CSE2410 Fall 2014 Bounce

# 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 constant 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, domains) {

          if (err) {

            throw err;

          }

          console.log('reverse for ' + a + ': ' + JSON.stringify(domains));

        });

      });

    });

## dns.lookup(domain, [family], callback)

Resolves a domain (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 domain does not exist but also when the lookup fails in other ways

such as no available file descriptors.

## dns.resolve(domain, [rrtype], callback)

Resolves a domain (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) and `'CNAME'` (canonical name records).

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(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.resolveNs(domain, 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 `domain`

(e.g., `['ns1.example.com', 'ns2.example.com']`).

## dns.resolveCname(domain, 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

`domain` (e.g., `['bar.example.com']`).

## dns.reverse(ip, callback)

Reverse resolves an ip address to an array of domain names.

The callback has arguments `(err, domains)`.

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 domain 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 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.