如何修復 Boost::Asio Client Http 請求錯誤？

Question

我正在嘗試通過觀看此視頻來精簡 C++ 的Boost ::Asio 網絡庫，但我堅持使用異步線程發出請求。

編碼：

#include "stdafx.h"
#include <iostream>
#include <boost/asio.hpp>
#include <boost/asio/ts/buffer.hpp>
#include <boost/asio/ts/internet.hpp>
#include <boost/system/error_code.hpp>

std::vector<char> vBuffrer(20 * 1024);

void GrabSomeData(boost::asio::ip::tcp::socket& socket) {

    socket.async_read_some(boost::asio::buffer(vBuffrer.data(), vBuffrer.size()),
        [&](std::error_code ec, std::size_t length)
        //boost::system::error_code ec
    {
        if (!ec)
        {
            std::cout << "\n\nRead" << length << "bytes\n\n";

            for (int i = 0; i < length; i++)
                std::cout << vBuffrer[i];
            GrabSomeData(socket);
        }
    });


}

int main()
{
    boost::system::error_code ec;
    boost::asio::io_context context;
    boost::asio::io_context::work idleWork(context);
    boost::asio::ip::tcp::endpoint endpoint(boost::asio::ip::make_address("13.107.21.200",ec),80);
    boost::asio::ip::tcp::socket socket(context);
    std::thread thrContext = std::thread([&]() {context.run(); });
    std::cout << "Starting " << std::endl;
    socket.connect(endpoint,ec);

    if (!ec)
    {
        std::cout << "Connected ! " << std::endl;
    }
    else {
        std::cout << "Fail to connect ! " << ec.message() << std::endl;

    }

    if (socket.is_open()) {

        GrabSomeData(socket);
        std::string sRequest =
            "GET /index.html HTTP/1.1\r\n"
            "Host: www.example.com\r\n"
            "Connection: close\r\n\r\n";
        socket.write_some(boost::asio::buffer(sRequest.data(), sRequest.size()), ec);

        using namespace std::chrono_literals;
        std::this_thread::sleep_for(2800ms);
        //std::this_thread::sleep_for(1ms);

        context.stop();
        if (thrContext.joinable()) thrContext.join();
    }

    system("pause");

    return 0;
}

Microsoft Visual Studio 給我這個：

Error C2752 'asio_prefer_fn::call_traits<boost::asio::execution::any_executor<boost::asio::execution::context_as_t<boost::asio::execution_context &>,boost::asio::execution::detail::blocking::never_t<0>,boost::asio::execution::prefer_only<boost::asio::execution::detail::blocking::possibly_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::tracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::untracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::fork_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::continuation_t<0>>> &,void (const boost::asio::execution::detail::blocking::possibly_t<0> &,boost::asio::execution::allocator_t<std::allocator<void>>),void>': more than one partial specialization matches the template argument list  boostasiotest   c:\boost\boost_1_75_0\boost\asio\detail\handler_work.hpp    353


Error   C2893   Failed to specialize function template 'enable_if<asio_prefer_fn::call_traits<T,void(P0,P1,PN...),void>::overload==,call_traits<T,void(P0,P1,PN...),void>::result_type>::type asio_prefer_fn::impl::operator ()(T &&,P0 &&,P1 &&,PN &&...) noexcept(<expr>) const'  boostasiotest   c:\boost\boost_1_75_0\boost\asio\detail\handler_work.hpp    353

在我添加GrabSomeData function 之前一切正常，我完全不知道如何修復它，任何幫助將不勝感激。

PS： Boost網站上有一個關於這個主題的例子，但它是面向object的，所有的指針都指向class，我（認為）它無濟於事。

Answer 1

像評論者一樣，我無法復制您的信息：它只是編譯，

• MSVC 19，/std:c++14，Boost 1.75.0：編譯器資源管理器

現在，我確實看到了其他問題：

1. write_some可能不會寫入所有數據 - 您需要確保組合寫入操作

2. 競爭條件：由於您在線程上執行GrabSomeData ，因此您需要同步對tcp::socket和buffer （共享資源）的訪問。

   io_context本身是線程安全的。

   在這種情況下，很容易避免，因為在發送請求之前不需要啟動異步操作：

    write(socket, boost::asio::buffer(sRequest)); GrabSomeData(socket);

3. async_read_some與寫入端有類似的問題。 您將需要一個組合讀取操作來讀取預期的 output so read_until(socket, buf, "\r\n\r\n")然后根據Content-Length header、 Connection: Close等讀取預期的內容量（想想分塊編碼）。

   您目前沒有存儲和訪問響應的好方法。 使用streambuf（單個組合讀取）會容易得多。

   如果您想真正可靠，請使用 Beast 接收 HTTP/1.1 響應（甚至可以分塊），而不必擔心它何時完成（庫會為您完成）：

    auto GrabSomeData(tcp::socket& socket) { http::response<http::string_body> res; auto buf = boost::asio::dynamic_buffer(vBuffer); http::read(socket, buf, res); return res; }

   哦，不要在線程上這樣做（為什么會這樣？它實際上只是引入了未定義的行為而沒有任何收獲）：

簡化代碼

住在科利魯

在 MSVC 上編譯：Godbolt

#include <boost/asio.hpp>
#include <boost/beast/http.hpp>
#include <iostream>
#include <iomanip>
using boost::asio::ip::tcp;

std::vector<char> vBuffer; // TODO FIXME global variable

auto GrabSomeData(tcp::socket& socket) {
    namespace http = boost::beast::http;

    http::response<http::string_body> res;

    auto buf = boost::asio::dynamic_buffer(vBuffer);
    http::read(socket, buf, res);

    return res;
}

int main() try {
    boost::asio::io_context context;

    std::cout << "Starting " << std::endl;
    tcp::endpoint endpoint(boost::asio::ip::make_address("13.107.21.200"), 80);
    tcp::socket   socket(context);
    socket.connect(endpoint);

    std::cout << "Connected" << std::endl;

    std::string const sRequest = "GET /index.html HTTP/1.1\r\n"
        "Host: www.example.com\r\n"
        "Connection: close\r\n"
        "\r\n";

    write(socket, boost::asio::buffer(sRequest));

    auto response = GrabSomeData(socket);

    std::cout << "Response body length: " << response.body().size() << std::endl;
    std::cout << "Response headers: " << response.base() << std::endl;
    std::cout << "Response body: " << std::quoted(response.body()) << std::endl;

    context.run(); // run_for(10s) e.g.
} catch (boost::system::system_error const& se) {
    std::cerr << "Error: " << se.code().message() << std::endl;
}

此示例打印：

Starting 
Connected
Response body length: 194
Response headers: HTTP/1.1 400 Bad Request
Transfer-Encoding: chunked
X-MSEdge-Ref: 0BstXYAAAAACeQ2y+botzQISiBe2U3iGCQ0hHRURHRTE0MDgARWRnZQ==
Date: Sun, 21 Mar 2021 22:39:02 GMT
Connection: close

Response body: "<h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>0BstXYAAAAACeQ2y+botzQISiBe2U3iGCQ0hHRURHRTE0MDgARWRnZQ=="

注意它確實使用了分塊編碼，您似乎沒有預料到。

Answer 2

感謝@sehe 的回答和建議，花了很長時間，但我已經升級到 New Windows10和Visual Studio 2019和Boost 1_76並且問題解決了！

這些錯誤與代碼完全無關！