Add late installed listeners

Signed-off-by: Rahix <rahix@rahix.de>

README.md

@@ -172,8 +172,10 @@ the node will come online later.  `query` must be a valid query, chosen from
 `BaseControl.Query`.  A full list of currently supported queries was shown above.
 The `callback` function will get one argument:  The new value of the noun that
 triggered the event.  `listen` returns a unique id for the installed listener
-that could later be used to cancel it.
-
+that could later be used to cancel it.  `listen` also returns a boolean as the
+second value:  It indicates whether an attempt was made at installing the
+listener.  If the noun was not yet known (`false`), the listener is still kept
+and will be installed as soon as the noun is registered.
 ```lua
 bc = require("bc"):finalize{"some_noun"}
 bc:listen("some_noun", bc.Query.Change, function(value)

bc.lua

@@ -433,6 +433,14 @@ function BaseControl:_network_handler(remote, msg)
   elseif msg.ty == Message.Register then
     for _, noun in ipairs(msg.nouns or {}) do
       self.remote_nouns[noun] = remote
+      for id, l in pairs(self.listeners[noun] or {}) do
+        self.network:send(remote, {
+          ty=Message.ListenRequest,
+          noun=noun,
+          id=id,
+          query=l.query,
+        })
+      end
     end
     for _, verb in ipairs(msg.verbs or {}) do
       self.remote_verbs[verb] = remote

tests/listening.lua

@@ -195,3 +195,22 @@ function test_listen_cancel_remote()
   bc1:set("lcanr1", 21)
   assert_equal(1, n, "wrong number of listener invokations")
 end
+
+function test_listen_late_install()
+  local bc1 = BaseControl:new()
+  local addr1 = network.get_scene()
+
+  local n = 0
+  bc1:listen("late1", BaseControl.Query.Change, function()
+    n = n + 1
+  end)
+
+  local bc2 = BaseControl:new()
+  local addr2 = network.get_scene()
+  bc2:register("late1", 1234)
+  bc2:finalize()
+
+  assert_equal(0, n, "wrong number of listener invokations")
+  bc2:set("late1", 34)
+  assert_equal(1, n, "wrong number of listener invokations")
+end