交换前 bluez 配对

Question

我正在使用来自 An Introduction to Bluetooth Programming ► Chapter 4. Bluetooth programming in C with BlueZ4.2. ► RFCOMM sockets 的代码在两个 Raspberry Pi 之间发送消息。

但是，如果我没有通过 bluetoothctl 在两台设备之间进行配对，我将无法使用客户端，因为它给了我错误：

呃哦：交换无效。

您能否给我一些提示，告诉我如何通过 C 代码进行配对？我需要“自动”使用它，而无需在 C 代码之前通过 bluetoothctl 进行配对。

Answer 1

在回答之前，我不确定如何使用“libbluetooth”API 来实现这一点。但我下面的答案是基于使用 GDBUS 的 DBUS API。这很可能适用于任何最近运行的 bluez（带有蓝牙）。

注意，对于 Bluez5，建议使用 DBUS API。

简而言之，您需要开发一个自动接受配对请求的代理，假设这里是“确认”代理。请参考代理能力here。

在最近的 bluez 版本（至少 5.47+）中，我们有一个新的 API“ConnectDevice”，可用于连接设备而无需扫描/发现。根据您的问题，我了解到您正在尝试在两个 RPi 之间进行通信，因此您可以找到两个蓝牙控制器的 BT 地址。有BT地址的地方，

/*
 * bluez_adapter_connect.c - Connect with device without StartDiscovery
 *  - This example registers an agen with NoInputOutput capability for the purpose of
 *    auto pairing
 *  - Use ConnectDevice method to connect with device using provided MAC address
 *  - Usual signal subscription to get the details of the connected device
 *  - Introduced new signal handler to exit the program gracefully
 *
 *  Note: As "ConnectDevice" is new API and in experimental state (but mostly stable)
 *  one need to use "-E" option when starting "bluetoothd". Systems running systemd can
 *  edit /lib/systemd/system/bluetooth.service in ExecStart option
 *
 *  When this API is useful?
 *  - When you already have the MAC address of end bluetooth Device to connect with, then
 *    you don't need to scan for the device (with or without filter) and connect it.
 *  - StartDiscovery + Pair + Connect => ConnectDevice
 *
 *  How you will have MAC address before scanning?
 *  - When you have other communication (wired or wireless) medium to exchange the MAC address
 *  - For example, NFC OOB can be used to exchange the MAC address
 *  - Testing Bluetooth with same device (MAC address known)
 *
 *  - Here Agent capability is registered as "NoInputOutput" for experimental purpose only, in
 *    real world scenario, Pair + Connect involves real Agents.
 *  - Also note, bluez_agent_call_method and bluez_adapter_call_method are two different methods doing
 *    the same work with difference in interface name and object path. This exist just to make the
 *    understanding more clear.
 *
 * gcc `pkg-config --cflags glib-2.0 gio-2.0` -Wall -Wextra -o ./bin/bluez_adapter_connect ./bluez_adapter_connect.c `pkg-config --libs glib-2.0 gio-2.0`
 */
#include <glib.h>
#include <gio/gio.h>
#include <signal.h>

GMainLoop *loop;
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;
    }
}

typedef void (*method_cb_t)(GObject *, GAsyncResult *, gpointer);
static int bluez_adapter_call_method(const char *method, GVariant *param, method_cb_t method_cb)
{
    g_dbus_connection_call(con,
                 "org.bluez",
            /* TODO Find the adapter path runtime */
                 "/org/bluez/hci0",
                 "org.bluez.Adapter1",
                 method,
                 param,
                 NULL,
                 G_DBUS_CALL_FLAGS_NONE,
                 -1,
                 NULL,
                 method_cb,
                 (void *)method);
    return 0;
}

static void bluez_result_async_cb(GObject *con,
                  GAsyncResult *res,
                  gpointer data)
{
    const gchar *key = (gchar *)data;
    GVariant *result = NULL;
    GError *error = NULL;

    result = g_dbus_connection_call_finish((GDBusConnection *)con, res, &error);
    if(error != NULL) {
        g_print("Unable to get result: %s\n", error->message);
        return;
    }

    if(result) {
        result = g_variant_get_child_value(result, 0);
        bluez_property_value(key, result);
    }
    g_variant_unref(result);
}

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, "(&oa{sa{sv}})", &object, &interfaces);
    while(g_variant_iter_next(interfaces, "{&s@a{sv}}", &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(strcmp(signature, "(sa{sv}as)") != 0) {
        g_print("Invalid signature for %s: %s != %s", signal, signature, "(sa{sv}as)");
        goto done;
    }

    g_variant_get(params, "(&sa{sv}as)", &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_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;
}

static int bluez_adapter_connect_device(char **argv)
{
    int rc;
    GVariantBuilder *b = g_variant_builder_new(G_VARIANT_TYPE_VARDICT);
    g_variant_builder_add(b, "{sv}", "Address", g_variant_new_string(argv[1]));
    GVariant *device_dict = g_variant_builder_end(b);
    g_variant_builder_unref(b);

    rc = bluez_adapter_call_method("ConnectDevice",
                    g_variant_new_tuple(&device_dict, 1),
                    bluez_result_async_cb);
    if(rc) {
        g_print("Not able to call ConnectDevice\n");
        return 1;
    }

    return 0;
}

#define AGENT_PATH "/org/bluez/AutoPinAgent"
static int bluez_agent_call_method(const gchar *method, GVariant *param)
{
        GVariant *result;
        GError *error = NULL;

        result = g_dbus_connection_call_sync(con,
                                             "org.bluez",
                                             "/org/bluez",
                                             "org.bluez.AgentManager1",
                                             method,
                                             param,
                                             NULL,
                                             G_DBUS_CALL_FLAGS_NONE,
                                             -1,
                                             NULL,
                                             &error);
        if(error != NULL) {
        g_print("Register %s: %s\n", AGENT_PATH, error->message);
                return 1;
    }

        g_variant_unref(result);
        return 0;
}

static int bluez_register_autopair_agent(void)
{
    int rc;

    rc = bluez_agent_call_method("RegisterAgent", g_variant_new("(os)", AGENT_PATH, "NoInputNoOutput"));
    if(rc)
        return 1;

    rc = bluez_agent_call_method("RequestDefaultAgent", g_variant_new("(o)", AGENT_PATH));
    if(rc) {
        bluez_agent_call_method("UnregisterAgent", g_variant_new("(o)", AGENT_PATH));
        return 1;
    }

    return 0;
}

static void cleanup_handler(int signo)
{
    if (signo == SIGINT) {
        g_print("received SIGINT\n");
        g_main_loop_quit(loop);
    }
}

int main(int argc, char **argv)
{
    int rc;
    guint prop_changed;
    guint iface_added;
    guint iface_removed;

    if(signal(SIGINT, cleanup_handler) == SIG_ERR)
        g_print("can't catch SIGINT\n");

    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_register_autopair_agent();
    if(rc) {
        g_print("Not able to register default autopair agent\n");
        goto fail;
    }

    if(argc == 2) {
        rc = bluez_adapter_connect_device(argv);
        if(rc)
            goto fail;
    }

    g_main_loop_run(loop);

    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;
}

您应该可以使用上述程序连接设备。在此示例中，代理注册为“NoInputOutput”功能，类似于蓝牙耳机，因此不需要配对响应。

但是您应该将此示例修改为客户端（假设此示例将在 RPi 1 作为服务器中运行，修改此示例以在客户端 RPi 2 中接受请求）。

您可以找到有关此示例的详细说明 here 以及一些基于 GDBUS 的相关示例 here。