c++: BOOST_ASIO Server reply isn't as expected? - c++

Question

Basically I have a client where I send a string of 10 bytes hellohello to a server and within the server I expect the reply to be 0123456789 back to the client but instead I get hellohello again? I changed the char data_ to char data_out on line 58 in the tcp_server.cpp because I thought that was the place to send packet data out? I'm pretty sure that gets called but for some reason things aren't working like I thought.
This is the server output,
handle read: bytes_transferred10
10
handle write:
0123456789
handle read: bytes_transferred0
I also wonder why did handle read: bytes_transferred0 get called again?
This is the client output,
Enter message: hellohello
Reply is: hellohello
Process returned 0 (0x0) execution time : 6.484 s
Press any key to continue.
This is the tcp_server.cpp
#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()
{
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));
}
void read_handler(const boost::system::error_code& ec, std::size_t bytes_transferred);
private:
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
std::cout<<"handle read: bytes_transferred"<<bytes_transferred<<std::endl;
if (!error)
{
read_handler(error, bytes_transferred);
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)
{
std::cout<<"handle write: "<<std::endl;
data_out = {'0','1','2','3','4','5','6','7','8','9'};
if (!error)
{
std::cout<<data_out<<std::endl;
socket_.async_read_some(boost::asio::buffer(data_out, max_length),
boost::bind(&session::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
delete this;
}
}
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
char data_out[max_length];
};
void session::read_handler(const boost::system::error_code& ec, std::size_t bytes_transferred)
{
std::cout<<bytes_transferred<<std::endl;
}
class server
{
public:
server(boost::asio::io_service& io_service, short port)
: io_service_(io_service),
acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
{
start_accept();
}
private:
void start_accept()
{
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();
}
else
{
delete new_session;
}
start_accept();
}
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
int main()
{
try
{
boost::asio::io_service io_service;
server s(io_service, 4000);
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
tcp_client.cpp
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
enum { max_length = 1024 };
int main(int argc, char* argv[])
{
try
{
boost::asio::io_service io_service;
tcp::resolver resolver(io_service);
tcp::resolver::query query(tcp::v4(), "127.0.0.1", "4000");
tcp::resolver::iterator iterator = resolver.resolve(query);
tcp::socket s(io_service);
s.connect(*iterator);
using namespace std; // For strlen.
std::cout << "Enter message: ";
char request[max_length];
std::cin.getline(request, max_length);
size_t request_length = strlen(request);
boost::asio::write(s, boost::asio::buffer(request, request_length));
char reply[max_length];
size_t reply_length = boost::asio::read(s,boost::asio::buffer(reply, request_length));
std::cout << "Reply is: ";
std::cout.write(reply, reply_length);
std::cout << "\n";
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}

Answer 1

Your comment
I think handle_read() calls handle_write() recursively?
is close but not quite correct as there is no recursion here. The documentation explains this nicely:
Regardless of whether the asynchronous operation completes immediately
or not, the handler will not be invoked from within this function.
Invocation of the handler will be performed in a manner equivalent to
using boost::asio::io_service::post().
Added emphasis is mine. Instead of recursion, It is better to think of these concepts as chaining since one operation such as async_write() is initiated in the handler of another, such as async_read(). The exact specifics depend on the protocol in use.
If you want the server to send the string 0123456789 to the client, fill your buffer before invoking async_write().