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Note on topological-sort of CNAMEs

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Tony Garnock-Jones 2012-02-19 16:43:42 -05:00
parent 42280b8d91
commit d33e251dd7
1 changed files with 8 additions and 0 deletions
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zonedb.rkt
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@ -179,7 +179,15 @@
;; rr-set->list : SetOf<RR> -> ListOf<RR>
;; Like set->list, but places all CNAME records first.
;; This is apparently to work around bugs in old versions of BIND?
;;
;; TODO: Perhaps the CNAMEs even need to be in topologically-sorted order?
;; http://homepage.ntlworld.com./jonathan.deboynepollard/FGA/dns-response-taxonomy.html
;; has this to say on this topic:
;; "A content DNS server following the algorithm in § 4.3.2 of RFC
;; 1034 will insert this chain in first-to-last order in the
;; response. The response parsing code in most resolving proxy DNS
;; servers and DNS client libraries expects this order. However,
;; the actual text of RFC 1034 itself does not guarantee it."
(define (rr-set->list rrs)
(append (set->list (filter-by-type rrs 'cname))
(set->list (set-filter (lambda (rr) (not (eqv? (rr-type rr) 'cname))) rrs))))