ASIO例子HTTP客户端,异步的例子async_client.cpp
// // async_client.cpp // ~~~~~~~~~~~~~~~~ //异步的HTTP客户端,与同步的非常类似。较不同的是最后一点同步循环的地方 // Copyright (c) 2003-2013 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; //client客户端类 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. //异步解析DNS,并返回列表 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. //这是每个都尝试连接吗? 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. //连接成功后尝试连接 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)); } //读到eof就退出? 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]); //会停止结束吗?没有异步任务就结束 io_service.run(); } catch (std::exception& e) { std::cout << "Exception: " << e.what() << "\n"; } return 0; }
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