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## DNS
Use `require('dns')` to access this module.
Here is an example which resolves `'www.google.com'` then reverse
resolves the IP addresses which are returned.
var dns = require('dns');
dns.resolve4('www.google.com', function (err, addresses) {
if (err) throw err;
console.log('addresses: ' + JSON.stringify(addresses));
addresses.forEach(function (a) {
dns.reverse(a, function (err, domains) {
if (err) {
console.log('reverse for ' + a + ' failed: ' +
err.message);
} else {
console.log('reverse for ' + a + ': ' +
JSON.stringify(domains));
}
});
});
});
### dns.lookup(domain, family=null, callback)
Resolves a domain (e.g. `'google.com'`) into the first found A (IPv4) or
AAAA (IPv6) record.
The callback has arguments `(err, address, family)`. The `address` argument
is a string representation of a IP v4 or v6 address. The `family` argument
is either the integer 4 or 6 and denotes the family of `address` (not
neccessarily the value initially passed to `lookup`).
### dns.resolve(domain, rrtype='A', callback)
Resolves a domain (e.g. `'google.com'`) into an array of the record types
specified by rrtype. Valid rrtypes are `A` (IPV4 addresses), `AAAA` (IPV6
addresses), `MX` (mail exchange records), `TXT` (text records), `SRV` (SRV
records), and `PTR` (used for reverse IP lookups).
The callback has arguments `(err, addresses)`. The type of each item
in `addresses` is determined by the record type, and described in the
documentation for the corresponding lookup methods below.
On error, `err` would be an instanceof `Error` object, where `err.errno` is
one of the error codes listed below and `err.message` is a string describing
the error in English.
### dns.resolve4(domain, callback)
The same as `dns.resolve()`, but only for IPv4 queries (`A` records).
`addresses` is an array of IPv4 addresses (e.g.
`['74.125.79.104', '74.125.79.105', '74.125.79.106']`).
### dns.resolve6(domain, callback)
The same as `dns.resolve4()` except for IPv6 queries (an `AAAA` query).
### dns.resolveMx(domain, callback)
The same as `dns.resolve()`, but only for mail exchange queries (`MX` records).
`addresses` is an array of MX records, each with a priority and an exchange
attribute (e.g. `[{'priority': 10, 'exchange': 'mx.example.com'},...]`).
### dns.resolveTxt(domain, callback)
The same as `dns.resolve()`, but only for text queries (`TXT` records).
`addresses` is an array of the text records available for `domain` (e.g.,
`['v=spf1 ip4:0.0.0.0 ~all']`).
### dns.resolveSrv(domain, callback)
The same as `dns.resolve()`, but only for service records (`SRV` records).
`addresses` is an array of the SRV records available for `domain`. Properties
of SRV records are priority, weight, port, and name (e.g.,
`[{'priority': 10, {'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]`).
### dns.reverse(ip, callback)
Reverse resolves an ip address to an array of domain names.
The callback has arguments `(err, domains)`.
If there an an error, `err` will be non-null and an instanceof the Error
object.
Each DNS query can return an error code.
- `dns.TEMPFAIL`: timeout, SERVFAIL or similar.
- `dns.PROTOCOL`: got garbled reply.
- `dns.NXDOMAIN`: domain does not exists.
- `dns.NODATA`: domain exists but no data of reqd type.
- `dns.NOMEM`: out of memory while processing.
- `dns.BADQUERY`: the query is malformed.