Boost::Asio 同步客户端超时

Posted 2023-02-21

【中文标题】Boost::Asio 同步客户端超时

【英文标题】：Boost::Asio synchronous client with timeout

【发布时间】：2016-03-05 18:39:08

【问题描述】：

我正在尝试使用线程作为超时控制来构建具有超时的同步 FTP 客户端代码。线程将在每个事务上启动，并在超时的情况下关闭套接字 - 这将强制同步调用返回错误。

这是我的代码：

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <thread>
#include <chrono>
#include <boost/asio.hpp>

#define TIMEOUT_SECONDS 5
#define MAX_MESSAGE_SIZE 4096
using boost::asio::ip::tcp;

enum  max_length = 1024 ;

bool timerOn;

void socket_timer(tcp::socket& s, int seconds)

    std::chrono::system_clock::time_point start = std::chrono::system_clock::now();

    while (timerOn)
    
        std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
        auto interval = std::chrono::duration_cast<std::chrono::seconds>(now - start).count();

        if (interval > seconds)
            break;

        std::this_thread::sleep_for(std::chrono::milliseconds(10)); //  Not to run in 100% CPU
    


    if (timerOn)
        s.close();


void start_timer(int seconds, tcp::socket& s) 

    timerOn = true;
    std::thread t(socket_timer, s, seconds);
    t.detach();


void stop_timer()

    timerOn = false;


int main(int argc, char* argv[])

  std::string address;

  while(address != "END")
  
      try
      
        boost::asio::io_service io_service;

        std::cout << "Enter FTP server address to connect or END to finish: " << std::endl;
        std::cin >> address;

        if (address == "END")
            break;

        tcp::socket s(io_service);
        tcp::resolver resolver(io_service);
        boost::asio::ip::tcp::endpoint endpoint(boost::asio::ip::address::from_string(address), 21);

        start_timer(TIMEOUT_SECONDS, s);
        boost::system::error_code ec;
        s.connect(endpoint, ec);
        stop_timer();

        if (ec)
        
            throw std::runtime_error("Error connecting to server.");
        

        std::cout << "Connected to " << s.remote_endpoint().address().to_string() << std::endl;

        char reply[max_length];

        start_timer(TIMEOUT_SECONDS, s);
        size_t bytes = s.receive(boost::asio::buffer(reply, MAX_MESSAGE_SIZE), 0, ec);
        stop_timer();

        if (ec)
        
            throw std::runtime_error("Error receiving message.");
        

        std::cout << "Received message is: ";
        std::cout.write(reply, bytes);
        std::cout << "\n";

        std::cout << "Enter message: ";
        char request[max_length];
        std::cin.getline(request, max_length);
        size_t request_length = std::strlen(request);

        start_timer(TIMEOUT_SECONDS, s);
        boost::asio::write(s, boost::asio::buffer(request, request_length));
        stop_timer();

        if (ec)
        
            throw std::runtime_error("Error sending message.");
        
      
      catch (std::exception& e)
      
        std::cerr << "COMMUNICATIONS ERROR." << "\n";
        std::cerr << "Exception: " << e.what() << "\n";
      
    

   return 0;

我根本无法编译这段代码，因为 boost 向我显示以下错误：

1>------ Build started: Project: TestAsio, Configuration: Debug Win32 ------
1>  main.cpp
1>c:\boost_1_60\boost\asio\basic_socket.hpp(1513): error C2248: 'boost::asio::basic_io_object<IoObjectService>::basic_io_object' : cannot access private member declared in class 'boost::asio::basic_io_object<IoObjectService>'
1>          with
1>          [
1>              IoObjectService=boost::asio::stream_socket_service<boost::asio::ip::tcp>
1>          ]
1>          c:\boost_1_60\boost\asio\basic_io_object.hpp(230) : see declaration of 'boost::asio::basic_io_object<IoObjectService>::basic_io_object'
1>          with
1>          [
1>              IoObjectService=boost::asio::stream_socket_service<boost::asio::ip::tcp>
1>          ]
1>          This diagnostic occurred in the compiler generated function 'boost::asio::basic_socket<Protocol,SocketService>::basic_socket(const boost::asio::basic_socket<Protocol,SocketService> &)'
1>          with
1>          [
1>              Protocol=boost::asio::ip::tcp,
1>              SocketService=boost::asio::stream_socket_service<boost::asio::ip::tcp>
1>          ]
========== Build: 0 succeeded, 1 failed, 9 up-to-date, 0 skipped ==========

所以，我想知道两件事：

a) 我在代码中做错了什么？

b) 这种在并行线程上关闭套接字的方法是否可以使套接字超时？请随意发表评论。

感谢您的帮助。

【问题讨论】：

回答问题 a) 我猜你在 std::thread t(socket_timer, std::ref(s), seconds); 中需要 std::ref(s)，因为套接字不可复制。

真的...现在代码可以编译并且运行良好...

【参考方案1】：

我已经创建了一个辅助工具来“同步”执行任何 Asio 异步操作，这里有超时，请查找 await_operation：

boost::asio + std::future - Access violation after closing socket

您应该能够为您的样本调整模式。

演示

我想用 ftp 服务器测试它花了一段时间。

注意事项：

您没有解析地址（实际上要求用户输入 IP 地址） 你没有确保命令是用换行符关闭的 您没有处理任何类型的输入错误

修复这些东西和使用我的await_operation 你会得到这个：

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <thread>
#include <chrono>
#include <boost/asio.hpp>
#include <boost/asio/high_resolution_timer.hpp>

#define TIMEOUT std::chrono::seconds(5)
#define MAX_MESSAGE_SIZE 4096
using boost::asio::ip::tcp;

enum  max_length = 2048 ;

struct Service 
    using error_code = boost::system::error_code;

    template<typename AllowTime, typename Cancel> void await_operation_ex(AllowTime const& deadline_or_duration, Cancel&& cancel) 
        using namespace boost::asio;

        ioservice.reset();
        
            high_resolution_timer tm(ioservice, deadline_or_duration);
            tm.async_wait([&cancel](error_code ec)  if (ec != error::operation_aborted) std::forward<Cancel>(cancel)(); );
            ioservice.run_one();
        
        ioservice.run();
    

    template<typename AllowTime, typename ServiceObject> void await_operation(AllowTime const& deadline_or_duration, ServiceObject& so) 
        return await_operation_ex(deadline_or_duration, [&so] so.cancel(); );
    

    boost::asio::io_service ioservice;
;

int main()

  while(true)
  
    try
    
      Service service;

      std::cout << "Enter FTP server address to connect or END to finish: " << std::endl;

      std::string address;
      if (std::cin >> address) 
        if (address == "END") break;
       else 
        if (std::cin.eof())
          break;
        std::cerr << "Invalid input ignored\n";
        std::cin.clear();
        std::cin.ignore(1024, '\n');

        continue;
      

      tcp::socket s(service.ioservice);
      tcp::resolver resolver(service.ioservice);

      boost::asio::async_connect(s, resolver.resolve(address, "21"), [](boost::system::error_code ec, tcp::resolver::iterator it) 
            if (ec) throw std::runtime_error("Error connecting to server: " + ec.message());
            std::cout << "Connected to " << it->endpoint() << std::endl;
          );
      service.await_operation_ex(TIMEOUT, [&]
            throw std::runtime_error("Error connecting to server: timeout\n");
          );

      auto receive = [&] 
        boost::asio::streambuf sb;
        size_t bytes;

        boost::asio::async_read_until(s, sb, '\n', [&](boost::system::error_code ec, size_t bytes_transferred) 
              if (ec) throw std::runtime_error("Error receiving message: " + ec.message());
              bytes = bytes_transferred;

              std::cout << "Received message is: " << &sb;
            );

        service.await_operation(TIMEOUT, s);
        return bytes;
      ;

      receive(); // banner

      auto send = [&](std::string cmd) 
        boost::asio::async_write(s, boost::asio::buffer(cmd), [](boost::system::error_code ec, size_t /*bytes_transferred*/) 
              if (ec) throw std::runtime_error("Error sending message: " + ec.message());
            );
        service.await_operation(TIMEOUT, s);
      ;

      auto ftp_command = [&](std::string cmd) 
        send(cmd + "\r\n");
        receive(); // response
      ;

      //ftp_command("USER bob");
      //ftp_command("PASS hello");

      while (true) 
        std::cout << "Enter command: ";

        std::string request;
        if (!std::getline(std::cin, request))
          break;

        ftp_command(request);
      

    
    catch (std::exception const& e)
    
      std::cerr << "COMMUNICATIONS ERROR " << e.what() << "\n";
    
  

  return 0;

在我的测试运行中，打印例如：

【讨论】：

添加了一个演示。捕获 lambda 的数量表明将其设为class FtpClient 的明确机会。另外，如果您想传输任何真实数据，我强烈建议您使用适当的异步 IO，因为我觉得这样会更简单。

sehe: 虽然这是一个很好的例子，但这并不能回答我原来的问题，因为你把整个代码变成了异步的。我实际上正在构建一个需要同步的FtpClient 类 - 一个接一个的操作 - 连接、列出文件、下载文件、发送文件、关闭......以在远程客户端上用于上传和下载数据文件...

门德斯：密切关注。我确实没有使代码异步。谁在乎函数调用是 named 的？正如我非常明确地解释的那样，我以同步方式使用它们。我这样做正是因为这回答了你的问题（“同步客户端超时”）