added windows support to dns-find-nameserver

original commit: 2b67432b43888c7c93f5384616a5bb2defba7170

collects/net/dns-unit.ss

@@ -334,5 +334,22 @@
 			    (and m (cadr m))))
 		     (and (not (eof-object? l))
 			  (loop))))))))]
+      [(windows)
+       (let ([nslookup (find-executable-path "nslookup.exe" #f)])
+         (and nslookup
+              (let-values ([(p pout pin perr)
+                            (subprocess
+                             #f (open-input-file "NUL") (current-error-port)
+                             nslookup)])
+                (let loop ([dns #f])
+                  (let ([line (read-line pout 'any)])
+                    (cond [(eof-object? line)
+                           (subprocess-wait p)
+                           dns]
+                          [(and (not dns)
+                                (regexp-match #rx"^Default Server: +(.*)$"
+                                              line))
+                           => (lambda (m) (loop (cadr m)))]
+                          [else (loop dns)]))))))]
       [else #f])))))