services: openvpn: Allow the client to hardcode DNS servers to use.

* gnu/services/vpn.scm (%ipv4-regex): New variable.
(dhcp-option-dns-list?): New variable.
(serialize-dhcp-option-dns-list): New variable.
(openvpn-client-configuration)[dns]: New field.

Change-Id: Ic4e8184f47bf3f1d5b683c4dc737f6abba8d2f9e

1 files changed, 16 insertions, 0 deletions

diff --git a/gnu/services/vpn.scm b/gnu/services/vpn.scm
index d3caafb363..e3e3313902 100644
--- a/gnu/services/vpn.scm
+++ b/gnu/services/vpn.scm
@@ -149,6 +149,18 @@
   (when value
     (serialize-ip-mask field-name value)))
 
+(define %ipv4-regex
+  (let ((ipv4-octet-group "(25[0-5]|(2[0-4]|1[0-9]|[1-9]|)[0-9])"))
+    (make-regexp (format #f "^(~a\\.){3}~@*~a$" ipv4-octet-group))))
+(define (dhcp-option-dns-list? value)
+  (and (list? value)
+       (and-map (lambda (elem)
+                  (and (string? elem)
+                       (regexp-exec %ipv4-regex elem)))
+                value)))
+(define (serialize-dhcp-option-dns-list field-name value)
+  (format #t "~{dhcp-option DNS ~a~%~}" value))
+
 (define-syntax define-enumerated-field-type
   (lambda (x)
     (define (id-append ctx . parts)
@@ -457,6 +469,10 @@ would be added to the store and readable by any user.")
     (maybe-ip-mask #f)
     "Network routed through the VPN.")
 
+   (dns
+    (dhcp-option-dns-list '())
+    "DNS")
+
    (use-up-down-scripts?
     (use-up-down-scripts #f)
     "Run client.up and client.down scripts included with OpenVPN."))