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node:module
API - Modules: Packages
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Node.js v21.0.0-nightly202308036ad8318373 documentation
- Node.js v21.0.0-nightly202308036ad8318373
-
►
Table of contents
- DNS
- Class:
dns.Resolver
dns.getServers()
dns.lookup(hostname[, options], callback)
dns.lookupService(address, port, callback)
dns.resolve(hostname[, rrtype], callback)
dns.resolve4(hostname[, options], callback)
dns.resolve6(hostname[, options], callback)
dns.resolveAny(hostname, callback)
dns.resolveCname(hostname, callback)
dns.resolveCaa(hostname, callback)
dns.resolveMx(hostname, callback)
dns.resolveNaptr(hostname, callback)
dns.resolveNs(hostname, callback)
dns.resolvePtr(hostname, callback)
dns.resolveSoa(hostname, callback)
dns.resolveSrv(hostname, callback)
dns.resolveTxt(hostname, callback)
dns.reverse(ip, callback)
dns.setDefaultResultOrder(order)
dns.getDefaultResultOrder()
dns.setServers(servers)
- DNS promises API
- Class:
dnsPromises.Resolver
resolver.cancel()
dnsPromises.getServers()
dnsPromises.lookup(hostname[, options])
dnsPromises.lookupService(address, port)
dnsPromises.resolve(hostname[, rrtype])
dnsPromises.resolve4(hostname[, options])
dnsPromises.resolve6(hostname[, options])
dnsPromises.resolveAny(hostname)
dnsPromises.resolveCaa(hostname)
dnsPromises.resolveCname(hostname)
dnsPromises.resolveMx(hostname)
dnsPromises.resolveNaptr(hostname)
dnsPromises.resolveNs(hostname)
dnsPromises.resolvePtr(hostname)
dnsPromises.resolveSoa(hostname)
dnsPromises.resolveSrv(hostname)
dnsPromises.resolveTxt(hostname)
dnsPromises.reverse(ip)
dnsPromises.setDefaultResultOrder(order)
dnsPromises.getDefaultResultOrder()
dnsPromises.setServers(servers)
- Class:
- Error codes
- Implementation considerations
- Class:
- DNS
-
►
Index
- Assertion testing
- Asynchronous context tracking
- Async hooks
- Buffer
- C++ addons
- C/C++ addons with Node-API
- C++ embedder API
- Child processes
- Cluster
- Command-line options
- Console
- Corepack
- Crypto
- Debugger
- Deprecated APIs
- Diagnostics Channel
- DNS
- Domain
- Errors
- Events
- File system
- Globals
- HTTP
- HTTP/2
- HTTPS
- Inspector
- Internationalization
- Modules: CommonJS modules
- Modules: ECMAScript modules
- Modules:
node:module
API - Modules: Packages
- Net
- OS
- Path
- Performance hooks
- Permissions
- Process
- Punycode
- Query strings
- Readline
- REPL
- Report
- Single executable applications
- Stream
- String decoder
- Test runner
- Timers
- TLS/SSL
- Trace events
- TTY
- UDP/datagram
- URL
- Utilities
- V8
- VM
- WASI
- Web Crypto API
- Web Streams API
- Worker threads
- Zlib
- ► Other versions
- ► Options
Table of contents
- DNS
- Class:
dns.Resolver
dns.getServers()
dns.lookup(hostname[, options], callback)
dns.lookupService(address, port, callback)
dns.resolve(hostname[, rrtype], callback)
dns.resolve4(hostname[, options], callback)
dns.resolve6(hostname[, options], callback)
dns.resolveAny(hostname, callback)
dns.resolveCname(hostname, callback)
dns.resolveCaa(hostname, callback)
dns.resolveMx(hostname, callback)
dns.resolveNaptr(hostname, callback)
dns.resolveNs(hostname, callback)
dns.resolvePtr(hostname, callback)
dns.resolveSoa(hostname, callback)
dns.resolveSrv(hostname, callback)
dns.resolveTxt(hostname, callback)
dns.reverse(ip, callback)
dns.setDefaultResultOrder(order)
dns.getDefaultResultOrder()
dns.setServers(servers)
- DNS promises API
- Class:
dnsPromises.Resolver
resolver.cancel()
dnsPromises.getServers()
dnsPromises.lookup(hostname[, options])
dnsPromises.lookupService(address, port)
dnsPromises.resolve(hostname[, rrtype])
dnsPromises.resolve4(hostname[, options])
dnsPromises.resolve6(hostname[, options])
dnsPromises.resolveAny(hostname)
dnsPromises.resolveCaa(hostname)
dnsPromises.resolveCname(hostname)
dnsPromises.resolveMx(hostname)
dnsPromises.resolveNaptr(hostname)
dnsPromises.resolveNs(hostname)
dnsPromises.resolvePtr(hostname)
dnsPromises.resolveSoa(hostname)
dnsPromises.resolveSrv(hostname)
dnsPromises.resolveTxt(hostname)
dnsPromises.reverse(ip)
dnsPromises.setDefaultResultOrder(order)
dnsPromises.getDefaultResultOrder()
dnsPromises.setServers(servers)
- Class:
- Error codes
- Implementation considerations
- Class:
DNS#
Source Code: lib/dns.js
The node:dns
module enables name resolution. For example, use it to look up IP
addresses of host names.
Although named for the Domain Name System (DNS), it does not always use the
DNS protocol for lookups. dns.lookup()
uses the operating system
facilities to perform name resolution. It may not need to perform any network
communication. To perform name resolution the way other applications on the same
system do, use dns.lookup()
.
const dns = require('node:dns');
dns.lookup('example.org', (err, address, family) => {
console.log('address: %j family: IPv%s', address, family);
});
// address: "93.184.216.34" family: IPv4
All other functions in the node:dns
module connect to an actual DNS server to
perform name resolution. They will always use the network to perform DNS
queries. These functions do not use the same set of configuration files used by
dns.lookup()
(e.g. /etc/hosts
). Use these functions to always perform
DNS queries, bypassing other name-resolution facilities.
const dns = require('node:dns');
dns.resolve4('archive.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
See the Implementation considerations section for more information.
Class: dns.Resolver
#
An independent resolver for DNS requests.
Creating a new resolver uses the default server settings. Setting
the servers used for a resolver using
resolver.setServers()
does not affect
other resolvers:
const { Resolver } = require('node:dns');
const resolver = new Resolver();
resolver.setServers(['4.4.4.4']);
// This request will use the server at 4.4.4.4, independent of global settings.
resolver.resolve4('example.org', (err, addresses) => {
// ...
});
The following methods from the node:dns
module are available:
resolver.getServers()
resolver.resolve()
resolver.resolve4()
resolver.resolve6()
resolver.resolveAny()
resolver.resolveCaa()
resolver.resolveCname()
resolver.resolveMx()
resolver.resolveNaptr()
resolver.resolveNs()
resolver.resolvePtr()
resolver.resolveSoa()
resolver.resolveSrv()
resolver.resolveTxt()
resolver.reverse()
resolver.setServers()
Resolver([options])
#
Create a new resolver.
options
<Object>
resolver.cancel()
#
Cancel all outstanding DNS queries made by this resolver. The corresponding
callbacks will be called with an error with code ECANCELLED
.
resolver.setLocalAddress([ipv4][, ipv6])
#
ipv4
<string> A string representation of an IPv4 address. Default:'0.0.0.0'
ipv6
<string> A string representation of an IPv6 address. Default:'::0'
The resolver instance will send its requests from the specified IP address. This allows programs to specify outbound interfaces when used on multi-homed systems.
If a v4 or v6 address is not specified, it is set to the default and the operating system will choose a local address automatically.
The resolver will use the v4 local address when making requests to IPv4 DNS
servers, and the v6 local address when making requests to IPv6 DNS servers.
The rrtype
of resolution requests has no impact on the local address used.
dns.getServers()
#
- Returns: <string[]>
Returns an array of IP address strings, formatted according to RFC 5952, that are currently configured for DNS resolution. A string will include a port section if a custom port is used.
[
'4.4.4.4',
'2001:4860:4860::8888',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]
dns.lookup(hostname[, options], callback)
#
hostname
<string>options
<integer> | <Object>family
<integer> | <string> The record family. Must be4
,6
, or0
. For backward compatibility reasons,'IPv4'
and'IPv6'
are interpreted as4
and6
respectively. The value0
indicates that IPv4 and IPv6 addresses are both returned. Default:0
.hints
<number> One or more supportedgetaddrinfo
flags. Multiple flags may be passed by bitwiseOR
ing their values.all
<boolean> Whentrue
, the callback returns all resolved addresses in an array. Otherwise, returns a single address. Default:false
.verbatim
<boolean> Whentrue
, the callback receives IPv4 and IPv6 addresses in the order the DNS resolver returned them. Whenfalse
, IPv4 addresses are placed before IPv6 addresses. Default:true
(addresses are not reordered). Default value is configurable usingdns.setDefaultResultOrder()
or--dns-result-order
.
callback
<Function>
Resolves a host name (e.g. 'nodejs.org'
) into the first found A (IPv4) or
AAAA (IPv6) record. All option
properties are optional. If options
is an
integer, then it must be 4
or 6
– if options
is 0
or not provided, then
IPv4 and IPv6 addresses are both returned if found.
With the all
option set to true
, the arguments for callback
change to
(err, addresses)
, with addresses
being an array of objects with the
properties address
and family
.
On error, err
is an Error
object, where err.code
is the error code.
Keep in mind that err.code
will be set to 'ENOTFOUND'
not only when
the host name does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dns.lookup()
does not necessarily have anything to do with the DNS protocol.
The implementation uses an operating system facility that can associate names
with addresses and vice versa. This implementation can have subtle but
important consequences on the behavior of any Node.js program. Please take some
time to consult the Implementation considerations section before using
dns.lookup()
.
Example usage:
const dns = require('node:dns');
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.com', options, (err, address, family) =>
console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.com', options, (err, addresses) =>
console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
If this method is invoked as its util.promisify()
ed version, and all
is not set to true
, it returns a Promise
for an Object
with address
and
family
properties.
Supported getaddrinfo flags#
The following flags can be passed as hints to dns.lookup()
.
dns.ADDRCONFIG
: Limits returned address types to the types of non-loopback addresses configured on the system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured.dns.V4MAPPED
: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. It is not supported on some operating systems (e.g. FreeBSD 10.1).dns.ALL
: Ifdns.V4MAPPED
is specified, return resolved IPv6 addresses as well as IPv4 mapped IPv6 addresses.
dns.lookupService(address, port, callback)
#
address
<string>port
<number>callback
<Function>
Resolves the given address
and port
into a host name and service using
the operating system's underlying getnameinfo
implementation.
If address
is not a valid IP address, a TypeError
will be thrown.
The port
will be coerced to a number. If it is not a legal port, a TypeError
will be thrown.
On an error, err
is an Error
object, where err.code
is the error code.
const dns = require('node:dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
If this method is invoked as its util.promisify()
ed version, it returns a
Promise
for an Object
with hostname
and service
properties.
dns.resolve(hostname[, rrtype], callback)
#
hostname
<string> Host name to resolve.rrtype
<string> Resource record type. Default:'A'
.callback
<Function>err
<Error>records
<string[]> | <Object[]> | <Object>
Uses the DNS protocol to resolve a host name (e.g. 'nodejs.org'
) into an array
of the resource records. The callback
function has arguments
(err, records)
. When successful, records
will be an array of resource
records. The type and structure of individual results varies based on rrtype
:
rrtype | records contains | Result type | Shorthand method |
---|---|---|---|
'A' | IPv4 addresses (default) | <string> | dns.resolve4() |
'AAAA' | IPv6 addresses | <string> | dns.resolve6() |
'ANY' | any records | <Object> | dns.resolveAny() |
'CAA' | CA authorization records | <Object> | dns.resolveCaa() |
'CNAME' | canonical name records | <string> | dns.resolveCname() |
'MX' | mail exchange records | <Object> | dns.resolveMx() |
'NAPTR' | name authority pointer records | <Object> | dns.resolveNaptr() |
'NS' | name server records | <string> | dns.resolveNs() |
'PTR' | pointer records | <string> | dns.resolvePtr() |
'SOA' | start of authority records | <Object> | dns.resolveSoa() |
'SRV' | service records | <Object> | dns.resolveSrv() |
'TXT' | text records | <string[]> | dns.resolveTxt() |
On error, err
is an Error
object, where err.code
is one of the
DNS error codes.
dns.resolve4(hostname[, options], callback)
#
hostname
<string> Host name to resolve.options
<Object>ttl
<boolean> Retrieves the Time-To-Live value (TTL) of each record. Whentrue
, the callback receives an array of{ address: '1.2.3.4', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
callback
<Function>err
<Error>addresses
<string[]> | <Object[]>
Uses the DNS protocol to resolve a IPv4 addresses (A
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv4 addresses (e.g.
['74.125.79.104', '74.125.79.105', '74.125.79.106']
).
dns.resolve6(hostname[, options], callback)
#
hostname
<string> Host name to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. Whentrue
, the callback receives an array of{ address: '0:1:2:3:4:5:6:7', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
callback
<Function>err
<Error>addresses
<string[]> | <Object[]>
Uses the DNS protocol to resolve IPv6 addresses (AAAA
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv6 addresses.
dns.resolveAny(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>ret
<Object[]>
Uses the DNS protocol to resolve all records (also known as ANY
or *
query).
The ret
argument passed to the callback
function will be an array containing
various types of records. Each object has a property type
that indicates the
type of the current record. And depending on the type
, additional properties
will be present on the object:
Type | Properties |
---|---|
'A' | address /ttl |
'AAAA' | address /ttl |
'CNAME' | value |
'MX' | Refer to dns.resolveMx() |
'NAPTR' | Refer to dns.resolveNaptr() |
'NS' | value |
'PTR' | value |
'SOA' | Refer to dns.resolveSoa() |
'SRV' | Refer to dns.resolveSrv() |
'TXT' | This type of record contains an array property called entries which refers to dns.resolveTxt() , e.g. { entries: ['...'], type: 'TXT' } |
Here is an example of the ret
object passed to the callback:
[ { type: 'A', address: '127.0.0.1', ttl: 299 },
{ type: 'CNAME', value: 'example.com' },
{ type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 },
{ type: 'NS', value: 'ns1.example.com' },
{ type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] },
{ type: 'SOA',
nsname: 'ns1.example.com',
hostmaster: 'admin.example.com',
serial: 156696742,
refresh: 900,
retry: 900,
expire: 1800,
minttl: 60 } ]
DNS server operators may choose not to respond to ANY
queries. It may be better to call individual methods like dns.resolve4()
,
dns.resolveMx()
, and so on. For more details, see RFC 8482.
dns.resolveCname(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve CNAME
records for the hostname
. The
addresses
argument passed to the callback
function
will contain an array of canonical name records available for the hostname
(e.g. ['bar.example.com']
).
dns.resolveCaa(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>records
<Object[]>
Uses the DNS protocol to resolve CAA
records for the hostname
. The
addresses
argument passed to the callback
function
will contain an array of certification authority authorization records
available for the hostname
(e.g. [{critical: 0, iodef: 'mailto:[email protected]'}, {critical: 128, issue: 'pki.example.com'}]
).
dns.resolveMx(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve mail exchange records (MX
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of objects containing both a priority
and exchange
property (e.g. [{priority: 10, exchange: 'mx.example.com'}, ...]
).
dns.resolveNaptr(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve regular expression-based records (NAPTR
records) for the hostname
. The addresses
argument passed to the callback
function will contain an array of objects with the following properties:
flags
service
regexp
replacement
order
preference
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
dns.resolveNs(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve name server records (NS
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of name server records available for hostname
(e.g. ['ns1.example.com', 'ns2.example.com']
).
dns.resolvePtr(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve pointer records (PTR
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of strings containing the reply records.
dns.resolveSoa(hostname, callback)
#
hostname
<string>callback
<Function>
Uses the DNS protocol to resolve a start of authority record (SOA
record) for
the hostname
. The address
argument passed to the callback
function will
be an object with the following properties:
nsname
hostmaster
serial
refresh
retry
expire
minttl
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dns.resolveSrv(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve service records (SRV
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of objects with the following properties:
priority
weight
port
name
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
dns.resolveTxt(hostname, callback)
#
hostname
<string>callback
<Function>err
<Error>records
<string[][]>
Uses the DNS protocol to resolve text queries (TXT
records) for the
hostname
. The records
argument passed to the callback
function is a
two-dimensional 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, these could be either joined together or
treated separately.
dns.reverse(ip, callback)
#
ip
<string>callback
<Function>err
<Error>hostnames
<string[]>
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names.
On error, err
is an Error
object, where err.code
is
one of the DNS error codes.
dns.setDefaultResultOrder(order)
#
order
<string> must be'ipv4first'
or'verbatim'
.
Set the default value of verbatim
in dns.lookup()
and
dnsPromises.lookup()
. The value could be:
ipv4first
: sets defaultverbatim
false
.verbatim
: sets defaultverbatim
true
.
The default is verbatim
and dns.setDefaultResultOrder()
have higher
priority than --dns-result-order
. When using worker threads,
dns.setDefaultResultOrder()
from the main thread won't affect the default
dns orders in workers.
dns.getDefaultResultOrder()
#
Get the default value for verbatim
in dns.lookup()
and
dnsPromises.lookup()
. The value could be:
ipv4first
: forverbatim
defaulting tofalse
.verbatim
: forverbatim
defaulting totrue
.
dns.setServers(servers)
#
servers
<string[]> array of RFC 5952 formatted addresses
Sets the IP address and port of servers to be used when performing DNS
resolution. The servers
argument is an array of RFC 5952 formatted
addresses. If the port is the IANA default DNS port (53) it can be omitted.
dns.setServers([
'4.4.4.4',
'[2001:4860:4860::8888]',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]);
An error will be thrown if an invalid address is provided.
The dns.setServers()
method must not be called while a DNS query is in
progress.
The dns.setServers()
method affects only dns.resolve()
,
dns.resolve*()
and dns.reverse()
(and specifically not
dns.lookup()
).
This method works much like
resolve.conf.
That is, if attempting to resolve with the first server provided results in a
NOTFOUND
error, the resolve()
method will not attempt to resolve with
subsequent servers provided. Fallback DNS servers will only be used if the
earlier ones time out or result in some other error.
DNS promises API#
The dns.promises
API provides an alternative set of asynchronous DNS methods
that return Promise
objects rather than using callbacks. The API is accessible
via require('node:dns').promises
or require('node:dns/promises')
.
Class: dnsPromises.Resolver
#
An independent resolver for DNS requests.
Creating a new resolver uses the default server settings. Setting
the servers used for a resolver using
resolver.setServers()
does not affect
other resolvers:
const { Resolver } = require('node:dns').promises;
const resolver = new Resolver();
resolver.setServers(['4.4.4.4']);
// This request will use the server at 4.4.4.4, independent of global settings.
resolver.resolve4('example.org').then((addresses) => {
// ...
});
// Alternatively, the same code can be written using async-await style.
(async function() {
const addresses = await resolver.resolve4('example.org');
})();
The following methods from the dnsPromises
API are available:
resolver.getServers()
resolver.resolve()
resolver.resolve4()
resolver.resolve6()
resolver.resolveAny()
resolver.resolveCaa()
resolver.resolveCname()
resolver.resolveMx()
resolver.resolveNaptr()
resolver.resolveNs()
resolver.resolvePtr()
resolver.resolveSoa()
resolver.resolveSrv()
resolver.resolveTxt()
resolver.reverse()
resolver.setServers()
resolver.cancel()
#
Cancel all outstanding DNS queries made by this resolver. The corresponding
promises will be rejected with an error with the code ECANCELLED
.
dnsPromises.getServers()
#
- Returns: <string[]>
Returns an array of IP address strings, formatted according to RFC 5952, that are currently configured for DNS resolution. A string will include a port section if a custom port is used.
[
'4.4.4.4',
'2001:4860:4860::8888',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]
dnsPromises.lookup(hostname[, options])
#
hostname
<string>options
<integer> | <Object>family
<integer> The record family. Must be4
,6
, or0
. The value0
indicates that IPv4 and IPv6 addresses are both returned. Default:0
.hints
<number> One or more supportedgetaddrinfo
flags. Multiple flags may be passed by bitwiseOR
ing their values.all
<boolean> Whentrue
, thePromise
is resolved with all addresses in an array. Otherwise, returns a single address. Default:false
.verbatim
<boolean> Whentrue
, thePromise
is resolved with IPv4 and IPv6 addresses in the order the DNS resolver returned them. Whenfalse
, IPv4 addresses are placed before IPv6 addresses. Default: currentlyfalse
(addresses are reordered) but this is expected to change in the not too distant future. Default value is configurable usingdns.setDefaultResultOrder()
or--dns-result-order
. New code should use{ verbatim: true }
.
Resolves a host name (e.g. 'nodejs.org'
) into the first found A (IPv4) or
AAAA (IPv6) record. All option
properties are optional. If options
is an
integer, then it must be 4
or 6
– if options
is not provided, then IPv4
and IPv6 addresses are both returned if found.
With the all
option set to true
, the Promise
is resolved with addresses
being an array of objects with the properties address
and family
.
On error, the Promise
is rejected with an Error
object, where err.code
is the error code.
Keep in mind that err.code
will be set to 'ENOTFOUND'
not only when
the host name does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dnsPromises.lookup()
does not necessarily have anything to do with the DNS
protocol. The implementation uses an operating system facility that can
associate names with addresses and vice versa. This implementation can have
subtle but important consequences on the behavior of any Node.js program. Please
take some time to consult the Implementation considerations section before
using dnsPromises.lookup()
.
Example usage:
const dns = require('node:dns');
const dnsPromises = dns.promises;
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dnsPromises.lookup('example.com', options).then((result) => {
console.log('address: %j family: IPv%s', result.address, result.family);
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
});
// When options.all is true, the result will be an Array.
options.all = true;
dnsPromises.lookup('example.com', options).then((result) => {
console.log('addresses: %j', result);
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
});
dnsPromises.lookupService(address, port)
#
Resolves the given address
and port
into a host name and service using
the operating system's underlying getnameinfo
implementation.
If address
is not a valid IP address, a TypeError
will be thrown.
The port
will be coerced to a number. If it is not a legal port, a TypeError
will be thrown.
On error, the Promise
is rejected with an Error
object, where err.code
is the error code.
const dnsPromises = require('node:dns').promises;
dnsPromises.lookupService('127.0.0.1', 22).then((result) => {
console.log(result.hostname, result.service);
// Prints: localhost ssh
});
dnsPromises.resolve(hostname[, rrtype])
#
Uses the DNS protocol to resolve a host name (e.g. 'nodejs.org'
) into an array
of the resource records. When successful, the Promise
is resolved with an
array of resource records. The type and structure of individual results vary
based on rrtype
:
rrtype | records contains | Result type | Shorthand method |
---|---|---|---|
'A' | IPv4 addresses (default) | <string> | dnsPromises.resolve4() |
'AAAA' | IPv6 addresses | <string> | dnsPromises.resolve6() |
'ANY' | any records | <Object> | dnsPromises.resolveAny() |
'CAA' | CA authorization records | <Object> | dnsPromises.resolveCaa() |
'CNAME' | canonical name records | <string> | dnsPromises.resolveCname() |
'MX' | mail exchange records | <Object> | dnsPromises.resolveMx() |
'NAPTR' | name authority pointer records | <Object> | dnsPromises.resolveNaptr() |
'NS' | name server records | <string> | dnsPromises.resolveNs() |
'PTR' | pointer records | <string> | dnsPromises.resolvePtr() |
'SOA' | start of authority records | <Object> | dnsPromises.resolveSoa() |
'SRV' | service records | <Object> | dnsPromises.resolveSrv() |
'TXT' | text records | <string[]> | dnsPromises.resolveTxt() |
On error, the Promise
is rejected with an Error
object, where err.code
is one of the DNS error codes.
dnsPromises.resolve4(hostname[, options])
#
hostname
<string> Host name to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. Whentrue
, thePromise
is resolved with an array of{ address: '1.2.3.4', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
Uses the DNS protocol to resolve IPv4 addresses (A
records) for the
hostname
. On success, the Promise
is resolved with an array of IPv4
addresses (e.g. ['74.125.79.104', '74.125.79.105', '74.125.79.106']
).
dnsPromises.resolve6(hostname[, options])
#
hostname
<string> Host name to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. Whentrue
, thePromise
is resolved with an array of{ address: '0:1:2:3:4:5:6:7', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
Uses the DNS protocol to resolve IPv6 addresses (AAAA
records) for the
hostname
. On success, the Promise
is resolved with an array of IPv6
addresses.
dnsPromises.resolveAny(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve all records (also known as ANY
or *
query).
On success, the Promise
is resolved with an array containing various types of
records. Each object has a property type
that indicates the type of the
current record. And depending on the type
, additional properties will be
present on the object:
Type | Properties |
---|---|
'A' | address /ttl |
'AAAA' | address /ttl |
'CNAME' | value |
'MX' | Refer to dnsPromises.resolveMx() |
'NAPTR' | Refer to dnsPromises.resolveNaptr() |
'NS' | value |
'PTR' | value |
'SOA' | Refer to dnsPromises.resolveSoa() |
'SRV' | Refer to dnsPromises.resolveSrv() |
'TXT' | This type of record contains an array property called entries which refers to dnsPromises.resolveTxt() , e.g. { entries: ['...'], type: 'TXT' } |
Here is an example of the result object:
[ { type: 'A', address: '127.0.0.1', ttl: 299 },
{ type: 'CNAME', value: 'example.com' },
{ type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 },
{ type: 'NS', value: 'ns1.example.com' },
{ type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] },
{ type: 'SOA',
nsname: 'ns1.example.com',
hostmaster: 'admin.example.com',
serial: 156696742,
refresh: 900,
retry: 900,
expire: 1800,
minttl: 60 } ]
dnsPromises.resolveCaa(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve CAA
records for the hostname
. On success,
the Promise
is resolved with an array of objects containing available
certification authority authorization records available for the hostname
(e.g. [{critical: 0, iodef: 'mailto:[email protected]'},{critical: 128, issue: 'pki.example.com'}]
).
dnsPromises.resolveCname(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve CNAME
records for the hostname
. On success,
the Promise
is resolved with an array of canonical name records available for
the hostname
(e.g. ['bar.example.com']
).
dnsPromises.resolveMx(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve mail exchange records (MX
records) for the
hostname
. On success, the Promise
is resolved with an array of objects
containing both a priority
and exchange
property (e.g.
[{priority: 10, exchange: 'mx.example.com'}, ...]
).
dnsPromises.resolveNaptr(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve regular expression-based records (NAPTR
records) for the hostname
. On success, the Promise
is resolved with an array
of objects with the following properties:
flags
service
regexp
replacement
order
preference
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
dnsPromises.resolveNs(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve name server records (NS
records) for the
hostname
. On success, the Promise
is resolved with an array of name server
records available for hostname
(e.g.
['ns1.example.com', 'ns2.example.com']
).
dnsPromises.resolvePtr(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve pointer records (PTR
records) for the
hostname
. On success, the Promise
is resolved with an array of strings
containing the reply records.
dnsPromises.resolveSoa(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve a start of authority record (SOA
record) for
the hostname
. On success, the Promise
is resolved with an object with the
following properties:
nsname
hostmaster
serial
refresh
retry
expire
minttl
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dnsPromises.resolveSrv(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve service records (SRV
records) for the
hostname
. On success, the Promise
is resolved with an array of objects with
the following properties:
priority
weight
port
name
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
dnsPromises.resolveTxt(hostname)
#
hostname
<string>
Uses the DNS protocol to resolve text queries (TXT
records) for the
hostname
. On success, the Promise
is resolved with a two-dimensional 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, these could be either joined together or
treated separately.
dnsPromises.reverse(ip)
#
ip
<string>
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of host names.
On error, the Promise
is rejected with an Error
object, where err.code
is one of the DNS error codes.
dnsPromises.setDefaultResultOrder(order)
#
order
<string> must be'ipv4first'
or'verbatim'
.
Set the default value of verbatim
in dns.lookup()
and
dnsPromises.lookup()
. The value could be:
ipv4first
: sets defaultverbatim
false
.verbatim
: sets defaultverbatim
true
.
The default is verbatim
and dnsPromises.setDefaultResultOrder()
have
higher priority than --dns-result-order
. When using worker threads,
dnsPromises.setDefaultResultOrder()
from the main thread won't affect the
default dns orders in workers.
dnsPromises.getDefaultResultOrder()
#
Get the value of dnsOrder
.
dnsPromises.setServers(servers)
#
servers
<string[]> array of RFC 5952 formatted addresses
Sets the IP address and port of servers to be used when performing DNS
resolution. The servers
argument is an array of RFC 5952 formatted
addresses. If the port is the IANA default DNS port (53) it can be omitted.
dnsPromises.setServers([
'4.4.4.4',
'[2001:4860:4860::8888]',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053',
]);
An error will be thrown if an invalid address is provided.
The dnsPromises.setServers()
method must not be called while a DNS query is in
progress.
This method works much like
resolve.conf.
That is, if attempting to resolve with the first server provided results in a
NOTFOUND
error, the resolve()
method will not attempt to resolve with
subsequent servers provided. Fallback DNS servers will only be used if the
earlier ones time out or result in some other error.
Error codes#
Each DNS query can return one of the following error codes:
dns.NODATA
: DNS server returned an 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 the requested operation.dns.REFUSED
: DNS server refused query.dns.BADQUERY
: Misformatted DNS query.dns.BADNAME
: Misformatted host name.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 host name is not numeric.dns.BADHINTS
: Illegal hints flags specified.dns.NOTINITIALIZED
: c-ares library initialization not yet performed.dns.LOADIPHLPAPI
: Error loadingiphlpapi.dll
.dns.ADDRGETNETWORKPARAMS
: Could not findGetNetworkParams
function.dns.CANCELLED
: DNS query cancelled.
The dnsPromises
API also exports the above error codes, e.g., dnsPromises.NODATA
.
Implementation considerations#
Although dns.lookup()
and the various dns.resolve*()/dns.reverse()
functions have the same goal of associating a network name with a network
address (or vice versa), their behavior is quite different. These differences
can have subtle but significant consequences on the behavior of Node.js
programs.
dns.lookup()
#
Under the hood, dns.lookup()
uses the same operating system facilities
as most other programs. For instance, dns.lookup()
will almost always
resolve a given name the same way as the ping
command. On most POSIX-like
operating systems, the behavior of the dns.lookup()
function can be
modified by changing settings in nsswitch.conf(5)
and/or resolv.conf(5)
,
but changing these files will change the behavior of all other
programs running on the same operating system.
Though the call to dns.lookup()
will be asynchronous from JavaScript's
perspective, it is implemented as a synchronous call to getaddrinfo(3)
that runs
on libuv's threadpool. This can have surprising negative performance
implications for some applications, see the UV_THREADPOOL_SIZE
documentation for more information.
Various networking APIs will call dns.lookup()
internally to resolve
host names. If that is an issue, consider resolving the host name to an address
using dns.resolve()
and using the address instead of a host name. Also, some
networking APIs (such as socket.connect()
and dgram.createSocket()
)
allow the default resolver, dns.lookup()
, to be replaced.
dns.resolve()
, dns.resolve*()
, and dns.reverse()
#
These functions are implemented quite differently than dns.lookup()
. They
do not use getaddrinfo(3)
and they always perform a DNS query on the
network. This network communication is always done asynchronously and does not
use libuv's threadpool.
As a result, these functions cannot have the same negative impact on other
processing that happens on libuv's threadpool that dns.lookup()
can have.
They do not use the same set of configuration files that dns.lookup()
uses. For instance, they do not use the configuration from /etc/hosts
.