/* telnet.cpp
	A simple demonstration telnet client with Boost asio
	
	Parameters:
		hostname or address
		port - typically 23 for telnet service
		
	To end the application, send Ctrl-C on standard input
*/

#include <deque>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>

#ifdef POSIX
#include <termios.h>
#endif

using boost::asio::ip::tcp;
using namespace std;

class telnet_client
{
public:
	enum { max_read_length = 512 };
	
	telnet_client(boost::asio::io_service& io_service, tcp::resolver::iterator endpoint_iterator)
		: io_service_(io_service), socket_(io_service)
	{
		connect_start(endpoint_iterator);
	}
	
	void write(const char msg) // pass the write data to the do_write function via the io service in the other thread
	{
		io_service_.post(boost::bind(&telnet_client::do_write, this, msg));
	}
	
	void close() // call the do_close function via the io service in the other thread
	{
		io_service_.post(boost::bind(&telnet_client::do_close, this));
	}

private:

	void connect_start(tcp::resolver::iterator endpoint_iterator)
	{ // asynchronously connect a socket to the specified remote endpoint and call connect_complete when it completes or fails
		tcp::endpoint endpoint = *endpoint_iterator;
		socket_.async_connect(endpoint,
			boost::bind(&telnet_client::connect_complete,
				this,
				boost::asio::placeholders::error,
				++endpoint_iterator));
	}
	
	void connect_complete(const boost::system::error_code& error, tcp::resolver::iterator endpoint_iterator)
	{ // the connection to the server has now completed or failed and returned an error
		if (!error) // success, so start waiting for read data
			read_start();
		else if (endpoint_iterator != tcp::resolver::iterator())
		{ // failed, so wait for another connection event
			socket_.close();
			connect_start(endpoint_iterator);
		}
	}

	void read_start(void)
	{ // Start an asynchronous read and call read_complete when it completes or fails
		socket_.async_read_some(boost::asio::buffer(read_msg_, max_read_length),
			boost::bind(&telnet_client::read_complete,
				this,
				boost::asio::placeholders::error,
				boost::asio::placeholders::bytes_transferred));
	}
	
	void read_complete(const boost::system::error_code& error, size_t bytes_transferred)
	{ // the asynchronous read operation has now completed or failed and returned an error
		if (!error)
		{ // read completed, so process the data
			cout.write(read_msg_, bytes_transferred); // echo to standard output
			//cout << "\n";
			read_start(); // start waiting for another asynchronous read again
		}
		else
			do_close();
	}
	
	void do_write(const char msg)
	{ // callback to handle write call from outside this class
		bool write_in_progress = !write_msgs_.empty(); // is there anything currently being written?
		write_msgs_.push_back(msg); // store in write buffer
		if (!write_in_progress) // if nothing is currently being written, then start
			write_start();
	}
	
	void write_start(void)
	{ // Start an asynchronous write and call write_complete when it completes or fails
		boost::asio::async_write(socket_,
			boost::asio::buffer(&write_msgs_.front(), 1),
			boost::bind(&telnet_client::write_complete,
				this,
				boost::asio::placeholders::error));
	}
	
	void write_complete(const boost::system::error_code& error)
	{ // the asynchronous read operation has now completed or failed and returned an error
		if (!error)
		{ // write completed, so send next write data
			write_msgs_.pop_front(); // remove the completed data
			if (!write_msgs_.empty()) // if there is anthing left to be written
				write_start(); // then start sending the next item in the buffer
		}
		else
			do_close();
	}
	
	void do_close()
	{
		socket_.close();
	}

private:
	boost::asio::io_service& io_service_; // the main IO service that runs this connection
	tcp::socket socket_; // the socket this instance is connected to
	char read_msg_[max_read_length]; // data read from the socket
	deque<char> write_msgs_; // buffered write data
};

int main(int argc, char* argv[])
{
// on Unix POXIS based systems, turn off line buffering of input, so cin.get() returns after every keypress
// On other systems, you'll need to look for an equivalent
#ifdef POSIX
	termios stored_settings;
	tcgetattr(0, &stored_settings);
	termios new_settings = stored_settings;
	new_settings.c_lflag &= (~ICANON);
	new_settings.c_lflag &= (~ISIG); // don't automatically handle control-C
	tcsetattr(0, TCSANOW, &new_settings);
#endif
	try
	{
		if (argc != 3)
		{
			cerr << "Usage: telnet <host> <port>\n";
			return 1;
		}
		boost::asio::io_service io_service;
		// resolve the host name and port number to an iterator that can be used to connect to the server
		tcp::resolver resolver(io_service);
		tcp::resolver::query query(argv[1], argv[2]);
		tcp::resolver::iterator iterator = resolver.resolve(query);
		// define an instance of the main class of this program
		telnet_client c(io_service, iterator);
		// run the IO service as a separate thread, so the main thread can block on standard input
		boost::thread t(boost::bind(&boost::asio::io_service::run, &io_service));
		while (1)
		{
			char ch;
			cin.get(ch); // blocking wait for standard input
			if (ch == 3) // ctrl-C to end program
				break;
			c.write(ch);
		}
		c.close(); // close the telnet client connection
		t.join(); // wait for the IO service thread to close
	}
	catch (exception& e)
	{
		cerr << "Exception: " << e.what() << "\n";
	}
#ifdef POSIX // restore default buffering of standard input
	tcsetattr(0, TCSANOW, &stored_settings);
#endif
	return 0;
}