Python 正确有效地获取 DBUS 对象路径（例如 /org/bluez/dev_XX_XX_XX_XX_XX_XX/playerY）

Posted 2023-04-14

【中文标题】Python 正确有效地获取 DBUS 对象路径（例如 /org/bluez/dev_XX_XX_XX_XX_XX_XX/playerY）

【英文标题】：Python properly and effectively obtaining DBUS object path (e.g. /org/bluez/dev_XX_XX_XX_XX_XX_XX/playerY)

【发布时间】：2019-03-04 10:54:31

【问题描述】：

我想获取我正在创建的基于 bluez 的 A2DP 蓝牙播放器的设备路径。我坚持有效地执行播放/暂停/下一个/上一个命令，因为 dbus 可用性和播放器路径会根据您选择的媒体播放器而变化。此外，bluez 有时会决定发送大量无用信息（对我而言），例如播放列表详细信息，这会使我的应用程序处理的负载更大。所以这里的目标是在调用函数时获取/org/bluez/dev_XX_XX_XX_XX_XX_XX/playerY。

def update_player():
    manager = dbus.Interface(self.bus.get_object("org.bluez", "/"), "org.freedesktop.DBus.ObjectManager")
    objects = manager.GetManagedObjects()
    player_path = getFromDict(objects,[self.devicepath,"org.bluez.MediaControl1", "Player"])

当我尝试更换媒体播放器，或者 bluez 发送一些日志时（通常是 5% 的时间），dbus org.freedesktop.DBus.ObjectManager 会收到很多信息，这会使 manager.GetManagedObjects() 卡住 10~20 秒。

有没有办法确定 bluez 对象路径而不必接收整个org.freedesktop.DBus.ObjectManager 对象；或者有没有办法限制bluez 发送的消息量。我真的很想有效地获得对象路径。非常感谢任何帮助。

编辑： 虽然我没有在嵌入式系统中测试它，但由于 Partiban 的好建议，我能够使用 InterfacesAdded 和一些正则表达式来匹配我需要的路径。

self.bus.add_signal_receiver(self.objectPathHandler, 
    bus_name="org.bluez",
    dbus_interface="org.freedesktop.DBus.ObjectManager",
    signal_name="InterfacesAdded",
    path_keyword="path")

def objectPathHandler(self, interface, changed, path):
    iface = interface[interface.rfind(".") + 1:]
    #print("InterfacesAdded: ; changed: ; path ".format(iface, changed, path))
    self.playerpath = re.findall('/org/bluez/hci[0-9]/dev_[\dA-F]2_[\dA-F]2_[\dA-F]2_[\dA-F]2_[\dA-F]2_[\dA-F]2/player[0-9]+', iface)[0]
    print "Object path:"
    print self.playerpath

def update_player(self):
    print "Updating player"
    if self.devicepath != "None" and self.playerpath != "None":
    if self.playerpath:
        self.connected = 1
        self.getPlayer (self.playerpath)
        player_properties = self.player.GetAll(PLAYER_IFACE, dbus_interface="org.freedesktop.DBus.Properties")

【参考方案1】：

您不应该每次都使用org.freedesktop.DBus.ObjectManager.GetManagedObjects 来获取对象路径。此GetManagedObjects 旨在获取现有或以前可用的接口以及应用程序启动时的详细信息。

例如，假设 Bluez 已启动并连接了 1 个终端设备。稍后您的应用程序启动，在您的应用程序的初始化/启动期间，您可能需要获取所有可用/连接的设备，因此您可以使用GetManagedObjects 来获取它。

为了在运行时创建接口、对象路径，您应该依赖对象管理器的InterfacesAdded 和InterfacesRemoved 信号。

我在 python 中没有示例，但以下 C 中的示例通常使用 StartDiscovery 并使用信号监视新设备。因此，您可以使用信号来适应 python 中的类似示例。下面的示例只是为了清楚起见（有关此示例的更多详细信息，请参见Linumiz）。

/*
 * bluez_adapter_scan.c - Scan for bluetooth devices
 *  - This example scans for new devices after powering the adapter, if any devices
 *    appeared in /org/hciX/dev_XX_YY_ZZ_AA_BB_CC, it is monitered using "InterfaceAdded"
 *    signal and all the properties of the device is printed
 *  - Scanning continues to run until any device is disappered, this happens after 180 seconds
 *    automatically if the device is not used.
 * gcc `pkg-config --cflags glib-2.0 gio-2.0` -Wall -Wextra -o ./bin/bluez_adapter_scan ./bluez_adapter_scan.c `pkg-config --libs glib-2.0 gio-2.0`
 */
#include <glib.h>
#include <gio/gio.h>

GDBusConnection *con;
static void bluez_property_value(const gchar *key, GVariant *value)

    const gchar *type = g_variant_get_type_string(value);

    g_print("\t%s : ", key);
    switch(*type) 
        case 'o':
        case 's':
            g_print("%s\n", g_variant_get_string(value, NULL));
            break;
        case 'b':
            g_print("%d\n", g_variant_get_boolean(value));
            break;
        case 'u':
            g_print("%d\n", g_variant_get_uint32(value));
            break;
        case 'a':
        /* TODO Handling only 'as', but not array of dicts */
            if(g_strcmp0(type, "as"))
                break;
            g_print("\n");
            const gchar *uuid;
            GVariantIter i;
            g_variant_iter_init(&i, value);
            while(g_variant_iter_next(&i, "s", &uuid))
                g_print("\t\t%s\n", uuid);
            break;
        default:
            g_print("Other\n");
            break;
    


static void bluez_device_appeared(GDBusConnection *sig,
                const gchar *sender_name,
                const gchar *object_path,
                const gchar *interface,
                const gchar *signal_name,
                GVariant *parameters,
                gpointer user_data)

    (void)sig;
    (void)sender_name;
    (void)object_path;
    (void)interface;
    (void)signal_name;
    (void)user_data;

    GVariantIter *interfaces;
    const char *object;
    const gchar *interface_name;
    GVariant *properties;

    g_variant_get(parameters, "(&oasasv)", &object, &interfaces);
    while(g_variant_iter_next(interfaces, "&s@asv", &interface_name, &properties)) 
        if(g_strstr_len(g_ascii_strdown(interface_name, -1), -1, "device")) 
            g_print("[ %s ]\n", object);
            const gchar *property_name;
            GVariantIter i;
            GVariant *prop_val;
            g_variant_iter_init(&i, properties);
            while(g_variant_iter_next(&i, "&sv", &property_name, &prop_val))
                bluez_property_value(property_name, prop_val);
            g_variant_unref(prop_val);
        
        g_variant_unref(properties);
    
    return;


#define BT_ADDRESS_STRING_SIZE 18
static void bluez_device_disappeared(GDBusConnection *sig,
                const gchar *sender_name,
                const gchar *object_path,
                const gchar *interface,
                const gchar *signal_name,
                GVariant *parameters,
                gpointer user_data)

    (void)sig;
    (void)sender_name;
    (void)object_path;
    (void)interface;
    (void)signal_name;

    GVariantIter *interfaces;
    const char *object;
    const gchar *interface_name;
    char address[BT_ADDRESS_STRING_SIZE] = '\0';

    g_variant_get(parameters, "(&oas)", &object, &interfaces);
    while(g_variant_iter_next(interfaces, "s", &interface_name)) 
        if(g_strstr_len(g_ascii_strdown(interface_name, -1), -1, "device")) 
            int i;
            char *tmp = g_strstr_len(object, -1, "dev_") + 4;

            for(i = 0; *tmp != '\0'; i++, tmp++) 
                if(*tmp == '_') 
                    address[i] = ':';
                    continue;
                
                address[i] = *tmp;
            
            g_print("\nDevice %s removed\n", address);
            g_main_loop_quit((GMainLoop *)user_data);
        
    
    return;


static void bluez_signal_adapter_changed(GDBusConnection *conn,
                    const gchar *sender,
                    const gchar *path,
                    const gchar *interface,
                    const gchar *signal,
                    GVariant *params,
                    void *userdata)

    (void)conn;
    (void)sender;
    (void)path;
    (void)interface;
    (void)userdata;

    GVariantIter *properties = NULL;
    GVariantIter *unknown = NULL;
    const char *iface;
    const char *key;
    GVariant *value = NULL;
    const gchar *signature = g_variant_get_type_string(params);

    if(g_strcmp0(signature, "(sasvas)") != 0) 
        g_print("Invalid signature for %s: %s != %s", signal, signature, "(sasvas)");
        goto done;
    

    g_variant_get(params, "(&sasvas)", &iface, &properties, &unknown);
    while(g_variant_iter_next(properties, "&sv", &key, &value)) 
        if(!g_strcmp0(key, "Powered")) 
            if(!g_variant_is_of_type(value, G_VARIANT_TYPE_BOOLEAN)) 
                g_print("Invalid argument type for %s: %s != %s", key,
                        g_variant_get_type_string(value), "b");
                goto done;
            
            g_print("Adapter is Powered \"%s\"\n", g_variant_get_boolean(value) ? "on" : "off");
        
        if(!g_strcmp0(key, "Discovering")) 
            if(!g_variant_is_of_type(value, G_VARIANT_TYPE_BOOLEAN)) 
                g_print("Invalid argument type for %s: %s != %s", key,
                        g_variant_get_type_string(value), "b");
                goto done;
            
            g_print("Adapter scan \"%s\"\n", g_variant_get_boolean(value) ? "on" : "off");
        
    
done:
    if(properties != NULL)
        g_variant_iter_free(properties);
    if(value != NULL)
        g_variant_unref(value);


static int bluez_adapter_call_method(const char *method)

    GVariant *result;
    GError *error = NULL;

    result = g_dbus_connection_call_sync(con,
                         "org.bluez",
                    /* TODO Find the adapter path runtime */
                         "/org/bluez/hci0",
                         "org.bluez.Adapter1",
                         method,
                         NULL,
                         NULL,
                         G_DBUS_CALL_FLAGS_NONE,
                         -1,
                         NULL,
                         &error);
    if(error != NULL)
        return 1;

    g_variant_unref(result);
    return 0;


static int bluez_adapter_set_property(const char *prop, GVariant *value)

    GVariant *result;
    GError *error = NULL;

    result = g_dbus_connection_call_sync(con,
                         "org.bluez",
                         "/org/bluez/hci0",
                         "org.freedesktop.DBus.Properties",
                         "Set",
                         g_variant_new("(ssv)", "org.bluez.Adapter1", prop, value),
                         NULL,
                         G_DBUS_CALL_FLAGS_NONE,
                         -1,
                         NULL,
                         &error);
    if(error != NULL)
        return 1;

    g_variant_unref(result);
    return 0;


int main(void)

    GMainLoop *loop;
    int rc;
    guint prop_changed;
    guint iface_added;
    guint iface_removed;

    con = g_bus_get_sync(G_BUS_TYPE_SYSTEM, NULL, NULL);
    if(con == NULL) 
        g_print("Not able to get connection to system bus\n");
        return 1;
    

    loop = g_main_loop_new(NULL, FALSE);

    prop_changed = g_dbus_connection_signal_subscribe(con,
                        "org.bluez",
                        "org.freedesktop.DBus.Properties",
                        "PropertiesChanged",
                        NULL,
                        "org.bluez.Adapter1",
                        G_DBUS_SIGNAL_FLAGS_NONE,
                        bluez_signal_adapter_changed,
                        NULL,
                        NULL);

    iface_added = g_dbus_connection_signal_subscribe(con,
                            "org.bluez",
                            "org.freedesktop.DBus.ObjectManager",
                            "InterfacesAdded",
                            NULL,
                            NULL,
                            G_DBUS_SIGNAL_FLAGS_NONE,
                            bluez_device_appeared,
                            loop,
                            NULL);

    iface_removed = g_dbus_connection_signal_subscribe(con,
                            "org.bluez",
                            "org.freedesktop.DBus.ObjectManager",
                            "InterfacesRemoved",
                            NULL,
                            NULL,
                            G_DBUS_SIGNAL_FLAGS_NONE,
                            bluez_device_disappeared,
                            loop,
                            NULL);

    rc = bluez_adapter_set_property("Powered", g_variant_new("b", TRUE));
    if(rc) 
        g_print("Not able to enable the adapter\n");
        goto fail;
    

    rc = bluez_adapter_call_method("StartDiscovery");
    if(rc) 
        g_print("Not able to scan for new devices\n");
        goto fail;
    

    g_main_loop_run(loop);
    rc = bluez_adapter_call_method("StopDiscovery");
    if(rc)
        g_print("Not able to stop scanning\n");
    g_usleep(100);

    rc = bluez_adapter_set_property("Powered", g_variant_new("b", FALSE));
    if(rc)
        g_print("Not able to disable the adapter\n");
fail:
    g_dbus_connection_signal_unsubscribe(con, prop_changed);
    g_dbus_connection_signal_unsubscribe(con, iface_added);
    g_dbus_connection_signal_unsubscribe(con, iface_removed);
    g_object_unref(con);
    return 0;

在这个使用StartDiscovery 扫描设备的示例中，我使用了InterfaceRemoved 和InterfaceAdded 这两个信号来进行演示。因此，当/org/hciX/ 上出现新设备时，会调用bluez_device_appeared 并以相同的方式进行删除。

如果您连接了多个蓝牙适配器，您可以通过指定适配器路径（例如 /org/bluez/hciX）在 g_dbus_connection_signal_subscribe 下过滤它们。

所有基于 DBUS 的守护进程都使用信号来通知总线上的客户端，因此我们在总线上看到很多消息。所以我们需要根据确切的需要订阅。此过滤器在 dbus 守护程序级别应用并转发消息。

添加MediaControl1 bluez 接口已过时且不推荐使用。所有新应用程序都应使用MediaPlayer 定义的here。

【讨论】：

谢谢，您提供的信息指导我使用 InterfacesAdded，检查我的编辑