Enhancements

Enable the AirPlay 2 build to operate an optional classic-AirPlay-only service or to gracefully degrade to classic AirPlay, as follows:
  1. Add a new command-line option '-—service-type=<type>' and an equivalent configuration entry 'service_type = "<type>"' in the 'general' section of the configuration file,
     where <type> can be "auto", "classic" or "airplay2":
      1. "auto" (default) means that the service will be AirPlay 2 if NQPTP is running. If NQPTP is not running, classic AirPlay service will be provided instead, and in that case,
      "(Classic)" will be appended to the default AirPlay service name visible to AirPlay clients like Apple Music, for example "RaspberryPi3B (Classic)".
      2. "classic" means the service will be classic AirPlay (aka AirPlay 1).
      3. "airplay2" means the service will be the modern AirPlay 2. In this case, as distinct from "auto", if NQPTP is not running, Shairport Sync will log an error and terminate.
  2. In the systemd service file, NQPTP is now a "Want" rather than a "Require". If it's present, then it will be launched before Shairport Sync. If it's absent, Shairport Sync will launch anyway.
  3. Improve the delivery of input format changes and emit 'sdsc' metadata when changes occur.
  4. Emit new format information in the log if statistics is enabled.

Docker Changes
  1. Support for linux/arm/v6 has been dropped, as Docker is no longer supported.
  2. NQPTP is not started in the AirPlay 2 Docker image if '--service-type=classic' or '--service-type=airplay1' is in the command line options at the end of the docker run command.
     The purpose is to ensure that ports 319 and 320 are left alone when the AirPlay 2 image is set to provide Classic service only.
     Note that setting the configuration file 'service_type' to 'classic' will not prevent NQPTP from starting up -- you must use the command line option.
  3. A new "dev" target has been added. It is a large image containing the custom-built FFmpeg library, NQPTP, Avahi and D-Bus along with the Shairport Sync source and
     all necessary development tools. When started, Avahi, D-Bus and NQPTP are all installed and running. The bash shell has also been added and is entered.

Stability Improvements
  Reorganise session preemption to fully terminate the existing session before starting a new one.
  Don't delay closing the event port to wait for it to be closed at the client end.
  Add a safe_socket_close() function to ensure sockets are fully closed. Use -1 to designate closed rather than 0, to prevent attempts to reclose sockets, causing mayhem.
  Re-order FFmpeg decommissioning during teardown.

mqtt.c

@@ -8,14 +8,16 @@
 #include "common.h"
 #include "player.h"
 #include "rtsp.h"
+#include "utilities/string_utilities.h"
 
 #include "rtp.h"
 
 #ifdef CONFIG_DACP_CLIENT
 #include "dacp.h"
 #endif
-#include "metadata/hub.h"
+
 #include "metadata/core.h"
+#include "metadata/hub.h"
 #include "metadata/pc_queue.h"
 
 #include "mqtt.h"
@@ -79,7 +81,7 @@ void on_message(__attribute__((unused)) struct mosquitto *mosq,
       debug(2, "[MQTT]: Received Recognized Command: %s\n", commands[it]);
       if (strcmp(commands[it], "disconnect") == 0) {
         debug(2, "[MQTT]: Disconnect Command: %s\n", commands[it]);
-        release_play_lock(NULL); // stop any current session and don't replace it
+        stop_play(); // stop any current session and don't replace it
       } else {
         debug(2, "[MQTT]: DACP Command: %s\n", commands[it]);
 #ifdef CONFIG_DACP_CLIENT
@@ -211,10 +213,10 @@ void send_autodiscovery_messages(struct mosquitto *mosq) {
         (strcmp(sensors[i], "active") == 0 || strcmp(sensors[i], "playing") == 0);
     bool is_volume_sensor = strcmp(sensors[i], "volume") == 0;
 
-    const char* entity_type = is_binary_sensor ? "binary_sensor" : "sensor";
+    const char *entity_type = is_binary_sensor ? "binary_sensor" : "sensor";
 
-    snprintf(topic, sizeof(topic), "%s/%s/%s_%s/%s/config", autodiscovery_prefix,
-             entity_type, model, device_id_no_colons, sensors[i]);
+    snprintf(topic, sizeof(topic), "%s/%s/%s_%s/%s/config", autodiscovery_prefix, entity_type,
+             model, device_id_no_colons, sensors[i]);
 
     snprintf(id_string, sizeof(id_string), "%s_%s_%s", model, device_name, sensors[i]);
 
@@ -232,12 +234,12 @@ void send_autodiscovery_messages(struct mosquitto *mosq) {
         "\"default_entity_id\": \"%s.%s\","
         "%s%s%s"
         "}",
-        sensor_names[i], // name
-        config.mqtt_topic, sensors[i], //state_topic
-        icons[i], // icon
-        id_string, // unique_id
-        id_string, // object_id
-        entity_type, id_string, // default_entity_id
+        sensor_names[i],               // name
+        config.mqtt_topic, sensors[i], // state_topic
+        icons[i],                      // icon
+        id_string,                     // unique_id
+        id_string,                     // object_id
+        entity_type, id_string,        // default_entity_id
         is_binary_sensor ? "\"payload_on\": \"1\",\"payload_off\": \"0\"," : "",
         is_volume_sensor
             ? "\"value_template\": \"{{ ((value | regex_findall_index("
@@ -268,8 +270,7 @@ void mqtt_publish(char *topic, char *data_in, uint32_t length_in) {
 
   int rc;
   if ((rc = mosquitto_publish(global_mosq, NULL, fulltopic, length, data, 0,
-                              config.mqtt_publish_retain)) !=
-      MOSQ_ERR_SUCCESS) {
+                              config.mqtt_publish_retain)) != MOSQ_ERR_SUCCESS) {
     switch (rc) {
     case MOSQ_ERR_NO_CONN:
       debug(1, "[MQTT]: Publish failed: not connected to broker");
@@ -503,15 +504,13 @@ void metadata_mqtt_queue_init() {
     debug(1, "Failed to create metadata mqtt thread!");
 }
 void metadata_mqtt_queue_stop() {
-    // debug(2, "metadata stop mqtt thread.");
-    pthread_cancel(metadata_mqtt_thread);
-    pthread_join(metadata_mqtt_thread, NULL);
-    pc_queue_delete(&metadata_mqtt_queue);
-    // debug(2, "metadata stop mqtt done.");
+  // debug(2, "metadata stop mqtt thread.");
+  pthread_cancel(metadata_mqtt_thread);
+  pthread_join(metadata_mqtt_thread, NULL);
+  pc_queue_delete(&metadata_mqtt_queue);
+  // debug(2, "metadata stop mqtt done.");
 }
-int send_metadata_to_mqtt_queue(const uint32_t type, const uint32_t code,
-                           const char *data, const uint32_t length, rtsp_message *carrier,
-                           int block) {
-    return send_metadata_to_queue(&metadata_mqtt_queue, type, code, data, length, carrier, block);
+int send_metadata_to_mqtt_queue(const uint32_t type, const uint32_t code, const char *data,
+                                const uint32_t length, rtsp_message *carrier, int block) {
+  return send_metadata_to_queue(&metadata_mqtt_queue, type, code, data, length, carrier, block);
 }
-