#lang racket/base ;; Noddy representation of a zone, and various zone and RRSet utilities. (require racket/set) (require "api.rkt") (require "codec.rkt") (provide compile-zone-db in-bailiwick? set-filter filter-by-type referral-for additional-section/a filter-rrs) ;; A CompiledZone is a Hash>, representing a ;; collection of DNS RRSets indexed by DomainName. ;; TODO: maybe store domain names big-end first? It'd make bailiwick ;; and subzone checks into prefix rather than suffix checks. It makes ;; domain names into paths through the DNS DB tree. ;; compile-zone-db : ListOf -> CompiledZone ;; Builds an immutable hash table from the given RRs, suitable for ;; quickly looking up answers to queries. (define (compile-zone-db rrs) ;; RR Hash -> Hash (define (incorporate-rr rr db) (hash-set db (rr-name rr) (set-add (hash-ref db (rr-name rr) (set)) rr))) (foldl incorporate-rr (make-immutable-hash) rrs)) ;; in-bailiwick? : DomainName DomainName -> Boolean ;; Answers #t iff dn falls within the bailiwick of the zone with ;; origin root. (define (in-bailiwick? dn root) (cond ((equal? dn root) #t) ((null? dn) #f) (else (in-bailiwick? (cdr dn) root)))) ;; set-filter : (X -> Boolean) SetOf -> SetOf ;; Retains only those elements of its argument for which the predicate ;; answers #t. (define (set-filter predicate in) (for/set ([x (in-set in)] #:when (predicate x)) x)) ;; filter-by-type : SetOf RRType -> SetOf ;; Selects only those members of rrset having rr-type type. (define (filter-by-type rrset type) (set-filter (lambda (rr) (eqv? (rr-type rr) type)) rrset)) (define (referral-for name soa-rr zone) (define limit (rr-name soa-rr)) (let search ((name name)) (cond ((or (null? name) (equal? name limit)) ;; We've walked up the tree to the top of the zone. No referrals ;; are possible. #f) ((hash-ref zone name #f) => ;; There's an entry for this suffix of the original name. Check ;; to see if it has an NS record indicating a subzone. (lambda (rrset) (define ns-rrset (filter-by-type rrset 'ns)) (if (set-empty? ns-rrset) (search (cdr name)) ;; no NS records for this suffix. Keep looking. ns-rrset))) (else ;; Nothing for this suffix. Keep lookup. (search (cdr name)))))) ;; additional-section/a : CompiledZone ListOf ;; Implements the "additional section" rules from RFC 1035 (and the ;; rules for IPv6 from RFC 3596). Provides A and AAAA records for ;; names mentioned in the "names" list that have entries in "zone". (define (additional-section/a zone names) ;; RFC 3596 (section 3) requires that we process AAAA here as well ;; as A. (foldl (lambda (name section) (set-union section (set-filter (lambda (rr) (and (memv (rr-type rr) '(a aaaa)) (eqv? (rr-class rr) 'in))) (hash-ref zone name)))) (set) names)) ;; filter-rrs : SetOf QueryType QueryClass ;; Returns a set like its argument with RRs not matching the given ;; type and class removed. (define (filter-rrs rrs qtype qclass) (define filtered-by-type (case qtype ((*) rrs) (else (filter-by-type rrs qtype)))) (define filtered-by-type-and-class (case qclass ((*) filtered-by-type) (else (set-filter (lambda (rr) (eqv? (rr-class rr) qclass)) filtered-by-type)))) filtered-by-type-and-class)