Implement listen cancelling

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

README.md

@@ -184,7 +184,7 @@ bc:listen("some_noun", bc.Query.Below(0), function(value)
 end)
 ```
 
-### `BaseControl:cancel(id)`
+### `BaseControl:cancel(noun, id)`
 Cancel a previously installed listener.  The id will be invalid after this call.
 ```lua
 local listenid = bc:listen("some_noun", bc.Query.Change, function(value)
@@ -192,7 +192,7 @@ local listenid = bc:listen("some_noun", bc.Query.Change, function(value)
 end)
 
 -- Later ...
-bc:cancel(listenid)
+bc:cancel("some_noun", listenid)
 ```
 
 ### `BaseControl:close()`

bc.lua

@@ -390,7 +390,7 @@ function BaseControl:listen(noun, query, callback)
     callback=callback,
   }
   if self.local_nouns[noun] ~= nil then
-    return true
+    return id, true
   elseif self.remote_nouns[noun] ~= nil then
     self.network:send(self.remote_nouns[noun], {
       ty=Message.ListenRequest,
@@ -398,10 +398,24 @@ function BaseControl:listen(noun, query, callback)
       id=id,
       query=query,
     })
-    return true
+    return id, true
   else
-    return false
+    return id, false
+  end
+end
+
+function BaseControl:cancel(noun, id)
+  if self.listeners[noun] == nil or self.listeners[noun][id] == nil then
+    error("can't cancel unknown listener on \""..noun.."\"")
+  end
+  if self.local_nouns[noun] == nil and self.remote_nouns[noun] ~= nil then
+    self.network:send(self.remote_nouns[noun], {
+      ty=Message.ListenCancel,
+      noun=noun,
+      id=id,
+    })
   end
+  self.listeners[noun][id] = nil
 end
 -- }}}
 
@@ -469,6 +483,12 @@ function BaseControl:_network_handler(remote, msg)
     if self.listeners[msg.noun][msg.id] ~= nil then
       self.listeners[msg.noun][msg.id].callback(msg.value)
     end
+  elseif msg.ty == Message.ListenCancel then
+    if self.listeners[msg.noun][msg.id] ~= nil then
+      if self.listeners[msg.noun][msg.id].addr == remote then
+        self.listeners[msg.noun][msg.id] = nil
+      end
+    end
   else
     error("TODO: MessageType Unknown")
   end

tests/listening.lua

@@ -134,3 +134,64 @@ do
     end
   end
 end
+
+function test_listen_cancel()
+  local bc = BaseControl:new()
+  bc:register("lcan1", 123)
+  bc:finalize()
+
+  local n = 0
+  local id = bc:listen("lcan1", BaseControl.Query.Change, function()
+    n = n + 1
+  end)
+
+
+  assert_equal(0, n, "wrong number of listener invokations")
+  bc:set("lcan1", 321)
+  assert_equal(1, n, "wrong number of listener invokations")
+
+  -- Cancel the listener
+  bc:cancel("lcan1", id)
+
+  bc:set("lcan1", 12)
+  assert_equal(1, n, "wrong number of listener invokations")
+
+  assert_error_match("unknown", function()
+    bc:cancel("lcan1", id)
+  end)
+
+  assert_error_match("unknown", function()
+    bc:cancel("lcan2", "fooid")
+  end)
+end
+
+function test_listen_cancel_remote()
+  local bc1 = BaseControl:new()
+  local addr1 = network.get_scene()
+  bc1:register("lcanr1", 123)
+  bc1:finalize()
+
+  local bc2 = BaseControl:new()
+  local addr2 = network.get_scene()
+
+  local n = 0
+  local id, ok = bc2:listen("lcanr1", BaseControl.Query.Change, function()
+    n = n + 1
+  end)
+  assert_true(ok, "failed installing")
+
+  network.set_scene(addr1)
+  assert_equal(0, n, "wrong number of listener invokations")
+  bc1:set("lcanr1", 34)
+  assert_equal(1, n, "wrong number of listener invokations")
+
+  -- Dirty hack to get the test working
+  local save = bc2.listeners["lcanr1"][id]
+  network.set_scene(addr2)
+  bc2:cancel("lcanr1", id)
+  bc2.listeners["lcanr1"][id] = save
+
+  network.set_scene(addr1)
+  bc1:set("lcanr1", 21)
+  assert_equal(1, n, "wrong number of listener invokations")
+end