sd_bus_message_enter_container() "a{sv}" 实例代码

以下是一个使用`sd_bus_message_enter_container()`函数解析DBus消息中类型为"a{sv}"（即字典）的示例代码：

#include <systemd/sd-bus.h>
#include <stdio.h>

int main() {
    sd_bus *bus = NULL;
    sd_bus_message *msg = NULL;
    sd_bus_error error = SD_BUS_ERROR_NULL;
    int r;

    // Connect to the system bus
    r = sd_bus_open_system(&bus);
    if (r < 0) {
        fprintf(stderr, "Failed to connect to system bus: %s\n", strerror(-r));
        goto finish;
    }

    // Call a method on a remote object
    r = sd_bus_call_method(bus,
                           "org.freedesktop.systemd1",
                           "/org/freedesktop/systemd1",
                           "org.freedesktop.systemd1.Manager",
                           "ListUnits",
                           &error,
                           &msg,
                           "");
    if (r < 0) {
        fprintf(stderr, "Failed to call ListUnits: %s\n", error.message);
        goto finish;
    }

    // Parse the response message
    r = sd_bus_message_enter_container(msg, 'a', "{sv}");
    if (r < 0) {
        fprintf(stderr, "Failed to enter dictionary container: %s\n", strerror(-r));
        goto finish;
    }

    const char *name;
    sd_bus_message *dict_msg;
    r = sd_bus_message_read(msg, "{&s^v}", &name, &dict_msg);
    while (r > 0) {
        printf("Unit: %s\n", name);

        // Parse the dictionary message
        r = sd_bus_message_enter_container(dict_msg, 'e', NULL);
        if (r < 0) {
            fprintf(stderr, "Failed to enter dictionary entry container: %s\n", strerror(-r));
            goto finish;
        }

        const char *key;
        sd_bus_message *variant_msg;
        r = sd_bus_message_read(dict_msg, "{&s^v}", &key, &variant_msg);
        while (r > 0) {
            printf("    %s: ", key);

            // Parse the variant message
            r = sd_bus_message_enter_container(variant_msg, 'v', NULL);
            if (r < 0) {
                fprintf(stderr, "Failed to enter variant container: %s\n", strerror(-r));
                goto finish;
            }

            uint64_t value;
            r = sd_bus_message_read(variant_msg, "t", &value);
            if (r < 0) {
                fprintf(stderr, "Failed to read uint64_t: %s\n", strerror(-r));
                goto finish;
            }
            printf("%llu\n", value);

            r = sd_bus_message_exit_container(variant_msg);
            if (r < 0) {
                fprintf(stderr, "Failed to exit variant container: %s\n", strerror(-r));
                goto finish;
            }

            r = sd_bus_message_read(dict_msg, "{&s^v}", &key, &variant_msg);
        }
        if (r < 0) {
            fprintf(stderr, "Failed to read dictionary entry: %s\n", strerror(-r));
            goto finish;
        }

        r = sd_bus_message_exit_container(dict_msg);
        if (r < 0) {
            fprintf(stderr, "Failed to exit dictionary entry container: %s\n", strerror(-r));
            goto finish;
        }

        r = sd_bus_message_read(msg, "{&s^v}", &name, &dict_msg);
    }
    if (r < 0) {
        fprintf(stderr, "Failed to read dictionary: %s\n", strerror(-r));
        goto finish;
    }

    r = sd_bus_message_exit_container(msg);
    if (r < 0) {
        fprintf(stderr, "Failed to exit dictionary container: %s\n", strerror(-r));
        goto finish;
    }

finish:
    sd_bus_error_free(&error);
    sd_bus_message_unref(msg);
    sd_bus_unref(bus);

    return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}

此代码连接到系统DBus总线，调用`org.freedesktop.systemd1.Manager.ListUnits`方法，并解析返回的字典数据。在解析字典时，它首先使用`sd_bus_message_enter_container()`进入字典容器，然后使用`sd_bus_message_read()`读取字典键值对。对于每个字典键值对，它使用`sd_bus_message_enter_container()`进入变体容器，读取值，然后使用`sd_bus_message_exit_container()`退出变体容器。最后，它使用`sd_bus_message_exit_container()`退出字典容器。