Boost上 Http的一个Get示例分析

有的时候需要实现C++编写http客户端更新网页服务器上的内容，Boost 编程有一个Get的示例如下。是取得WEB server的license。

以下是Boost 官方实例：

//// sync_client.cpp// ~~~~~~~~~~~~~~~//// Copyright (c) 2003-2012 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>using boost::asio::ip::tcp;int main(int argc, char* argv[]){  try  {  argc =3 ;  argv[1] = "127.0.0.1";  argv[2] = "/License";    if (argc != 3)    {      std::cout << "Usage: sync_client <server> <path>\n";      std::cout << "Example:\n";      std::cout << "  sync_client www.boost.org /LICENSE_1_0.txt\n";      return 1;    }    boost::asio::io_service io_service;    // Get a list of endpoints corresponding to the server name.    tcp::resolver resolver(io_service);    tcp::resolver::query query(argv[1], "http");    tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);    // Try each endpoint until we successfully establish a connection.    tcp::socket socket(io_service);    boost::asio::connect(socket, endpoint_iterator);    // 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.

    // 以上 和服务器建立了一个TCP的连接。

    boost::asio::streambuf request;    std::ostream request_stream(&request);    request_stream << "GET " << argv[2] << " HTTP/1.0\r\n";    request_stream << "Host: " << argv[1] << "\r\n";    request_stream << "Accept: */*\r\n";    request_stream << "Connection: close\r\n\r\n";    

    //这里确定了URL的命令，命令的解释： GET获取HTTP上的 argv[2]中内容 也就是license.txt 获取完后接受 Accept ，最后关闭 Connection Close    // Send the request.    boost::asio::write(socket, request);    // 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::streambuf response;    boost::asio::read_until(socket, response, "\r\n");    // 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 1;    }    if (status_code != 200)    {      std::cout << "Response returned with status code " << status_code << "\n";      return 1;    }    // Read the response headers, which are terminated by a blank line.    boost::asio::read_until(socket, response, "\r\n\r\n");    // Process the response headers.    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;    // Read until EOF, writing data to output as we go.    boost::system::error_code error;    while (boost::asio::read(socket, response,          boost::asio::transfer_at_least(1), error))      std::cout << &response;    if (error != boost::asio::error::eof)      throw boost::system::system_error(error);  }  catch (std::exception& e)  {    std::cout << "Exception: " << e.what() << "\n";  }  return 0;}