如何修复Boost::Asio客户端Http请求错误

Question

我正试图通过观看此视频来精简C++的Boost:：Asio网络库，但我坚持使用异步线程发出请求。

代码：

#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 << "nnRead" << length << "bytesnn";
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/1.1rn"
"Host: www.example.comrn"
"Connection: closernrn";
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给我这个：

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:boostboost_1_75_0boostasiodetailhandler_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:boostboost_1_75_0boostasiodetailhandler_work.hpp    353

一切都很好，直到我添加了GrabSomeData函数，我完全不知道如何修复它，如果有任何帮助，我将不胜感激。

PS:Boost网站上有一个关于这个主题的例子，但它是面向对象的，所有的指针都指向这个类，我(认为(这无济于事。

Answer 1

就像评论者一样，我不能重新编译你的消息：它只是编译，

• MSVC 19，/std:c++14，Boost 1.75.0：编译器资源管理器

现在，我做查看其他问题：

1. write_some可能不会写入所有数据-您需要确保一个组合的写入操作

2. 竞赛条件：由于您在线程上执行GrabSomeData，因此需要同步对CCD_ 3和CCD_共享资源(。

   io_context本身是线程安全的。

   在这种情况下，很容易避免，因为您不需要启动异步操作，直到发送请求之后：

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

3. CCD_ 6具有与写入侧类似的问题。您将需要一个组合读取操作，该操作读取read_until(socket, buf, "rnrn")的预期输出，然后读取基于Content-Length标头、Connection: Close和其他内容的预期内容(想想分块编码(。

   您目前没有存储和访问响应的好方法。使用streambuf，一个单独的组合阅读会容易得多。

   如果你想真正稳定，可以使用Beast接收HTTP/1.1响应(甚至可以分块(，而不用担心它何时完成(库为你做这件事(：

   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，不要在线程上做这件事(无论如何，为什么会这样？它实际上只是引入了未定义的行为，没有任何好处(：

简化代码

在Coliru上直播

在MSVC:Godbolt上编译

#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/1.1rn"
"Host: www.example.comrn"
"Connection: closern"
"rn";
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;
}

打印的样本：

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=="

注意它确实使用了分块编码，这似乎是您没有预料到的。

Answer 2

感谢@she的回答和推荐，花了这么长时间，但我已经升级到新的Windows10和Visual Studio 2019，以及Boost 1_76并解决了问题！

这些错误与代码完全无关！