doc/html/boost_asio/example/http/client/async_client.cpp

//
// async_client.cpp
// ~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2010 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 the first endpoint in the list. Each endpoint
			// will be tried until we successfully establish a connection.
			tcp::endpoint endpoint = *endpoint_iterator;
			socket_.async_connect(endpoint,
				boost::bind(&client::handle_connect, this,
					boost::asio::placeholders::error, ++endpoint_iterator));
		}
		else
		{
			std::cout << "Error: " << err.message() << "\n";
		}
	}

	void handle_connect(const boost::system::error_code& err,
		tcp::resolver::iterator endpoint_iterator)
	{
		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 if (endpoint_iterator != tcp::resolver::iterator())
		{
			// The connection failed. Try the next endpoint in the list.
			socket_.close();
			tcp::endpoint endpoint = *endpoint_iterator;
			socket_.async_connect(endpoint,
				boost::bind(&client::handle_connect, this,
					boost::asio::placeholders::error, ++endpoint_iterator));
		}
		else
		{
			std::cout << "Error: " << err.message() << "\n";
		}
	}

	void handle_write_request(const boost::system::error_code& err)
	{
		if (!err)
		{
			// Read the response status line.
			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;
}