@hackage / dnsbase

Base DNS library with extensible core types

A DNS stub-resolver library with a typed RData model and a runtime extension API. The IO layer is derived from Kazu Yamamoto's dns package; what dnsbase layers on top sits in the RR-data model and the configuration story.

Every RR type's payload is modeled via a dedicated Haskell type — these include, for example, the recent SVCB / HTTPS service-binding records, with up-to-date extensible SvcParam coverage. EDNS option support includes Extended DNS Errors (EDE) with a user-extensible info-code name table. Coverage of both widely used and historical DNS RR types is comprehensive — only the most marginal obsolete or experimental types remain unimplemented.

Applications can extend the library with any missing RRtypes, EDNS(0) options, or SVCB / HTTPS SvcParam values. Application-specified data types take precedence over any existing or later-added built-in implementations.

Extensions are registered by constructing a pure resolver configuration value, rather than via IO actions on mutable global state. Adding custom data types to the library does not require a source-code fork. See Adding a custom RR type and Adding a custom EDNS option for detailed examples.

The basic lookup interface (lookupA, lookupMX, lookupTXT, …) is deliberately similar to dns; the differences are concentrated in the typed-data layer and the configuration surface.

Basic MX lookup example

The example below prints the MX records of ietf.org, if any, or an error message if the answer can't be obtained.

The compile-time literal splice used here is dnLit8, the octet-level form that accepts any RFC 1035 master-file string (the input is treated as raw bytes, with \DDD and \C escapes). For IDN-aware literals — strict IDNA2008 validation, U-label encoding to A-labels, optional cross-label Bidi checks — use dnLit from Net.DNSBase.Domain with a parser from the companion idna2008 package; see the dnLit haddock for the composition idiom.

{-# LANGUAGE
    BlockArguments
  , LambdaCase
  , RecordWildCards
  , TemplateHaskell
  #-}
import Control.Exception (throwIO)
import Net.DNSBase
import System.IO (stdout)

main :: IO ()
main = makeResolvSeed defaultResolvConf >>= \ case
    Right seed -> withResolver seed \ r ->
        lookupMX r $$(dnLit8 "ietf.org") >>= \ case
            Right mxs -> hPutBuilder stdout $ foldr presentLn mempty mxs
            Left errs -> throwIO errs
    Left errs -> throwIO errs

Custom extensions

The demos/ directory contains worked examples for each of the three extension targets:

• demoextrr.hs — adding a custom RR type, by shadowing the standard A record with a raw-Word32 representation that presents each address as eight hex nibbles under a made-up name HEXA. Shows the KnownRData instance shape and registration via registerRRtype.
• demoextopt.hs — adding an EDNS(0) option (the EDNS cookie, RFC 7873), queried directly against ns1.isc.org to elicit a server cookie. Shows the KnownEdnsOption instance shape, registration via registerEdnsOption, and per-call option injection via optCtlAdd.
• demoextspv.hs — adding (here, shadowing) an HTTPS / SVCB service parameter, by re-implementing the ipv4hint key (codepoint 4) with a raw-Word32-list representation and a hex presentation form under a made-up name IPV4HEX. Shows the KnownSVCParamValue instance shape and the registration via extendRRwithType applied to both T_svcb and T_https (SVCB-shaped RRs share the SvcParam codec map).

Each demo is a self-contained program; copy one into a project and adjust the queries to taste.