simplify protocol for watchers of service output directories

Previously: the service wrote a timestamp and the receiver
read and parsed it to see if there was new data

Now: the service writes and removes a .lock file to prevent
the receiver reading partial data. The receiver is responsible
for remembering the *previous* state and only updating if it's changed

examples/acquire-delegated-prefix.fnl

@@ -1,6 +1,39 @@
-
 (local inotify (require :inotify))
 
+(fn merge [table1 table2]
+  (collect [k v (pairs table2) &into table1]
+    k v))
+
+(fn split [sep string]
+  (icollect [v (string.gmatch string (.. "([^" sep "]+)"))]
+    v))
+
+(fn parse-prefix [str]
+  (fn parse-extra [s]
+    (let [out {}]
+      (each [name val (string.gmatch s ",(.-)=([^,]+)")]
+        (tset out name val))
+      out))
+  (let [(prefix len preferred valid extra)
+        (string.match str "(.-)::/(%d+),(%d+),(%d+)(.*)$")]
+    (merge {: prefix : len : preferred : valid} (parse-extra extra))))
+
+
+;; Format: <prefix>/<length>,preferred,valid[,excluded=<excluded-prefix>/<length>][,class=<prefix class #>]
+
+;;(parse-prefix "2001:8b0:de3a:40dc::/64,7198,7198")
+;;(parse-prefix "2001:8b0:de3a:1001::/64,7198,7188,excluded=1/2,thi=10")
+
+
+(fn file-exists? [name]
+  (match (io.open name :r)
+    f (do (f:close) true)
+    _ false))
+
+(fn read-line [name]
+  (with-open [f (assert (io.open name :r) (.. "can't open file " name))]
+    (f:read "*l")))
+
 (fn watch-fsevents [directory-name]
   (let [handle (inotify.init)]
     (handle:addwatch directory-name
@@ -13,58 +46,56 @@
                      inotify.IN_CLOSE_WRITE)
     handle))
 
+(fn watch-directory [pathname]
+  (let [watcher (watch-fsevents pathname)]
+    {
+     :has-file? (fn [_ filename] (file-exists? (.. pathname "/" filename)))
+     :wait-events (fn [] (watcher:read))
+     :ready? (fn [self]
+               (and (self:has-file? "state") (not (self:has-file? ".lock"))))
+     :read-line (fn [_ filename] (read-line (.. pathname "/" filename)))
+     :close #(watcher:close)
+     }))
 
-(fn merge [table1 table2]
-  (collect [k v (pairs table2) &into table1]
-    k v))
+(local bound-states
+       { :bound true
+         :rebound true
+         :informed true
+         :updated true
+         :ra-updated true
+         })
 
-(fn parse-extra [s]
-  (let [out {}]
-    (each [name val (string.gmatch s ",(.-)=([^,]+)")]
-      (tset out name val))
-    out))
+; (local { : view } (require :fennel))
 
-(fn parse-prefixes [prefixes]
-  (icollect [val (string.gmatch prefixes "([^ ]+)")]
-    (let [(prefix len preferred valid extra)
-          (string.match val "(.-)::/(%d+),(%d+),(%d+)(.*)$")]
-      (merge {: prefix : len : preferred : valid} (parse-extra extra))
-      )))
+(fn changes [old-prefixes new-prefixes]
+  (let [added {}
+        deleted {}
+        old-set (collect [_ v (ipairs old-prefixes)] (values v true))
+        new-set (collect [_ v (ipairs new-prefixes)] (values v true))]
+    (each [_ prefix (ipairs new-prefixes)]
+      (if (not (. old-set prefix))
+          (table.insert added (parse-prefix prefix))))
+    (each [_ prefix (ipairs old-prefixes)]
+      (if (not (. new-set prefix))
+          (table.insert deleted (parse-prefix prefix))))
+    (values added deleted)))
 
-;; Format: <prefix>/<length>,preferred,valid[,excluded=<excluded-prefix>/<length>][,class=<prefix class #>]
-
-;; (parse-prefixes "2001:8b0:de3a:40dc::/64,7198,7198 2001:8b0:de3a:1001::/64,7198,7188,excluded=1/2,thi=10")
-
-
-(fn file-exists? [name]
-  (match (io.open name :r)
-    f (do (f:close) true)
-    _ false))
-
-
-(fn read-line [name]
-  (with-open [f (assert (io.open name :r) (.. "can't open file " name))]
-    (f:read "*l")))
-
-(var last-update 0)
-(fn event-time [directory]
-  (if (file-exists? (.. directory "/state"))
-      (tonumber (read-line (.. directory "/last-update")))
-      nil))
-
-(fn wait-for-update [directory fsevents]
-  (while (<= (or (event-time directory) 0) last-update)
-    (fsevents:read))
-  (set last-update (event-time directory))
-  true)
+;;(fn execute [s] (do (print s) true))
+(fn execute [s] (assert (os.execute s)))
 
 (let [[state-directory lan-device] arg
-      fsevents (watch-fsevents state-directory)]
-  (while (wait-for-update state-directory fsevents)
-    (match (read-line (.. state-directory "/state"))
-      (where (or :bound :rebound :informed :updated :ra-updated))
-      (let [[{ : prefix : len : preferred : valid }]
-            (parse-prefixes (read-line (.. state-directory  "/prefixes")))]
-        (os.execute (.. "ip address add " prefix "::1/" len
-    		        " dev " lan-device)))
-      _ (os.exit 1))))
+      dir (watch-directory state-directory)]
+  (var prefixes [])
+  (while true
+    (while (not (dir:ready?)) (dir:wait-events))
+    (if (. bound-states (dir:read-line "state"))
+        (let [new-prefixes (split " " (dir:read-line "/prefixes"))
+              (added deleted) (changes prefixes new-prefixes)]
+          (each [_ p (ipairs added)]
+            (execute
+             (.. "ip address add " p.prefix "::1/" p.len " dev " lan-device)))
+          (each [_ p (ipairs deleted)]
+            (execute
+             (.. "ip address del " p.prefix "::1/" p.len " dev " lan-device)))
+    	  (set prefixes new-prefixes)))
+    (dir:wait-events)))

pkgs/odhcp-script/odhcp6-script.fnl

@@ -56,8 +56,9 @@
               "unbound" false
               "stopped" false
               _ true)]
-  (write-value "last-update" (tostring (os.time)))
+  (write-value ".lock" (tostring (os.time)))
   (write-value "ifname" ifname)
   (write-value "state" state)
+  (os.remove (.. state-directory "/.lock"))
   (when ready
     (with-open [fd (io.open "/proc/self/fd/10" :w)] (fd:write "\n"))))