Improve dbus and add some dacp services

dacp.h

@@ -0,0 +1,24 @@
+#pragma once
+#include "common.h"
+#include "config.h"
+#include <sys/socket.h>
+
+#include "player.h"
+
+typedef struct dacp_speaker_stuff {
+  int64_t speaker_number;
+  int active;
+  int32_t volume;
+  char *name; // this is really just for debugging
+} dacp_spkr_stuff;
+
+uint32_t dacp_tlv_crawl(
+    char **p,
+    int32_t *length); // return the code of the next TLV entity and advance the pointer beyond it.
+ssize_t dacp_send_client_command(rtsp_conn_info *conn, const char *command, char *response,
+                                 size_t max_response_length);
+int32_t dacp_get_client_volume(rtsp_conn_info *conn); // return the overall volume from the client
+int dacp_set_include_speaker_volume(rtsp_conn_info *conn, int64_t machine_number, int32_t vo);
+int dacp_set_speaker_volume(rtsp_conn_info *conn, int64_t machine_number, int32_t vo);
+int dacp_get_speaker_list(rtsp_conn_info *conn, dacp_spkr_stuff *speaker_array,
+                          int max_size_of_array);