audio: Prefer Pipewire over Pulseaudio (take 2)

src/audio/SDL_audio.c

@@ -28,6 +28,9 @@
 // Available audio drivers
 static const AudioBootStrap *const bootstrap[] = {
 #ifdef SDL_AUDIO_DRIVER_PULSEAUDIO
+#ifdef SDL_AUDIO_DRIVER_PIPEWIRE
+    &PIPEWIRE_PREFERRED_bootstrap,
+#endif
     &PULSEAUDIO_bootstrap,
 #endif
 #ifdef SDL_AUDIO_DRIVER_PIPEWIRE
@@ -98,15 +101,41 @@ static const AudioBootStrap *const bootstrap[] = {
 
 static SDL_AudioDriver current_audio;
 
+// Deduplicated list of audio bootstrap drivers.
+static const AudioBootStrap *deduped_bootstrap[SDL_arraysize(bootstrap) - 1];
+
 int SDL_GetNumAudioDrivers(void)
 {
-    return SDL_arraysize(bootstrap) - 1;
+    static int num_drivers = -1;
+
+    if (num_drivers >= 0) {
+        return num_drivers;
+    }
+
+    num_drivers = 0;
+
+    // Build a list of unique audio drivers.
+    for (int i = 0; bootstrap[i] != NULL; ++i) {
+        SDL_bool duplicate = SDL_FALSE;
+        for (int j = 0; j < i; ++j) {
+            if (SDL_strcmp(bootstrap[i]->name, bootstrap[j]->name) == 0) {
+                duplicate = SDL_TRUE;
+                break;
+            }
+        }
+
+        if (!duplicate) {
+            deduped_bootstrap[num_drivers++] = bootstrap[i];
+        }
+    }
+
+    return num_drivers;
 }
 
 const char *SDL_GetAudioDriver(int index)
 {
     if (index >= 0 && index < SDL_GetNumAudioDrivers()) {
-        return bootstrap[index]->name;
+        return deduped_bootstrap[index]->name;
     }
     return NULL;
 }
@@ -884,8 +913,8 @@ int SDL_InitAudio(const char *driver_name)
                         current_audio.name = bootstrap[i]->name;
                         current_audio.desc = bootstrap[i]->desc;
                         initialized = SDL_TRUE;
+                        break;
                     }
-                    break;
                 }
             }
 

src/audio/SDL_sysaudio.h

@@ -335,6 +335,7 @@ typedef struct AudioBootStrap
 } AudioBootStrap;
 
 // Not all of these are available in a given build. Use #ifdefs, etc.
+extern AudioBootStrap PIPEWIRE_PREFERRED_bootstrap;
 extern AudioBootStrap PIPEWIRE_bootstrap;
 extern AudioBootStrap PULSEAUDIO_bootstrap;
 extern AudioBootStrap ALSA_bootstrap;

src/audio/pipewire/SDL_pipewire.c

@@ -29,6 +29,17 @@
 #include <spa/param/audio/format-utils.h>
 #include <spa/utils/json.h>
 
+#include "../../core/linux/SDL_dbus.h"
+
+static SDL_bool CheckPipewirePulseService()
+{
+#ifdef SDL_USE_LIBDBUS
+    return SDL_DBus_QuerySystemdUnitRunning("pipewire-pulse.service", SDL_TRUE);
+#else
+    return SDL_FALSE;
+#endif
+}
+
 /*
  * The following keys are defined for compatibility when building against older versions of Pipewire
  * prior to their introduction and can be removed if the minimum required Pipewire build version is
@@ -1251,7 +1262,7 @@ static void PIPEWIRE_Deinitialize(void)
     }
 }
 
-static SDL_bool PIPEWIRE_Init(SDL_AudioDriverImpl *impl)
+static SDL_bool PipewireInitialize(SDL_AudioDriverImpl *impl)
 {
     if (!pipewire_initialized) {
         if (init_pipewire_library() < 0) {
@@ -1282,6 +1293,25 @@ static SDL_bool PIPEWIRE_Init(SDL_AudioDriverImpl *impl)
     return SDL_TRUE;
 }
 
-AudioBootStrap PIPEWIRE_bootstrap = { "pipewire", "Pipewire", PIPEWIRE_Init, SDL_FALSE };
+static SDL_bool PIPEWIRE_PREFERRED_Init(SDL_AudioDriverImpl *impl)
+{
+    if (CheckPipewirePulseService()) {
+        return PipewireInitialize(impl);
+    }
+
+    return SDL_FALSE;
+}
+
+static SDL_bool PIPEWIRE_Init(SDL_AudioDriverImpl *impl)
+{
+    return PipewireInitialize(impl);
+}
+
+AudioBootStrap PIPEWIRE_PREFERRED_bootstrap = {
+    "pipewire", "Pipewire", PIPEWIRE_PREFERRED_Init, SDL_FALSE
+};
+AudioBootStrap PIPEWIRE_bootstrap = {
+    "pipewire", "Pipewire", PIPEWIRE_Init, SDL_FALSE
+};
 
 #endif // SDL_AUDIO_DRIVER_PIPEWIRE

src/core/linux/SDL_dbus.c

@@ -632,4 +632,73 @@ char **SDL_DBus_DocumentsPortalRetrieveFiles(const char *key, int *path_count)
     return NULL;
 }
 
+/* Check to see if a Systemd unit exists and is currently running. */
+SDL_bool SDL_DBus_QuerySystemdUnitRunning(const char *unit_name, SDL_bool user_unit)
+{
+    const char *path, *prop;
+    DBusError err;
+    SDL_bool running = SDL_FALSE;
+
+    /* Make sure we have a connection to the dbus session bus */
+    if (!SDL_DBus_GetContext() || !dbus.session_conn) {
+        /* We either cannot connect to the session bus or were unable to
+         * load the D-Bus library at all. */
+        return SDL_FALSE;
+    }
+
+    /* Make sure the appropriate bus is available. */
+    if ((user_unit && !dbus.session_conn) || (!user_unit && !dbus.system_conn)) {
+        return SDL_FALSE;
+    }
+
+    dbus.error_init(&err);
+
+    /* Get the object path for the unit. */
+    DBusMessage *method = dbus.message_new_method_call("org.freedesktop.systemd1",
+                                                       "/org/freedesktop/systemd1",
+                                                       "org.freedesktop.systemd1.Manager",
+                                                       "GetUnit");
+    if (!method) {
+        return SDL_FALSE;
+    }
+
+    if (!dbus.message_append_args(method, DBUS_TYPE_STRING, &unit_name, DBUS_TYPE_INVALID)) {
+        SDL_OutOfMemory();
+        dbus.message_unref(method);
+        return SDL_FALSE;
+    }
+
+    DBusMessage *reply = dbus.connection_send_with_reply_and_block(user_unit ? dbus.session_conn : dbus.system_conn, method, DBUS_TIMEOUT_USE_DEFAULT, &err);
+    dbus.message_unref(method);
+    if (!reply) {
+        if (dbus.error_is_set(&err)) {
+            SDL_SetError("%s: %s", err.name, err.message);
+            dbus.error_free(&err);
+        }
+        return SDL_FALSE;
+    }
+
+    DBusMessageIter reply_iter;
+    if (!dbus.message_iter_init(reply, &reply_iter)) {
+        goto done;
+    }
+
+    if (dbus.message_iter_get_arg_type(&reply_iter) != DBUS_TYPE_OBJECT_PATH) {
+        goto done;
+    }
+
+    dbus.message_iter_get_basic(&reply_iter, &path);
+
+    /* We want to know the substate of the unit, which should be the string "running". */
+    if (SDL_DBus_QueryPropertyOnConnection(user_unit ? dbus.session_conn : dbus.system_conn,
+                                           "org.freedesktop.systemd1", path, "org.freedesktop.systemd1.Unit",
+                                           "SubState", DBUS_TYPE_STRING, &prop)) {
+        running = SDL_strcmp(prop, "running") == 0;
+    }
+
+done:
+    dbus.message_unref(reply);
+    return running;
+}
+
 #endif

src/core/linux/SDL_dbus.h

@@ -109,6 +109,8 @@ extern char *SDL_DBus_GetLocalMachineId(void);
 
 extern char **SDL_DBus_DocumentsPortalRetrieveFiles(const char *key, int *files_count);
 
+extern SDL_bool SDL_DBus_QuerySystemdUnitRunning(const char *unit_name, SDL_bool user_unit);
+
 #endif /* HAVE_DBUS_DBUS_H */
 
 #endif /* SDL_dbus_h_ */