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15.1 Functions
dns-get-address
dns-get-srv
srv-rr
dns-get-name
dns-get-mail-exchanger
dns-find-nameserver
15.2 DNS Unit
[email protected]
15.3 DNS Signature
dns^

15 DNS: Domain Name Service Queries

 (require net/dns) package: net-lib
The net/dns library provides utilities for looking up hostnames.
Thanks to Eduardo Cavazos and Jason Crowe for repairs and improvements.

15.1 Functions

procedure

(dns-get-address nameserver    
  address    
  [#:ipv6? ipv6?])  string?
  nameserver : string?
  address : string?
  ipv6? : any/c = #f
Consults the specified nameserver (normally a numerical address like "128.42.1.30") to obtain a numerical address for the given Internet address.

The query record sent to the DNS server includes the "recursive" bit, but dns-get-address also implements a recursive search itself in case the server does not provide this optional feature.

If ipv6? is a true value, then the numerical address that is returned will be an IPv6 address. If no AAAA record exists, an error will be raised.

procedure

(dns-get-srv nameserver name service [proto])  (listof srv-rr?)

  nameserver : string?
  name : string?
  service : string?
  proto : string? = "tcp"

struct

(struct srv-rr (priority weight port target)
    #:prefab)
  priority : (integer-in 0 65535)
  weight : (integer-in 0 65535)
  port : (integer-in 0 65535)
  target : string?

An SRV record is a particular kind of DNS resource record that maps an abstract service name onto a hostname and port combination. For more information, see the Wikipedia page on SRV records.

Consults the specified nameserver (normally a numerical address like "128.42.1.30") to retrieve the SRV records corresponding to the given name, service, and protocol. Returns a list of srv-rr structs if any corresponding SRV records are found; otherwise, returns '().

If service is "X", proto is "Y", and name is "example.com", then this will retrieve any SRV records at the domain name _X._Y.example.com.

The query record sent to the DNS server includes the "recursive" bit, but dns-get-srv also implements a recursive search itself in case the server does not provide this optional feature.

Examples:
> (dns-get-srv (dns-find-nameserver) "racket-lang.org" "xmpp-client")

'(#s(srv-rr 0 0 5222 "xmpp.racket-lang.org"))

> (dns-get-srv (dns-find-nameserver) "racket-lang.org" "nonexistent-protocol")

'()

> (dns-get-srv (dns-find-nameserver) "racket-lang.org" "xmpp-client" "tcp")

'(#s(srv-rr 0 0 5222 "xmpp.racket-lang.org"))

> (dns-get-srv (dns-find-nameserver) "racket-lang.org" "xmpp-client" "udp")

'()

Added in version 6.4.0.8 of package net-lib.

procedure

(dns-get-name nameserver address)  string?

  nameserver : string?
  address : string?
Consults the specified nameserver (normally a numerical address like "128.42.1.30") to obtain a name for the given numerical address.

procedure

(dns-get-mail-exchanger nameserver address)  string?

  nameserver : string?
  address : string?
Consults the specified nameserver to obtain the address for a mail exchanger the given mail host address. For example, the mail exchanger for "ollie.cs.rice.edu" might be "cs.rice.edu".

Attempts to find the address of a nameserver on the present system. On Unix and Mac OS, this procedure parses "/etc/resolv.conf" to extract the first nameserver address. On Windows, it runs nslookup.exe.

15.2 DNS Unit

[email protected] and dns^ are deprecated. They exist for backward-compatibility and will likely be removed in the future. New code should use the net/dns module.

 (require net/dns-unit) package: compatibility-lib

value

[email protected] : unit?

Imports nothing, exports dns^.

15.3 DNS Signature

 (require net/dns-sig) package: compatibility-lib

signature

dns^ : signature

Includes dns-get-address, dns-get-name, dns-get-mail-exchanger and dns-find-nameserver.