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      evdns.h

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evdns.h
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/*
* Copyright (c) 2006 Niels Provos <provos@citi.umich.edu>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* The original DNS code is due to Adam Langley with heavy
* modifications by Nick Mathewson. Adam put his DNS software in the
* public domain. You can find his original copyright below. Please,
* aware that the code as part of libevent is governed by the 3-clause
* BSD license above.
*
* This software is Public Domain. To view a copy of the public domain dedication,
* visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
* Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
*
* I ask and expect, but do not require, that all derivative works contain an
* attribution similar to:
* Parts developed by Adam Langley <agl@imperialviolet.org>
*
* You may wish to replace the word "Parts" with something else depending on
* the amount of original code.
*
* (Derivative works does not include programs which link against, run or include
* the source verbatim in their source distributions)
*/
/*
* 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.
*
* This code is based on libevent and you must call event_init before
* any of the APIs in this file. You must also seed the OpenSSL random
* source if you are using OpenSSL for ids (see below).
*
* This library is designed to be included and shipped with your source
* code. You statically link with it. You should also test for the
* existence of strtok_r and define HAVE_STRTOK_R if you have it.
*
* The DNS protocol requires a good source of id numbers and these
* numbers should be unpredictable for spoofing reasons. There are
* three methods for generating them here and you must define exactly
* one of them. In increasing order of preference:
*
* DNS_USE_GETTIMEOFDAY_FOR_ID:
* Using the bottom 16 bits of the usec result from gettimeofday. This
* is a pretty poor solution but should work anywhere.
* DNS_USE_CPU_CLOCK_FOR_ID:
* Using the bottom 16 bits of the nsec result from the CPU's time
* counter. This is better, but may not work everywhere. Requires
* POSIX realtime support and you'll need to link against -lrt on
* glibc systems at least.
* DNS_USE_OPENSSL_FOR_ID:
* Uses the OpenSSL RAND_bytes call to generate the data. You must
* have seeded the pool before making any calls to this library.
*
* 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
*
* API reference:
*
* int evdns_nameserver_add(unsigned long int address)
* Add a nameserver. The address should be an IP address in
* network byte order. The type of address is chosen so that
* it matches in_addr.s_addr.
* Returns non-zero on error.
*
* int evdns_nameserver_ip_add(const char *ip_as_string)
* This wraps the above function by parsing a string as an IP
* address and adds it as a nameserver.
* Returns non-zero on error
*
* int evdns_resolve(const char *name, int flags,
* evdns_callback_type callback,
* void *ptr)
* Resolve a name. The name parameter should be a DNS name.
* The flags parameter should be 0, or DNS_QUERY_NO_SEARCH
* which disables searching for this query. (see defn of
* searching above).
*
* The callback argument is a function which is called when
* this query completes and ptr is an argument which is passed
* to that callback function.
*
* Returns non-zero on error
*
* void evdns_search_clear()
* Clears the list of search domains
*
* void evdns_search_add(const char *domain)
* Add a domain to the list of search domains
*
* void evdns_search_ndots_set(int ndots)
* Set the number of dots which, when found in a name, causes
* the first query to be without any search domain.
*
* int evdns_count_nameservers(void)
* Return 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.
*
* int evdns_clear_nameservers_and_suspend(void)
* Remove all currently configured nameservers, and suspend all pending
* resolves. Resolves will not necessarily be re-attempted until
* evdns_resume() is called.
*
* int evdns_resume(void)
* Re-attempt resolves left in limbo after an earlier call to
* evdns_clear_nameservers_and_suspend().
*
* int evdns_config_windows_nameservers(void)
* 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 on success, nonzero on failure.
*
* int evdns_resolv_conf_parse(int flags, const char *filename)
* Parse a resolv.conf like file from the given filename.
*
* See the man page for resolv.conf for the format of this file.
* The flags argument determines what information is parsed from
* this file:
* DNS_OPTION_SEARCH - domain, search and ndots options
* DNS_OPTION_NAMESERVERS - nameserver lines
* DNS_OPTION_MISC - timeout and attempts options
* DNS_OPTIONS_ALL - all of the above
* The following directives are not parsed from the file:
* sortlist, rotate, no-check-names, inet6, debug
*
* Returns non-zero on error:
* 0 no errors
* 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 in file
*
* 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.
*/
#ifndef EVENTDNS_H
#define EVENTDNS_H
#ifdef __cplusplus
extern "C" {
#endif
/* Error codes 0-5 are as described in RFC 1035. */
#define DNS_ERR_NONE 0
/* The name server was unable to interpret the query */
#define DNS_ERR_FORMAT 1
/* The name server was unable to process this query due to a problem with the
* name server */
#define DNS_ERR_SERVERFAILED 2
/* The domain name does not exist */
#define DNS_ERR_NOTEXIST 3
/* The name server does not support the requested kind of query */
#define DNS_ERR_NOTIMPL 4
/* The name server refuses to reform the specified operation for policy
* reasons */
#define DNS_ERR_REFUSED 5
/* The reply was truncated or ill-formated */
#define DNS_ERR_TRUNCATED 65
/* An unknown error occurred */
#define DNS_ERR_UNKNOWN 66
/* Communication with the server timed out */
#define DNS_ERR_TIMEOUT 67
/* The request was canceled because the DNS subsystem was shut down. */
#define DNS_ERR_SHUTDOWN 68
#define DNS_IPv4_A 1
#define DNS_PTR 2
#define DNS_IPv6_AAAA 3
#define DNS_QUERY_NO_SEARCH 1
#define DNS_OPTION_SEARCH 1
#define DNS_OPTION_NAMESERVERS 2
#define DNS_OPTION_MISC 4
#define DNS_OPTIONS_ALL 7
/*
* The callback that contains the results from a lookup.
* - 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
*/
typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);
int evdns_init(void);
void evdns_shutdown(int fail_requests);
const char *evdns_err_to_string(int err);
int evdns_nameserver_add(unsigned long int address);
int evdns_count_nameservers(void);
int evdns_clear_nameservers_and_suspend(void);
int evdns_resume(void);
int evdns_nameserver_ip_add(const char *ip_as_string);
int evdns_resolve_ipv4(const char *name, int flags, evdns_callback_type callback, void *ptr);
int evdns_resolve_ipv6(const char *name, int flags, evdns_callback_type callback, void *ptr);
struct in_addr;
struct in6_addr;
int evdns_resolve_reverse(struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
int evdns_resolve_reverse_ipv6(struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr);
int evdns_set_option(const char *option, const char *val, int flags);
int evdns_resolv_conf_parse(int flags, const char *);
#ifdef MS_WINDOWS
int evdns_config_windows_nameservers(void);
#endif
void evdns_search_clear(void);
void evdns_search_add(const char *domain);
void evdns_search_ndots_set(const int ndots);
typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
void evdns_set_log_fn(evdns_debug_log_fn_type fn);
#define DNS_NO_SEARCH 1
#ifdef __cplusplus
}
#endif
/*
* Structures and functions used to implement a DNS server.
*/
struct evdns_server_request {
int flags;
int nquestions;
struct evdns_server_question **questions;
};
struct evdns_server_question {
int type;
int class;
char name[1];
};
typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
#define EVDNS_ANSWER_SECTION 0
#define EVDNS_AUTHORITY_SECTION 1
#define EVDNS_ADDITIONAL_SECTION 2
#define EVDNS_TYPE_A 1
#define EVDNS_TYPE_NS 2
#define EVDNS_TYPE_CNAME 5
#define EVDNS_TYPE_SOA 6
#define EVDNS_TYPE_PTR 12
#define EVDNS_TYPE_MX 15
#define EVDNS_TYPE_TXT 16
#define EVDNS_TYPE_AAAA 28
#define EVDNS_QTYPE_AXFR 252
#define EVDNS_QTYPE_ALL 255
#define EVDNS_CLASS_INET 1
struct evdns_server_port *evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data);
void evdns_close_server_port(struct evdns_server_port *port);
int evdns_server_request_add_reply(struct evdns_server_request *req, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data);
int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, 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_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
int evdns_server_request_respond(struct evdns_server_request *req, int err);
int evdns_server_request_drop(struct evdns_server_request *req);
struct sockaddr;
int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len);
#endif /* !EVENTDNS_H */
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