Update

pipewire/.config/wireplumber/scripts/linking/prepare-link.lua

@@ -0,0 +1,125 @@
+-- WirePlumber
+--
+-- Copyright © 2022 Collabora Ltd.
+--
+-- SPDX-License-Identifier: MIT
+--
+-- remove the existing link if needed, check the properties of target, which
+-- indicate it is not available for linking. If no target is available, send
+-- down an error to the corresponding client.
+
+lutils = require ("linking-utils")
+cutils = require ("common-utils")
+log = Log.open_topic ("s-linking")
+
+SimpleEventHook {
+  name = "linking/prepare-link",
+  interests = {
+    EventInterest {
+      Constraint { "event.type", "=", "select-target" },
+    },
+  },
+  execute = function (event)
+    local source, _, si, si_props, si_flags, target =
+        lutils:unwrap_select_target_event (event)
+
+    local si_id = si.id
+    local reconnect = not cutils.parseBool (si_props ["node.dont-reconnect"])
+    local exclusive = cutils.parseBool (si_props ["node.exclusive"])
+    local si_must_passthrough = cutils.parseBool (si_props ["item.node.encoded-only"])
+
+    log:info (si, string.format ("handling item %d: %s (%s)", si_id,
+        tostring (si_props ["node.name"]), tostring (si_props ["node.id"])))
+
+    -- Check if item is linked to proper target, otherwise re-link
+    if si_flags.peer_id then
+      if target and si_flags.peer_id == target.id then
+        log:info (si, "... already linked to proper target")
+
+        -- Check this also here, in case in default targets changed
+        if Settings.get_boolean ("linking.follow-default-target") and
+            si_flags.has_node_defined_target then
+          lutils.checkFollowDefault (si, target)
+        end
+
+        target = nil
+        goto done
+      end
+
+      local link = lutils.lookupLink (si_id, si_flags.peer_id)
+      if reconnect then
+        if link ~= nil then
+          -- remove old link
+          if ((link:get_active_features () & Feature.SessionItem.ACTIVE) == 0)
+          then
+            -- remove also not yet activated links: they might never become
+            -- active, and we need not wait for it to become active
+            log:warning (link, "Link was not activated before removing")
+          end
+          si_flags.peer_id = nil
+          link:remove ()
+          log:info (si, "... moving to new target")
+        end
+      else
+        if link ~= nil then
+          log:info (si, "... dont-reconnect, not moving")
+          goto done
+        end
+      end
+    end
+
+    -- if the stream has dont-reconnect and was already linked before,
+    -- don't link it to a new target
+    if not reconnect and si_flags.was_handled then
+      target = nil
+      goto done
+    end
+
+    -- check target's availability
+    if target then
+      local target_is_linked, target_is_exclusive = lutils.isLinked (target)
+      if target_is_exclusive then
+        log:info (si, "... target is linked exclusively")
+        target = nil
+      end
+
+      if target_is_linked then
+        if exclusive or si_must_passthrough then
+          log:info (si, "... target is already linked, cannot link exclusively")
+          target = nil
+        else
+          -- disable passthrough, we can live without it
+          si_flags.can_passthrough = false
+        end
+      end
+    end
+
+    if not target then
+      log:info (si, "... target not found, reconnect:" .. tostring (reconnect))
+
+      local node = si:get_associated_proxy ("node")
+      if reconnect and si_flags.was_handled then
+        log:info (si, "... waiting reconnect")
+        return
+      end
+
+      local linger = cutils.parseBool (si_props ["node.linger"])
+
+      if linger then
+        log:info (si, "... node linger")
+        return
+      end
+
+      lutils.sendClientError (event, node, -2,
+          reconnect and "no target node available" or "target not found")
+
+      if not reconnect then
+        log:info (si, "... destroy node")
+        node:request_destroy ()
+      end
+    end
+
+    ::done::
+    event:set_data ("target", target)
+  end
+}:register ()