Boost inflate 算法解压

Question

我正在使用 c++ boost 使用 Websocket 客户端开发一个简单的测试代码。我收到响应的服务器说我需要使用膨胀算法解压缩消息。我发现 boost Websocket 库中有 deflate 选项，但它不起作用。请告诉我如何将数据转换为解压缩的字符串。

#include <iostream>
#include <string>
#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/connect.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/beast/websocket/ssl.hpp>
#include <boost/asio/ssl.hpp>
#include <chrono>

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

int main()
{
    std::ostringstream stream;
    std::string host = "real.okex.com";
    auto const port = "8443";
    auto const path = "/ws/v3";
    boost::beast::multi_buffer buffer;
    boost::asio::io_context ioc;
    boost::asio::ssl::context ctx{boost::asio::ssl::context::sslv23};
    tcp::resolver resolver{ioc};
    websocket::stream<boost::asio::ssl::stream<boost::asio::ip::tcp::socket>> wss{ioc, ctx};

    ctx.set_verify_mode(boost::asio::ssl::verify_none);
    tcp::resolver::results_type results = resolver.resolve(host, port);
    boost::asio::connect(wss.next_layer().next_layer(), results.begin(), results.end());

    // SSL handshake
    wss.next_layer().handshake(boost::asio::ssl::stream_base::client);

    // websocket handshake
    wss.handshake(host, path);

    std::cout << "connected" << std::endl;

    // send request to the websocket
    wss.write(boost::asio::buffer("{'op':'subscribe', 'args':['spot/ticker:ETH-USDT']}"));

    // read message
    wss.read(buffer);
    std::cout << buffer.size() << std::endl;
    buffer.consume(buffer.size());

    /*
    stream << boost::beast::buffers(buffer.data());
    buffer.consume(buffer.size());
    std::string incoming = stream.str();
    std::cout << incoming << std::endl;
    */
}

谢谢！

Answer 1

我挣扎了很久，然后我想，如果我换个服务器试试呢？

这有帮助。我拿了echo_compressed/server.py from Autobahn：

wget 'https://github.com/crossbario/autobahn-python/raw/master/examples/twisted/websocket/echo_compressed/server.py'
virtualenv venv && . venv/bin/activate && pip install autobahn twisted
python server.py

这会在端口 9000 上启动一个 WS 服务器。虽然它没有使用 SSL，所以我在代码中禁用了它（参见下面的 #ifdef SSL）。

现在关键是设置permessage_deflate扩展选项之前 WS握手：

websocket::permessage_deflate opt;
opt.client_enable = true; // for clients
opt.server_enable = true; // for servers
s.set_option(opt);

还注意到，当不在标准端口上运行时，某些服务器要求端口名称出现在 Host 标头中：

s.handshake(host + ":" + port, path);

现在阅读效果很好，并且会像您期望的那样放气，例如写信给response.txt:

beast::multi_buffer buffer;
s.read(buffer);
{
    std::ofstream ofs("response.txt", std::ios::binary);
    std::copy(
            net::buffers_begin(buffer.data()),
            net::buffers_end(buffer.data()),
            std::ostreambuf_iterator<char>(ofs));
}

或者，当用 Asio 流缓冲区替换 multi_buffer 时，很容易将其流式传输：

net::streambuf buffer;
s.read(buffer);
std::cout << &buffer;

放气的证据

使用 tcpdump/Wireshark 检查流量显示了这一点。此外，高速公路记录证实了这一点：

2020-06-22 02:12:05+0200 [-] Log opened.
2020-06-22 02:12:05+0200 [-] WebSocketServerFactory starting on 9000
2020-06-22 02:12:05+0200 [-] Starting factory <autobahn.twisted.websocket.WebSocketServerFactory object at 0x7f7af3fa5710>
2020-06-22 02:12:05+0200 [-] Site starting on 8080
2020-06-22 02:12:05+0200 [-] Starting factory <twisted.web.server.Site instance at 0x7f7af3850910>
2020-06-22 02:12:11+0200 [-] WebSocket connection request by tcp4:127.0.0.1:48658
2020-06-22 02:12:11+0200 [-] WebSocket extensions in use: [PerMessageDeflate(is_server = True, server_no_context_takeover = False, client_no_context_takeover = False, server_max_window_bits = 15, client_max_window_bits = 15, mem_level = 8)]

那个服务器的问题 (real.okex.com)

我真的不知道它是怎么回事，但似乎服务器没有发送标准响应。也许其他人可以告诉。将响应写入文件并不会生成看起来像 zlib 压缩的文件。

尝试的其他工具也无法解码数据：

• zlib-flate -uncompress

• 与 python oneliner 相同：

  python -c 'import zlib; import sys; sys.stdout.write(zlib.decompress(sys.stdin.read()))' < response.txt 
  

完整列表

正如我所测试的那样：

#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/ssl.hpp>
#include <boost/asio.hpp>
#include <boost/beast.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/beast/websocket/ssl.hpp>
#include <iostream>
#include <string>
#include <fstream>

namespace net       = boost::asio;
namespace ssl       = net::ssl;
namespace beast     = boost::beast;
namespace http      = beast::http;
namespace websocket = beast::websocket;
using tcp = net::ip::tcp;
//#define SSL
#ifdef SSL
using stream_t = websocket::stream<ssl::stream<tcp::socket>>;
#else
using stream_t = websocket::stream<tcp::socket/*, true*/>;
#endif

int main(int argc, char** argv) {
    if (argc<4) {
        std::cerr << "Usage: " << argv[0] << " host port path\n";
        return 1;
    }
    std::string host = argc>=2? argv[1] : "real.okex.com";
    auto const port  = argc>=3? argv[2] : "8443";
    auto const path  = argc>=3? argv[3] : "/ws/v3";

    net::io_context ioc;
    ssl::context ctx{ ssl::context::sslv23 };
    tcp::resolver resolver{ ioc };
#ifdef SSL
    stream_t s{ ioc, ctx };
#else
    stream_t s{ ioc };
#endif

    ctx.set_verify_mode(ssl::verify_none);
    tcp::resolver::results_type results = resolver.resolve(host, port);
    net::connect(
            beast::get_lowest_layer(s),
            //s.next_layer().next_layer(),
            results.begin());

#ifdef SSL
    // SSL handshake
    s.next_layer().handshake(ssl::stream_base::client);
#endif

    // websocket handshake
    websocket::permessage_deflate opt;
    opt.client_enable = true; // for clients
    opt.server_enable = true; // for servers
    s.set_option(opt);

    s.handshake(host + ":" + port, path);

    std::cout << "connected" << std::endl;

    // send request to the websocket
    s.write(net::buffer("{'op':'subscribe', 'args':['spot/ticker:ETH-USDT']}"));

    {
        net::streambuf buffer;
        s.read(buffer);
        std::cout << &buffer << std::endl;
    }
}

然后我跑了

Answer 2

在协议升级响应中，websocket 服务器应该包含一个字段“Sec-WebSocket-Extensions”，告诉客户端使用Compression Extensions for WebSocket。

但是很多像 okex/huobi 这样的加密货币交易所的 websocket 服务器并没有这样做。您必须在应用程序代码中对消息进行放气。

您可以将其视为将 deflate/inflate 从协议层移至应用层。