提升 asio 异步 http 客户端超时？

Question

在 boost asio async http 客户端中，如何设置 http 下载操作的超时时间？

我检查了示例，但它们没有为 http 客户端提供超时。

更具体地说，如何修改此示例以支持超时：

#include <iostream>
#include <istream>
#include <ostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/bind.hpp>

using boost::asio::ip::tcp;

class client
{
public:
  client(boost::asio::io_service& io_service,
      const std::string& server, const std::string& path)
    : resolver_(io_service),
      socket_(io_service)
  {
    std::ostream request_stream(&request_);
    request_stream << "GET " << path << " HTTP/1.0\r\n";
    request_stream << "Host: " << server << "\r\n";
    request_stream << "Accept: */*\r\n";
    request_stream << "Connection: close\r\n\r\n";

    tcp::resolver::query query(server, "http");
    resolver_.async_resolve(query,
        boost::bind(&client::handle_resolve, this,
          boost::asio::placeholders::error,
          boost::asio::placeholders::iterator));
  }

private:
  void handle_resolve(const boost::system::error_code& err,
      tcp::resolver::iterator endpoint_iterator)
  {
    if (!err)
    {
      boost::asio::async_connect(socket_, endpoint_iterator,
          boost::bind(&client::handle_connect, this,
            boost::asio::placeholders::error));
    }
    else
    {
      std::cout << "Error: " << err.message() << "\n";
    }
  }

  void handle_connect(const boost::system::error_code& err)
  {
    if (!err)
    {
      boost::asio::async_write(socket_, request_,
          boost::bind(&client::handle_write_request, this,
            boost::asio::placeholders::error));
    }
    else
    {
      std::cout << "Error: " << err.message() << "\n";
    }
  }

  void handle_write_request(const boost::system::error_code& err)
  {
    if (!err)
    {
      boost::asio::async_read_until(socket_, response_, "\r\n",
          boost::bind(&client::handle_read_status_line, this,
            boost::asio::placeholders::error));
    }
    else
    {
      std::cout << "Error: " << err.message() << "\n";
    }
  }

  void handle_read_status_line(const boost::system::error_code& err)
  {
    if (!err)
    {
      std::istream response_stream(&response_);
      std::string http_version;
      response_stream >> http_version;
      unsigned int status_code;
      response_stream >> status_code;
      std::string status_message;
      std::getline(response_stream, status_message);
      if (!response_stream || http_version.substr(0, 5) != "HTTP/")
      {
        std::cout << "Invalid response\n";
        return;
      }
      if (status_code != 200)
      {
        std::cout << "Response returned with status code ";
        std::cout << status_code << "\n";
        return;
      }

      boost::asio::async_read_until(socket_, response_, "\r\n\r\n",
          boost::bind(&client::handle_read_headers, this,
            boost::asio::placeholders::error));
    }
    else
    {
      std::cout << "Error: " << err << "\n";
    }
  }

  void handle_read_headers(const boost::system::error_code& err)
  {
    if (!err)
    {
      std::istream response_stream(&response_);
      std::string header;
      while (std::getline(response_stream, header) && header != "\r")
        std::cout << header << "\n";
      std::cout << "\n";

      if (response_.size() > 0)
        std::cout << &response_;

      boost::asio::async_read(socket_, response_,
          boost::asio::transfer_at_least(1),
          boost::bind(&client::handle_read_content, this,
            boost::asio::placeholders::error));
    }
    else
    {
      std::cout << "Error: " << err << "\n";
    }
  }

  void handle_read_content(const boost::system::error_code& err)
  {
    if (!err)
    {
      std::cout << &response_;

      boost::asio::async_read(socket_, response_,
          boost::asio::transfer_at_least(1),
          boost::bind(&client::handle_read_content, this,
            boost::asio::placeholders::error));
    }
    else if (err != boost::asio::error::eof)
    {
      std::cout << "Error: " << err << "\n";
    }
  }

  tcp::resolver resolver_;
  tcp::socket socket_;
  boost::asio::streambuf request_;
  boost::asio::streambuf response_;
};

int http_download(string &server, string &path)
{
  try
  {
    boost::asio::io_service io_service;
    client c(io_service, server, path);
    io_service.run();
  }
  catch (std::exception& e)
  {
    std::cout << "Exception: " << e.what() << "\n";
  }

  return 0;
}

Answer 1

如果您需要简单地退出 http_download 10 秒（例如） 你可以这样使用：

将deadline_timer添加到类客户端：

boost::asio::deadline_timer timer_;

在构造函数中初始化它：

timer_(io_service,boost::posix_time::seconds(10)),

为计时器添加处理程序：

timer_.async_wait(boost::bind(&client::close_connection, this));

在您需要的类客户端中创建方法 close_connection 关闭套接字。 可能的构造函数：

  client(boost::asio::io_service& io_service,
      const std::string& server, const std::string& path)
    : resolver_(io_service),
      socket_(io_service),
      timer_(io_service,boost::posix_time::seconds(10))
  {
    timer_.async_wait(boost::bind(&client::close_connection, this));
    std::ostream request_stream(&request_);
    request_stream << "GET " << path << " HTTP/1.0\r\n";
    request_stream << "Host: " << server << "\r\n";
    request_stream << "Accept: */*\r\n";
    request_stream << "Connection: close\r\n\r\n";
    ...

  }

Answer 2

您可以同时运行一个deadline_timer，然后在它到期时调用socket.cancel()，这将导致当前操作中止。然后，您可以根据需要专门处理取消错误代码。

例如，这是the approach taken by MS's Casablanca code。