s/create-item: add setting to enforce a media.role on streams that don't have one

src/config/wireplumber.conf

@@ -787,6 +787,11 @@ wireplumber.settings.schema = {
     min = 0.0
     max = 1.0
   }
+  node.stream.default-media-role = {
+    description = "A media.role to assign on streams that have none specified"
+    type = "string"
+    default = null
+  }
   node.filter.forward-format = {
     description = "Whether to forward format on filter nodes or not"
     type = "bool"

src/config/wireplumber.conf.d.examples/media-role-nodes.conf

@@ -12,6 +12,14 @@ wireplumber.profiles = {
   }
 }
 
+wireplumber.settings = {
+  # This sets a default media role to be applied to streams that don't have
+  # a role already set. This allows you to force all streams to go through
+  # the role loopbacks. If not set, then streams without a role will follow
+  # the standard desktop policy and will link to the default sink
+  node.stream.default-media-role = "Multimedia"
+}
+
 wireplumber.components.rules = [
   # This encodes common arguments and dependencies of the role loopbacks so that
   # we don't have to repeateadly write them on all instances below
@@ -29,7 +37,13 @@ wireplumber.components.rules = [
             media.class = Audio/Sink
           }
           playback.props = {
+            # This must be set to ensure that the real audio sink is suspended
+            # when there is no active client stream linked
             node.passive = true
+            # Set this to an unused role to make sure that loopbacks don't
+            # accidentally chain-link on to one another, especially when
+            # node.stream.default-media-role is configured in the settings
+            media.role = "Loopback"
           }
         }
         requires = [ support.export-core, pw.node-factory.adapter ]

src/scripts/node/create-item.lua

@@ -41,6 +41,15 @@ function configProperties (node)
       Settings.get_boolean ("node.features.audio.control-port")
   properties ["node.id"] = node ["bound-id"]
 
+  -- set the default media.role, if configured
+  -- avoid Settings.get_string(), as it will parse the default "null" value
+  -- as a string instead of returning nil
+  local default_role = Settings.get ("node.stream.default-media-role")
+  if default_role then
+    default_role = default_role:parse()
+    properties ["media.role"] = properties ["media.role"] or default_role
+  end
+
   return properties
 end