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问使用zlib压缩的boost socket iostreams回波服务器休眠，直到连接被关闭。
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Stack Overflow用户

提问于 2021-01-18 10:21:11

回答 2查看 304关注 0票数 2

我尝试使用zlib压缩创建简单的回显服务器，如这和这示例所示。

我的想法是现在发送一些字符串，因为我可以在发送之前将POD类型转换为string (std::string(reinterpret_cast<const char *>(&pod), sizeof(pod)))，然后我将确保传输层正常工作。

这里有个问题。客户端压缩数据，发送数据，并表示数据已发送，但服务器在读取数据时被阻塞。我不明白为什么会这样。

我尝试将operator<<与out.flush()结合使用，也尝试使用boost::iostreams::copy()。结果是一样的。代码示例是(我根据args为服务器和客户端使用相同的源文件)：

#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/filter/zlib.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/asio.hpp>

#include <iostream>
#include <sstream>

namespace ip = boost::asio::ip;
using ip::tcp;

const unsigned short port = 9999;
const char host[] = "127.0.0.1";

void receive()
{
    boost::asio::io_context ctx;
    tcp::endpoint ep(ip::address::from_string(host), port);
    tcp::acceptor a(ctx, ep);

    tcp::iostream stream;
    a.accept(stream.socket());

    std::stringstream buffer;

    std::cout << "start session" << std::endl;

    try
    {
        for (;;)
        {
            {
                boost::iostreams::filtering_istream in;
                in.push(boost::iostreams::zlib_decompressor());
                in.push(stream);

                std::cout << "start reading" << std::endl;

                // looks like server is blocked here
                boost::iostreams::copy(in, buffer);
            }

            std::cout << "data: " << buffer.str() << std::endl;

            {
                boost::iostreams::filtering_ostream out;
                out.push(boost::iostreams::zlib_compressor());
                out.push(stream);

                boost::iostreams::copy(buffer, out);
            }

            std::cout << "Reply is sended" << std::endl;
        }
    }
    catch(const boost::iostreams::zlib_error &e)
    {
        std::cerr << e.what() << e.error() << '\n';
        stream.close();
    }
}

void send(const std::string &data)
{
    tcp::endpoint ep(ip::address::from_string(host), port);
    
    tcp::iostream stream;
    stream.connect(ep);

    std::stringstream buffer;
    buffer << data;

    if (!stream)
    {
        std::cerr << "Cannot connect to " << host << ":" << port << std::endl;
        return;
    }

    try
    {
        {
            boost::iostreams::filtering_ostream out;
            out.push(boost::iostreams::zlib_compressor());
            out.push(stream);

            out << buffer.str();
            out.flush();
        }

        std::cout << "sended: " << data << std::endl;
        buffer.str("");

        {
            boost::iostreams::filtering_istream in;
            in.push(boost::iostreams::zlib_decompressor());
            in.push(stream);

            // looks like client is blocked here
            boost::iostreams::copy(in, buffer);
        }

        std::cout << "result: " << buffer.str() << std::endl;
    }
    catch(const boost::iostreams::zlib_error &e)
    {
        std::cerr << e.what() << '\n';
    }
}

int main(int argc, const char *argv[])
{
    if (argc > 1 && argv[1] ==  std::string("sender"))
        send("hello world");
    else
        receive();

    return 0;
}

首先启动服务器，然后启动客户端。产生了下列产出：

服务器

$ ./example
# now it waits while client will be accepted
start session
start reading

客户端

$ ./example sender
sended: hello world

程序会被上面的输出阻塞。我猜服务器仍然在等待来自客户端的数据，并且它不知道客户机发送了它所拥有的所有信息。

如果我用Ctrl + C关闭客户端，则输出如下：

$ ./example
# now it waits while client will be accepted
start session
start reading
# now it is blocked until I press Ctrl + C
data: hello world
Reply is sended
start reading
zlib error-5

和

$ ./example sender
sended: hello world
^C

我猜zlib error-5是因为服务器认为存档是不完整的。

预期的行为没有阻塞。启动客户端时，该消息必须出现在服务器程序输出中。

为什么程序在阅读时被屏蔽了？我怎么才能修好它？

c++

boost

boost-asio

boost-iostreams

回答 2

Stack Overflow用户

回答已采纳

发布于 2021-01-18 14:56:05

iostreams::copy就是这样做的:它复制流。

恭维你的代码。它非常可读的:)它让我想起了这个答案，用boost iostream套接字读写文件。主要的区别是，这个答案发送一个压缩的blob并关闭。

您是“正确的”，解压缩器知道何时一个压缩块是完整的，但它并不决定另一个将不会跟随。

所以你需要增加框架。传统的方法是通过一个长度的带外.通过使用IO操作器，我实现了这些更改，同时也减少了代码重复。

template <typename T> struct LengthPrefixed {
    T _wrapped;

    friend std::ostream& operator<<(std::ostream& os, LengthPrefixed lp) ;
    friend std::istream& operator>>(std::istream& is, LengthPrefixed lp) ;
};

和

template <typename T> struct ZLIB {
    T& data;
    ZLIB(T& ref) : data(ref){}

    friend std::ostream& operator<<(std::ostream& os, ZLIB z) ;
    friend std::istream& operator>>(std::istream& is, ZLIB z) ;
};

ZLIB机械手

此代码主要封装在发送方/接收方之间复制的代码：

template <typename T> struct ZLIB {
    T& data;
    ZLIB(T& ref) : data(ref){}

    friend std::ostream& operator<<(std::ostream& os, ZLIB z) {
        {
            boost::iostreams::filtering_ostream out;
            out.push(boost::iostreams::zlib_compressor());
            out.push(os);
            out << z.data << std::flush;
        }
        return os.flush();
    }

    friend std::istream& operator>>(std::istream& is, ZLIB z) {
        boost::iostreams::filtering_istream in;
        in.push(boost::iostreams::zlib_decompressor());
        in.push(is);

        std::ostringstream oss;
        copy(in, oss);
        z.data = oss.str();

        return is;
    }
};

我制作了T模板，这样它就可以根据需要存储std::string&或std::string const&。

LengthPrefixed机械手

这个机械手并不关心正在序列化的是什么，只是简单地在其前缀加上线路上的有效长度：

template <typename T> struct LengthPrefixed {
    T _wrapped;

    friend std::ostream& operator<<(std::ostream& os, LengthPrefixed lp) {
        std::ostringstream oss;
        oss << lp._wrapped;
        auto on_the_wire = std::move(oss).str();

        debug << "Writing length " << on_the_wire.length() << std::endl;
        return os << on_the_wire.length() << "\n" << on_the_wire << std::flush;
    }

    friend std::istream& operator>>(std::istream& is, LengthPrefixed lp) {
        size_t len;
        if (is >> std::noskipws >> len && is.ignore(1, '\n')) {
            debug << "Reading length " << len << std::endl;

            std::string on_the_wire(len, '\0');
            if (is.read(on_the_wire.data(), on_the_wire.size())) {
                std::istringstream iss(on_the_wire);
                iss >> lp._wrapped;
            }
        }
        return is;
    }
};

我们添加了一个微妙之处:通过存储一个引用或值，取决于我们使用的是什么构造，我们还可以接受临时人员(比如ZLIB机械手)：

template <typename T> LengthPrefixed(T&&) -> LengthPrefixed<T>;
template <typename T> LengthPrefixed(T&) -> LengthPrefixed<T&>;

我没有想过让ZLIB机械手同样通用。所以我把它作为驱魔仪式留给读者

演示程序

将这两者结合起来，您可以简单地将发送方/接收方写成：

void server() {
    boost::asio::io_context ctx;
    tcp::endpoint ep(ip::address::from_string(host), port);
    tcp::acceptor a(ctx, ep);

    tcp::iostream stream;
    a.accept(stream.socket());

    std::cout << "start session" << std::endl;

    for (std::string data; stream >> LengthPrefixed{ZLIB{data}};) {
        std::cout << "data: " << std::quoted(data) << std::endl;
        stream << LengthPrefixed{ZLIB{data}} << std::flush;
    }
}

void client(std::string data) {
    tcp::endpoint ep(ip::address::from_string(host), port);
    tcp::iostream stream(ep);

    stream << LengthPrefixed{ZLIB{data}} << std::flush;
    std::cout << "sent: " << std::quoted(data) << std::endl;

    stream >> LengthPrefixed{ZLIB{data}};
    std::cout << "result: " << std::quoted(data) << std::endl;
}

实际上，它打印：

reader: start session
sender: Writing length 19
reader: Reading length 19
sender: sent: "hello world"
reader: data: "hello world"
reader: Writing length 19
sender: Reading length 19
sender: result: "hello world"

完整上市

#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/filter/zlib.hpp>
#include <boost/iostreams/copy.hpp>
#include <boost/asio.hpp>

#include <iostream>
#include <iomanip>
#include <sstream>

namespace ip = boost::asio::ip;
using ip::tcp;

const unsigned short port = 9999;
const char host[] = "127.0.0.1";

#ifdef DEBUG
    std::ostream debug(std::cerr.rdbuf());
#else
    std::ostream debug(nullptr);
#endif

template <typename T> struct LengthPrefixed {
    T _wrapped;

    friend std::ostream& operator<<(std::ostream& os, LengthPrefixed lp) {
        std::ostringstream oss;
        oss << lp._wrapped;
        auto on_the_wire = std::move(oss).str();

        debug << "Writing length " << on_the_wire.length() << std::endl;
        return os << on_the_wire.length() << "\n" << on_the_wire << std::flush;
    }

    friend std::istream& operator>>(std::istream& is, LengthPrefixed lp) {
        size_t len;
        if (is >> std::noskipws >> len && is.ignore(1, '\n')) {
            debug << "Reading length " << len << std::endl;

            std::string on_the_wire(len, '\0');
            if (is.read(on_the_wire.data(), on_the_wire.size())) {
                std::istringstream iss(on_the_wire);
                iss >> lp._wrapped;
            }
        }
        return is;
    }
};

template <typename T> LengthPrefixed(T&&) -> LengthPrefixed<T>;
template <typename T> LengthPrefixed(T&) -> LengthPrefixed<T&>;

template <typename T> struct ZLIB {
    T& data;
    ZLIB(T& ref) : data(ref){}

    friend std::ostream& operator<<(std::ostream& os, ZLIB z) {
        {
            boost::iostreams::filtering_ostream out;
            out.push(boost::iostreams::zlib_compressor());
            out.push(os);
            out << z.data << std::flush;
        }
        return os.flush();
    }

    friend std::istream& operator>>(std::istream& is, ZLIB z) {
        boost::iostreams::filtering_istream in;
        in.push(boost::iostreams::zlib_decompressor());
        in.push(is);

        std::ostringstream oss;
        copy(in, oss);
        z.data = oss.str();

        return is;
    }
};

void server() {
    boost::asio::io_context ctx;
    tcp::endpoint ep(ip::address::from_string(host), port);
    tcp::acceptor a(ctx, ep);

    tcp::iostream stream;
    a.accept(stream.socket());

    std::cout << "start session" << std::endl;

    for (std::string data; stream >> LengthPrefixed{ZLIB{data}};) {
        std::cout << "data: " << std::quoted(data) << std::endl;
        stream << LengthPrefixed{ZLIB{data}} << std::flush;
    }
}

void client(std::string data) {
    tcp::endpoint ep(ip::address::from_string(host), port);
    tcp::iostream stream(ep);

    stream << LengthPrefixed{ZLIB{data}} << std::flush;
    std::cout << "sent: " << std::quoted(data) << std::endl;

    stream >> LengthPrefixed{ZLIB{data}};
    std::cout << "result: " << std::quoted(data) << std::endl;
}

int main(int argc, const char**) {
    try {
        if (argc > 1)
            client("hello world");
        else
            server();
    } catch (const std::exception& e) {
        std::cerr << e.what() << '\n';
    }
}

票数 1

Stack Overflow用户

发布于 2021-01-18 14:50:39

使用boost::serialization解决问题的步骤如下：

首先，我移动到像这样的函数：

namespace io = boost::iostreams;

namespace my {
std::string compress(const std::string &data)
{
    std::stringstream input, output;

    input << data;

    io::filtering_ostream io_out;
    io_out.push(io::zlib_compressor());
    io_out.push(output);

    io::copy(input, io_out);

    return output.str();
}

std::string decompress(const std::string &data)
{
    std::stringstream input, output;

    input << data;

    io::filtering_istream io_in;
    io_in.push(io::zlib_decompressor());
    io_in.push(input);

    io::copy(io_in, output);

    return output.str();
}
} // namespace my

然后，我为字符串缓冲区创建了一个包装器，如下所示(遵循文档的教程)：

class Package
{
public:
    Package(const std::string &buffer) : buffer(buffer) {}

private:
    std::string buffer;

    friend class boost::serialization::access;

    template<class Archive>
    void serialize(Archive &ar, const unsigned int)
    {
        ar & buffer;
    }

};

最后，在阅读和发送之前，我附加了序列化。

/**
 * receiver
 */
Package request;

{
    boost::archive::text_iarchive ia(*stream);
    ia >> request;
}

std::string data = my::decompress(request.buffer);

// do something with data

Package response(my::compress(data));

{
    boost::archive::text_oarchive oa(*stream);
    oa << response;
}

/**
 * sender
 */
std::string data = "hello world";
Package package(my::compress(data));

// send request
{
    boost::archive::text_oarchive oa(*m_stream);
    oa << package;
}

// waiting for a response
{
    boost::archive::text_iarchive ia(*m_stream);
    ia >> package;
}

// decompress response buffer
result = my::decompress(package.get_buffer());

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/65772623

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