Can't set keep_alive to socket in asio - c++

Question

I'm trying to create a ServerSocket as a singleton. Here's the code:
ServerSocket.h
#pragma once
#include <asio.hpp>
#include <iostream>
#include <optional>
using asio::ip::tcp;
class ServerSocket
{
public:
ServerSocket(ServerSocket& otherSingleton) = delete;
void operator= (const ServerSocket& copySingleton) = delete;
tcp::acceptor* InitAcceptor();
tcp::socket* InitSocket();
void StartServerSocket();
void SendData(std::string);
std::optional<std::string> RecieveData();
static ServerSocket* GetInstance();
private:
static ServerSocket* instance;
tcp::acceptor* acceptor;
tcp::socket* socket;
asio::io_context io_context;
ServerSocket()
{
acceptor = InitAcceptor();
socket = InitSocket();
}
~ServerSocket() {
delete socket;
delete acceptor;
std::cout << "Server closed";
}
};
ServerSocket.cpp
#include "ServerSocket.h"
#include <optional>
tcp::acceptor* ServerSocket::InitAcceptor()
{
try
{
return new tcp::acceptor(io_context, tcp::endpoint(tcp::v4(), 27015));
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return nullptr;
}
tcp::socket* ServerSocket::InitSocket()
{
try
{
tcp::socket* deReturnat = new tcp::socket(io_context);
asio::socket_base::keep_alive option(true);
deReturnat->set_option(option);
return deReturnat;
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return nullptr;
}
void ServerSocket::StartServerSocket()
{
try
{
std::cout << "Server started";
acceptor->accept(*socket);
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
void ServerSocket::SendData(std::string)
{
}
std::optional<std::string> ServerSocket::RecieveData()
{
try
{
char data[5000];
asio::error_code error;
size_t length = socket->read_some(asio::buffer(data), error);
if (error == asio::error::eof) return std::nullopt; // Connection closed cleanly by peer.
else if (error)
throw asio::system_error(error); // Some other error.
return std::string{ data, length };
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return {};
}
ServerSocket* ServerSocket::instance(nullptr);
ServerSocket* ServerSocket::GetInstance()
{
if (instance == nullptr)
{
instance = new ServerSocket();
}
return instance;
}
The problem is that in InitSocket, when running a debugger, it seems like set_option doesn't work for some reason, and then an exception is thrown - and I can't understand why.
The exception that is thrown is: set_option: The file handle supplied is not valid.
How can I set the keep_alive option to true in my socket? It seems like this way doesn't work.

Answer 1

#Vasile, your problem, as #dewaffed told you, is that you are setting the options before the socket has been opened.
I don't know what you are trying to do but I can see that you creating a new socket, which is not open, and setting the properties, that's the problem. The correct way is:
Create the Socket
Accept the new connection, with the previous socket you've created.
Once the acceptor has ended to accept a new connection, the socket has a valid File Descriptor, which is required to set the option over the socket.
Check these links:
https://en.wikipedia.org/wiki/Berkeley_sockets
Modifying boost::asio::socket::set_option, which talks about your exception.
https://www.boost.org/doc/libs/1_77_0/doc/html/boost_asio/tutorial/tutdaytime2.html