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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 */