我想用boost编程HTTP客户端。如果我设法执行以下操作，我可以使用异步模型：
这是一个类似于我所生产的类：
class HTTPClient {
public:
void sendTheRequest(...) {
// Send the HTTP request
}
std::string getTheResponse(...) {
// return the already (asynchronously) received response, or wait for it
// in this function
}
}
有人能指出如何实现这一目标吗？我担心我缺乏增强的知识。
编辑以澄清：将在某个时刻调用sendTheRequest方法。也许直接在它之后调用getTheResponse，但这也可能在一些（毫秒）之后发生。这就是为什么我想异步发送请求，但也需要同步等待它。
答案 0 :(得分：4)
Mabye有点晚了，但我认为应该这样做。 std::future::get返回send_request_function的值，如果尚未返回则等待，并在完成后返回。
class HTTPClient {
public:
void sendTheRequest(...) {
// Send the HTTP request
f = std::async(std::launch::async, send_request_function, args ...);
}
std::string getTheResponse(...) {
// return the already (asynchronously) received response, or wait for it
// in this function
return f.get();
}
private:
std::future<std::string> f;
}
答案 1 :(得分：0)
为什么不使用这个带有boost的async http客户端示例？
//
// async_client.cpp
// ~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#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)
{
// Form the request. We specify the "Connection: close" header so that the
// server will close the socket after transmitting the response. This will
// allow us to treat all data up until the EOF as the content.
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";
// Start an asynchronous resolve to translate the server and service names
// into a list of endpoints.
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)
{
// Attempt a connection to each endpoint in the list until we
// successfully establish a connection.
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)
{
// The connection was successful. Send the request.
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)
{
// Read the response status line. The response_ streambuf will
// automatically grow to accommodate the entire line. The growth may be
// limited by passing a maximum size to the streambuf constructor.
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)
{
// Check that response is OK.
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;
}
// Read the response headers, which are terminated by a blank line.
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)
{
// Process the response headers.
std::istream response_stream(&response_);
std::string header;
while (std::getline(response_stream, header) && header != "\r")
std::cout << header << "\n";
std::cout << "\n";
// Write whatever content we already have to output.
if (response_.size() > 0)
std::cout << &response_;
// Start reading remaining data until EOF.
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)
{
// Write all of the data that has been read so far.
std::cout << &response_;
// Continue reading remaining data until EOF.
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 main(int argc, char* argv[])
{
try
{
if (argc != 3)
{
std::cout << "Usage: async_client <server> <path>\n";
std::cout << "Example:\n";
std::cout << " async_client www.boost.org /LICENSE_1_0.txt\n";
return 1;
}
boost::asio::io_service io_service;
client c(io_service, argv[1], argv[2]);
io_service.run();
}
catch (std::exception& e)
{
std::cout << "Exception: " << e.what() << "\n";
}
return 0;
}