dhcpc6 scripts: simplify (and improve correctness)

modules/dhcp6c/acquire-delegated-prefix.fnl

@@ -1,40 +1,32 @@
 (local { : system } (require :anoia))
 (local svc (require :anoia.svc))
 
-(fn changes [old-addresses new-addresses]
-  (let [added {}
-        deleted {}]
-    (each [n address (pairs new-addresses)]
-      (if (not (. old-addresses n))
-          (table.insert added address)))
+(fn deletions [old-addresses new-addresses]
+  (let [deleted {}]
     (each [n address (pairs old-addresses)]
-      (if (not (. new-addresses n))
-          (table.insert deleted address)))
-    (values added deleted)))
+      (let [now (. new-addresses n)]
+        (if (or (not now) (not (= now.len address.len)))
+            (table.insert deleted address))))
+    deleted))
 
-(fn update-prefixes [device prefixes new-prefixes]
-  (let [(added deleted) (changes prefixes new-prefixes)]
-    ;; if some address has changed (e.g. preferred/valid lifetime)
-    ;; then we don't want to delete it before re-adding it because
-    ;; the kernel will drop any routes that go through it. On the
-    ;; other hand, we can't add it _before_ deleting it as we'll
-    ;; get an error that it already exists. Therefore, use "change"
-    ;; instead of "add", it works a bit more like an upsert
-    (each [_ p (ipairs added)]
-      (system
-       (.. "ip address change " p.address "1/" p.len " dev " device
-           " valid_lft " p.valid
-           " preferred_lft " p.preferred
-           )))
-    (each [_ p (ipairs deleted)]
-      (system
-       (.. "ip address del " p.address "1/" p.len " dev " device)))))
+(fn update-prefixes [wan-device addresses new-addresses exec]
+  (each [_ p (ipairs (deletions addresses new-addresses))]
+    (exec
+     (.. "ip address del " p.address "1/" p.len " dev " wan-device)))
+  (each [_ p (pairs new-addresses)]
+    (exec
+     (.. "ip address change " p.address "1/" p.len
+         " dev " wan-device
+         " valid_lft " p.valid
+         " preferred_lft " p.preferred
+         )))
+  new-addresses)
 
 (fn run []
   (let [[state-directory lan-device] arg
         dir (svc.open state-directory)]
     (accumulate [addresses []
                  v (dir:events)]
-      (update-prefixes lan-device addresses (v:output "prefix")))))
+      (update-prefixes lan-device addresses (v:output "prefix") system))))
 
 { : changes : run }