Documentation

Look up all 'A' records for the given hostname.

A straightforward example:

>>> let hostname = Data.ByteString.Char8.pack "www.mew.org"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupA resolver hostname
Right [202.232.15.101]

This function will also follow a CNAME and resolve its target if one exists for the queries hostname:

>>> let hostname = Data.ByteString.Char8.pack "www.kame.net"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupA resolver hostname
Right [203.178.141.194]

Look up all (IPv6) 'AAAA' records for the given hostname.

Examples:

>>> let hostname = Data.ByteString.Char8.pack "www.mew.org"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupAAAA resolver hostname
Right [2001:240:11e:c00:00:00:00:101]

Look up all 'MX' records for the given hostname. Two parts constitute an MX record: a hostname , and an integer priority. We therefore return each record as a (Domain, Int).

In this first example, we look up the MX for the domain "example.com". It has no MX (to prevent a deluge of spam from examples posted on the internet). But remember, "no results" is still a successful result.

>>> let hostname = Data.ByteString.Char8.pack "example.com"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupMX resolver hostname
Right []

The domain "mew.org" does however have a single MX:

>>> let hostname = Data.ByteString.Char8.pack "mew.org"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupMX resolver hostname
Right [("mail.mew.org.",10)]

Also note that all hostnames are returned with a trailing dot to indicate the DNS root.

Look up all 'MX' records for the given hostname, and then resolve their hostnames to IPv4 addresses by calling lookupA. The priorities are not retained.

Examples:

>>> import Data.List (sort)
>>> let hostname = Data.ByteString.Char8.pack "iij.ad.jp"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> ips <- withResolver rs $ \resolver -> lookupAviaMX resolver hostname
>>> fmap sort ips
Right [202.232.30.70,202.232.30.144]

Since there is more than one result, it is necessary to sort the list in order to check for equality.

Look up all 'MX' records for the given hostname, and then resolve their hostnames to IPv6 addresses by calling lookupAAAA. The priorities are not retained.

Look up all 'NS' records for the given hostname. The results are taken from the ANSWER section of the response (as opposed to AUTHORITY). For details, see e.g. http://www.zytrax.com/books/dns/ch15/.

There will typically be more than one name server for a domain. It is therefore extra important to sort the results if you prefer them to be at all deterministic.

Examples:

>>> import Data.List (sort)
>>> let hostname = Data.ByteString.Char8.pack "mew.org"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> ns <- withResolver rs $ \resolver -> lookupNS resolver hostname
>>> fmap sort ns
Right ["ns1.mew.org.","ns2.mew.org."]

Look up all 'NS' records for the given hostname. The results are taken from the AUTHORITY section of the response and not the usual ANSWER (use lookupNS for that). For details, see e.g. http://www.zytrax.com/books/dns/ch15/.

There will typically be more than one name server for a domain. It is therefore extra important to sort the results if you prefer them to be at all deterministic.

For an example, we can look up the nameservers for "example.com" from one of the root servers, a.gtld-servers.net, the IP address of which was found beforehand:

>>> import Data.List (sort)
>>> let hostname = Data.ByteString.Char8.pack "example.com"
>>> 
>>> let ri = RCHostName "192.5.6.30" -- a.gtld-servers.net
>>> let rc = defaultResolvConf { resolvInfo = ri }
>>> rs <- makeResolvSeed rc
>>> ns <- withResolver rs $ \resolver -> lookupNSAuth resolver hostname
>>> fmap sort ns
Right ["a.iana-servers.net.","b.iana-servers.net."]

Look up all 'TXT' records for the given hostname. The results are free-form ByteStrings.

Two common uses for 'TXT' records are http://en.wikipedia.org/wiki/Sender_Policy_Framework and http://en.wikipedia.org/wiki/DomainKeys_Identified_Mail. As an example, we find the SPF record for "mew.org":

>>> let hostname = Data.ByteString.Char8.pack "mew.org"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupTXT resolver hostname
Right ["v=spf1 +mx -all"]

Look up all 'PTR' records for the given hostname. To perform a reverse lookup on an IP address, you must first reverse its octets and then append the suffix ".in-addr.arpa."

We look up the PTR associated with the IP address 210.130.137.80, i.e., 80.137.130.210.in-addr.arpa:

>>> let hostname = Data.ByteString.Char8.pack "164.2.232.202.in-addr.arpa"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupPTR resolver hostname
Right ["www.iij.ad.jp."]

The lookupRDNS function is more suited to this particular task.

Convenient wrapper around lookupPTR to perform a reverse lookup on a single IP address.

We repeat the example from lookupPTR, except now we pass the IP address directly:

>>> let hostname = Data.ByteString.Char8.pack "202.232.2.164"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupRDNS resolver hostname
Right ["www.iij.ad.jp."]

Look up all 'SRV' records for the given hostname. A SRV record comprises four fields,

• Priority (lower is more-preferred)
  • Weight (relative frequency with which to use this record amongst all results with the same priority)
  • Port (the port on which the service is offered)
  • Target (the hostname on which the service is offered)

The first three are integral, and the target is another DNS hostname. We therefore return a four-tuple (Int,Int,Int,Domain).

Examples:

>>> let hostname = Data.ByteString.Char8.pack "_sip._tcp.cisco.com"
>>> 
>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupSRV resolver hostname
Right [(1,0,5060,"vcsgw.cisco.com.")]