;;;; DNS implementation for COMMON-NET

(in-package :common-net)

(defstruct dns-packet
  (txid (random 65536) :type (unsigned-byte 16))
  (is-response nil)
  (opcode :query :type (member :query :iquery :status))
  (authoritative nil)
  (truncated nil)
  (recurse nil)
  (will-recurse nil)
  (resp-code :success :type (member :success :format-error :server-failure :name-error :not-implemented :refused))
  (queries '() :type list)
  (answers '() :type list)
  (authority '() :type list)
  (additional '() :type list))

(defclass resource-query ()
  ((name :initarg :name)
   (type :initarg :type)))

(defclass resource-record ()
  ((name :initarg :name)
   (ttl :initarg :ttl)))

(defvar *rr-coding-types* '())

(defmacro define-rr-type (name class type slots)
  (let ((format (mapcar #'(lambda (slot)
			    (list* (if (listp (car slot))
				      (caar slot)
				      (car slot))
				   (cdr slot)))
			slots))
	(slot-desc (mapcar #'(lambda (slot)
			       (let ((name (car slot)))
				 `(,name :initarg ,(intern (symbol-name name) (find-package :keyword))))) slots)))
    `(progn
       (defclass ,name (resource-record) ,slot-desc)
       (setf *rr-coding-types* (cons '(,name (,class ,type) ,format)
				     (remove ',name *rr-coding-types* :key #'car)))
       (export '(,name)))))

(define-rr-type a-record #x1 #x1
		((address ipv4-address)))
(define-rr-type ns-record #x1 #x2
		((ns-name domain-name)))
(define-rr-type cname-record #x1 #x5
		((cname domain-name)))
(define-rr-type soa-record #x1 #x6
		((mname domain-name)
		 (rname domain-name)
		 (serial uint-32)
		 (refresh uint-32)
		 (retry uint-32)
		 (expire uint-32)))
(define-rr-type ptr-record #x1 #xc
		((pointed domain-name)))
(define-rr-type mx-record #x1 #xf
		((prio uint-16)
		 (mail-host domain-name)))
(define-rr-type txt-record #x1 #x10
		((text text)))
(define-rr-type aaaa-record #x1 #x1c
		((address ipv6-address)))
(define-rr-type srv-record #x1 #x21
		((prio uint-16)
		 (weigth uint-16)
		 (port uint-16)
		 (host-name domain-name)))

(export '(resource-record))

;;; Packet decoding logic

(defstruct dns-decode-state
  (packet nil :type (array (unsigned-byte 8)))
  (pos 0 :type (mod 65536))
  (prev-names '() :type list))

(define-condition dns-error (network-error) ())
(define-condition dns-decode-error (dns-error)
  ((packet :initarg :packet)))
(define-condition simple-dns-decode-error (dns-decode-error simple-error) ())

(defun simple-dns-decode-error (packet format &rest args)
  (error 'simple-dns-decode-error :packet packet :format-control format :format-argument args))

(defun decode-uint-8 (buf)
 (declare (type dns-decode-state buf))
  (with-slots (packet pos) buf
    (when (< (- (length packet) pos) 1)
      (simple-dns-decode-error buf "DNS packet is too short (wanted a 8-bit number)."))
    (prog1 (aref packet pos)
      (incf pos))))

(defun decode-uint-16 (buf)
  (declare (type dns-decode-state buf))
  (with-slots (packet pos) buf
    (when (< (- (length packet) pos) 2)
      (simple-dns-decode-error buf "DNS packet is too short (wanted a 16-bit number)."))
    (prog1
	(+ (* (aref packet pos) 256)
	   (aref packet (1+ pos)))
      (incf pos 2))))

(defun decode-uint-32 (buf)
  (declare (type dns-decode-state buf))
  (with-slots (packet pos) buf
    (when (< (- (length packet) pos) 4)
      (simple-dns-decode-error buf "DNS packet is too short (wanted a 32-bit number)."))
    (prog1
	(+ (* (aref packet pos) #x1000000)
	   (* (aref packet (+ pos 1)) #x10000)
	   (* (aref packet (+ pos 2)) #x100)
	   (aref packet (+ pos 3)))
      (incf pos 4))))

(defun decode-domain-name (buf)
  (declare (type dns-decode-state buf))
  (labels ((decode-label ()
	     (let* ((orig-off (dns-decode-state-pos buf))
		    (len (decode-uint-8 buf)))
	       (case (ldb (byte 2 6) len)
		 ((0)
		  (if (zerop len)
		      '()
		      (with-slots (packet pos) buf
			(let* ((label (prog1
					  (handler-bind
					      ((charcode:coding-error
						(lambda (c)
						  (declare (ignore c))
						  (simple-dns-decode-error buf "DNS label was not ASCII."))))
					    (charcode:decode-string (subseq packet
									    pos (+ pos len))
								    :ascii))
					(incf pos len)))
			       (decoded (append (list label) (decode-label))))
			  (push (cons orig-off decoded) (slot-value buf 'prev-names))
			  decoded))))
		 ((3) (let* ((offset (+ (* 256 (ldb (byte 6 0) len))
					(decode-uint-8 buf)))
			     (prev (assoc offset (dns-decode-state-prev-names buf))))
			(unless prev
			  (simple-dns-decode-error buf "Domain name label pointed to non-label position."))
			(cdr prev)))
		 (t (simple-dns-decode-error buf "Illegal DNS label flags: ~D" (ldb (byte 2 6) len)))))))
    (decode-label)))

(defun decode-dns-query (buf)
  (declare (type dns-decode-state buf))
  (let* ((name (decode-domain-name buf))
	 (type (decode-uint-16 buf))
	 (class (decode-uint-16 buf))
	 (desc (find (list class type) *rr-coding-types* :key 'second :test 'equal)))
    (if desc
	(make-instance 'resource-query :name name :type (first desc))
	(progn (warn "Unknown DNS RR type: ~D, ~D" class type)
	       nil))))

(defun decode-dns-record (buf)
  (declare (type dns-decode-state buf))
  (let* ((name (decode-domain-name buf))
	 (type (decode-uint-16 buf))
	 (class (decode-uint-16 buf))
	 (ttl (decode-uint-32 buf))
	 (dlen (decode-uint-16 buf))
	 (desc (find (list class type) *rr-coding-types* :key 'second :test 'equal)))
    (when (< (length (dns-decode-state-packet buf))
	     (+ (dns-decode-state-pos buf) dlen))
      (simple-dns-decode-error buf "Not enough data left in DNS packet to decode indicated RR data length."))
    (if desc
	(let ((orig-off (dns-decode-state-pos buf))
	      (rr (make-instance (first desc)
				 :name name
				 :ttl ttl)))
	  (dolist (slot-desc (third desc))
	    (destructuring-bind (slot-name type) slot-desc
	      (setf (slot-value rr slot-name)
		    (with-slots (packet pos) buf
		      (ecase type
			((uint-16) (decode-uint-16 buf))
			((uint-32) (decode-uint-32 buf))
			((domain-name) (decode-domain-name buf))
			((text)
			 (let ((len (decode-uint-8 buf)))
			   (prog1 (subseq packet pos (+ pos len))
			     (incf pos len))))
			((ipv4-address)
			 (prog1 (make-instance 'ipv4-host-address :host-bytes (subseq packet pos (+ pos 4)))
			   (incf pos 4)))
			((ipv6-address)
			 (prog1 (make-instance 'ipv6-host-address :host-bytes (subseq packet pos (+ pos 16)))
			   (incf pos 16))))))))
	  (unless (= (dns-decode-state-pos buf) (+ orig-off dlen))
	    (simple-dns-decode-error buf "DNS RR data length did not match up with actual decoded data."))
	  rr)
	(progn (warn "Unknown DNS RR type: ~D, ~D" class type)
	       (incf (dns-decode-state-pos buf) dlen)
	       nil))))

(defun decode-dns-packet (buf)
  (declare (type dns-decode-state buf))
  (let* ((txid (decode-uint-16 buf))
	 (flags (decode-uint-16 buf))
	 (qnum (decode-uint-16 buf))
	 (ansnum (decode-uint-16 buf))
	 (autnum (decode-uint-16 buf))
	 (auxnum (decode-uint-16 buf))
	 (packet (make-dns-packet :txid txid
				  :is-response (ldb-test (byte 1 15) flags)
				  :opcode (case (ldb (byte 4 11) flags)
					    ((0) :query)
					    ((1) :iquery)
					    ((2) :status)
					    (t (simple-dns-decode-error buf "Unknown DNS opcode: ~D" (ldb (byte 4 11) flags))))
				  :authoritative (ldb-test (byte 1 10) flags)
				  :truncated (ldb-test (byte 1 9) flags)
				  :recurse (ldb-test (byte 1 8) flags)
				  :will-recurse (ldb-test (byte 1 7) flags)
				  :resp-code (case (ldb (byte 4 0) flags)
					       ((0) :success)
					       ((1) :format-error)
					       ((2) :server-failure)
					       ((3) :name-error)
					       ((4) :not-implemented)
					       ((5) :refused)
					       (t (simple-dns-decode-error buf "Unknown DNS response code: ~D" (ldb (byte 4 0) flags)))))))
    (with-slots (queries answers authority additional) packet
	(dotimes (i qnum)
	  (setf queries (append queries (list (decode-dns-query buf)))))
	(dotimes (i ansnum)
	  (setf answers (append answers (list (decode-dns-record buf)))))
	(dotimes (i autnum)
	  (setf authority (append authority (list (decode-dns-record buf)))))
	(dotimes (i auxnum)
	  (setf additional (append additional (list (decode-dns-record buf))))))
    packet))

(defun dns-decode (packet)
  (decode-dns-packet (make-dns-decode-state :packet packet)))

;;; Packet encoding logic

(defstruct dns-encode-state
  (packet-buf (make-array '(512) :element-type '(unsigned-byte 8) :adjustable t :fill-pointer 0) :type (array (unsigned-byte 8)))
  (prev-names '() :type list))

(defun encode-uint-8 (buf num)
  (declare (type dns-encode-state buf)
	   (type (unsigned-byte 8) num))
  (with-slots (packet-buf) buf
    (vector-push-extend num packet-buf)))

(defun encode-uint-16 (buf num)
  (declare (type dns-encode-state buf)
	   (type (unsigned-byte 16) num))
  (with-slots (packet-buf) buf
    (vector-push-extend (ldb (byte 8 8) num) packet-buf)
    (vector-push-extend (ldb (byte 8 0) num) packet-buf)))

(defun encode-uint-32 (buf num)
  (declare (type dns-encode-state buf)
	   (type (unsigned-byte 32) num))
  (with-slots (packet-buf) buf
    (vector-push-extend (ldb (byte 8 24) num) packet-buf)
    (vector-push-extend (ldb (byte 8 16) num) packet-buf)
    (vector-push-extend (ldb (byte 8 8) num) packet-buf)
    (vector-push-extend (ldb (byte 8 0) num) packet-buf)))

(defun encode-bytes (buf bytes)
  (declare (type dns-encode-state buf)
	   (type (array (unsigned-byte 8)) bytes))
  (with-slots (packet-buf) buf
    (dotimes (i (length bytes) (values))
      (vector-push-extend (elt bytes i) packet-buf))))

(defun encode-domain-name (buf name)
  (declare (type dns-encode-state buf)
	   (type list name))
  (with-slots (packet-buf prev-names) buf
    (labels ((encode-label (name)
	       (let ((prev (find name prev-names :key 'first :test 'equal)))
		 (cond ((null name)
			(encode-uint-8 buf 0))
		       (prev
			(encode-uint-16 buf (+ #xc000 (cdr prev))))
		       (t
			(when (< (length packet-buf) 16384)
			  (push (cons name (length packet-buf)) prev-names))
			(let ((encoded (charcode:encode-string (car name) :ascii)))
			  (unless (< (length encoded) 64)
			    (simple-dns-decode-error buf "DNS labels cannot exceed 63 octets in length: ~S" (car name)))
			  (encode-uint-8 buf (length encoded))
			  (encode-bytes buf encoded))
			(encode-label (cdr name)))))))
      (encode-label name))))

(defun encode-dns-query (buf query)
  (declare (type dns-encode-state buf)
	   (type resource-query query))
  (let ((desc (find (slot-value query 'type) *rr-coding-types* :key 'first)))
    (encode-domain-name buf (slot-value query 'name))
    (encode-uint-16 buf (second (second desc)))
    (encode-uint-16 buf (first (second desc)))))

(defun encode-dns-record (buf record)
  (declare (type dns-encode-state buf)
	   (type resource-record record))
  (let ((desc (find (class-name (class-of record)) *rr-coding-types* :key 'first)))
    (encode-domain-name buf (slot-value record 'name))
    (encode-uint-16 buf (second (second desc)))
    (encode-uint-16 buf (first (second desc)))
    (encode-uint-32 buf (slot-value record 'ttl))
    (with-slots (packet-buf) buf
      (let ((orig-off (length packet-buf)))
	(encode-uint-16 buf 0)
	(dolist (slot-desc (third desc))
	  (destructuring-bind (slot-name type) slot-desc
	    (let ((val (slot-value record slot-name)))
	      (ecase type
		((uint-16) (encode-uint-16 buf val))
		((uint-32) (encode-uint-32 buf val))
		((domain-name) (encode-domain-name buf val))
		((text) (let ((data (etypecase val
				      (string (charcode:encode-string val :ascii))
				      ((array (unsigned-byte 8)) val))))
			  (unless (< (length data) 256)
			    (simple-dns-decode-error buf "DNS text data length cannot exceed 255 octets."))
			  (encode-uint-8 buf (length data))
			  (encode-bytes buf data)))
		((ipv4-address)
		 (check-type val ipv4-host-address)
		 (encode-bytes buf (slot-value val 'host-bytes)))
		((ipv6-address)
		 (check-type val ipv6-host-address)
		 (encode-bytes buf (slot-value val 'host-bytes)))))))
	(let ((dlen (- (length packet-buf) orig-off)))
	  (setf (aref packet-buf orig-off) (ldb (byte 8 8) dlen)
		(aref packet-buf (1+ orig-off)) (ldb (byte 8 0) dlen)))))))

(defun encode-dns-packet (buf packet)
  (declare (type dns-encode-state buf)
	   (type dns-packet packet))
  (with-slots (txid is-response opcode authoritative truncated
		    recurse will-recurse resp-code
		    queries answers authority additional) packet
    (encode-uint-16 buf txid)
    (let ((flags 0))
      (setf (ldb (byte 1 15) flags) (if is-response 1 0)
	    (ldb (byte 4 11) flags) (ecase opcode
				      ((:query) 0)
				      ((:iquery) 1)
				      ((:status) 2))
	    (ldb (byte 1 10) flags) (if authoritative 1 0)
	    (ldb (byte 1 9) flags) (if truncated 1 0)
	    (ldb (byte 1 8) flags) (if recurse 1 0)
	    (ldb (byte 1 7) flags) (if will-recurse 1 0)
	    (ldb (byte 4 0) flags) (ecase resp-code
				     ((:success) 0)
				     ((:format-error) 1)
				     ((:server-failure) 2)
				     ((:name-error) 3)
				     ((:not-implemented) 4)
				     ((:refused) 5)))
      (encode-uint-16 buf flags))
    (encode-uint-16 buf (length queries))
    (encode-uint-16 buf (length answers))
    (encode-uint-16 buf (length authority))
    (encode-uint-16 buf (length additional))
    (dolist (query queries)
      (encode-dns-query buf query))
    (dolist (rr answers)
      (encode-dns-record buf rr))
    (dolist (rr authority)
      (encode-dns-record buf rr))
    (dolist (rr additional)
      (encode-dns-record buf rr)))
  (values))

(defun dns-encode (packet)
  (check-type packet dns-packet)
  (let ((buf (make-dns-encode-state)))
    (encode-dns-packet buf packet)
    (slot-value buf 'packet-buf)))

;;; DN format

(defun parse-domain-name (name)
  (declare (type string name))
  (let ((l '())
	(p 0))
    (loop (let ((p2 (position #\. name :start p)))
	    (if p2
		(if (= p2 (1- (length name)))
		    (return (values l t))
		    (setf l (append l (list (subseq name p p2)))
			  p (1+ p2)))
		(return (values (append l (list (subseq name p))) nil)))))))

(defun unparse-domain-name (name)
  (declare (type list name))
  (let ((buf nil))
    (dolist (label name buf)
      (setf buf (if buf
		    (concatenate 'string buf "." label)
		    label)))))

;;; Basic communication

(define-condition name-server-timeout (dns-error)
  ((server :initarg :server)))

(defun dns-do-request (server packet)
  (declare (type address server)
	   (type dns-packet packet))
  (with-connection (sk server)
    (socket-send sk (dns-encode packet))
    (loop
       (let ((resp (dns-decode (socket-recv sk))))
	 (when (= (dns-packet-txid resp)
		(dns-packet-txid packet))
	   (return resp))))))

(defun dns-std-request (queries &key (txid (random 65536)) (recurse t))
  (let ((qlist (map 'list #'(lambda (o)
			      (let ((name (first o))
				    (type (second o)))
				(make-instance 'resource-query
					       :name (etypecase name
						       (string (parse-domain-name name))
						       (list name))
					       :type type)))
		    queries)))
    (make-dns-packet :txid txid
		     :recurse recurse
		     :queries qlist)))

;;; RR caching

(defstruct domain-cache-entry
  (expire nil :type (or number null))
  (records '() :type list))

(defun domain-cache-key (name type)
  (list name (etypecase type
	       (symbol type)
	       (resource-record (class-name (class-of type))))))

(defun domain-cache-key-rr (record)
  (declare (type resource-record record))
  (list (slot-value record 'name) (class-name (class-of record))))

(defun domain-cache-get-entry (cache name type &optional create)
  (let* ((key (domain-cache-key name type))
	 (cur (gethash key cache)))
    (when (and cur (or (eq create :clear)
		       (let ((expire (domain-cache-entry-expire cur)))
			 (and expire
			      (> (/ (get-internal-real-time) internal-time-units-per-second)
				 expire)))))
      (remhash key cache)
      (setf cur nil))
    (cond (cur cur)
	  (create
	   (setf (gethash key cache) (make-domain-cache-entry))))))

(defun domain-cache-put (cache record)
  (with-slots (name ttl) record
    (let ((entry (domain-cache-get-entry cache name record t)))
      (push record (domain-cache-entry-records entry)))))

(defun dns-cache-records (cache records)
  (loop (unless records (return))
     (let* ((key (domain-cache-key-rr (car records)))
	    (matching (remove key records :test-not 'equal :key #'domain-cache-key-rr))
	    (ttl (block no-expire
		   (+ (/ (get-internal-real-time) internal-time-units-per-second)
		      (apply 'min (mapcar #'(lambda (rr)
					      (with-slots (ttl) rr
						(if ttl ttl (return-from no-expire nil))))
					  matching)))))
	    (entry (make-domain-cache-entry :expire ttl :records matching)))
       (setf (gethash key cache) entry
	     records (set-difference records matching)))))

(defun dns-cache-response (cache packet)
  (let ((records (append (dns-packet-answers packet)
			 (dns-packet-authority packet)
			 (dns-packet-additional packet))))
    (flet ((on-root (rr)
	     (equal (slot-value rr 'name) '())))
      (when (some #'on-root records)
	(warn "DNS packet purports to contain RRs on the root zone.")
	(setf records (delete-if #'on-root records))))
    (when (dns-packet-authoritative packet)
      (dolist (rq (dns-packet-queries packet))
	(with-slots (name type) rq
	  (unless (equal name '())
	    (let ((key (domain-cache-key name type)))
	      (unless (find key records :test 'equal :key #'domain-cache-key-rr)
		(let ((entry (domain-cache-get-entry cache name type :clear)))
		  (setf (domain-cache-entry-expire entry)
			(+ (/ (get-internal-real-time) internal-time-units-per-second)
			   60)))))))))	; XXX: Or something. It needs
					; to last for the query in
					; progress, at least. One
					; should probably look at an
					; SOA RR, if there is one.
    (dns-cache-records cache records)))

(defun make-domain-cache ()
  (let ((table (make-hash-table :test 'equal)))
    (dolist (server (labels ((ipv4 (address)
			       (make-instance 'ipv4-host-address :host-string address)))
		      `(("a.root-servers.net" ,(ipv4 "198.41.0.4"))
			("b.root-servers.net" ,(ipv4 "192.228.79.201"))
			("c.root-servers.net" ,(ipv4 "192.33.4.12"))
			("d.root-servers.net" ,(ipv4 "128.8.10.90"))
			("e.root-servers.net" ,(ipv4 "192.203.230.10"))
			("f.root-servers.net" ,(ipv4 "192.5.5.241"))
			("g.root-servers.net" ,(ipv4 "192.112.36.4"))
			("h.root-servers.net" ,(ipv4 "128.63.2.53"))
			("i.root-servers.net" ,(ipv4 "192.36.148.17"))
			("j.root-servers.net" ,(ipv4 "192.58.128.30"))
			("k.root-servers.net" ,(ipv4 "193.0.14.129"))
			("l.root-servers.net" ,(ipv4 "199.7.83.42"))
			("m.root-servers.net" ,(ipv4 "202.12.27.33")))))
      (let ((parsed (parse-domain-name (first server))))
	(domain-cache-put table (make-instance 'ns-record :name '() :ttl nil :ns-name parsed))
	;; Ensure that the cache is initialized at least with empty
	;; lists, so that the resolver doesn't try to resolve the root
	;; servers.
	(domain-cache-get-entry table parsed 'a-record t)
	(domain-cache-get-entry table parsed 'aaaa-record t)
	
	(dolist (address (cdr server))
	  (domain-cache-put table (etypecase address
				    (ipv4-host-address (make-instance 'a-record :name parsed :ttl nil :address address)))))))
    table))

;;; Resolver

(defstruct resolver-config
  (cache (make-domain-cache))
  (default-domains '() :type list)
  (help-servers '() :type list))

(defun initialize-default-resolver ()
  #+unix (with-open-file (s #p"/etc/resolv.conf" :if-does-not-exist nil)
	   (when s
	     (let ((cfg (make-resolver-config)))
	       (labels ((whitespace-p (char)
			  (declare (type character char))
			  (or (char= char #\space)
			      (char= char #\tab)))
			(split-line (line)
			  (let ((l '())
				(p 0))
			    (loop (let* ((p1 (or (position-if-not #'whitespace-p line :start p)
						(return l)))
					 (p2 (position-if #'whitespace-p line :start p1)))
				    (if p2
					(setf l (append l (list (subseq line p1 p2)))
					      p p2)
					(progn (setf l (append l (list (subseq line p1 p2))))
					       (return l))))))))
		 (let ((domain nil)
		       (search '()))
		   (loop (let ((line (read-line s nil nil)))
			   (unless line (return))
			   (let ((line (split-line line)))
			     (when line
			       (cond ((equal (car line) "nameserver")
				      (push (make-instance 'ipv4-address :host-string (second line))
					    (resolver-config-help-servers cfg)))
				     ((equal (car line) "search")
				      (setf search (append search (cdr line))))
				     ((equal (car line) "domain")
				      (setf domain (second line))))))))
		   (setf (resolver-config-default-domains cfg)
			 (or search (and domain (list domain)))))
		 cfg))))
  #-unix nil)

(defvar *dns-resolver-config* (initialize-default-resolver))

(defgeneric dns-server-address-for-record (record))
(defmethod dns-server-address-for-record ((record a-record))
  (make-instance 'udp4-address
		 :host-address (slot-value record 'address)
		 :port 53))
(defmethod dns-server-address-for-record ((record aaaa-record))
  (make-instance 'udp6-address
		 :host-address (slot-value record 'address)
		 :port 53))

(define-condition dns-resolver-condition (condition)
  ((query-name :initarg :query-name)
   (query-type :initarg :query-type)
   (config :initarg :config)))

(define-condition dns-resolver-error (dns-error dns-resolver-condition) ())
(define-condition domain-not-found-error (dns-resolver-error) ()
  (:report (lambda (c s)
	     (with-slots (query-name) c
	       (format s "No name servers found for domain name ~A." query-name)))))
(define-condition dns-name-error (dns-error dns-resolver-condition) ()
  (:report (lambda (c s)
	     (with-slots (query-name) c
	       (format s "The domain name ~A does not exist." query-name)))))

(define-condition dns-resolver-querying (dns-resolver-condition)
  ((server :initarg :server)))

(define-condition dns-resolver-got-resp (dns-resolver-condition)
  ((server :initarg :server)
   (response :initarg :response)))

(define-condition dns-resolver-help (dns-resolver-condition) ())
(define-condition dns-resolver-recursing (dns-resolver-condition) ())

(define-condition dns-resolver-following-cname (dns-resolver-condition)
  ((cname-rr :initarg :cname-rr)))

(defun dns-resolve-name (name types &key (require-all t) (config *dns-resolver-config*))
  (let ((name (etypecase name
		(list name)
		(string (parse-domain-name name))))
	(types (etypecase types
		 (list types)
		 (symbol (list types))))
	(cache (resolver-config-cache config)))
    (flet ((check-cache ()
	     (let ((cn-entry (domain-cache-get-entry cache name 'cname-record)))
	       (when (and cn-entry (domain-cache-entry-records cn-entry))
		 (let ((record (car (domain-cache-entry-records cn-entry))))
		   (signal 'dns-resolver-following-cname :cname-rr record
			   :query-name (unparse-domain-name name) :query-type types
			   :config config)
		   (return-from dns-resolve-name
		     (dns-resolve-name (slot-value record 'cname) types :config config)))))
	     (block skip
	       (let ((records '())
		     (got-some nil))
		 (dolist (type types)
		   (let ((entry (domain-cache-get-entry cache name type)))
		     (cond (entry
			    (setf records (append records (domain-cache-entry-records entry))
				  got-some t))
			   (require-all
			    (return-from skip)))))
		 (when got-some
		   (return-from dns-resolve-name (values records name))))))
	   (nearest-known-servers (name)
	     (labels ((check1 (name)
			(let ((entry (domain-cache-get-entry cache name 'ns-record)))
			  (cond ((and entry (domain-cache-entry-records entry))
				 (values (domain-cache-entry-records entry) name))
				(name (check1 (cdr name)))
				(t (values '() name))))))
	       (check1 name)))
	   (do-request (server)
	     (signal 'dns-resolver-querying :server server
		     :query-name (unparse-domain-name name) :query-type types
		     :config config)
	     (handler-case
		 (let ((resp (dns-do-request (udp-address-for server 53)
					     (dns-std-request (mapcar #'(lambda (type)
									  `(,name ,type))
								      types)))))
		   (signal 'dns-resolver-got-resp :server server :response resp
			   :query-name (unparse-domain-name name) :query-type types
			   :config config)
		   (dns-cache-response cache resp)
		   (with-slots (resp-code) resp
		     (when (eq (dns-packet-resp-code resp) :name-error)
		       (error 'dns-name-error :query-name (unparse-domain-name name) :query-type types
			      :config config))
		     (eq resp-code :success)))
	       (network-error () nil))))
      (check-cache)
      (signal 'dns-resolver-help :query-name (unparse-domain-name name) :query-type types
	      :config config)
      (dolist (help-server (resolver-config-help-servers config))
	(do-request help-server)
	(check-cache))
      (signal 'dns-resolver-recursing :query-name (unparse-domain-name name) :query-type types
	      :config config)
      (let ((checked-domains '()))
	(loop (multiple-value-bind (servers domain)
		  (nearest-known-servers name)
		(unless servers
		  (error 'domain-not-found-error :query-name (unparse-domain-name name) :query-type types
			 :config config))
		(if (find domain checked-domains :test 'equal)
		    (error 'domain-not-found-error :query-name (unparse-domain-name name) :query-type types
			   :config config)
		    (push domain checked-domains))
		(macrolet ((dolist-random ((var list) &body body)
			     (let ((copy (gensym "COPY")))
			       `(let ((,copy ,list))
				  (loop (unless ,copy (return))
				     (let ((,var (elt ,list (random (length ,list)))))
				       (setf ,copy (remove ,var ,copy))
				       ,@body))))))
		  (block found-server
		    (dolist-random (record servers)
		      (let* ((server (slot-value record 'ns-name)))
			(dolist-random (record (handler-case
						   (dns-resolve-name server '(a-record aaaa-record) :require-all nil :config config)
						 (dns-resolver-error () '())))
			  (when (do-request (dns-server-address-for-record record))
			    (return-from found-server))))))
		  (check-cache))))))))

(export '(*dns-resolver-config*))

;;; Misc.

(defmethod print-object ((q resource-query) stream)
  (with-slots (name type) q
    (if *print-readably*
	(format stream "~A: ~A" type (unparse-domain-name name))
	(format stream "#<~S ~S ~S>" 'resource-query type (unparse-domain-name name)))))