_base'.  void evdns_getaddrinfo_cancel (struct
           evdns_getaddrinfo_request *req)
           int evdns_server_request_add_a_reply (struct evdns_server_request
           *req, const char *name, int n, const void *addrs, int ttl)
           int evdns_server_request_add_aaaa_reply (struct
           evdns_server_request *req, const char *name, int n, const void
           *addrs, int ttl)
           int evdns_server_request_add_cname_reply (struct
           evdns_server_request *req, const char *name, const char *cname, int
           ttl)
           int evdns_server_request_add_ptr_reply (struct evdns_server_request
           *req, struct in_addr *in, const char *inaddr_name, const char
           *hostname, int ttl)
           int evdns_server_request_add_reply (struct evdns_server_request
           *req, int section, const char *name, int type, int dns_class, int
           ttl, int datalen, int is_name, const char *data)
           int evdns_server_request_drop (struct evdns_server_request *req)
           Free a DNS request without sending back a reply.  int
           evdns_server_request_get_requesting_addr (struct
           evdns_server_request *_req, struct sockaddr *sa, int addr_len)
           Get the address that made a DNS request.  int
           evdns_server_request_respond (struct evdns_server_request *req, int
           err)
           Send back a response to a DNS request, and free the request
           structure.  void evdns_server_request_set_flags (struct
           evdns_server_request *req, int flags)
           Sets some flags in a reply we're building.  void evdns_set_log_fn
           (evdns_debug_log_fn_type fn)
           Set the callback function to handle DNS log messages.  void
           evdns_set_random_bytes_fn (void(*fn)(char *, size_t))
           Set a callback used to generate random bytes.  void
           evdns_set_transaction_id_fn (ev_uint16_t(*fn)(void))
           Set a callback that will be invoked to generate transaction IDs.

Detailed Description
       Welcome, gentle reader.

       Async DNS lookups are really a whole lot harder than they should be,
       mostly stemming from the fact that the libc resolver has never been
       very good at them. Before you use this library you should see if libc
       can do the job for you with the modern async call getaddrinfo_a (see
       http://www.imperialviolet.org/page25.html#e498). Otherwise, please
       continue.

       The library keeps track of the state of nameservers and will avoid them
       when they go down. Otherwise it will round robin between them.

       Quick start guide: #include 'evdns.h' void callback(int result, char
       type, int count, int ttl, void *addresses, void *arg);
       evdns_resolv_conf_parse(DNS_OPTIONS_ALL, '/etc/resolv.conf');
       evdns_resolve('www.hostname.com', 0, callback, NULL);

       When the lookup is complete the callback function is called. The first
       argument will be one of the DNS_ERR_* defines in evdns.h. Hopefully it
       will be DNS_ERR_NONE, in which case type will be DNS_IPv4_A, count will
       be the number of IP addresses, ttl is the time which the data can be
       cached for (in seconds), addresses will point to an array of uint32_t's
       and arg will be whatever you passed to evdns_resolve.

       Searching:

       In order for this library to be a good replacement for glibc's resolver
       it supports searching. This involves setting a list of default domains,
       in which names will be queried for. The number of dots in the query
       name determines the order in which this list is used.

       Searching appears to be a single lookup from the point of view of the
       API, although many DNS queries may be generated from a single call to
       evdns_resolve. Searching can also drastically slow down the resolution
       of names.

       To disable searching:

       1.  Never set it up. If you never call evdns_resolv_conf_parse or
           evdns_search_add then no searching will occur.

       2.  If you do call evdns_resolv_conf_parse then don't pass
           DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).

       3.  When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.

       The order of searches depends on the number of dots in the name. If the
       number is greater than the ndots setting then the names is first tried
       globally. Otherwise each search domain is appended in turn.

       The ndots setting can either be set from a resolv.conf, or by calling
       evdns_search_ndots_set.

       For example, with ndots set to 1 (the default) and a search domain list
       of ['myhome.net']: Query: www Order: www.myhome.net, www.

       Query: www.abc Order: www.abc., www.abc.myhome.net

       Internals:

       Requests are kept in two queues. The first is the inflight queue. In
       this queue requests have an allocated transaction id and nameserver.
       They will soon be transmitted if they haven't already been.

       The second is the waiting queue. The size of the inflight ring is
       limited and all other requests wait in waiting queue for space. This
       bounds the number of concurrent requests so that we don't flood the
       nameserver. Several algorithms require a full walk of the inflight
       queue and so bounding its size keeps thing going nicely under huge
       (many thousands of requests) loads.

       If a nameserver loses too many requests it is considered down and we
       try not to use it. After a while we send a probe to that nameserver (a
       lookup for google.com) and, if it replies, we consider it working
       again. If the nameserver fails a probe we wait longer to try again with
       the next probe.

Macro Definition Documentation
   #define DNS_ERR_NODATA   70
       There were no answers and no error condition in the DNS packet. This
       can happen when you ask for an address that exists, but a record type
       that doesn't.

   #define DNS_ERR_NONE   0
       Error codes 0-5 are as described in RFC 1035.

   #define DNS_ERR_SHUTDOWN   68
       The request was canceled because the DNS subsystem was shut down.

Typedef Documentation
   typedef void(* evdns_callback_type)(int result, char type, int count, int
   ttl, void *addresses, void *arg)
       The callback that contains the results from a lookup. .IP "o" 2 result
       is one of the DNS_ERR_* values (DNS_ERR_NONE for success)

       o type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA

       o count contains the number of addresses of form type

       o ttl is the number of seconds the resolution may be cached for.

       o addresses needs to be cast according to type. It will be an array of
         4-byte sequences for ipv4, or an array of 16-byte sequences for ipv6,
         or a nul-terminated string for PTR.


   typedef void(* evdns_debug_log_fn_type)(int is_warning, const char *msg)
       A callback that is invoked when a log message is generated. Parameters:
           is_warning indicates if the log message is a 'warning'
           msg the content of the log message


   typedef void(* evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo
   *res, void *arg)
       Callback for evdns_getaddrinfo.

   typedef void(* evdns_request_callback_fn_type)(struct evdns_server_request
   *, void *)
       A callback to implement a DNS server. The callback function receives a
       DNS request. It should then optionally add a number of answers to the
       reply using the evdns_server_request_add_*_reply functions, before
       calling either evdns_server_request_respond to send the reply back, or
       evdns_server_request_drop to decline to answer the request.

       Parameters:
           req A newly received request
           user_data A pointer that was passed to
           evdns_add_server_port_with_base().


Function Documentation
   struct evdns_server_port* evdns_add_server_port_with_base (struct
   event_base *base, evutil_socket_tsocket, intflags,
   evdns_request_callback_fn_typecallback, void *user_data) [read]
       Create a new DNS server port. Parameters:
           base The event base to handle events for the server port.
           socket A UDP socket to accept DNS requests.
           flags Always 0 for now.
           callback A function to invoke whenever we get a DNS request on the
           socket.
           user_data Data to pass to the callback.

       Returns:
           an evdns_server_port structure for this server port.


   int evdns_base_clear_nameservers_and_suspend (struct evdns_base *base)
       Remove all configured nameservers, and suspend all pending resolves.
       Resolves will not necessarily be re-attempted until evdns_base_resume()
       is called.

       Parameters:
           base the evdns_base to which to apply this operation

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           evdns_base_resume()


   int evdns_base_count_nameservers (struct evdns_base *base)
       Get the number of configured nameservers. This returns the number of
       configured nameservers (not necessarily the number of running
       nameservers). This is useful for double-checking whether our calls to
       the various nameserver configuration functions have been successful.

       Parameters:
           base the evdns_base to which to apply this operation

       Returns:
           the number of configured nameservers

       See Also:
           evdns_base_nameserver_add()


   void evdns_base_free (struct evdns_base *base, intfail_requests)
       Shut down the asynchronous DNS resolver and terminate all active
       requests. If the 'fail_requests' option is enabled, all active requests
       will return an empty result with the error flag set to
       DNS_ERR_SHUTDOWN. Otherwise, the requests will be silently discarded.

       Parameters:
           evdns_base the evdns base to free
           fail_requests if zero, active requests will be aborted; if non-
           zero, active requests will return DNS_ERR_SHUTDOWN.

       See Also:
           evdns_base_new()


   int evdns_base_load_hosts (struct evdns_base *base, const char
   *hosts_fname)
       Load an /etc/hosts-style file from 'hosts_fname' into 'base'. If
       hosts_fname is NULL, add minimal entries for localhost, and nothing
       else.

       Note that only evdns_getaddrinfo uses the /etc/hosts entries.

       Return 0 on success, negative on failure.

   int evdns_base_nameserver_add (struct evdns_base *base, unsigned long
   intaddress)
       Add a nameserver. The address should be an IPv4 address in network byte
       order. The type of address is chosen so that it matches in_addr.s_addr.

       Parameters:
           base the evdns_base to which to add the name server
           address an IP address in network byte order

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           evdns_base_nameserver_ip_add()


   int evdns_base_nameserver_ip_add (struct evdns_base *base, const char
   *ip_as_string)
       Add a nameserver by string address. This function parses a n IPv4 or
       IPv6 address from a string and adds it as a nameserver. It supports the
       following formats:

       o [IPv6Address]:port

       o [IPv6Address]

       o IPv6Address

       o IPv4Address:port

       o IPv4Address

       If no port is specified, it defaults to 53.

       Parameters:
           base the evdns_base to which to apply this operation

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           evdns_base_nameserver_add()


   struct evdns_base* evdns_base_new (struct event_base *event_base,
   intinitialize_nameservers) [read]
       Initialize the asynchronous DNS library. This function initializes
       support for non-blocking name resolution by calling
       evdns_resolv_conf_parse() on UNIX and
       evdns_config_windows_nameservers() on Windows.

       Parameters:
           event_base the event base to associate the dns client with
           initialize_nameservers 1 if resolve.conf processing should occur

       Returns:
           evdns_base object if successful, or NULL if an error occurred.

       See Also:
           evdns_base_free()


   int evdns_base_resolv_conf_parse (struct evdns_base *base, intflags, const
   char *constfilename)
       Parse a resolv.conf file. The 'flags' parameter determines what
       information is parsed from the resolv.conf file. See the man page for
       resolv.conf for the format of this file.

       The following directives are not parsed from the file: sortlist,
       rotate, no-check-names, inet6, debug.

       If this function encounters an error, the possible return values are: 1
       = failed to open file, 2 = failed to stat file, 3 = file too large, 4 =
       out of memory, 5 = short read from file, 6 = no nameservers listed in
       the file

       Parameters:
           base the evdns_base to which to apply this operation
           flags any of
           DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC|
           DNS_OPTIONS_HOSTSFILE|DNS_OPTIONS_ALL
           filename the path to the resolv.conf file

       Returns:
           0 if successful, or various positive error codes if an error
           occurred (see above)

       See Also:
           resolv.conf(3), evdns_config_windows_nameservers()


   struct evdns_request* evdns_base_resolve_ipv4 (struct evdns_base *base,
   const char *name, intflags, evdns_callback_typecallback, void *ptr) [read]
       Lookup an A record for a given name. Parameters:
           base the evdns_base to which to apply this operation
           name a DNS hostname
           flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for
           this query.
           callback a callback function to invoke when the request is
           completed
           ptr an argument to pass to the callback function

       Returns:
           an evdns_request object if successful, or NULL if an error
           occurred.

       See Also:
           evdns_resolve_ipv6(), evdns_resolve_reverse(),
           evdns_resolve_reverse_ipv6(), evdns_cancel_request()


   struct evdns_request* evdns_base_resolve_ipv6 (struct evdns_base *base,
   const char *name, intflags, evdns_callback_typecallback, void *ptr) [read]
       Lookup an AAAA record for a given name. Parameters:
           base the evdns_base to which to apply this operation
           name a DNS hostname
           flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for
           this query.
           callback a callback function to invoke when the request is
           completed
           ptr an argument to pass to the callback function

       Returns:
           an evdns_request object if successful, or NULL if an error
           occurred.

       See Also:
           evdns_resolve_ipv4(), evdns_resolve_reverse(),
           evdns_resolve_reverse_ipv6(), evdns_cancel_request()


   struct evdns_request* evdns_base_resolve_reverse (struct evdns_base *base,
   const struct in_addr *in, intflags, evdns_callback_typecallback, void *ptr)
   [read]
       Lookup a PTR record for a given IP address. Parameters:
           base the evdns_base to which to apply this operation
           in an IPv4 address
           flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for
           this query.
           callback a callback function to invoke when the request is
           completed
           ptr an argument to pass to the callback function

       Returns:
           an evdns_request object if successful, or NULL if an error
           occurred.

       See Also:
           evdns_resolve_reverse_ipv6(), evdns_cancel_request()


   struct evdns_request* evdns_base_resolve_reverse_ipv6 (struct evdns_base
   *base, const struct in6_addr *in, intflags, evdns_callback_typecallback,
   void *ptr) [read]
       Lookup a PTR record for a given IPv6 address. Parameters:
           base the evdns_base to which to apply this operation
           in an IPv6 address
           flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for
           this query.
           callback a callback function to invoke when the request is
           completed
           ptr an argument to pass to the callback function

       Returns:
           an evdns_request object if successful, or NULL if an error
           occurred.

       See Also:
           evdns_resolve_reverse_ipv6(), evdns_cancel_request()


   int evdns_base_resume (struct evdns_base *base)
       Resume normal operation and continue any suspended resolve requests.
       Re-attempt resolves left in limbo after an earlier call to
       evdns_base_clear_nameservers_and_suspend().

       Parameters:
           base the evdns_base to which to apply this operation

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           evdns_base_clear_nameservers_and_suspend()


   void evdns_base_search_add (struct evdns_base *base, const char *domain)
       Add a domain to the list of search domains. Parameters:
           domain the domain to be added to the search list


   void evdns_base_search_clear (struct evdns_base *base)
       Obtain nameserver information using the Windows API. Attempt to
       configure a set of nameservers based on platform settings on a win32
       host. Preferentially tries to use GetNetworkParams; if that fails,
       looks in the registry.

       Returns:
           0 if successful, or -1 if an error occurred

       See Also:
           evdns_resolv_conf_parse() Clear the list of search domains.


   void evdns_base_search_ndots_set (struct evdns_base *base, const intndots)
       Set the 'ndots' parameter for searches. Sets the number of dots which,
       when found in a name, causes the first query to be without any search
       domain.

       Parameters:
           ndots the new ndots parameter


   int evdns_base_set_option (struct evdns_base *base, const char *option,
   const char *val)
       Set the value of a configuration option. The currently available
       configuration options are:

       ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case,
       bind-to, initial-probe-timeout, getaddrinfo-allow-skew.

       In versions before Libevent 2.0.3-alpha, the option name needed to end
       with a colon.

       Parameters:
           base the evdns_base to which to apply this operation
           option the name of the configuration option to be modified
           val the value to be set

       Returns:
           0 if successful, or -1 if an error occurred


   void evdns_cancel_request (struct evdns_base *base, struct evdns_request
   *req)
       Cancels a pending DNS resolution request. Parameters:
           base the evdns_base that was used to make the request
           req the evdns_request that was returned by calling a resolve
           function

       See Also:
           evdns_base_resolve_ipv4(), evdns_base_resolve_ipv6,
           evdns_base_resolve_reverse


   void evdns_close_server_port (struct evdns_server_port *port)
       Close down a DNS server port, and free associated structures.

   const char* evdns_err_to_string (interr)
       Convert a DNS error code to a string. Parameters:
           err the DNS error code

       Returns:
           a string containing an explanation of the error code


   struct evdns_getaddrinfo_request* evdns_getaddrinfo (struct evdns_base
   *dns_base, const char *nodename, const char *servname, const struct
   evutil_addrinfo *hints_in, evdns_getaddrinfo_cbcb, void *arg) [read]
       Make a non-blocking getaddrinfo request using the dns_base in
       'dns_base'. If we can answer the request immediately (with an error or
       not!), then we invoke cb immediately and return NULL. Otherwise we
       return an evdns_getaddrinfo_request and invoke cb later.

       When the callback is invoked, we pass as its first argument the error
       code that getaddrinfo would return (or 0 for no error). As its second
       argument, we pass the evutil_addrinfo structures we found (or NULL on
       error). We pass 'arg' as the third argument.

       Limitations:

       o The AI_V4MAPPED and AI_ALL flags are not currently implemented.

       o For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0.

       o For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0.


   void evdns_server_request_set_flags (struct evdns_server_request *req,
   intflags)
       Sets some flags in a reply we're building. Allows setting of the AA or
       RD flags

   void evdns_set_log_fn (evdns_debug_log_fn_typefn)
       Set the callback function to handle DNS log messages. If this callback
       is not set, evdns log messages are handled with the regular Libevent
       logging system.

       Parameters:
           fn the callback to be invoked when a log message is generated


   void evdns_set_random_bytes_fn (void(*)(char *, size_t)fn)
       Set a callback used to generate random bytes. By default, we use the
       same function as passed to evdns_set_transaction_id_fn to generate
       bytes two at a time. If a function is provided here, it's also used to
       generate transaction IDs.

       NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
       since Libevent now provides its own secure RNG.

   void evdns_set_transaction_id_fn (ev_uint16_t(*)(void)fn)
       Set a callback that will be invoked to generate transaction IDs. By
       default, we pick transaction IDs based on the current clock time, which
       is bad for security.

       Parameters:
           fn the new callback, or NULL to use the default.

       NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
       since Libevent now provides its own secure RNG.

Author
       Generated automatically by Doxygen for libevent from the source code.



libevent                        Wed Apr 10 2013                       evdns(3)