scripts: Add an intended-roles policy script

This routes streams of a given media.role to devices which specify that
role in device.intended-roles.

src/config/main.lua.d/90-enable-all.lua

@@ -12,6 +12,9 @@ v4l2_monitor.enable()
 -- Track/store/restore user choices about devices
 device_defaults.enable()
 
+-- Link nodes by stream role and device intended role
+load_script("intended-roles.lua")
+
 -- Automatically suspends idle nodes after 3 seconds
 load_script("suspend-node.lua")
 

src/scripts/intended-roles.lua

@@ -0,0 +1,66 @@
+-- WirePlumber
+--
+-- Copyright © 2021 Asymptotic
+--    @author Arun Raghavan <arun@asymptotic.io>
+--
+-- SPDX-License-Identifier: MIT
+--
+-- Route streams of a given role (media.role property) to devices that are
+-- intended for that role (device.intended-roles property)
+
+metadata_om = ObjectManager {
+  Interest {
+    type = "metadata",
+    Constraint { "metadata.name", "=", "default" },
+  }
+}
+
+devices_om = ObjectManager {
+  Interest {
+    type = "node",
+    Constraint { "media.class", "matches", "Audio/*", type = "pw-global" },
+    Constraint { "device.intended-roles", "is-present", type = "pw" },
+  }
+}
+
+streams_om = ObjectManager {
+  Interest {
+    type = "node",
+    Constraint { "media.class", "matches", "Stream/*/Audio", type = "pw-global" },
+    Constraint { "media.role", "is-present", type = "pw-global" }
+  }
+}
+
+streams_om:connect("object-added", function (streams_om, stream)
+  local stream_role = stream.properties["media.role"]
+  local is_input = stream.properties["media.class"]:find("Input") ~= nil
+
+  for dev in devices_om:iterate() do
+    local is_source = dev.properties["media.class"]:find("Source") ~= nil
+    local dev_roles = dev.properties["device.intended-roles"]
+
+    -- Make sure the stream and device direction match
+    if is_input ~= is_source then
+      goto next
+    end
+
+    for role in dev_roles:gmatch("(%a+)") do
+      if role == stream_role then
+        Log.info(stream,
+          string.format("Routing stream '%s' (%d) with role '%s' to '%s' (%d)",
+            stream.properties["node.name"], stream["bound-id"], stream_role,
+            dev.properties["node.name"], dev["bound-id"])
+        )
+
+        local metadata = metadata_om:lookup()
+        metadata:set(stream["bound-id"], "target.node", "Spa:Id", dev["bound-id"])
+      end
+    end
+
+    ::next::
+  end
+end)
+
+metadata_om:activate()
+devices_om:activate()
+streams_om:activate()