boost asio stateful socket interface - c++

Question

I want a Stateful communication but not like boost's echo server example. My socket will be ready for reading forever and whenever it receives a new data it will call a virtual method dataAvailable(string) however it can do async_write anytime.
void connected(const boost::system::error_code &ec) {
_socket.async_read_some(boost::asio::buffer(_buffer, max_length),
boost::bind(&Session::handler_read, this, boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
//boost::asio::async_read(_socket, boost::asio::buffer(_buffer, max_length),
// boost::bind(&Session::handler_read, this, boost::asio::placeholders::error,
// boost::asio::placeholders::bytes_transferred));
std::cout << ">> Session::connected()" << std::endl;
}
void handler_read(const boost::system::error_code &ec, size_t bytes_transferred) {
if(ec) {
std::cout << ec.message() << std::endl;
} else {
//std::copy(_buffer, _buffer+bytes_transferred, data.begin());
std::string data(_buffer, _buffer+bytes_transferred);
std::cout << ">> Session[ " << id() << "]" << "::handler_read(): " <<
bytes_transferred << " " << data << std::endl;
boost::asio::async_write(_socket, boost::asio::buffer(_buffer, max_length),
boost::bind(&Session::handler_write, this,
boost::asio::placeholders::error));
_socket.async_read_some(boost::asio::buffer(_buffer, max_length),
boost::bind(&Session::handler_read, this, boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
//boost::asio::async_read(_socket, boost::asio::buffer(_buffer, max_length),
// boost::bind(&Session::handler_read, this,
// boost::asio::placeholders::error,
// boost::asio::placeholders::bytes_transferred));
//call dataAvailable(_buffer);
}
}
void handler_write(const boost::system::error_code &ec) {
if(ec) {
std::cout << ec.message() << std::endl;
} else {
_socket.async_read_some(boost::asio::buffer(_buffer, max_length),
boost::bind(&Session::handler_read, this, boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
//boost::asio::async_read(_socket, boost::asio::buffer(_buffer, max_length),
// boost::bind(&Session::handler_read, this,
// boost::asio::placeholders::error,
// boost::asio::placeholders::bytes_transferred));
}
}
Is this Implementation Okay ? as multiple threads may do read and write operations. where in write operation is updation of some cells in matrix
Why it doesn't work (doesn't echo's the received string) when I use async_read instead of async_read_some
In my listening Server I am nowhere calling the listen method. but still its working. Then Why there is a listen method ? and when it is used ?
I want to get the notification when the client socket is exited from Client side. e.g. Client has closed connection. How can I do it ? I way comming out is by reading an End Of File in read_handler But is that the only Way ?
I've a Session class, and each session have one socket. I am storing Session* colection in a Session Manager. now when I close a socket and delete it that session becomes null. and it may happen in the middle of a vector. So How to safely remove that null session ?

Answer 1

There is one serious issue with your code. Imagine that you have asymmetric network link and are able to receive much faster than send.
Receive message
Do async_write (but it takes time)
Schedule next read
Receive next message
Do second async_write (the first one is not completed yet, you get garbage one other side of link)
Schedule next read
First async_write finishes and schedules one more async_read_some
To sum up, you request asio to do multiple reads and writes to the same socket at once.
Why it doesn't work (doesn't echo's the received string) when I use async_read instead of async_read_some
Are you sending enough data (max_length)? Maybe you would like to use boost::asio::transfer_at_least(min_length)?
In my listening Server I am nowhere calling the listen method. but still its working. Then Why there is a listen method ? and when it is used ?
You probably create acceptor object somewhere.
I want to get the notification when the client socket is exited from Client side. e.g. Client has closed connection. How can I do it ? I way comming out is by reading an End Of File in read_handler But is that the only Way ?
You could create wrapper, which will take EOF and do some cleanup. Then you wrap all your custom handlers with wrapper and pass wrapper as a handler to boost::asio. This way you have only one place to handle EOF error, if you prefer to.
I've a Session class, and each session have one socket. I am storing Session* colection in a Session Manager. now when I close a socket and delete it that session becomes null. and it may happen in the middle of a vector. So How to safely remove that null session ?
Use boost::shared_ptr in handlers and so on and boost::shared_ptr or boost::weak_ptr in Session Manager's vector.