boost::asio::async_write from outside class - c++

Question

If programming a tcp server using boost.asio using the example of the echo server , i have modified some of its codes to meet my requirements where i want to process the incoming data and send back the results, i used a class for socket handling "socket.h" and i want to make another handler in for the data in the file "handler.h" , my problem now is how can i pass data to the function in handler.h and send data back from this function passing through socket.h ??
socket.h
#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <json/json.h>
#include "handler.h"
using namespace std;
using boost::asio::ip::tcp;
class session {
public:
session(boost::asio::io_service& io_service) : socket_(io_service) {}
tcp::socket& socket() { return socket_; }
/* listen for first input data after connection established */
void start() {
socket_.async_read_some(boost::asio::buffer(data_, max_length),
boost::bind(&session::handleIncome,this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred)); }
/* handle incoming data */
void handleIncome(const boost::system::error_code& error, size_t bytes_transferred) {
/* data is recieved in var data_ */
if (!error) {
/********************* Data Handler ****************************/
callHandler(data_); //this is in handler.cpp
/**************************************************************/
} else { delete this; } }
/* get more input */
void getIncome(const boost::system::error_code& error) {
if (!error) {
socket_.async_read_some(boost::asio::buffer(data_, max_length),
boost::bind(&session::handleIncome, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred)); }
else { delete this; } }
/* send outcome back to client */
void sendOutcome(const std::string dout, size_t bytes_out) {
boost::asio::async_write(socket_,boost::asio::buffer(dout, bytes_out),
boost::bind(&session::getIncome, this,boost::asio::placeholders::error)); }
private:
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
};
class DServer {
public:
DServer(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(&DServer::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(&DServer::handle_accept, this, new_session,boost::asio::placeholders::error));}
else { delete new_session; } }
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
handler.cpp
void callHandler(string data) {
/* here i want to process data and after that i want to send back the result to the same client ofcourse using the function sendOutcome() in the socket.h file */
}

Answer 1

The most common way to return data from a function is by returning it:
string callHandler(string data);
sendOutcome(callHandler(data_));
If you need more flexibility (e.g. to send multiple responses, or to do something else with the socket), then either pass a reference to the socket, or pass a reference to the session object (perhaps using an abstract interface to decouple it from the class implementation).

Answer 2

First of all, you must make sure, that you have received all the data you need. Your handler should cope with a scenario where the handleIncome() callback is called with bytes_transferred being 1 even if the entire request is much larger.
And of cause, you should not use the read callback as parameter to the async_write() function.