internal/pipewire: implement Registry::GlobalRemove

This is emitted by PipeWire when a global object disappears, because PipeWire insists that all clients that had called Core::GetRegistry must constantly sync its local registry state with the remote.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pipewire/core.go

@@ -533,6 +533,30 @@ func (c *RegistryGlobal) MarshalBinary() ([]byte, error) { return Marshal(c) }
 // UnmarshalBinary satisfies [encoding.BinaryUnmarshaler] via [Unmarshal].
 func (c *RegistryGlobal) UnmarshalBinary(data []byte) error { return Unmarshal(data, c) }
 
+// A RegistryGlobalRemove event is emitted when a global with id was removed.
+type RegistryGlobalRemove struct {
+	// The global id that was removed.
+	ID Int `json:"id"`
+}
+
+// Opcode satisfies [Message] with a constant value.
+func (c *RegistryGlobalRemove) Opcode() byte { return PW_REGISTRY_EVENT_GLOBAL_REMOVE }
+
+// FileCount satisfies [Message] with a constant value.
+func (c *RegistryGlobalRemove) FileCount() Int { return 0 }
+
+// Size satisfies [KnownSize] with a constant value.
+func (c *RegistryGlobalRemove) Size() Word {
+	return SizePrefix +
+		Size(SizeInt)
+}
+
+// MarshalBinary satisfies [encoding.BinaryMarshaler] via [Marshal].
+func (c *RegistryGlobalRemove) MarshalBinary() ([]byte, error) { return Marshal(c) }
+
+// UnmarshalBinary satisfies [encoding.BinaryUnmarshaler] via [Unmarshal].
+func (c *RegistryGlobalRemove) UnmarshalBinary(data []byte) error { return Unmarshal(data, c) }
+
 // RegistryBind is sent when the client requests to bind to the
 // global object with id and use the client proxy with new_id as
 // the proxy. After this call, methods can be sent to the remote
@@ -714,6 +738,14 @@ func (e *GlobalIDCollisionError) Error() string {
 		" stepping on previous id " + strconv.Itoa(int(e.ID)) + " for " + e.Previous.Type
 }
 
+// An UnknownGlobalIDRemoveError describes a [RegistryGlobalRemove] event announcing the removal of
+// a global id that is not yet known to [Registry] or was already deleted.
+type UnknownGlobalIDRemoveError Int
+
+func (e UnknownGlobalIDRemoveError) Error() string {
+	return "Registry::GlobalRemove event targets unknown id " + strconv.Itoa(int(e))
+}
+
 func (registry *Registry) consume(opcode byte, files []int, unmarshal func(v any)) error {
 	closeReceivedFiles(files...)
 	switch opcode {
@@ -727,6 +759,17 @@ func (registry *Registry) consume(opcode byte, files []int, unmarshal func(v any
 		registry.Objects[global.ID] = global
 		return nil
 
+	case PW_REGISTRY_EVENT_GLOBAL_REMOVE:
+		var globalRemove RegistryGlobalRemove
+		unmarshal(&globalRemove)
+		l := len(registry.Objects)
+		delete(registry.Objects, globalRemove.ID)
+		if len(registry.Objects) != l-1 {
+			// this should never happen so is non-recoverable if it does
+			panic(UnknownGlobalIDRemoveError(globalRemove.ID))
+		}
+		return nil
+
 	default:
 		return &UnsupportedOpcodeError{opcode, registry.String()}
 	}