#include <evutil.h>
Go to the source code of this file.
Data Structures | |
| struct | evdns_server_question |
| struct | evdns_server_request |
Defines | |
| #define | DNS_ERR_FORMAT 1 |
| The name server was unable to interpret the query. | |
| #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-formated. | |
| #define | DNS_ERR_UNKNOWN 66 |
| An unknown error occurred. | |
| #define | DNS_IPv4_A 1 |
| #define | DNS_IPv6_AAAA 3 |
| #define | DNS_NO_SEARCH 1 |
| #define | DNS_OPTION_MISC 4 |
| #define | DNS_OPTION_NAMESERVERS 2 |
| #define | DNS_OPTION_SEARCH 1 |
| #define | DNS_OPTIONS_ALL 7 |
| #define | DNS_PTR 2 |
| #define | DNS_QUERY_NO_SEARCH 1 |
| #define | dns_question_class class |
| #define | EVDNS_ADDITIONAL_SECTION 2 |
| #define | EVDNS_ANSWER_SECTION 0 |
| #define | EVDNS_AUTHORITY_SECTION 1 |
| #define | EVDNS_CLASS_INET 1 |
| #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_request_callback_fn_type )(struct evdns_server_request *, void *) |
Functions | |
|
struct evdns_server_port * | evdns_add_server_port (int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data) |
| int | evdns_clear_nameservers_and_suspend (void) |
| Remove all configured nameservers, and suspend all pending resolves. | |
| void | evdns_close_server_port (struct evdns_server_port *port) |
| int | evdns_count_nameservers (void) |
| Get the number of configured nameservers. | |
| const char * | evdns_err_to_string (int err) |
| Convert a DNS error code to a string. | |
| int | evdns_init (void) |
| Initialize the asynchronous DNS library. | |
| int | evdns_nameserver_add (unsigned long int address) |
| Add a nameserver. | |
| int | evdns_nameserver_ip_add (const char *ip_as_string) |
| Add a nameserver. | |
| int | evdns_resolv_conf_parse (int flags, const char *const filename) |
| Parse a resolv.conf file. | |
| int | evdns_resolve_ipv4 (const char *name, int flags, evdns_callback_type callback, void *ptr) |
| Lookup an A record for a given name. | |
| int | evdns_resolve_ipv6 (const char *name, int flags, evdns_callback_type callback, void *ptr) |
| Lookup an AAAA record for a given name. | |
| int | evdns_resolve_reverse (struct in_addr *in, int flags, evdns_callback_type callback, void *ptr) |
| Lookup a PTR record for a given IP address. | |
| int | evdns_resolve_reverse_ipv6 (struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr) |
| Lookup a PTR record for a given IPv6 address. | |
| int | evdns_resume (void) |
| Resume normal operation and continue any suspended resolve requests. | |
| void | evdns_search_add (const char *domain) |
| Add a domain to the list of search domains. | |
| void | evdns_search_clear (void) |
| Obtain nameserver information using the Windows API. | |
| void | evdns_search_ndots_set (const int ndots) |
| Set the 'ndots' parameter for searches. | |
| 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_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) |
| int | evdns_server_request_get_requesting_addr (struct evdns_server_request *_req, struct sockaddr *sa, int addr_len) |
| int | evdns_server_request_respond (struct evdns_server_request *req, int err) |
| void | evdns_set_log_fn (evdns_debug_log_fn_type fn) |
| Set the callback function to handle log messages. | |
| int | evdns_set_option (const char *option, const char *val, int flags) |
| Set the value of a configuration option. | |
| void | evdns_set_transaction_id_fn (ev_uint16_t(*fn)(void)) |
| Set a callback that will be invoked to generate transaction IDs. | |
| void | evdns_shutdown (int fail_requests) |
| Shut down the asynchronous DNS resolver and terminate all active requests. | |
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
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.
| #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 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.
| is_warning | indicates if the log message is a 'warning' | |
| msg | the content of the log message |
| int evdns_clear_nameservers_and_suspend | ( | void | ) |
Remove all configured nameservers, and suspend all pending resolves.
Resolves will not necessarily be re-attempted until evdns_resume() is called.
| int evdns_count_nameservers | ( | void | ) |
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.
| const char* evdns_err_to_string | ( | int | err | ) |
Convert a DNS error code to a string.
| err | the DNS error code |
| int evdns_init | ( | void | ) |
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.
| int evdns_nameserver_add | ( | 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.
| address | an IP address in network byte order |
| int evdns_nameserver_ip_add | ( | const char * | ip_as_string | ) |
Add a nameserver.
This wraps the evdns_nameserver_add() function by parsing a string as an IP address and adds it as a nameserver.
| int evdns_resolv_conf_parse | ( | 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: 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
| flags | any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC| DNS_OPTIONS_ALL | |
| filename | the path to the resolv.conf file |
| int evdns_resolve_ipv4 | ( | const char * | name, | |
| int | flags, | |||
| evdns_callback_type | callback, | |||
| void * | ptr | |||
| ) |
Lookup an A record for a given name.
| 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 |
| int evdns_resolve_ipv6 | ( | const char * | name, | |
| int | flags, | |||
| evdns_callback_type | callback, | |||
| void * | ptr | |||
| ) |
Lookup an AAAA record for a given name.
| 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 |
| int evdns_resolve_reverse | ( | struct in_addr * | in, | |
| int | flags, | |||
| evdns_callback_type | callback, | |||
| void * | ptr | |||
| ) |
Lookup a PTR record for a given IP address.
| 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 |
| int evdns_resolve_reverse_ipv6 | ( | struct in6_addr * | in, | |
| int | flags, | |||
| evdns_callback_type | callback, | |||
| void * | ptr | |||
| ) |
Lookup a PTR record for a given IPv6 address.
| 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 |
| int evdns_resume | ( | void | ) |
Resume normal operation and continue any suspended resolve requests.
Re-attempt resolves left in limbo after an earlier call to evdns_clear_nameservers_and_suspend().
| void evdns_search_add | ( | const char * | domain | ) |
Add a domain to the list of search domains.
| domain | the domain to be added to the search list |
| void evdns_search_clear | ( | void | ) |
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.
| void evdns_search_ndots_set | ( | 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.
| ndots | the new ndots parameter |
| void evdns_set_log_fn | ( | evdns_debug_log_fn_type | fn | ) |
Set the callback function to handle log messages.
| fn | the callback to be invoked when a log message is generated |
| int evdns_set_option | ( | const char * | option, | |
| const char * | val, | |||
| int | flags | |||
| ) |
Set the value of a configuration option.
The currently available configuration options are:
ndots, timeout, max-timeouts, max-inflight, and attempts
| option | the name of the configuration option to be modified | |
| val | the value to be set | |
| flags | either 0 | DNS_OPTION_SEARCH | DNS_OPTION_MISC |
| 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.
| fn | the new callback, or NULL to use the default. |
| void evdns_shutdown | ( | 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.
| fail_requests | if zero, active requests will be aborted; if non-zero, active requests will return DNS_ERR_SHUTDOWN. |
1.5.3