How can I add an async timer to a boost UDP server? - c++

Question

I got this code online and have been trying to add a timer to it so that it reads a packet every so often. I can't seem to figure out how to pass a callback function to the boost::async_wait command because I am getting this error:
server1.cpp: In member function ‘void UDPClient::handle_receive(const boost::system::error_code&, size_t)’:
server1.cpp:51:66: error: invalid use of non-static member function ‘void UDPClient::time_to_receive(const boost::system::error_code&)’
boost::asio::placeholders::error));
^
server1.cpp:33:6: note: declared here
void UDPClient::time_to_receive(const boost::system::error_code& error)
^~~~~~~~~
UDPClient Class:
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/array.hpp>
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>
using boost::asio::ip::udp;
class UDPClient
{
public:
boost::asio::io_service io_service;
udp::socket socket;
udp::endpoint receiver_endpoint;
boost::asio::deadline_timer timer;
boost::array<char, 1024> recv_buffer;
UDPClient();
void time_to_receive(const boost::system::error_code& error);
void do_receive();
void handle_receive(const boost::system::error_code& error, size_t);
};
UDPClient::UDPClient()
: io_service(),
socket(io_service, {udp::v4(), 3643}),
timer(io_service, boost::posix_time::seconds(2))
{
do_receive();
io_service.run();
}
void UDPClient::time_to_receive(const boost::system::error_code& error)
{
do_receive();
}
void UDPClient::do_receive()
{
socket.async_receive_from(boost::asio::buffer(recv_buffer), receiver_endpoint,
boost::bind(&UDPClient::handle_receive, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "'\n";
timer.async_wait(boost::bind(time_to_receive,
boost::asio::placeholders::error));
}
int main()
{
UDPClient updclient;
}
One question I'm trying to answer with this code is if I spam the server from a client with a bunch of UDP packets will the server ignore all the packets during the async_wait?
Also, my main goal is to put this code into a quadcopter code I have. Will it work the way it is written to instantiate this class and have it read packets from a ground station to get user input?

Answer 1

The way you use bind with member function is wrong. Use it like shown below:
timer.async_wait(boost::bind(&UDPClient::time_to_receive, this,
boost::asio::placeholders::error));
As to why it is like that, I would recommend you to read the boost docs for that.
Also, I have modified the code to make it actually run like a server without exiting. For that I made following 2 changes:
Initialzation of io_service in main function and pass its reference to the class.
Initialize a io_service_work object. This acts as a perennial source of work to the io_service. Thus, io_service never returns from the run function unless the work object is destroyed.
The complete source:
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/array.hpp>
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>
using boost::asio::ip::udp;
class UDPClient
{
public:
boost::asio::io_service& io_service;
udp::socket socket;
udp::endpoint receiver_endpoint;
boost::asio::deadline_timer timer;
boost::array<char, 1024> recv_buffer;
UDPClient(boost::asio::io_service&);
void time_to_receive(const boost::system::error_code& error);
void do_receive();
void handle_receive(const boost::system::error_code& error, size_t);
};
UDPClient::UDPClient(boost::asio::io_service& ios)
: io_service(ios),
socket(io_service, {udp::v4(), 3643}),
timer(io_service, boost::posix_time::seconds(2))
{
do_receive();
}
void UDPClient::time_to_receive(const boost::system::error_code& error)
{
do_receive();
}
void UDPClient::do_receive()
{
socket.async_receive_from(boost::asio::buffer(recv_buffer), receiver_endpoint,
boost::bind(&UDPClient::handle_receive, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "'\n";
timer.expires_from_now(boost::posix_time::seconds(2));
timer.async_wait(boost::bind(&UDPClient::time_to_receive, this,
boost::asio::placeholders::error));
}
int main()
{
boost::asio::io_service ios;
boost::asio::io_service::work wrk(ios);
UDPClient updclient(ios);
ios.run();
}
NOTE: Even though it is a server, the class is name Client. I am ignoring that :)