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(defpackage :cl-mdns/client
(:use :cl
:cl-mdns/packet)
(:local-nicknames (:nb :nibbles)
(:f :fsocket))
(:export :lookup))
(in-package :cl-mdns/client)
(defvar *mdns-address* #(224 0 0 251))
(defvar *mdns-port* 5353)
(defun parse-ipv4-response (packet)
"Extracts the first IPv4 address found in a DNS response packet."
(let* ((qdcount (+ (ash (aref packet 4) 8) (aref packet 5)))
(ancount (+ (ash (aref packet 6) 8) (aref packet 7)))
(pos 12)) ; Start after header
;; Skip Question section
(loop repeat qdcount do
(loop while (not (zerop (aref packet pos)))
do (incf pos (1+ (aref packet pos))))
(incf pos 5)) ; Skip null byte + Type(2) + Class(2)
;; Parse Answer section
(if (> ancount 0)
(let ((type (+ (ash (aref packet (+ pos 2)) 8) (aref packet (+ pos 3))))
;(rdlen (+ (ash (aref packet (+ pos 10)) 8) (aref packet (+ pos 11))))
)
;; If Type is 1 (A record), return the next 4 bytes as an IP string
(if (= type 1)
(format nil "~D.~D.~D.~D"
(aref packet (+ pos 12)) (aref packet (+ pos 13))
(aref packet (+ pos 14)) (aref packet (+ pos 15)))
"Non-IPv4 record received"))
"No answers found")))
(defun lookup (domain)
(let ((fd (f:open-socket :type :datagram))
(packet (build-query-packet domain))
(buffer (make-array 512 :element-type '(unsigned-byte 8))))
(unwind-protect
(progn
(f:socket-bind fd (f:make-sockaddr-in))
(f:socket-sendto fd packet (f:make-sockaddr-in :addr *mdns-address* :port *mdns-port*))
(multiple-value-bind (count raddr) (f:socket-recvfrom fd buffer)
(declare (ignore raddr))
(parse-ipv4-response (subseq buffer 0 count))))
(f:close-socket fd))))
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