Provides a few APIs to use for resolving DNS names, and a facility for implementing simple DNS servers. More...

#include <event2/visibility.h>
#include <event2/util.h>

Macros
#define	DNS_CNAME 4

#define	DNS_CNAME_CALLBACK 0x80
	Make a separate callback for CNAME in answer.

#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. More...

#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_NAMESERVERS_NO_DEFAULT 16

#define	DNS_OPTION_SEARCH 1

#define	DNS_OPTIONS_ALL
	All above: More...

#define	DNS_PTR 2

#define	DNS_QUERY_IGNTC 0x04
	Ignore truncation flag in responses (don't fallback to TCP connections).

#define	DNS_QUERY_NO_SEARCH 0x01
	Disable searching for the query.

#define	DNS_QUERY_USEVC 0x02
	Use TCP connections ("virtual circuits") for queries rather than UDP datagrams.

#define	EVDNS_ADDITIONAL_SECTION 2

#define	EVDNS_ANSWER_SECTION 0

#define	EVDNS_AUTHORITY_SECTION 1

#define	EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED

#define	EVDNS_BASE_DISABLE_WHEN_INACTIVE 0x8000
	Flag for evdns_base_new: Do not prevent the libevent event loop from exiting when we have no active dns requests.

#define	EVDNS_BASE_INITIALIZE_NAMESERVERS 1
	Flag for evdns_base_new: process resolv.conf. More...

#define	EVDNS_BASE_NAMESERVERS_NO_DEFAULT 0x10000
	Flag for evdns_base_new: If EVDNS_BASE_INITIALIZE_NAMESERVERS isset, do not add default nameserver if there are no nameservers in resolv.conf. More...

#define	EVDNS_BASE_NO_CACHE 0x10
	Flag for evdns_base_new: disable caching of DNS responses by default for async resolver.

#define	EVDNS_CLASS_INET 1

#define	EVDNS_ERROR_FAILED_TO_OPEN_FILE 1

#define	EVDNS_ERROR_FAILED_TO_STAT_FILE 2

#define	EVDNS_ERROR_FILE_TOO_LARGE 3

#define	EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED 6

#define	EVDNS_ERROR_NONE 0

#define	EVDNS_ERROR_OUT_OF_MEMORY 4

#define	EVDNS_ERROR_SHORT_READ_FROM_FILE 5

#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. More...

typedef void(*	evdns_debug_log_fn_type) (int is_warning, const char *msg)
	A callback that is invoked when a log message is generated. More...

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. More...

Enumerations
enum	evdns_server_option { EVDNS_SOPT_TCP_MAX_CLIENTS, EVDNS_SOPT_TCP_IDLE_TIMEOUT }
	List of configurable evdns_server_port options. More...

Functions
EVENT2_EXPORT_SYMBOL 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 UDP DNS server port. More...

EVENT2_EXPORT_SYMBOL struct evdns_server_port *	evdns_add_server_port_with_listener (struct event_base base, struct evconnlistener listener, int flags, evdns_request_callback_fn_type callback, void *user_data)
	Create a new TCP DNS server port. More...

EVENT2_EXPORT_SYMBOL void	evdns_base_clear_host_addresses (struct evdns_base *base)
	Remove all hosts entries that have been loaded into the event_base via evdns_base_load_hosts or via event_base_resolv_conf_parse. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_clear_nameservers_and_suspend (struct evdns_base *base)
	Remove all configured nameservers, and suspend all pending resolves. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_config_windows_nameservers (struct evdns_base *)
	Obtain nameserver information using the Windows API. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_count_nameservers (struct evdns_base *base)
	Get the number of configured nameservers. More...

EVENT2_EXPORT_SYMBOL void	evdns_base_free (struct evdns_base *base, int fail_requests)
	Shut down the asynchronous DNS resolver and terminate all active requests. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_get_nameserver_addr (struct evdns_base base, int idx, struct sockaddr sa, ev_socklen_t len)
	Retrieve the address of the 'idx'th configured nameserver. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_get_nameserver_fd (struct evdns_base *base, int idx)
	Retrieve the fd of the 'idx'th configured nameserver. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_load_hosts (struct evdns_base base, const char hosts_fname)
	Load an /etc/hosts-style file from 'hosts_fname' into 'base'. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_nameserver_add (struct evdns_base *base, unsigned long int address)
	Add a nameserver. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_nameserver_ip_add (struct evdns_base base, const char ip_as_string)
	Add a nameserver by string address. More...

EVENT2_EXPORT_SYMBOL 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.

EVENT2_EXPORT_SYMBOL struct evdns_base *	evdns_base_new (struct event_base *event_base, int flags)
	Initialize the asynchronous DNS library. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_resolv_conf_parse (struct evdns_base base, int flags, const char const filename)
	Parse a resolv.conf file. More...

EVENT2_EXPORT_SYMBOL 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. More...

EVENT2_EXPORT_SYMBOL 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. More...

EVENT2_EXPORT_SYMBOL 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. More...

EVENT2_EXPORT_SYMBOL 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. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_resume (struct evdns_base *base)
	Resume normal operation and continue any suspended resolve requests. More...

EVENT2_EXPORT_SYMBOL void	evdns_base_search_add (struct evdns_base base, const char domain)
	Add a domain to the list of search domains. More...

EVENT2_EXPORT_SYMBOL void	evdns_base_search_clear (struct evdns_base *base)
	Clear the list of search domains.

EVENT2_EXPORT_SYMBOL void	evdns_base_search_ndots_set (struct evdns_base *base, const int ndots)
	Set the 'ndots' parameter for searches. More...

EVENT2_EXPORT_SYMBOL int	evdns_base_set_option (struct evdns_base base, const char option, const char *val)
	Set the value of a configuration option. More...

EVENT2_EXPORT_SYMBOL int	evdns_cache_lookup (struct evdns_base base, const char nodename, struct evutil_addrinfo hints, ev_uint16_t port, struct evutil_addrinfo *res)
	Lookup an entry from the evdns cache. More...

EVENT2_EXPORT_SYMBOL void	evdns_cache_write (struct evdns_base dns_base, char nodename, struct evutil_addrinfo *res, int ttl)
	Write an entry to the evdns cache. More...

EVENT2_EXPORT_SYMBOL void	evdns_cancel_request (struct evdns_base base, struct evdns_request req)
	Cancels a pending DNS resolution request. More...

EVENT2_EXPORT_SYMBOL void	evdns_close_server_port (struct evdns_server_port *port)
	Close down a DNS server port, and free associated structures.

const EVENT2_EXPORT_SYMBOL char *	evdns_err_to_string (int err)
	Convert a DNS error code to a string. More...

EVENT2_EXPORT_SYMBOL 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'. More...

EVENT2_EXPORT_SYMBOL void	evdns_getaddrinfo_cancel (struct evdns_getaddrinfo_request *req)

EVENT2_EXPORT_SYMBOL int	evdns_server_port_set_option (struct evdns_server_port *port, enum evdns_server_option option, size_t value)
	Configure DNS server. More...

EVENT2_EXPORT_SYMBOL int	evdns_server_request_add_a_reply (struct evdns_server_request req, const char name, int n, const void *addrs, int ttl)

EVENT2_EXPORT_SYMBOL int	evdns_server_request_add_aaaa_reply (struct evdns_server_request req, const char name, int n, const void *addrs, int ttl)

EVENT2_EXPORT_SYMBOL int	evdns_server_request_add_cname_reply (struct evdns_server_request req, const char name, const char *cname, int ttl)

EVENT2_EXPORT_SYMBOL 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)

EVENT2_EXPORT_SYMBOL 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)

EVENT2_EXPORT_SYMBOL int	evdns_server_request_drop (struct evdns_server_request *req)
	Free a DNS request without sending back a reply.

EVENT2_EXPORT_SYMBOL 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.

EVENT2_EXPORT_SYMBOL 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.

EVENT2_EXPORT_SYMBOL void	evdns_server_request_set_flags (struct evdns_server_request *req, int flags)
	Sets some flags in a reply we're building. More...

EVENT2_EXPORT_SYMBOL void	evdns_set_log_fn (evdns_debug_log_fn_type fn)
	Set the callback function to handle DNS log messages. More...

Detailed Description

Provides a few APIs to use for resolving DNS names, and a facility for implementing simple DNS servers.

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:

Never set it up. If you never call evdns_resolv_conf_parse or evdns_search_add then no searching will occur.
If you do call evdns_resolv_conf_parse then don't pass DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).
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

◆ DNS_ERR_NODATA

#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.

◆ DNS_OPTIONS_ALL

#define DNS_OPTIONS_ALL

Value:

    (    \
    DNS_OPTION_SEARCH      | \
    DNS_OPTION_NAMESERVERS | \
    DNS_OPTION_MISC        | \
    DNS_OPTION_HOSTSFILE   | \
    0                        \
)

All above:

DNS_OPTION_SEARCH
DNS_OPTION_NAMESERVERS
DNS_OPTION_MISC
DNS_OPTION_HOSTSFILE

◆ EVDNS_BASE_INITIALIZE_NAMESERVERS

#define EVDNS_BASE_INITIALIZE_NAMESERVERS 1

Flag for evdns_base_new: process resolv.conf.

◆ EVDNS_BASE_NAMESERVERS_NO_DEFAULT

#define EVDNS_BASE_NAMESERVERS_NO_DEFAULT 0x10000

Flag for evdns_base_new: If EVDNS_BASE_INITIALIZE_NAMESERVERS isset, do not add default nameserver if there are no nameservers in resolv.conf.

See also: DNS_OPTION_NAMESERVERS_NO_DEFAULT

Typedef Documentation

◆ evdns_callback_type

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.

result is one of the DNS_ERR_* values (DNS_ERR_NONE for success)
type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA
count contains the number of addresses of form type
ttl is the number of seconds the resolution may be cached for.
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.

◆ evdns_debug_log_fn_type

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

◆ evdns_request_callback_fn_type

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().

Enumeration Type Documentation

◆ evdns_server_option

enum evdns_server_option

List of configurable evdns_server_port options.

See also: evdns_server_port_set_option()

Enumerator

EVDNS_SOPT_TCP_MAX_CLIENTS

Maximum number of simultaneous tcp connections (clients) that server can hold.

Can be set only for TCP DNS servers.

EVDNS_SOPT_TCP_IDLE_TIMEOUT

Idle timeout (in seconds) of incoming TCP connections.

If client doesn't send any requests via the connection during this period connection is closed by the server. Can be set only for TCP DNS servers.

Function Documentation

◆ evdns_add_server_port_with_base()

EVENT2_EXPORT_SYMBOL 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 UDP 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 or NULL if an error occurred.

◆ evdns_add_server_port_with_listener()

EVENT2_EXPORT_SYMBOL struct evdns_server_port* evdns_add_server_port_with_listener	(	struct event_base *	base,
		struct evconnlistener *	listener,
		int	flags,
		evdns_request_callback_fn_type	callback,
		void *	user_data
	)

Create a new TCP DNS server port.

Parameters

base	The event base to handle events for the server port.
listener	A TCP listener 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 or NULL if an error occurred.

◆ evdns_base_clear_host_addresses()

EVENT2_EXPORT_SYMBOL void evdns_base_clear_host_addresses ( struct evdns_base * base )

Remove all hosts entries that have been loaded into the event_base via evdns_base_load_hosts or via event_base_resolv_conf_parse.

Parameters

base	the evdns base to remove outdated host addresses from

◆ evdns_base_clear_nameservers_and_suspend()

EVENT2_EXPORT_SYMBOL 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()

◆ evdns_base_config_windows_nameservers()

EVENT2_EXPORT_SYMBOL int evdns_base_config_windows_nameservers ( struct evdns_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()

◆ evdns_base_count_nameservers()

EVENT2_EXPORT_SYMBOL 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()

◆ evdns_base_free()

EVENT2_EXPORT_SYMBOL void evdns_base_free	(	struct evdns_base *	base,
		int	fail_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

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()

◆ evdns_base_get_nameserver_addr()

EVENT2_EXPORT_SYMBOL int evdns_base_get_nameserver_addr	(	struct evdns_base *	base,
		int	idx,
		struct sockaddr *	sa,
		ev_socklen_t	len
	)

Retrieve the address of the 'idx'th configured nameserver.

Parameters

base	The evdns_base to examine.
idx	The index of the nameserver to get the address of.
sa	A location to receive the server's address.
len	The number of bytes available at sa.

Returns: the number of bytes written into sa on success. On failure, returns -1 if idx is greater than the number of configured nameservers, or a value greater than 'len' if len was not high enough.

◆ evdns_base_get_nameserver_fd()

EVENT2_EXPORT_SYMBOL int evdns_base_get_nameserver_fd	(	struct evdns_base *	base,
		int	idx
	)

Retrieve the fd of the 'idx'th configured nameserver.

Parameters

base	The evdns_base to examine.
idx	The index of the nameserver to get the address of.

Returns: the fd value. On failure, returns -1 if idx is greater than the number of configured nameservers

◆ evdns_base_load_hosts()

EVENT2_EXPORT_SYMBOL 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.

This function does not replace previously loaded hosts entries; to do that, call evdns_base_clear_host_addresses first.

Return 0 on success, negative on failure.

◆ evdns_base_nameserver_add()

EVENT2_EXPORT_SYMBOL int evdns_base_nameserver_add	(	struct evdns_base *	base,
		unsigned long int	address
	)

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. base must not be NULL.
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()

◆ evdns_base_nameserver_ip_add()

EVENT2_EXPORT_SYMBOL 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:

[IPv6Address]:port
[IPv6Address]
IPv6Address
IPv4Address:port
IPv4Address

If no port is specified, it defaults to 53.

Parameters

base	the evdns_base to which to apply this operation. base must not be NULL

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

See also: evdns_base_nameserver_add()

◆ evdns_base_new()

EVENT2_EXPORT_SYMBOL struct evdns_base* evdns_base_new	(	struct event_base *	event_base,
		int	flags
	)

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
flags	any of EVDNS_BASE_INITIALIZE_NAMESERVERS\| EVDNS_BASE_DISABLE_WHEN_INACTIVE\|EVDNS_BASE_NAMESERVERS_NO_DEFAULT\| EVDNS_BASE_NO_CACHE

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

See also: evdns_base_free()

◆ evdns_base_resolv_conf_parse()

EVENT2_EXPORT_SYMBOL int evdns_base_resolv_conf_parse	(	struct evdns_base *	base,
		int	flags,
		const char *const	filename
	)

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: EVDNS_ERROR_FAILED_TO_OPEN_FILE (1) - failed to open file EVDNS_ERROR_FAILED_TO_STAT_FILE (2) - failed to stat file EVDNS_ERROR_FILE_TOO_LARGE (3) - file too large EVDNS_ERROR_OUT_OF_MEMORY (4) - out of memory EVDNS_ERROR_SHORT_READ_FROM_FILE (5) - short read from file EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED (6) - no nameservers configured.

Parameters

base	the evdns_base to which to apply this operation. base must not be NULL.
flags	any of DNS_OPTION_NAMESERVERS\|DNS_OPTION_SEARCH\|DNS_OPTION_MISC\| DNS_OPTION_HOSTSFILE\|DNS_OPTIONS_ALL\|DNS_OPTION_NAMESERVERS_NO_DEFAULT
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()

◆ evdns_base_resolve_ipv4()

EVENT2_EXPORT_SYMBOL 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.

Parameters

base	the evdns_base to which to apply this operation
name	a DNS hostname
flags	either 0, or combination of DNS_QUERY_* flags.
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()

◆ evdns_base_resolve_ipv6()

EVENT2_EXPORT_SYMBOL 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.

Parameters

base	the evdns_base to which to apply this operation
name	a DNS hostname
flags	either 0, or combination of DNS_QUERY_* flags.
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()

◆ evdns_base_resolve_reverse()

EVENT2_EXPORT_SYMBOL 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.

Parameters

base	the evdns_base to which to apply this operation
in	an IPv4 address
flags	either 0, or combination of DNS_QUERY_* flags.
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()

◆ evdns_base_resolve_reverse_ipv6()

EVENT2_EXPORT_SYMBOL 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.

Parameters

base	the evdns_base to which to apply this operation
in	an IPv6 address
flags	either 0, or combination of DNS_QUERY_* flags.
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()

◆ evdns_base_resume()

EVENT2_EXPORT_SYMBOL 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()

◆ evdns_base_search_add()

EVENT2_EXPORT_SYMBOL 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

◆ evdns_base_search_ndots_set()

EVENT2_EXPORT_SYMBOL void evdns_base_search_ndots_set	(	struct evdns_base *	base,
		const int	ndots
	)

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

◆ evdns_base_set_option()

EVENT2_EXPORT_SYMBOL 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, max-probe-timeout, probe-backoff-factor, getaddrinfo-allow-skew, so-rcvbuf, so-sndbuf, tcp-idle-timeout, use-vc, ignore-tc, edns-udp-size.

probe-backoff-factor Backoff factor of probe timeout
max-probe-timeout Maximum timeout between two probe packets will change initial-probe-timeout when this value is smaller

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

In case of options without values (use-vc, ingore-tc) val should be an empty string or NULL.

Parameters

base	the evdns_base to which to apply this operation. base must not be NULL.
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

◆ evdns_cache_lookup()

EVENT2_EXPORT_SYMBOL int evdns_cache_lookup	(	struct evdns_base *	base,
		const char *	nodename,
		struct evutil_addrinfo *	hints,
		ev_uint16_t	port,
		struct evutil_addrinfo **	res
	)

Lookup an entry from the evdns cache.

Parameters

base	the evdns base associated with the cache
nodename	the DNS name for which information is being sought
hints	see man getaddrinfo()
port	used to fill in port numbers in the resulting address list
res	pointer to an evutil_addrinfo struct for result

◆ evdns_cache_write()

EVENT2_EXPORT_SYMBOL void evdns_cache_write	(	struct evdns_base *	dns_base,
		char *	nodename,
		struct evutil_addrinfo *	res,
		int	ttl
	)

Write an entry to the evdns cache.

Parameters

dns_base	the evdns base to add the entry to
nodename	the DNS name
res	the address information associated with the DNS name
ttl	the time to live associated with the address information

◆ evdns_cancel_request()

EVENT2_EXPORT_SYMBOL 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

◆ evdns_err_to_string()

const EVENT2_EXPORT_SYMBOL char* evdns_err_to_string ( int err )

Convert a DNS error code to a string.

Parameters

err	the DNS error code

Returns: a string containing an explanation of the error code

◆ evdns_getaddrinfo()

EVENT2_EXPORT_SYMBOL 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'.

If we can answer the request immediately (with an error or not!), then we invoke cb immediately and return NULL. This can happen e.g. if the requested address is in the hosts file, or cached, or invalid. 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:

The AI_V4MAPPED and AI_ALL flags are not currently implemented.
For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0.
For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0.
If we cached a response exclusively for a different address type (e.g. PF_INET), we will set addrinfo to NULL (e.g. queried with PF_INET6) and return EVUTIL_EAI_ADDRFAMILY.
Cache isn't hit when AI_CANONNAME is set but cached server response doesn't contain CNAME.
If we can answer immediately (e.g. using hosts file, there is an error or when cache is hit), we invoke the call back and return NULL.

◆ evdns_server_port_set_option()

EVENT2_EXPORT_SYMBOL int evdns_server_port_set_option	(	struct evdns_server_port *	port,
		enum evdns_server_option	option,
		size_t	value
	)

Configure DNS server.

Parameters

port	the evdns_server_port to which to apply this operation
option

See also: evdns_server_option for the list of possible options

Parameters

val	value of the option

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

◆ evdns_server_request_set_flags()

EVENT2_EXPORT_SYMBOL void evdns_server_request_set_flags	(	struct evdns_server_request *	req,
		int	flags
	)

Sets some flags in a reply we're building.

Allows setting of the AA or RD flags

◆ evdns_set_log_fn()

EVENT2_EXPORT_SYMBOL void evdns_set_log_fn ( evdns_debug_log_fn_type fn )

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

Macros

Typedefs

Enumerations

Functions

Detailed Description

Macro Definition Documentation

◆ DNS_ERR_NODATA

◆ DNS_OPTIONS_ALL

◆ EVDNS_BASE_INITIALIZE_NAMESERVERS

◆ EVDNS_BASE_NAMESERVERS_NO_DEFAULT

Typedef Documentation

◆ evdns_callback_type

◆ evdns_debug_log_fn_type

◆ evdns_request_callback_fn_type

Enumeration Type Documentation

◆ evdns_server_option

Function Documentation

◆ evdns_add_server_port_with_base()

◆ evdns_add_server_port_with_listener()

◆ evdns_base_clear_host_addresses()

◆ evdns_base_clear_nameservers_and_suspend()

◆ evdns_base_config_windows_nameservers()

◆ evdns_base_count_nameservers()

◆ evdns_base_free()

◆ evdns_base_get_nameserver_addr()

◆ evdns_base_get_nameserver_fd()

◆ evdns_base_load_hosts()

◆ evdns_base_nameserver_add()

◆ evdns_base_nameserver_ip_add()

◆ evdns_base_new()

◆ evdns_base_resolv_conf_parse()

◆ evdns_base_resolve_ipv4()

◆ evdns_base_resolve_ipv6()

◆ evdns_base_resolve_reverse()

◆ evdns_base_resolve_reverse_ipv6()

◆ evdns_base_resume()

◆ evdns_base_search_add()

◆ evdns_base_search_ndots_set()

◆ evdns_base_set_option()

◆ evdns_cache_lookup()

◆ evdns_cache_write()

◆ evdns_cancel_request()

◆ evdns_err_to_string()

◆ evdns_getaddrinfo()

◆ evdns_server_port_set_option()

◆ evdns_server_request_set_flags()

◆ evdns_set_log_fn()