boost::asio::async_read_until problem - c++

Question

I'm trying to modify the echo server example from boost asio and I'm running into problem when I try to use boost::asio::async_read_until. Here's the code:
#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
class session
{
public:
session(boost::asio::io_service& io_service)
: socket_(io_service)
{
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
std::cout<<"starting"<<std::endl;
boost::asio::async_read_until(socket_, boost::asio::buffer(data_, max_length), ' ',
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
std::cout<<"handling read"<<std::endl;
if (!error)
{
boost::asio::async_write(socket_,
boost::asio::buffer(data_, bytes_transferred),
boost::bind(&session::handle_write, this,
boost::asio::placeholders::error));
}
else
{
delete this;
}
}
void handle_write(const boost::system::error_code& error)
{
if (!error)
{
/*
socket_.async_read_some(boost::asio::buffer(data_, max_length),
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
*/ }
else
{
delete this;
}
}
private:
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
};
class server
{
public:
server(boost::asio::io_service& io_service, short port)
: io_service_(io_service),
acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
{
session* new_session = new session(io_service_);
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
void handle_accept(session* new_session,
const boost::system::error_code& error)
{
if (!error)
{
new_session->start();
new_session = new session(io_service_);
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
else
{
delete new_session;
}
}
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
int main(int argc, char* argv[])
{
try
{
if (argc != 2)
{
std::cerr << "Usage: async_tcp_echo_server <port>\n";
return 1;
}
boost::asio::io_service io_service;
using namespace std; // For atoi.
server s(io_service, atoi(argv[1]));
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
The problem is when I try to compile I get this weird error:
server.cpp: In member function ‘void session::start()’:
server.cpp:27: error: no matching function for call to ‘async_read_until(boost::asio::basic_stream_socket >&, boost::asio::mutable_buffers_1, char, boost::_bi::bind_t, boost::_bi::list3, boost::arg<1> ()(), boost::arg<2> ()()> >)’
Can someone please explain what's going on? From what I can tell the arguments to async_read_until are correct.
Thanks!

Answer 1

The second argument of async_read_until should be a streambuf object into which the data will be read. To put it simple, you need to pass a boost::asio::streambuf by reference, not a boost::asio::buffer by value.

Answer 2

There is no need to use streambufs. There are overloads that accept dynamic buffers. Dynamic is key since read_until implies the need for a buffer that can increase its size at the callee's discretion. Therefore, all you need is to replace the call to boost::asio::buffer with boost::asio::dynamic_buffer and call it on either std::string or std::vector<char>.
...
void start()
{
std::cout<<"starting"<<std::endl;
boost::asio::async_read_until(
socket_, boost::asio::dynamic_buffer(data_), ' ',
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
...
private:
tcp::socket socket_;
std::string data_;
// or
//std::vector<char> data_;
};
I would also get rid of boost::bind since it's an overkill and use a lambda (use them as much as you can)
[this](const boost::system::error_code& error, size_t bytes_transferred) {
handle_read(error, bytes_transferred);
}

Answer 3

const (in)correctness may also cause this type of error message.