Network.DNS.LookupRaw

Lookups returning requested RData

lookup :: Resolver -> Domain -> TYPE -> IO (Either DNSError [RData])

Look up resource records of a specified type for a domain, collecting the results from the ANSWER section of the response. See the documentation of lookupRaw to understand the concrete behavior. Cache is used if resolvCache is Just.

Example:

>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookup resolver "www.example.com" A
Right [93.184.216.34]

lookupAuth :: Resolver -> Domain -> TYPE -> IO (Either DNSError [RData])

Look up resource records of a specified type for a domain, collecting the results from the AUTHORITY section of the response. See the documentation of lookupRaw to understand the concrete behavior. Cache is used even if resolvCache is Just.

Lookups returning DNS Messages

lookupRaw

Arguments

:: Resolver

Resolver obtained via withResolver

-> Domain

Query domain

-> TYPE

Query RRtype

-> IO (Either DNSError DNSMessage)

Look up a name and return the entire DNS Response.

For a given DNS server, the queries are done:

• A new UDP socket bound to a new local port is created and a new identifier is created atomically from the cryptographically secure pseudo random number generator for the target DNS server. Then UDP queries are tried with the limitation of resolvRetry (use EDNS if specifiecd). If it appears that the target DNS server does not support EDNS, it falls back to traditional queries.
• If the response is truncated, a new TCP socket bound to a new local port is created. Then exactly one TCP query is retried.

If multiple DNS servers are specified ResolvConf ('RCHostNames ') or found (RCFilePath), either sequential lookup or concurrent lookup is carried out:

• In sequential lookup (resolvConcurrent is False), the query procedure above is processed in the order of the DNS servers sequentially until a successful response is received.
• In concurrent lookup (resolvConcurrent is True), the query procedure above is processed for each DNS server concurrently. The first received response is accepted even if it is an error.

Cache is not used even if resolvCache is Just.

The example code:

  rs <- makeResolvSeed defaultResolvConf
  withResolver rs $ \resolver -> lookupRaw resolver "www.example.com" A
  

And the (formatted) expected output:

  Right (DNSMessage
          { header = DNSHeader
                       { identifier = 1,
                         flags = DNSFlags
                                   { qOrR = QR_Response,
                                     opcode = OP_STD,
                                     authAnswer = False,
                                     trunCation = False,
                                     recDesired = True,
                                     recAvailable = True,
                                     rcode = NoErr,
                                     authenData = False
                                   },
                       },
            question = [Question { qname = "www.example.com.",
                                   qtype = A}],
            answer = [ResourceRecord {rrname = "www.example.com.",
                                      rrtype = A,
                                      rrttl = 800,
                                      rdlen = 4,
                                      rdata = 93.184.216.119}],
            authority = [],
            additional = []})
 

AXFR requests cannot be performed with this interface.

>>> rs <- makeResolvSeed defaultResolvConf
>>> withResolver rs $ \resolver -> lookupRaw resolver "mew.org" AXFR
Left InvalidAXFRLookup

lookupRawCtl

Arguments

:: Resolver

Resolver obtained via withResolver

-> Domain

Query domain

-> TYPE

Query RRtype

-> QueryControls

Query flag and EDNS overrides

-> IO (Either DNSError DNSMessage)

Similar to lookupRaw, but the default values of the RD, AD, CD and DO flag bits, as well as various EDNS features, can be adjusted via the QueryControls parameter.

DNS Message procesing

fromDNSMessage :: DNSMessage -> (DNSMessage -> a) -> Either DNSError a

Messages with a non-error RCODE are passed to the supplied function for processing. Other messages are translated to DNSError instances.

Note that NameError is not a lookup error. The lookup is successful, bearing the sad news that the requested domain does not exist. NameError responses may return a meaningful AD bit, may contain useful data in the authority section, and even initial CNAME records that lead to the ultimately non-existent domain. Applications that wish to process the content of NameError (NXDomain) messages will need to implement their own RCODE handling.