{ "source": "doc/api/dns.markdown", "modules": [ { "textRaw": "DNS", "name": "dns", "stability": 3, "stabilityText": "Stable", "desc": "
Use require('dns')
to access this module.\n\n
This module contains functions that belong to two different categories:\n\n
\n1) Functions that use the underlying operating system facilities to perform\nname resolution, and that do not necessarily do any network communication.\nThis category contains only one function: dns.lookup
. Developers looking\nto perform name resolution in the same way that other applications on the same\noperating system behave should use dns.lookup
.\n\n
Here is an example that does a lookup of www.google.com
.\n\n
var dns = require('dns');\n\ndns.lookup('www.google.com', function onLookup(err, addresses, family) {\n console.log('addresses:', addresses);\n});
\n2) Functions that connect to an actual DNS server to perform name resolution,\nand that always use the network to perform DNS queries. This category\ncontains all functions in the dns
module but dns.lookup
. These functions\ndo not use the same set of configuration files than what dns.lookup
uses.\nFor instance, they do not use the configuration from /etc/hosts
. These\nfunctions should be used by developers who do not want to use the underlying\noperating system's facilities for name resolution, and instead want to\nalways perform DNS queries.\n\n
Here is an example which resolves 'www.google.com'
then reverse\nresolves the IP addresses which are returned.\n\n
var dns = require('dns');\n\ndns.resolve4('www.google.com', function (err, addresses) {\n if (err) throw err;\n\n console.log('addresses: ' + JSON.stringify(addresses));\n\n addresses.forEach(function (a) {\n dns.reverse(a, function (err, hostnames) {\n if (err) {\n throw err;\n }\n\n console.log('reverse for ' + a + ': ' + JSON.stringify(hostnames));\n });\n });\n});
\nThere are subtle consequences in choosing one or another, please consult the\nImplementation considerations section\nfor more information.\n\n
\n", "methods": [ { "textRaw": "dns.lookup(hostname[, options], callback)", "type": "method", "name": "lookup", "desc": "Resolves a hostname (e.g. 'google.com'
) into the first found A (IPv4) or\nAAAA (IPv6) record. options
can be an object or integer. If options
is\nnot provided, then IP v4 and v6 addresses are both valid. If options
is\nan integer, then it must be 4
or 6
.\n\n
Alternatively, options
can be an object containing two properties,\nfamily
and hints
. Both properties are optional. If family
is provided,\nit must be the integer 4
or 6
. If family
is not provided then IP v4\nand v6 addresses are accepted. The hints
field, if present, should be one\nor more of the supported getaddrinfo
flags. If hints
is not provided,\nthen no flags are passed to getaddrinfo
. Multiple flags can be passed\nthrough hints
by logically OR
ing their values. An example usage of\noptions
is shown below.\n\n
{\n family: 4,\n hints: dns.ADDRCONFIG | dns.V4MAPPED\n}
\nSee supported getaddrinfo
flags below for\nmore information on supported flags.\n\n
The callback has arguments (err, address, family)
. The address
argument\nis a string representation of an IP v4 or v6 address. The family
argument\nis either the integer 4 or 6 and denotes the family of address
(not\nnecessarily the value initially passed to lookup
).\n\n
On error, err
is an Error
object, where err.code
is the error code.\nKeep in mind that err.code
will be set to 'ENOENT'
not only when\nthe hostname does not exist but also when the lookup fails in other ways\nsuch as no available file descriptors.\n\n
dns.lookup
doesn't necessarily have anything to do with the DNS protocol.\nIt's only an operating system facility that can associate name with addresses,\nand vice versa.\n\n
Its implementation can have subtle but important consequences on the behavior\nof any Node.js program. Please take some time to consult the Implementation\nconsiderations section before using it.\n\n
\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] } ], "type": "module", "displayName": "DNS" } ], "methods": [ { "textRaw": "dns.lookupService(address, port, callback)", "type": "method", "name": "lookupService", "desc": "Resolves the given address and port into a hostname and service using\ngetnameinfo
.\n\n
The callback has arguments (err, hostname, service)
. The hostname
and\nservice
arguments are strings (e.g. 'localhost'
and 'http'
respectively).\n\n
On error, err
is an Error
object, where err.code
is the error code.\n\n\n
Resolves a hostname (e.g. 'google.com'
) into an array of the record types\nspecified by rrtype.\n\n
Valid rrtypes are:\n\n
\n'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\nin addresses
is determined by the record type, and described in the\ndocumentation for the corresponding lookup methods below.\n\n
On error, err
is an Error
object, where err.code
is\none of the error codes listed below.\n\n\n
The same as dns.resolve()
, but only for IPv4 queries (A
records).\naddresses
is an array of IPv4 addresses (e.g.\n['74.125.79.104', '74.125.79.105', '74.125.79.106']
).\n\n
The same as dns.resolve4()
except for IPv6 queries (an AAAA
query).\n\n\n
The same as dns.resolve()
, but only for mail exchange queries (MX
records).\n\n
addresses
is an array of MX records, each with a priority and an exchange\nattribute (e.g. [{'priority': 10, 'exchange': 'mx.example.com'},...]
).\n\n
The same as dns.resolve()
, but only for text queries (TXT
records).\naddresses
is a 2-d array of the text records available for hostname
(e.g.,\n[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]
). Each sub-array contains TXT chunks of\none record. Depending on the use case, the could be either joined together or\ntreated separately.\n\n
The same as dns.resolve()
, but only for service records (SRV
records).\naddresses
is an array of the SRV records available for hostname
. Properties\nof SRV records are priority, weight, port, and name (e.g.,\n[{'priority': 10, 'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]
).\n\n
The same as dns.resolve()
, but only for start of authority record queries\n(SOA
record).\n\n
addresses
is an object with the following structure:\n\n
{\n nsname: 'ns.example.com',\n hostmaster: 'root.example.com',\n serial: 2013101809,\n refresh: 10000,\n retry: 2400,\n expire: 604800,\n minttl: 3600\n}
\n",
"signatures": [
{
"params": [
{
"name": "hostname"
},
{
"name": "callback"
}
]
}
]
},
{
"textRaw": "dns.resolveNs(hostname, callback)",
"type": "method",
"name": "resolveNs",
"desc": "The same as dns.resolve()
, but only for name server records (NS
records).\naddresses
is an array of the name server records available for hostname
\n(e.g., ['ns1.example.com', 'ns2.example.com']
).\n\n
The same as dns.resolve()
, but only for canonical name records (CNAME
\nrecords). addresses
is an array of the canonical name records available for\nhostname
(e.g., ['bar.example.com']
).\n\n
Reverse resolves an ip address to an array of hostnames.\n\n
\nThe callback has arguments (err, hostnames)
.\n\n
On error, err
is an Error
object, where err.code
is\none of the error codes listed below.\n\n
Returns an array of IP addresses as strings that are currently being used for\nresolution\n\n
\n", "signatures": [ { "params": [] } ] }, { "textRaw": "dns.setServers(servers)", "type": "method", "name": "setServers", "desc": "Given an array of IP addresses as strings, set them as the servers to use for\nresolving\n\n
\nIf you specify a port with the address it will be stripped, as the underlying\nlibrary doesn't support that.\n\n
\nThis will throw if you pass invalid input.\n\n
\n", "signatures": [ { "params": [ { "name": "servers" } ] } ] } ], "modules": [ { "textRaw": "Error codes", "name": "error_codes", "desc": "Each DNS query can return one of the following error codes:\n\n
\ndns.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.The following flags can be passed as hints to dns.lookup
.\n\n
dns.ADDRCONFIG
: Returned address types are determined by the types\nof addresses supported by the current system. For example, IPv4 addresses\nare only returned if the current system has at least one IPv4 address\nconfigured. Loopback addresses are not considered.dns.V4MAPPED
: If the IPv6 family was specified, but no IPv6 addresses were\nfound, then return IPv4 mapped IPv6 addresses. Note that it is not supported\non some operating systems (e.g FreeBSD 10.1).Although dns.lookup
and dns.resolve*/dns.reverse
functions have the same\ngoal of associating a network name with a network address (or vice versa),\ntheir behavior is quite different. These differences can have subtle but\nsignificant consequences on the behavior of Node.js programs.\n\n
Under the hood, dns.lookup
uses the same operating system facilities as most\nother programs. For instance, dns.lookup
will almost always resolve a given\nname the same way as the ping
command. On most POSIX-like operating systems,\nthe behavior of the dns.lookup
function can be tweaked by changing settings\nin nsswitch.conf(5)
and/or resolv.conf(5)
, but be careful that changing\nthese files will change the behavior of all other programs running on the same\noperating system.\n\n
Though the call will be asynchronous from JavaScript's perspective, it is\nimplemented as a synchronous call to getaddrinfo(3)
that runs on libuv's\nthreadpool. Because libuv's threadpool has a fixed size, it means that if for\nwhatever reason the call to getaddrinfo(3)
takes a long time, other\noperations that could run on libuv's threadpool (such as filesystem\noperations) will experience degraded performance. In order to mitigate this\nissue, one potential solution is to increase the size of libuv's threadpool by\nsetting the 'UV_THREADPOOL_SIZE' environment variable to a value greater than\n4 (its current default value). For more information on libuv's threadpool, see\nthe official libuv\ndocumentation.\n\n
These functions are implemented quite differently than dns.lookup
. They do\nnot use getaddrinfo(3)
and they always perform a DNS query on the network.\nThis network communication is always done asynchronously, and does not use\nlibuv's threadpool.\n\n
As a result, these functions cannot have the same negative impact on other\nprocessing that happens on libuv's threadpool that dns.lookup
can have.\n\n
They do not use the same set of configuration files than what dns.lookup
\nuses. For instance, they do not use the configuration from /etc/hosts
.\n