policy-node: handle nodes-follow-default in handleLinkable

Since nodes may have a target specified in their props, the logic in
cleanupTargetNodeMetadata does not work correctly.

Instead, emulate what Pulseaudio does: if we see a reconnectable node
with target defined by node props, but not by metadata, which is linked
to the default sink, then make the stream follow the default from that
point on.

src/scripts/policy-node.lua

@@ -269,13 +269,16 @@ function findDefinedTarget (properties)
   local target_direction = getTargetDirection(properties)
   local target_key
   local target_value
+  local node_defined = false
 
   if properties["target.object"] ~= nil then
     target_value = properties["target.object"]
     target_key = "object.serial"
+    node_defined = true
   elseif properties["node.target"] ~= nil then
     target_value = properties["node.target"]
     target_key = "node.id"
+    node_defined = true
   end
 
   if metadata then
@@ -283,21 +286,27 @@ function findDefinedTarget (properties)
     if id ~= nil then
       target_value = id
       target_key = "object.serial"
+      node_defined = false
     else
       id = metadata:find(properties["node.id"], "target.node")
       if id ~= nil then
         target_value = id
         target_key = "node.id"
+        node_defined = false
       end
     end
   end
 
+  if target_value == "-1" then
+    return nil, false, node_defined
+  end
+
   if target_value and tonumber(target_value) then
     local si_target = linkables_om:lookup {
       Constraint { target_key, "=", target_value },
     }
     if si_target and canLink (properties, si_target) then
-      return si_target, true
+      return si_target, true, node_defined
     end
   end
 
@@ -308,11 +317,11 @@ function findDefinedTarget (properties)
           target_props["object.path"] == target_value) and
           target_props["item.node.direction"] == target_direction and
           canLink (properties, si_target) then
-        return si_target, true
+        return si_target, true, node_defined
       end
     end
   end
-  return nil, (target_value and target_value ~= "-1")
+  return nil, (target_value ~= nil), node_defined
 end
 
 function parseParam(param, id)
@@ -590,6 +599,30 @@ function checkPending ()
   return false
 end
 
+function checkFollowDefault (si, si_target, has_node_defined_target)
+  -- If it got linked to the default target that is defined by node
+  -- props but not metadata, start ignoring the node prop from now on.
+  -- This is what Pulseaudio does.
+  if not has_node_defined_target then
+    return
+  end
+
+  local si_props = si.properties
+  local target_props = si_target.properties
+  local reconnect = not parseBool(si_props["node.dont-reconnect"])
+
+  if config.follow and default_nodes ~= nil and reconnect then
+    local def_id = getDefaultNode(si_props, getTargetDirection(si_props))
+
+    if target_props["node.id"] == tostring(def_id) then
+      local metadata = metadata_om:lookup()
+      -- Set target.node, for backward compatibility
+      metadata:set(tonumber(si_props["node.id"]), "target.node", "Spa:Id", "-1")
+      Log.info (si, "... set metadata to follow default")
+    end
+  end
+end
+
 function handleLinkable (si)
   if checkPending () then
     return
@@ -621,7 +654,8 @@ function handleLinkable (si)
   local si_must_passthrough = parseBool(si_props["item.node.encoded-only"])
 
   -- find defined target
-  local si_target, has_defined_target = findDefinedTarget(si_props)
+  local si_target, has_defined_target, has_node_defined_target
+      = findDefinedTarget(si_props)
   local can_passthrough = si_target and canPassthrough(si, si_target)
 
   if si_target and si_must_passthrough and not can_passthrough then
@@ -650,6 +684,8 @@ function handleLinkable (si)
   if si_flags[si_id].peer_id then
     if si_target and si_flags[si_id].peer_id == si_target.id then
       Log.debug (si, "... already linked to proper target")
+      -- Check this also here, in case in default targets changed
+      checkFollowDefault (si, si_target, has_node_defined_target)
       return
     end
     local link = lookupLink (si_id, si_flags[si_id].peer_id)
@@ -723,6 +759,8 @@ function handleLinkable (si)
   else
     createLink (si, si_target, can_passthrough, exclusive)
     si_flags[si.id].was_handled = true
+
+    checkFollowDefault (si, si_target, has_node_defined_target)
   end
 end
 
@@ -796,38 +834,9 @@ links_om = ObjectManager {
   }
 }
 
-function cleanupTargetNodeMetadata()
-  local metadata = metadata_om:lookup()
-  if metadata and default_nodes ~= nil then
-    local to_remove = {}
-    for s, k, t, v in metadata:iterate(Id.ANY) do
-      if k == "target.node" then
-        if v == "-1" then
-          -- target.node == -1 is useless, it means the default node
-          table.insert(to_remove, s)
-        else
-          -- if the target.node value is the same as the default node
-          -- that would be selected for this stream, remove it
-          local si = linkables_om:lookup { Constraint { "node.id", "=", s } }
-          local properties = si.properties
-          local def_id = getDefaultNode(properties, getTargetDirection(properties))
-          if tostring(def_id) == v then
-            table.insert(to_remove, s)
-          end
-        end
-      end
-    end
-
-    for _, s in ipairs(to_remove) do
-      metadata:set(s, "target.node", nil, nil)
-    end
-  end
-end
-
 -- listen for default node changes if config.follow is enabled
 if config.follow and default_nodes ~= nil then
   default_nodes:connect("changed", function ()
-    cleanupTargetNodeMetadata()
     scheduleRescan ()
   end)
 end