added dns-inverse-query

dns.scm

@@ -740,7 +740,22 @@
 	(display "sorry, no answers received\n"))
     dns-msg))
 
-
+(define (dns-inverse-lookup ip)
+  (let* ((ip-string (ip-string->in-addr ip))
+	 (question (if ip-string ; if name is a ip-addr, the query is a in-addr.arpa address
+		       (make-octet-query-message (random 256) ip-string 'ptr 'in)
+		       (error "dns-inverse-lookup: no valid ip")))
+	 (use-cache? #t)
+	 (nameserver (dns-find-nameserver))
+	 (check-answer (lambda (dns-msg) (if *debug* (display "check-answer\n"))
+			       (let* ((reply (dns-message:reply dns-msg))
+				      (answers (message:answers reply)))
+				 (not (null? answers)))))
+	 (dns-msg (dns-get-information question use-cache? nameserver check-answer))
+	 (answers (message:answers (dns-message:reply dns-msg))))
+    (if (not (null? answers))
+	(rr-data-ptr:name (rr:data (car answers)))
+	#f)))
 
 
 

modules.scm

@@ -735,6 +735,7 @@
 (define-interface dns-interface
   (export dns-clear-cache
 	  dns-lookup
+	  dns-inverse-lookup
 	  show-dns-message
 	  dns-find-nameserver))