1NAME
2 `IO::Async::Resolver::DNS' - resolve DNS queries using `IO::Async'
3
4SYNOPSIS
5 use IO::Async::Loop;
6 use IO::Async::Resolver::DNS;
7
8 my $loop = IO::Async::Loop->new;
9 my $resolver = $loop->resolver;
10
11 $resolver->res_query(
12 dname => "cpan.org",
13 type => "MX",
14 )->then( sub {
15 my ( $pkt ) = @_;
16
17 foreach my $mx ( $pkt->answer ) {
18 next unless $mx->type eq "MX";
19
20 printf "preference=%d exchange=%s\n",
21 $mx->preference, $mx->exchange;
22 }
23 })->get;
24
25DESCRIPTION
26 This module extends the IO::Async::Resolver class with extra methods and
27 resolver functions to perform DNS-specific resolver lookups. It does not
28 directly provide any methods or functions of its own.
29
30 These functions are provided for performing DNS-specific lookups, to
31 obtain `MX' or `SRV' records, for example. For regular name resolution,
32 the usual `getaddrinfo' and `getnameinfo' methods on the standard
33 `IO::Async::Resolver' should be used.
34
35 If Net::LibResolv is installed then it will be used for actually sending
36 and receiving DNS packets, in preference to a internally-constructed
37 Net::DNS::Resolver object. `Net::LibResolv' will be more efficient and
38 shares its implementation with the standard resolver used by the rest of
39 the system. `Net::DNS::Resolver' reimplements the logic itself, so it
40 may have differences in behaviour from that provided by libresolv. The
41 ability to use the latter is provided to allow for an XS-free dependency
42 chain, or for other situations where `Net::LibResolv' is not available.
43
44 Record Extraction
45 If certain record type queries are made, extra information is returned
46 to the `on_resolved' continuation, containing the results from the DNS
47 packet in a more useful form. This information will be in a list of
48 extra values following the packet value.
49
50 my ( $pkt, @data ) = $f->get;
51
52 $on_resolved->( $pkt, @data )
53
54 The type of the elements in `@data' will depend on the DNS record query
55 type:
56
57 * A and AAAA
58 The `A' or `AAAA' records will be unpacked and returned in a list of
59 strings.
60
61 @data = ( "10.0.0.1",
62 "10.0.0.2" );
63
64 @data = ( "fd00:0:0:0:0:0:0:1" );
65
66 * PTR
67 The `PTR' records will be unpacked and returned in a list of domain
68 names.
69
70 @data = ( "foo.example.com" );
71
72 * MX
73 The `MX' records will be unpacked, in order of `preference', and
74 returned in a list of HASH references. Each HASH reference will
75 contain keys called `exchange' and `preference'. If the exchange
76 domain name is included in the DNS `additional' data, then the HASH
77 reference will also include a key called `address', its value
78 containing a list of `A' and `AAAA' record `address' fields.
79
80 @data = ( { exchange => "mail.example.com",
81 preference => 10,
82 address => [ "10.0.0.1", "fd00:0:0:0:0:0:0:1" ] } );
83
84 * SRV
85 The `SRV' records will be unpacked and sorted first by order of
86 priority, then by a weighted shuffle by weight, and returned in a
87 list of HASH references. Each HASH reference will contain keys
88 called `priority', `weight', `target' and `port'. If the target
89 domain name is included in the DNS `additional' data, then the HASH
90 reference will also contain a key called `address', its value
91 containing a list of `A' and `AAAA' record `address' fields.
92
93 @data = ( { priority => 10,
94 weight => 10,
95 target => "server1.service.example.com",
96 port => 1234,
97 address => [ "10.0.1.1" ] } );
98
99Error Reporting
100 The two possible back-end modules that implement the resolver query
101 functions provided here differ in their semantics for error reporting.
102 To account for this difference and to lead to more portable user code,
103 errors reported by the back-end modules are translated to one of the
104 following (exported) constants.
105
106 ERR_NO_HOST # The specified host name does not exist
107 ERR_NO_ADDRESS # The specified host name does not provide answers for the
108 given query type
109 ERR_TEMPORARY # A temporary failure that may disappear on retry
110 ERR_UNRECOVERABLE # Any other error
111
112RESOLVER METHODS
113 The following methods documented with a trailing call to `->get' return
114 Future instances.
115
116 res_query
117 ( $pkt, @data ) = $resolver->res_query( %params )->get
118
119 Performs a resolver query on the name, class and type, and invokes a
120 continuation when a result is obtained.
121
122 Takes the following named parameters:
123
124 dname => STRING
125 Domain name to look up
126
127 type => STRING
128 Name of the record type to look up (e.g. `MX')
129
130 class => STRING
131 Name of the record class to look up. Defaults to `IN' so
132 normally this argument is not required.
133
134 On failure on `IO::Async' versions that support extended failure results
135 (0.68 and later), the extra detail will be an error value matching one
136 of the `ERR_*' constants listed above.
137
138 ->fail( $message, resolve => res_query => $errnum )
139
140 Note that due to the two possible back-end implementations it is not
141 guaranteed that messages have any particular format; they are intended
142 for human consumption only, and the `$errnum' value should be used for
143 making decisions in other code.
144
145 When not returning a `Future', the following extra arguments are used as
146 callbacks instead:
147
148 on_resolved => CODE
149 Continuation which is invoked after a successful lookup. Will be
150 passed a Net::DNS::Packet object containing the result.
151
152 $on_resolved->( $pkt )
153
154 For certain query types, this continuation may also be passed
155 extra data in a list after the `$pkt'
156
157 $on_resolved->( $pkt, @data )
158
159 See the Record Extraction section above for more detail.
160
161 on_error => CODE
162 Continuation which is invoked after a failed lookup.
163
164 res_search
165 Performs a resolver query on the name, class and type, and invokes a
166 continuation when a result is obtained. Identical to `res_query' except
167 that it additionally implements the default domain name search
168 behaviour.
169
170AUTHOR
171 Paul Evans <leonerd@leonerd.org.uk>
172
173