{
  "source": "doc/api/dns.markdown",
  "modules": [
    {
      "textRaw": "DNS",
      "name": "dns",
      "stability": 2,
      "stabilityText": "Stable",
      "desc": "<p>Use <code>require(&#39;dns&#39;)</code> to access this module.\n\n</p>\n<p>This module contains functions that belong to two different categories:\n\n</p>\n<p>1) 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: <code>dns.lookup()</code>. <strong>Developers looking\nto perform name resolution in the same way that other applications on the same\noperating system behave should use [<code>dns.lookup()</code>][dns.lookup].</strong>\n\n</p>\n<p>Here is an example that does a lookup of <code>www.google.com</code>.\n\n</p>\n<pre><code>var dns = require(&#39;dns&#39;);\n\ndns.lookup(&#39;www.google.com&#39;, function onLookup(err, addresses, family) {\n  console.log(&#39;addresses:&#39;, addresses);\n});</code></pre>\n<p>2) Functions that connect to an actual DNS server to perform name resolution,\nand that <em>always</em> use the network to perform DNS queries. This category\ncontains all functions in the <code>dns</code> module but [<code>dns.lookup()</code>][dns.lookup]. These functions\ndo not use the same set of configuration files than what [<code>dns.lookup()</code>][dns.lookup] uses.\nFor instance, <em>they do not use the configuration from <code>/etc/hosts</code></em>. These\nfunctions should be used by developers who do not want to use the underlying\noperating system&#39;s facilities for name resolution, and instead want to\n<em>always</em> perform DNS queries.\n\n</p>\n<p>Here is an example which resolves <code>&#39;www.google.com&#39;</code> then reverse\nresolves the IP addresses which are returned.\n\n</p>\n<pre><code>var dns = require(&#39;dns&#39;);\n\ndns.resolve4(&#39;www.google.com&#39;, function (err, addresses) {\n  if (err) throw err;\n\n  console.log(&#39;addresses: &#39; + 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(&#39;reverse for &#39; + a + &#39;: &#39; + JSON.stringify(hostnames));\n    });\n  });\n});</code></pre>\n<p>There are subtle consequences in choosing one or another, please consult the\n<a href=\"#dns_implementation_considerations\">Implementation considerations section</a>\nfor more information.\n\n</p>\n",
      "methods": [
        {
          "textRaw": "dns.lookup(hostname[, options], callback)",
          "type": "method",
          "name": "lookup",
          "desc": "<p>Resolves a hostname (e.g. <code>&#39;google.com&#39;</code>) into the first found A (IPv4) or\nAAAA (IPv6) record. <code>options</code> can be an object or integer. If <code>options</code> is\nnot provided, then IP v4 and v6 addresses are both valid. If <code>options</code> is\nan integer, then it must be <code>4</code> or <code>6</code>.\n\n</p>\n<p>Alternatively, <code>options</code> can be an object containing these properties:\n\n</p>\n<ul>\n<li><code>family</code> {Number} - The record family. If present, must be the integer\n<code>4</code> or <code>6</code>. If not provided, both IP v4 and v6 addresses are accepted.</li>\n<li><code>hints</code>: {Number} - If present, it should be one or more of the supported\n<code>getaddrinfo</code> flags. If <code>hints</code> is not provided, then no flags are passed to\n<code>getaddrinfo</code>. Multiple flags can be passed through <code>hints</code> by logically\n<code>OR</code>ing their values.\nSee <a href=\"#dns_supported_getaddrinfo_flags\">supported <code>getaddrinfo</code> flags</a> below\nfor more information on supported flags.</li>\n<li><code>all</code>: {Boolean} - When <code>true</code>, the callback returns all resolved addresses\nin an array, otherwise returns a single address. Defaults to <code>false</code>.</li>\n</ul>\n<p>All properties are optional. An example usage of options is shown below.\n\n</p>\n<pre><code>{\n  family: 4,\n  hints: dns.ADDRCONFIG | dns.V4MAPPED,\n  all: false\n}</code></pre>\n<p>The callback has arguments <code>(err, address, family)</code>. <code>address</code> is a string\nrepresentation of an IP v4 or v6 address. <code>family</code> is either the integer 4 or 6\nand denotes the family of <code>address</code> (not necessarily the value initially passed\nto <code>lookup</code>).\n\n</p>\n<p>With the <code>all</code> option set, the arguments change to <code>(err, addresses)</code>, with\n<code>addresses</code> being an array of objects with the properties <code>address</code> and\n<code>family</code>.\n\n</p>\n<p>On error, <code>err</code> is an <code>Error</code> object, where <code>err.code</code> is the error code.\nKeep in mind that <code>err.code</code> will be set to <code>&#39;ENOENT&#39;</code> 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</p>\n<p><code>dns.lookup()</code> doesn&#39;t necessarily have anything to do with the DNS protocol.\nIt&#39;s only an operating system facility that can associate name with addresses,\nand vice versa.\n\n</p>\n<p>Its implementation can have subtle but important consequences on the behavior\nof any Node.js program. Please take some time to consult the <a href=\"#dns_implementation_considerations\">Implementation\nconsiderations section</a> before using it.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "options",
                  "optional": true
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.lookupService(address, port, callback)",
          "type": "method",
          "name": "lookupService",
          "desc": "<p>Resolves the given address and port into a hostname and service using\n<code>getnameinfo</code>.\n\n</p>\n<p>The callback has arguments <code>(err, hostname, service)</code>. The <code>hostname</code> and\n<code>service</code> arguments are strings (e.g. <code>&#39;localhost&#39;</code> and <code>&#39;http&#39;</code> respectively).\n\n</p>\n<p>On error, <code>err</code> is an <code>Error</code> object, where <code>err.code</code> is the error code.\n\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "address"
                },
                {
                  "name": "port"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolve(hostname[, rrtype], callback)",
          "type": "method",
          "name": "resolve",
          "desc": "<p>Resolves a hostname (e.g. <code>&#39;google.com&#39;</code>) into an array of the record types\nspecified by rrtype.\n\n</p>\n<p>Valid rrtypes are:\n\n</p>\n<ul>\n<li><code>&#39;A&#39;</code> (IPV4 addresses, default)</li>\n<li><code>&#39;AAAA&#39;</code> (IPV6 addresses)</li>\n<li><code>&#39;MX&#39;</code> (mail exchange records)</li>\n<li><code>&#39;TXT&#39;</code> (text records)</li>\n<li><code>&#39;SRV&#39;</code> (SRV records)</li>\n<li><code>&#39;PTR&#39;</code> (used for reverse IP lookups)</li>\n<li><code>&#39;NS&#39;</code> (name server records)</li>\n<li><code>&#39;CNAME&#39;</code> (canonical name records)</li>\n<li><code>&#39;SOA&#39;</code> (start of authority record)</li>\n</ul>\n<p>The callback has arguments <code>(err, addresses)</code>.  The type of each item\nin <code>addresses</code> is determined by the record type, and described in the\ndocumentation for the corresponding lookup methods below.\n\n</p>\n<p>On error, <code>err</code> is an <code>Error</code> object, where <code>err.code</code> is\none of the error codes listed below.\n\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "rrtype",
                  "optional": true
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolve4(hostname, callback)",
          "type": "method",
          "name": "resolve4",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for IPv4 queries (<code>A</code> records).\n<code>addresses</code> is an array of IPv4 addresses (e.g.\n<code>[&#39;74.125.79.104&#39;, &#39;74.125.79.105&#39;, &#39;74.125.79.106&#39;]</code>).\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolve6(hostname, callback)",
          "type": "method",
          "name": "resolve6",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve4_hostname_callback\"><code>dns.resolve4()</code></a> except for IPv6 queries (an <code>AAAA</code> query).\n\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveMx(hostname, callback)",
          "type": "method",
          "name": "resolveMx",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for mail exchange queries (<code>MX</code> records).\n\n</p>\n<p><code>addresses</code> is an array of MX records, each with a priority and an exchange\nattribute (e.g. <code>[{&#39;priority&#39;: 10, &#39;exchange&#39;: &#39;mx.example.com&#39;},...]</code>).\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveTxt(hostname, callback)",
          "type": "method",
          "name": "resolveTxt",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for text queries (<code>TXT</code> records).\n<code>addresses</code> is a 2-d array of the text records available for <code>hostname</code> (e.g.,\n<code>[ [&#39;v=spf1 ip4:0.0.0.0 &#39;, &#39;~all&#39; ] ]</code>). 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</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveSrv(hostname, callback)",
          "type": "method",
          "name": "resolveSrv",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for service records (<code>SRV</code> records).\n<code>addresses</code> is an array of the SRV records available for <code>hostname</code>. Properties\nof SRV records are priority, weight, port, and name (e.g.,\n<code>[{&#39;priority&#39;: 10, &#39;weight&#39;: 5, &#39;port&#39;: 21223, &#39;name&#39;: &#39;service.example.com&#39;}, ...]</code>).\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveSoa(hostname, callback)",
          "type": "method",
          "name": "resolveSoa",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for start of authority record queries\n(<code>SOA</code> record).\n\n</p>\n<p><code>addresses</code> is an object with the following structure:\n\n</p>\n<pre><code>{\n  nsname: &#39;ns.example.com&#39;,\n  hostmaster: &#39;root.example.com&#39;,\n  serial: 2013101809,\n  refresh: 10000,\n  retry: 2400,\n  expire: 604800,\n  minttl: 3600\n}</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveNs(hostname, callback)",
          "type": "method",
          "name": "resolveNs",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for name server records (<code>NS</code> records).\n<code>addresses</code> is an array of the name server records available for <code>hostname</code>\n(e.g., <code>[&#39;ns1.example.com&#39;, &#39;ns2.example.com&#39;]</code>).\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.resolveCname(hostname, callback)",
          "type": "method",
          "name": "resolveCname",
          "desc": "<p>The same as <a href=\"#dns_dns_resolve_hostname_rrtype_callback\"><code>dns.resolve()</code></a>, but only for canonical name records (<code>CNAME</code>\nrecords). <code>addresses</code> is an array of the canonical name records available for\n<code>hostname</code> (e.g., <code>[&#39;bar.example.com&#39;]</code>).\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "hostname"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.reverse(ip, callback)",
          "type": "method",
          "name": "reverse",
          "desc": "<p>Reverse resolves an ip address to an array of hostnames.\n\n</p>\n<p>The callback has arguments <code>(err, hostnames)</code>.\n\n</p>\n<p>On error, <code>err</code> is an <code>Error</code> object, where <code>err.code</code> is\none of the error codes listed below.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "ip"
                },
                {
                  "name": "callback"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "dns.getServers()",
          "type": "method",
          "name": "getServers",
          "desc": "<p>Returns an array of IP addresses as strings that are currently being used for\nresolution\n\n</p>\n",
          "signatures": [
            {
              "params": []
            }
          ]
        },
        {
          "textRaw": "dns.setServers(servers)",
          "type": "method",
          "name": "setServers",
          "desc": "<p>Given an array of IP addresses as strings, set them as the servers to use for\nresolving\n\n</p>\n<p>If you specify a port with the address it will be stripped, as the underlying\nlibrary doesn&#39;t support that.\n\n</p>\n<p>This will throw if you pass invalid input.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "servers"
                }
              ]
            }
          ]
        }
      ],
      "modules": [
        {
          "textRaw": "Error codes",
          "name": "error_codes",
          "desc": "<p>Each DNS query can return one of the following error codes:\n\n</p>\n<ul>\n<li><code>dns.NODATA</code>: DNS server returned answer with no data.</li>\n<li><code>dns.FORMERR</code>: DNS server claims query was misformatted.</li>\n<li><code>dns.SERVFAIL</code>: DNS server returned general failure.</li>\n<li><code>dns.NOTFOUND</code>: Domain name not found.</li>\n<li><code>dns.NOTIMP</code>: DNS server does not implement requested operation.</li>\n<li><code>dns.REFUSED</code>: DNS server refused query.</li>\n<li><code>dns.BADQUERY</code>: Misformatted DNS query.</li>\n<li><code>dns.BADNAME</code>: Misformatted hostname.</li>\n<li><code>dns.BADFAMILY</code>: Unsupported address family.</li>\n<li><code>dns.BADRESP</code>: Misformatted DNS reply.</li>\n<li><code>dns.CONNREFUSED</code>: Could not contact DNS servers.</li>\n<li><code>dns.TIMEOUT</code>: Timeout while contacting DNS servers.</li>\n<li><code>dns.EOF</code>: End of file.</li>\n<li><code>dns.FILE</code>: Error reading file.</li>\n<li><code>dns.NOMEM</code>: Out of memory.</li>\n<li><code>dns.DESTRUCTION</code>: Channel is being destroyed.</li>\n<li><code>dns.BADSTR</code>: Misformatted string.</li>\n<li><code>dns.BADFLAGS</code>: Illegal flags specified.</li>\n<li><code>dns.NONAME</code>: Given hostname is not numeric.</li>\n<li><code>dns.BADHINTS</code>: Illegal hints flags specified.</li>\n<li><code>dns.NOTINITIALIZED</code>: c-ares library initialization not yet performed.</li>\n<li><code>dns.LOADIPHLPAPI</code>: Error loading iphlpapi.dll.</li>\n<li><code>dns.ADDRGETNETWORKPARAMS</code>: Could not find GetNetworkParams function.</li>\n<li><code>dns.CANCELLED</code>: DNS query cancelled.</li>\n</ul>\n",
          "type": "module",
          "displayName": "Error codes"
        },
        {
          "textRaw": "Supported getaddrinfo flags",
          "name": "supported_getaddrinfo_flags",
          "desc": "<p>The following flags can be passed as hints to <code>dns.lookup()</code>.\n\n</p>\n<ul>\n<li><code>dns.ADDRCONFIG</code>: 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.</li>\n<li><code>dns.V4MAPPED</code>: 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).</li>\n</ul>\n",
          "type": "module",
          "displayName": "Supported getaddrinfo flags"
        },
        {
          "textRaw": "Implementation considerations",
          "name": "implementation_considerations",
          "desc": "<p>Although <code>dns.lookup()</code> and <code>dns.resolve*()/dns.reverse()</code> 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</p>\n",
          "properties": [
            {
              "textRaw": "dns.lookup",
              "name": "lookup",
              "desc": "<p>Under the hood, <code>dns.lookup()</code> uses the same operating system facilities as most\nother programs. For instance, <code>dns.lookup()</code> will almost always resolve a given\nname the same way as the <code>ping</code> command. On most POSIX-like operating systems,\nthe behavior of the <code>dns.lookup()</code> function can be tweaked by changing settings\nin <code>nsswitch.conf(5)</code> and/or <code>resolv.conf(5)</code>, but be careful that changing\nthese files will change the behavior of all other programs running on the same\noperating system.\n\n</p>\n<p>Though the call will be asynchronous from JavaScript&#39;s perspective, it is\nimplemented as a synchronous call to <code>getaddrinfo(3)</code> that runs on libuv&#39;s\nthreadpool. Because libuv&#39;s threadpool has a fixed size, it means that if for\nwhatever reason the call to <code>getaddrinfo(3)</code> takes a long time, other\noperations that could run on libuv&#39;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&#39;s threadpool by\nsetting the &#39;UV_THREADPOOL_SIZE&#39; environment variable to a value greater than\n4 (its current default value). For more information on libuv&#39;s threadpool, see\n<a href=\"http://docs.libuv.org/en/latest/threadpool.html\">the official libuv\ndocumentation</a>.\n\n</p>\n"
            }
          ],
          "modules": [
            {
              "textRaw": "dns.resolve, functions starting with dns.resolve and dns.reverse",
              "name": "dns.resolve,_functions_starting_with_dns.resolve_and_dns.reverse",
              "desc": "<p>These functions are implemented quite differently than <code>dns.lookup()</code>. They do\nnot use <code>getaddrinfo(3)</code> and they <em>always</em> perform a DNS query on the network.\nThis network communication is always done asynchronously, and does not use\nlibuv&#39;s threadpool.\n\n</p>\n<p>As a result, these functions cannot have the same negative impact on other\nprocessing that happens on libuv&#39;s threadpool that <code>dns.lookup()</code> can have.\n\n</p>\n<p>They do not use the same set of configuration files than what <code>dns.lookup()</code>\nuses. For instance, <em>they do not use the configuration from <code>/etc/hosts</code></em>.\n\n\n</p>\n",
              "type": "module",
              "displayName": "dns.resolve, functions starting with dns.resolve and dns.reverse"
            }
          ],
          "type": "module",
          "displayName": "Implementation considerations"
        }
      ],
      "type": "module",
      "displayName": "DNS"
    }
  ]
}