adapter: add adapter node

An adapter is like an audio-dsp node and client-stream combined.
It allows tighter control with the device (for rate control and
variable buffer sizes), software volume.

The idea is to also implement the client-stream with this
eventually.

src/modules/module-adapter/adapter.h

@@ -0,0 +1,48 @@
+/* PipeWire
+ *
+ * Copyright © 2019 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.
+ */
+
+#ifndef PIPEWIRE_ADAPTER_H
+#define PIPEWIRE_ADAPTER_H
+
+#include <pipewire/node.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define ADAPTER_USAGE	PW_KEY_NODE_NAME"=<string> "
+
+struct pw_node *
+pw_adapter_new(struct pw_core *core,
+		struct pw_node *slave,
+		struct pw_properties *properties,
+		size_t user_data_size);
+
+void *pw_adapter_get_user_data(struct pw_node *node);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* PIPEWIRE_ADAPTER_H */