c++ - CEPH + Librados++ 没有返回一致的结果

Question

嘿，我正在尝试使用 Ceph 来存储一些数据，但有一个问题，我写入 Ceph 的内容和通过 librados++ 从 Ceph 读取的内容是不一样的。

所以我有这个简单的例子:

#include <iostream>
#include <string>
#include <rados/librados.hpp>

int main(int argc, const char **argv)
{

    int ret = 0;

    /* Declare the cluster handle and required variables. */
    librados::Rados cluster;
    char cluster_name[] = "ceph";
    char user_name[] = "client.admin";
    uint64_t flags = 0;

    /* Initialize the cluster handle with the "ceph" cluster name and "client.admin" user */
    {
        ret = cluster.init2(user_name, cluster_name, flags);
        if (ret < 0)
        {
            std::cerr << "Couldn't initialize the cluster handle! error " << ret << std::endl;
            return EXIT_FAILURE;
        }
        else
        {
            std::cout << "Created a cluster handle." << std::endl;
        }
    }

    /* Read a Ceph configuration file to configure the cluster handle. */
    {
        ret = cluster.conf_read_file("/etc/ceph/ceph.conf");
        if (ret < 0)
        {
            std::cerr << "Couldn't read the Ceph configuration file! error " << ret << std::endl;
            return EXIT_FAILURE;
        }
        else
        {
            std::cout << "Read the Ceph configuration file." << std::endl;
        }
    }

    /* Read command line arguments */
    {
        ret = cluster.conf_parse_argv(argc, argv);
        if (ret < 0)
        {
            std::cerr << "Couldn't parse command line options! error " << ret << std::endl;
            return EXIT_FAILURE;
        }
        else
        {
            std::cout << "Parsed command line options." << std::endl;
        }
    }

    /* Connect to the cluster */
    {
        ret = cluster.connect();
        if (ret < 0)
        {
            std::cerr << "Couldn't connect to cluster! error " << ret
                    << std::endl;
            return EXIT_FAILURE;
        }
        else
        {
            std::cout << "Connected to the cluster." << std::endl;
        }
    }

    /* Continued from previous C++ example, where cluster handle and
     * connection are established. First declare an I/O Context.
     */

    librados::IoCtx io_ctx;
    const char *pool_name = "data";

    {
        ret = cluster.ioctx_create(pool_name, io_ctx);
        if (ret < 0)
        {
            std::cerr << "Couldn't set up ioctx! error " << ret << std::endl;
            exit(EXIT_FAILURE);
        }
        else
        {
            std::cout << "Created an ioctx for the pool." << std::endl;
        }

        librados::bufferlist bl;
        std::string hw = "hello world!";
        bl.append(hw.c_str());

        ret = io_ctx.write_full("hw", bl);

        librados::bufferlist rl;
        int read_len = hw.size();
        librados::AioCompletion* rc = librados::Rados::aio_create_completion();
        ret = io_ctx.aio_read("hw", rc, &rl, read_len, 0);
        rc->wait_for_complete();

        ret = rc->get_return_value();

        if (!(ret < 0))
        {
            auto out = std::string(rl.c_str());
            std::cout << out << std::endl;
        }
        else
        {
            std::cout << "da <expletive deleted>?" << std::endl;
        }

    }

    return 0;
}

当我多次运行该程序时，我如何得到 hello world!每次都出来，但出于某种原因，有时我得到一个 r , m , 或 z附加到我的字符串，我对此一无所知。

我试过 std::vector<uint8_t>到一个字符串并返回，结果相同。这就是我最初发现问题的方式。

我正在为 C++ 使用最新的 librados。

我希望有人能提供帮助。

在示例中我删除了很多 if (ret < 0)这仅适用于 stackoverflow，它们包含在我的完整示例中。

Answer 1

Ceph 缓冲区列表结构实际上并不是以 NULL 结尾的，即使您调用了 c_str() 函数。 (对糟糕的设计感到抱歉!)

因此，当您调用 bufferlist::c_str() 并将其提供给字符串构造函数时，它将具有任意长度，直到它后面的第一个随机 NULL 字节为止。您可以通过获取长度并在构造字符串时显式设置它来解决此问题。