1AnyEvent::DNS(3) User Contributed Perl Documentation AnyEvent::DNS(3)
2
6 AnyEvent::DNS - fully asynchronous DNS resolution
7
9 use AnyEvent::DNS;
10 my $cv = AnyEvent->condvar;
12 AnyEvent::DNS::a "www.google.de", $cv;
13 # ... later
14 my @addrs = $cv->recv;
15
17 This module offers both a number of DNS convenience functions as well
18 as a fully asynchronous and high-performance pure-perl stub resolver.
19 The stub resolver supports DNS over IPv4 and IPv6, UDP and TCP,
21 optional EDNS0 support for up to 4kiB datagrams and automatically falls
22 back to virtual circuit mode for large responses.
23 CONVENIENCE FUNCTIONS
25 AnyEvent::DNS::a $domain, $cb->(@addrs)
26 Tries to resolve the given domain to IPv4 address(es).
27 AnyEvent::DNS::aaaa $domain, $cb->(@addrs)
29 Tries to resolve the given domain to IPv6 address(es).
30 AnyEvent::DNS::mx $domain, $cb->(@hostnames)
32 Tries to resolve the given domain into a sorted (lower preference
33 value first) list of domain names.
34 AnyEvent::DNS::ns $domain, $cb->(@hostnames)
36 Tries to resolve the given domain name into a list of name servers.
37 AnyEvent::DNS::txt $domain, $cb->(@hostnames)
39 Tries to resolve the given domain name into a list of text records.
40 Only the first text string per record will be returned. If you want
41 all strings, you need to call the resolver manually:
42 resolver->resolve ($domain => "txt", sub {
44 for my $record (@_) {
45 my (undef, undef, undef, @txt) = @$record;
46 # strings now in @txt
47 }
48 });
49 AnyEvent::DNS::srv $service, $proto, $domain, $cb->(@srv_rr)
51 Tries to resolve the given service, protocol and domain name into a
52 list of service records.
53 Each $srv_rr is an array reference with the following contents:
55 "[$priority, $weight, $transport, $target]".
56 They will be sorted with lowest priority first, then randomly
58 distributed by weight as per RFC 2782.
59 Example:
61 AnyEvent::DNS::srv "sip", "udp", "schmorp.de", sub { ...
63 # @_ = ( [10, 10, 5060, "sip1.schmorp.de" ] )
64 AnyEvent::DNS::any $domain, $cb->(@rrs)
66 Tries to resolve the given domain and passes all resource records
67 found to the callback.
68 AnyEvent::DNS::ptr $domain, $cb->(@hostnames)
70 Tries to make a PTR lookup on the given domain. See
71 "reverse_lookup" and "reverse_verify" if you want to resolve an IP
72 address to a hostname instead.
73 AnyEvent::DNS::reverse_lookup $ipv4_or_6, $cb->(@hostnames)
75 Tries to reverse-resolve the given IPv4 or IPv6 address (in textual
76 form) into its hostname(s). Handles V4MAPPED and V4COMPAT IPv6
77 addresses transparently.
78 AnyEvent::DNS::reverse_verify $ipv4_or_6, $cb->(@hostnames)
80 The same as "reverse_lookup", but does forward-lookups to verify
81 that the resolved hostnames indeed point to the address, which
82 makes spoofing harder.
83 If you want to resolve an address into a hostname, this is the
85 preferred method: The DNS records could still change, but at least
86 this function verified that the hostname, at one point in the past,
87 pointed at the IP address you originally resolved.
88 Example:
90 AnyEvent::DNS::reverse_verify "2001:500:2f::f", sub { print shift };
92 # => f.root-servers.net
93 LOW-LEVEL DNS EN-/DECODING FUNCTIONS
95 $AnyEvent::DNS::EDNS0
96 This variable decides whether dns_pack automatically enables EDNS0
97 support. By default, this is disabled (0), unless overridden by
98 $ENV{PERL_ANYEVENT_EDNS0}, but when set to 1, AnyEvent::DNS will
99 use EDNS0 in all requests.
100 $pkt = AnyEvent::DNS::dns_pack $dns
102 Packs a perl data structure into a DNS packet. Reading RFC 1035 is
103 strongly recommended, then everything will be totally clear. Or
104 maybe not.
105 Resource records are not yet encodable.
107 Examples:
109 # very simple request, using lots of default values:
111 { rd => 1, qd => [ [ "host.domain", "a"] ] }
112 # more complex example, showing how flags etc. are named:
114 {
116 id => 10000,
117 op => "query",
118 rc => "nxdomain",
119 # flags
121 qr => 1,
122 aa => 0,
123 tc => 0,
124 rd => 0,
125 ra => 0,
126 ad => 0,
127 cd => 0,
128 qd => [@rr], # query section
130 an => [@rr], # answer section
131 ns => [@rr], # authority section
132 ar => [@rr], # additional records section
133 }
134 $dns = AnyEvent::DNS::dns_unpack $pkt
136 Unpacks a DNS packet into a perl data structure.
137 Examples:
139 # an unsuccessful reply
141 {
142 'qd' => [
143 [ 'ruth.plan9.de.mach.uni-karlsruhe.de', '*', 'in' ]
144 ],
145 'rc' => 'nxdomain',
146 'ar' => [],
147 'ns' => [
148 [
149 'uni-karlsruhe.de',
150 'soa',
151 'in',
152 600,
153 'netserv.rz.uni-karlsruhe.de',
154 'hostmaster.rz.uni-karlsruhe.de',
155 2008052201, 10800, 1800, 2592000, 86400
156 ]
157 ],
158 'tc' => '',
159 'ra' => 1,
160 'qr' => 1,
161 'id' => 45915,
162 'aa' => '',
163 'an' => [],
164 'rd' => 1,
165 'op' => 'query'
166 }
167 # a successful reply
169 {
171 'qd' => [ [ 'www.google.de', 'a', 'in' ] ],
172 'rc' => 0,
173 'ar' => [
174 [ 'a.l.google.com', 'a', 'in', 3600, '209.85.139.9' ],
175 [ 'b.l.google.com', 'a', 'in', 3600, '64.233.179.9' ],
176 [ 'c.l.google.com', 'a', 'in', 3600, '64.233.161.9' ],
177 ],
178 'ns' => [
179 [ 'l.google.com', 'ns', 'in', 3600, 'a.l.google.com' ],
180 [ 'l.google.com', 'ns', 'in', 3600, 'b.l.google.com' ],
181 ],
182 'tc' => '',
183 'ra' => 1,
184 'qr' => 1,
185 'id' => 64265,
186 'aa' => '',
187 'an' => [
188 [ 'www.google.de', 'cname', 'in', 3600, 'www.google.com' ],
189 [ 'www.google.com', 'cname', 'in', 3600, 'www.l.google.com' ],
190 [ 'www.l.google.com', 'a', 'in', 3600, '66.249.93.104' ],
191 [ 'www.l.google.com', 'a', 'in', 3600, '66.249.93.147' ],
192 ],
193 'rd' => 1,
194 'op' => 0
195 }
196 THE AnyEvent::DNS RESOLVER CLASS
198 This is the class which does the actual protocol work.
199 AnyEvent::DNS::resolver
201 This function creates and returns a resolver that is ready to use
202 and should mimic the default resolver for your system as good as
203 possible. It is used by AnyEvent itself as well.
204 It only ever creates one resolver and returns this one on
206 subsequent calls - see $AnyEvent::DNS::RESOLVER, below, for
207 details.
208 Unless you have special needs, prefer this function over creating
210 your own resolver object.
211 The resolver is created with the following parameters:
213 untaint enabled
215 max_outstanding $ENV{PERL_ANYEVENT_MAX_OUTSTANDING_DNS} (default 10)
216 "os_config" will be used for OS-specific configuration, unless
218 $ENV{PERL_ANYEVENT_RESOLV_CONF} is specified, in which case that
219 file gets parsed.
220 $AnyEvent::DNS::RESOLVER
222 This variable stores the default resolver returned by
223 "AnyEvent::DNS::resolver", or "undef" when the default resolver
224 hasn't been instantiated yet.
225 One can provide a custom resolver (e.g. one with caching
227 functionality) by storing it in this variable, causing all
228 subsequent resolves done via "AnyEvent::DNS::resolver" to be done
229 via the custom one.
230 $resolver = new AnyEvent::DNS key => value...
232 Creates and returns a new resolver.
233 The following options are supported:
235 server => [...]
237 A list of server addresses (default: "v127.0.0.1" or "::1") in
238 network format (i.e. as returned by
239 "AnyEvent::Socket::parse_address" - both IPv4 and IPv6 are
240 supported).
241 timeout => [...]
243 A list of timeouts to use (also determines the number of
244 retries). To make three retries with individual time-outs of 2,
245 5 and 5 seconds, use "[2, 5, 5]", which is also the default.
246 search => [...]
248 The default search list of suffixes to append to a domain name
249 (default: none).
250 ndots => $integer
252 The number of dots (default: 1) that a name must have so that
253 the resolver tries to resolve the name without any suffixes
254 first.
255 max_outstanding => $integer
257 Most name servers do not handle many parallel requests very
258 well. This option limits the number of outstanding requests to
259 $integer (default: 10), that means if you request more than
260 this many requests, then the additional requests will be queued
261 until some other requests have been resolved.
262 reuse => $seconds
264 The number of seconds (default: 300) that a query id cannot be
265 re-used after a timeout. If there was no time-out then query
266 ids can be reused immediately.
267 untaint => $boolean
269 When true, then the resolver will automatically untaint
270 results, and might also ignore certain environment variables.
271 $resolver->parse_resolv_conf ($string)
273 Parses the given string as if it were a resolv.conf file. The
274 following directives are supported (but not necessarily
275 implemented).
276 "#"- and ";"-style comments, "nameserver", "domain", "search",
278 "sortlist", "options" ("timeout", "attempts", "ndots").
279 Everything else is silently ignored.
281 $resolver->os_config
283 Tries so load and parse /etc/resolv.conf on portable operating
284 systems. Tries various egregious hacks on windows to force the DNS
285 servers and searchlist out of the system.
286 This method must be called at most once before trying to resolve
288 anything.
289 $resolver->timeout ($timeout, ...)
291 Sets the timeout values. See the "timeout" constructor argument
292 (and note that this method expects the timeout values themselves,
293 not an array-reference).
294 $resolver->max_outstanding ($nrequests)
296 Sets the maximum number of outstanding requests to $nrequests. See
297 the "max_outstanding" constructor argument.
298 $resolver->request ($req, $cb->($res))
300 This is the main low-level workhorse for sending DNS requests.
301 This function sends a single request (a hash-ref formated as
303 specified for "dns_pack") to the configured nameservers in turn
304 until it gets a response. It handles timeouts, retries and
305 automatically falls back to virtual circuit mode (TCP) when it
306 receives a truncated reply. It does not handle anything else, such
307 as the domain searchlist or relative names - use "->resolve" for
308 that.
309 Calls the callback with the decoded response packet if a reply was
311 received, or no arguments in case none of the servers answered.
312 $resolver->resolve ($qname, $qtype, %options, $cb->(@rr))
314 Queries the DNS for the given domain name $qname of type $qtype.
315 A $qtype is either a numerical query type (e.g. 1 for A records) or
317 a lowercase name (you have to look at the source to see which
318 aliases are supported, but all types from RFC 1035, "aaaa", "srv",
319 "spf" and a few more are known to this module). A $qtype of "*" is
320 supported and means "any" record type.
321 The callback will be invoked with a list of matching result records
323 or none on any error or if the name could not be found.
324 CNAME chains (although illegal) are followed up to a length of 10.
326 The callback will be invoked with arraryefs of the form "[$name,
328 $type, $class, $ttl, @data"], where $name is the domain name, $type
329 a type string or number, $class a class name, $ttl is the remaining
330 time-to-live and @data is resource-record-dependent data, in
331 seconds. For "a" records, this will be the textual IPv4 addresses,
332 for "ns" or "cname" records this will be a domain name, for "txt"
333 records these are all the strings and so on.
334 All types mentioned in RFC 1035, "aaaa", "srv", "naptr" and "spf"
336 are decoded. All resource records not known to this module will
337 have the raw "rdata" field as fifth array element.
338 Note that this resolver is just a stub resolver: it requires a name
340 server supporting recursive queries, will not do any recursive
341 queries itself and is not secure when used against an untrusted
342 name server.
343 The following options are supported:
345 search => [$suffix...]
347 Use the given search list (which might be empty), by appending
348 each one in turn to the $qname. If this option is missing then
349 the configured "ndots" and "search" values define its value
350 (depending on "ndots", the empty suffix will be prepended or
351 appended to that "search" value). If the $qname ends in a dot,
352 then the searchlist will be ignored.
353 accept => [$type...]
355 Lists the acceptable result types: only result types in this
356 set will be accepted and returned. The default includes the
357 $qtype and nothing else. If this list includes "cname", then
358 CNAME-chains will not be followed (because you asked for the
359 CNAME record).
360 class => "class"
362 Specify the query class ("in" for internet, "ch" for chaosnet
363 and "hs" for hesiod are the only ones making sense). The
364 default is "in", of course.
365 Examples:
367 # full example, you can paste this into perl:
369 use Data::Dumper;
370 use AnyEvent::DNS;
371 AnyEvent::DNS::resolver->resolve (
372 "google.com", "*", my $cv = AnyEvent->condvar);
373 warn Dumper [$cv->recv];
374 # shortened result:
376 # [
377 # [ 'google.com', 'soa', 'in', 3600, 'ns1.google.com', 'dns-admin.google.com',
378 # 2008052701, 7200, 1800, 1209600, 300 ],
379 # [
380 # 'google.com', 'txt', 'in', 3600,
381 # 'v=spf1 include:_netblocks.google.com ~all'
382 # ],
383 # [ 'google.com', 'a', 'in', 3600, '64.233.187.99' ],
384 # [ 'google.com', 'mx', 'in', 3600, 10, 'smtp2.google.com' ],
385 # [ 'google.com', 'ns', 'in', 3600, 'ns2.google.com' ],
386 # ]
387 # resolve a records:
389 $res->resolve ("ruth.plan9.de", "a", sub { warn Dumper [@_] });
390 # result:
392 # [
393 # [ 'ruth.schmorp.de', 'a', 'in', 86400, '129.13.162.95' ]
394 # ]
395 # resolve any records, but return only a and aaaa records:
397 $res->resolve ("test1.laendle", "*",
398 accept => ["a", "aaaa"],
399 sub {
400 warn Dumper [@_];
401 }
402 );
403 # result:
405 # [
406 # [ 'test1.laendle', 'a', 'in', 86400, '10.0.0.255' ],
407 # [ 'test1.laendle', 'aaaa', 'in', 60, '3ffe:1900:4545:0002:0240:0000:0000:f7e1' ]
408 # ]
409 $resolver->wait_for_slot ($cb->($resolver))
411 Wait until a free request slot is available and call the callback
412 with the resolver object.
413 A request slot is used each time a request is actually sent to the
415 nameservers: There are never more than "max_outstanding" of them.
416 Although you can submit more requests (they will simply be queued
418 until a request slot becomes available), sometimes, usually for
419 rate-limiting purposes, it is useful to instead wait for a slot
420 before generating the request (or simply to know when the request
421 load is low enough so one can submit requests again).
422 This is what this method does: The callback will be called when
424 submitting a DNS request will not result in that request being
425 queued. The callback may or may not generate any requests in
426 response.
427 Note that the callback will only be invoked when the request queue
429 is empty, so this does not play well if somebody else keeps the
430 request queue full at all times.
431
433 Marc Lehmann <schmorp@schmorp.de>
434 http://anyevent.schmorp.de
435perl v5.28.0 2017-06-10 AnyEvent::DNS(3)