Boost Asio不完整写入套接字

I'm writing a dead simple toy key-value store using Boost Asio, and something really weird is happening.

我正在使用Boost Asio编写一个简单的玩具键值商店，并且发生了一些非常奇怪的事情。

The string-based protocol is like this:

基于字符串的协议是这样的：

S <key> <value> // to set a key
G <key>         // to get the key value
L               // to list all key-value pairs

The write is synchronous, using

写是同步的，使用

boost::asio::write(socket_,boost::asio::buffer(resp, len));

boost :: asio :: write（socket_，boost :: asio :: buffer（resp，len））;

where socket_ is a boost::asio::ip::tcp::socket - with asynchrounous writes the story does not change, apparently.

其中socket_是一个boost :: asio :: ip :: tcp :: socket - 用asynchrounous写道，故事并没有改变。

The problem is that sometimes it does not write to the socket all the bytes it is supposed to write, or the outputs is mangled somehow...

问题是，有时它不会写入套接字应该写入的所有字节，或者输出会以某种方式损坏...

Example of mangled list output (on localhost, using nc, echo and hexdump):

已损坏的列表输出示例（在localhost上，使用nc，echo和hexdump）：

> echo S a 12 | nc localhost 5000       
A
> echo S b 23 | nc localhost 5000
A
> echo L | nc localhost 5000 | hexdump -C
00000000  61 3a 20 31 32 3b 20 62  60 00 00 00 00 00        |a: 12; b`.....|
0000000e
> echo L | nc localhost 5000 | hexdump -C
00000000  61 3a 20 31 32 3b 20 62  3a 20 32 33 3b 20        |a: 12; b: 23; |
0000000e

I'm using Boost 1.55 from Ubuntu 14.10 repository. Follows the code of the functions that serves the client.

我正在使用Ubuntu 14.10存储库中的Boost 1.55。遵循为客户端提供服务的功能代码。

Thank you in advance for any hint!

提前感谢您的任何提示！

void ClientSession::handle_read(const boost::system::error_code& error, size_t bytes_transferred) {
if (!error) {

    std::string cmd(data_, bytes_transferred);
    cmd = trim_str(cmd);

    const char* resp = NULL;
    int len = 0;

    switch(cmd.at(0)) {
    case SET: {
        std::size_t k_pos = cmd.find(" ") + 1;
        std::size_t v_pos = cmd.find(" ", k_pos+1) + 1;

        std::string key = trim_str(cmd.substr(k_pos, v_pos-3));
        std::string value = trim_str(cmd.substr(v_pos, cmd.length()-1));
        cout << "SET key " << key << ", value " << value << "*" <<endl;

        kvs->db[key] = std::atoi(value.c_str());

        resp = "A";
        len = 1;
        break;
    }
    case GET: {
        std::size_t k_pos = cmd.find(" ") + 1;
        std::string key = trim_str(cmd.substr(k_pos, cmd.length()));
        cout << "GET key " << key << "*" << endl;

        int value = kvs->db[key];
        char str[5];
        sprintf(str, "%d", value);
        resp = (const char*) str;
        len = strlen(resp);
        break;
    }
    case LIST: {
        ostringstream os;
        for (std::map<string, int>::iterator iter = kvs->db.begin();
              iter != kvs->db.end(); ++iter )
              os << iter->first << ": " << iter->second << "; ";
        cout << "list: " << os.str().c_str() << endl;

        resp = os.str().c_str();
        len = strlen(resp);
        break;
    }
    case DEL: {
        std::size_t k_pos = cmd.find(" ") + 1;
        std::string key = trim_str(cmd.substr(k_pos, cmd.length()));

        kvs->db.erase(key);
        resp = "A";
        len = 1;
        break;
    }
    default: {
        resp = "NACK.";
        len = 5;
    }
    }

    cout << "resp: " << resp << "*" << endl;
    cout << "len: " << len << "*" << endl;
    std::size_t written = boost::asio::write(socket_,
            boost::asio::buffer(resp, len));
    cout << "written: " << written << endl;

    boost::system::error_code ignored_ec;
    socket_.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
    socket_.close();

} else
    delete this;

1 个解决方案

#1

At the very least you're having undefined behaviour because of dangling resp pointer in case GET:

至少你有未定义的行为，因为在GET情况下悬挂resp指针：

{
    // ...
    char str[5];
    resp = (const char*) str; // WHOOOOOOOOOOOPS
    len = strlen(resp);
}

The exact same thing under case LIST:

案例LIST完全相同：

{
    std::ostringstream os;
    // ....
    resp = os.str().c_str(); // WHOOOOOOOOOOOPS
}

All reasoning about the program stops to be useful when you have Undefined Behaviour.

当您有未定义的行为时，关于该程序的所有推理都将停止有用。

Fix these issues (and potentially more that I didn't look for), and retest. Run under valgrind. Use static analysis tools.

修复这些问题（可能还有更多我不想要的），并重新测试。在valgrind下运行。使用静态分析工具。

Update: fixed up version for single threading: https://gist.github.com/sehe/69379e17350fb718892f#comment-1428235

更新：修复了单线程的版本：https：//gist.github.com/sehe/69379e17350fb718892f#comment-1428235

Test run output:

测试运行输出：

$ for a in S{a..d}\ $RANDOM Gnonexisting L; do echo "$a -> $(netcat 127.0.0.1 5000 <<< "$a")"; done | nl
     1  Sa 15936 -> A
     2  Sb 3671 -> A
     3  Sc 10550 -> A
     4  Sd 7741 -> A
     5  Gnonexisting -> 0
     6  L -> 1: 1; 2: 2; a: 15936; asdasd: 0; b: 3671; c: 10550; d: 7741; nonexisting: 0; 

The code for the handle_read looks like:

handle_read的代码如下所示：

void ClientSession::handle_read(const boost::system::error_code& error, size_t bytes_transferred) {
    if (!error) {
        std::istringstream request(std::string(data_, bytes_transferred));
        boost::asio::streambuf resp;
        std::ostream os(&resp);

        char cmd_char = 0;
        std::string key;
        int value;
        if (request >> cmd_char) switch(cmd_char) {
            case SET:                          
                if (request >> key >> value)
                    kvs->db[key] = value;

                os << "A";
                break;
            case GET:
                if (request >> key)
                    os << kvs->db[key];
                break;

            case LIST:
                for (auto const& e : kvs->db)
                    os << e.first << ": " << e.second << "; ";
                break;

            case DEL: 
                if (request >> key)
                    kvs->db.erase(key);

                os << "A";
                break;
            default: 
                os << "NACK.";
        }

        cout << "resp: " << &resp << "*" << endl;
        cout << "len: " << resp.size() << "*" << endl;
        std::size_t written = boost::asio::write(socket_, resp);
        cout << "written: " << written << endl;

        boost::system::error_code ignored_ec;
        socket_.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
        socket_.close();
    } else
        delete this;
}