6.4 KiB
DNS
Stability: 3 - Stable
Use require('dns') to access this module. All methods in the dns module
use C-Ares except for dns.lookup which uses getaddrinfo(3) in a thread
pool. C-Ares is much faster than getaddrinfo but the system resolver is
more consistent with how other programs operate. When a user does
net.connect(80, 'google.com') or http.get({ host: 'google.com' }) the
dns.lookup method is used. Users who need to do a large number of lookups
quickly should use the methods that go through C-Ares.
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, hostnames) {
if (err) {
throw err;
}
console.log('reverse for ' + a + ': ' + JSON.stringify(hostnames));
});
});
});
dns.lookup(hostname, [family], callback)
Resolves a hostname (e.g. 'google.com') into the first found A (IPv4) or
AAAA (IPv6) record.
The family can be the integer 4 or 6. Defaults to null that indicates
both Ip v4 and v6 address family.
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
necessarily the value initially passed to lookup).
On error, err is an Error object, where err.code is the error code.
Keep in mind that err.code will be set to 'ENOENT' not only when
the hostname does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dns.resolve(hostname, [rrtype], callback)
Resolves a hostname (e.g. 'google.com') into an array of the record types
specified by rrtype.
Valid rrtypes are:
'A'(IPV4 addresses, default)'AAAA'(IPV6 addresses)'MX'(mail exchange records)'TXT'(text records)'SRV'(SRV records)'PTR'(used for reverse IP lookups)'NS'(name server records)'CNAME'(canonical name records)'SOA'(start of authority record)
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 is an Error object, where err.code is
one of the error codes listed below.
dns.resolve4(hostname, 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(hostname, callback)
The same as dns.resolve4() except for IPv6 queries (an AAAA query).
dns.resolveMx(hostname, 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(hostname, callback)
The same as dns.resolve(), but only for text queries (TXT records).
addresses is an 2-d array of the text records available for hostname (e.g.,
[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]). Each sub-array contains TXT chunks of
one record. Depending on the use case, the could be either joined together or
treated separately.
dns.resolveSrv(hostname, callback)
The same as dns.resolve(), but only for service records (SRV records).
addresses is an array of the SRV records available for hostname. Properties
of SRV records are priority, weight, port, and name (e.g.,
[{'priority': 10, {'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]).
dns.resolveSoa(hostname, callback)
The same as dns.resolve(), but only for start of authority record queries
(SOA record).
addresses is an object with the following structure:
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dns.resolveNs(hostname, callback)
The same as dns.resolve(), but only for name server records (NS records).
addresses is an array of the name server records available for hostname
(e.g., ['ns1.example.com', 'ns2.example.com']).
dns.resolveCname(hostname, callback)
The same as dns.resolve(), but only for canonical name records (CNAME
records). addresses is an array of the canonical name records available for
hostname (e.g., ['bar.example.com']).
dns.reverse(ip, callback)
Reverse resolves an ip address to an array of hostnames.
The callback has arguments (err, hostnames).
On error, err is an Error object, where err.code is
one of the error codes listed below.
dns.getServers()
Returns an array of IP addresses as strings that are currently being used for resolution
dns.setServers(servers)
Given an array of IP addresses as strings, set them as the servers to use for resolving
If you specify a port with the address it will be stripped, as the underlying library doesn't support that.
This will throw if you pass invalid input.
Error codes
Each DNS query can return one of the following error codes:
dns.NODATA: DNS server returned answer with no data.dns.FORMERR: DNS server claims query was misformatted.dns.SERVFAIL: DNS server returned general failure.dns.NOTFOUND: Domain name not found.dns.NOTIMP: DNS server does not implement requested operation.dns.REFUSED: DNS server refused query.dns.BADQUERY: Misformatted DNS query.dns.BADNAME: Misformatted hostname.dns.BADFAMILY: Unsupported address family.dns.BADRESP: Misformatted DNS reply.dns.CONNREFUSED: Could not contact DNS servers.dns.TIMEOUT: Timeout while contacting DNS servers.dns.EOF: End of file.dns.FILE: Error reading file.dns.NOMEM: Out of memory.dns.DESTRUCTION: Channel is being destroyed.dns.BADSTR: Misformatted string.dns.BADFLAGS: Illegal flags specified.dns.NONAME: Given hostname is not numeric.dns.BADHINTS: Illegal hints flags specified.dns.NOTINITIALIZED: c-ares library initialization not yet performed.dns.LOADIPHLPAPI: Error loading iphlpapi.dll.dns.ADDRGETNETWORKPARAMS: Could not find GetNetworkParams function.dns.CANCELLED: DNS query cancelled.