pulse-server: add skeleton extension for stream-restore

Makes the system-volume slider show up again in pavucontrol
and gnome-control-setting. Does not work yet, though.

src/modules/module-protocol-pulse/extension.c

@@ -0,0 +1,64 @@
+/* PipeWire
+ *
+ * Copyright © 2020 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+struct extension_sub {
+	const char *name;
+	uint32_t command;
+	int (*process)(struct client *client, uint32_t command, uint32_t tag, struct message *m);
+};
+
+struct extension {
+	const char *name;
+	uint32_t idx;
+	int (*process)(struct client *client, uint32_t tag, struct message *m);
+};
+
+#include "ext-stream-restore.c"
+
+static int do_extension_device_restore(struct client *client, uint32_t tag, struct message *m)
+{
+	return -ENOTSUP;
+}
+
+static int do_extension_device_manager(struct client *client, uint32_t tag, struct message *m)
+{
+	return -ENOTSUP;
+}
+
+struct extension extensions[] = {
+	{ "module-stream-restore", 0 | EXTENSION_FLAG, do_extension_stream_restore, },
+	{ "module-device-restore", 1 | EXTENSION_FLAG, do_extension_device_restore, },
+	{ "module-device-manager", 2 | EXTENSION_FLAG, do_extension_device_manager, },
+};
+
+static struct extension *find_extension(uint32_t idx, const char *name)
+{
+	uint32_t i;
+	for (i = 0; i < SPA_N_ELEMENTS(extensions); i++) {
+		if (idx == extensions[i].idx ||
+		    (name && strcmp(name, extensions[i].name) == 0))
+			return &extensions[i];
+	}
+	return 0;
+}