boost.Asio lib

Documentation for Boost.Asio

http://www.boost.org/doc/libs/1_62_0/doc/html/boost_asio.html

https://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-started-with-boostasio?pg=7

1　 Your program will have at least one io_service object. The io_service represents your program's link to the operating system's I/O services.

　　Program->I/O Object-> I/O Service -> operating system
　　(1)　　only for asynchronous operation, should we call io_service.run()
　　(2)　　for synchornous operation, we don't have to call run() to block it

2　 A strand is defined as a strictly sequential invocation of event handlers,
　　that is, only when the privious handler has finished will the next one be executed
　　Use of strands allows execution of code in a multithreaded program without the need for explicit locking.

3　 Buffers, usually contiguous regions of memory, can be simply expressed as a tuple consisting of a pointer and a size in bytes: (char *, size_t )
　　the library also includes mechanisms for automatically determining the size of a buffer from an array, boost::array or std::vector of POD elements, or from a std::string
　　all buffers are of type of const_buffer or mutalbe_buffer

4    boost::asio::streambuf & boost::asio::buffers_begin()

5    Many I/O objects in Boost.Asio are stream-oriented, such as ip::tcp::socket, and provide stream read & write operation
　　Programs typically want to transfer an exact number of bytes. When a short read or short write occurs the program must restart the operation,
　　and continue to do so until the required number of bytes has been transferred.
　　Boost.Asio provides generic functions that do this automatically: read(), async_read(), write() and async_write().(for udp, iocp, they are receive()/send())
　　And streams are usually lined based, so there are functions like read_until()

6 　Resolver, where host and service names are looked up and converted into one or more endpoints

7 　Acceptor, accept incoming TCP connections:shall extract the first connection on the queue of pending connections, create a new socket with the same socket type protocol
　　and address family as the specified socket, and allocate a new file descriptor for that socket

8 　Boost.Asio includes classes that implement iostreams on top of sockets. These hide away the complexities associated with endpoint resolution, protocol independence, etc.

9 　when perform synchronous wait, Timer can be used to decide the deadline

10  supports signal handling using a class called signal_set. Programs may add one or more signals to the set, and then perform an async_wait() operation.
　　The specified handler will be called when one of the signals occurs. The same signal number may be registered with multiple signal_set objects,
　　however the signal number must be used only with Boost.Asio.

11. when there is any io_service::work, io_service::run() will block the thread where it's called
　　[io_service.post()->io_service.run()->io_service.dispacth()], like post(), async_read

12. if we had associated a work object with the io_service and wanted to let all queued work finish, we would not call stop but rather destroy the work objec,
　　that is , we dont have to call any stop(), just call work.reset()

13  since the io_service cannot be copied and that is what boost::bind does for us behind the scenes. To get around this, we must make use of shared_ptr. is reference or pointer OK?

14  The post function "is used to ask the io_service to execute the given handler, but without allowing the io_service to call the handler from inside this function."
　　The dispatch function "guarantees that the handler will only be called in a thread in which the run(), run_one(), poll() or poll_one() member functions is currently being invoked.
　　Dispatched events can execute from the current worker thread even if there are other pending events queued up.
　　This means if we post work1 -> work2 -> work3 through a strand, no matter how many worker threads we have, it will be executed in that order. will not Dispatch!!!

15  For variable on the stack, it's possible for it to go out of scope before the asynchronous operation completes.

16  io_service is thread-safe, but not sockets, so a socket be used in several threads should be lock!!!

17  The asynchronous support is based on the Proactor design pattern

18  Asynchronous completion handlers will only be called from threads that are currently calling io_service::run().

19  The open() function must be called before data can be sent or received on the socket

20  this is because the poll function will not block while there is more work to do. It simply executes the current
　　set of work and then returns.if there is an event get, then call the handler, if none, just go ahread;

21 all threads call the same io_service.run() will be put in the thread pool of this io_service
　　base on one io_service, there can more than one io object( socket)
　　we can use several io_service object to create diffent thread pool

SSL (Secure Sockets Layer) is a standard security technology for establishing an encrypted link between a server and a client,
　　allow encrypted communication to be layered on top of an existing stream
　　Normally, data sent between browsers and web servers is sent in plain text

Composed operation: a operation composed of two or more simpler operations

POD: Plain Old Data, a type is a POD when the only things in it are built-in types and combinations of them

Coroutines are program components that generalize subroutines to allow multiple entry points for suspending and resuming execution at certain locations.

socket::iostream, null-buffer, Half duplex protocol

asynchronization & multithread

UDP/TCP examples

// file : tcp-client.cpp
// copied from official website of Boost::asio
#include<iostream>
#include<boost/array.hpp>
#include<boost/asio.hpp>

using boost::asio::ip::tcp;

int main(int argc, char* argv[])
{
    try
    {
        if (argc != )
        {
            std::cerr << "Usage: client <host>" << std::endl;
            return ;
        }
        boost::asio::io_service io_service;
        tcp::resolver resolver(io_service);
        // query(host,service)
        // service: time, daytime, http, telnet, ftp, echo, smtp, "80"
        // service, A string identifying the requested service.
        // This may be a descriptive name or a numeric string corresponding to a port number.
        tcp::resolver::query query(argv[], "daytime");
        tcp::resolver::iterator endpointer_iterator = resolver.resolve(query);
        tcp::socket socket(io_service);
        // TCP::endpoint endpoint(boost::asio::ip::address_v4::from_string("127.0.0.1"), 10000);
        boost::asio::connect(socket, endpointer_iterator);

        char a[] = { 'a', 'b' };
        socket.write_some(boost::asio::buffer(a));

        for (;;)
        {
            boost::array<char, > buf;
            // read(socket, buf)
            // read() suuceeds only when he supplied buffers are full.That is, the bytes transferred is equal to the sum of the buffer sizes.
            // An error occurred.
            boost::system::error_code error;
            size_t len = socket.read_some(boost::asio::buffer(buf), error);
            std::cout << "lenth is " << len << std::endl;
            if (error == boost::asio::error::eof)
                break;
            else if (error)
            {
                throw boost::system::system_error(error);
            }
            std::cout.write(buf.data(), len);
        }
    }
    catch (std::exception &e)
    {
        std::cerr << e.what() << std::endl;
    }
}

#define _CRT_SECURE_NO_WARNINGS
#include<ctime>
#include<iostream>
#include<string>
#include<boost/bind.hpp>
#include<boost/shared_ptr.hpp>
#include<boost/enable_shared_from_this.hpp>
#include<boost/asio.hpp>

using boost::asio::ip::tcp;
using boost::asio::ip::udp;

std::string make_daytime_string()
{
    using namespace std;
    time_t now = time();
    return ctime(&now);
}

class tcp_connection
{
public:
    /*
    static pointer create(boost::asio::io_service& io_service)
    {
        return pointer(new tcp_connection(io_service));
    }
    */
    static tcp_connection * create(boost::asio::io_service& io_service)
    {
        tcp_connection * pConnection = NULL;
        pConnection = new tcp_connection(io_service);
        return pConnection;
    }
    tcp::socket& socket() {return socket_;}

    void start()
    {
        char a[] = { '\0' };
        socket_.read_some(boost::asio::buffer(a));
        std::cout << "get message " << a << std::endl;
        message_ = make_daytime_string();
        boost::asio::async_write(socket_, boost::asio::buffer(message_),
            boost::bind(&tcp_connection::handle_write, this,
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred));
    }

private:
    tcp_connection(boost::asio::io_service & io_service) :socket_(io_service){}
    void handle_write(const boost::system::error_code &, size_t) {
        std::cout << "current socket address is " << this->socket_.local_endpoint().address()
            << " prot " << this->socket_.local_endpoint().port() << " finished writing" << std::endl;
    }
    tcp::socket socket_;
    std::string message_;
};

class tcp_server
{
public:
    tcp_server(boost::asio::io_service & io_service) : acceptor_(io_service, tcp::endpoint(tcp::v4(), ))
    {
        start_accept();
    }
private:
    void start_accept()
    {
        // without using share_ptr() here will cause mem leak!!!
        tcp_connection * new_connection = tcp_connection::create(acceptor_.get_io_service());
        // accept() function shall extract the first connection on the queue of pending connections,
        // create a new socket with the same socket type protocol and address family as the specified socket,
        // and allocate a new file descriptor for that socket
        acceptor_.async_accept(new_connection->socket(), boost::bind(&tcp_server::handle_accept, this, new_connection,
            boost::asio::placeholders::error));
    }

    void handle_accept(tcp_connection * new_connection,
        const boost::system::error_code& error)
    {
        if (!error)
        {
            new_connection->start();
        }
        start_accept();
    }
    tcp::acceptor acceptor_;
};

class udp_server
{
public:
    udp_server(boost::asio::io_service& io_service)
        : socket_(io_service, udp::endpoint(udp::v4(), ))
    {
        start_receive();
    }

private:
    void start_receive()
    {
        socket_.async_receive_from(
            boost::asio::buffer(recv_buffer_), remote_endpoint_,
            boost::bind(&udp_server::handle_receive, this,
            boost::asio::placeholders::error));
    }

    void handle_receive(const boost::system::error_code& error)
    {
        if (!error || error == boost::asio::error::message_size)
        {
            std::cout << this->recv_buffer_ << std::endl;
            boost::shared_ptr<std::string> message(
                new std::string(make_daytime_string()));

            socket_.async_send_to(boost::asio::buffer(*message), remote_endpoint_,
                boost::bind(&udp_server::handle_send, this, message));

            start_receive();
        }
    }

    void handle_send(boost::shared_ptr<std::string> /*message*/)
    {
    }

    udp::socket socket_;
    udp::endpoint remote_endpoint_;
    char recv_buffer_ [];
};

int main()
{
    try
    {
        boost::asio::io_service io_service;
        tcp_server server(io_service);
        udp_server server2(io_service);
        io_service.run();
    }
    catch (std::exception &e)
    {
        std::cerr << e.what() << std::endl;
    }
    return ;
}

// file : udp-client.cpp
#include <iostream>
#include <string>
#include <boost/array.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>

using boost::asio::ip::udp;
using boost::thread;

/* one socket, synchronous, serial executtion
int main()
{
    boost::asio::io_service io;
    udp::socket socket(io);
    socket.open(udp::v4());
    udp::endpoint endpoint(boost::asio::ip::address::from_string("127.0.0.1"), 13);
    while(1)
    {
        std::string str;
        std::cout << "Input string: ";
        std::cin >> str;
        socket.send_to(boost::asio::buffer(str),endpoint);

        // receive
        char rec_buf[128];
        udp::endpoint sender_point;
        size_t len = socket.receive_from(boost::asio::buffer(rec_buf), sender_point);
        std::cout.write(rec_buf,len);
    }
}
*/

/* as socket is not thread-safe, two threads may conflict, add mutext to prevent it;
void rev(udp::socket * socket)
{
    while(1)
    {
        char rec_buf[128];
        udp::endpoint sender_point;
        // mutext.lock()
        size_t len = socket->receive_from(boost::asio::buffer(rec_buf), sender_point);
        // mutex.unlock()
        std::cout.write(rec_buf,len);
    }

}

int main()
{
    boost::asio::io_service io;
    udp::socket socket(io);
    socket.open(udp::v4());
    udp::endpoint endpoint(boost::asio::ip::address::from_string("127.0.0.1"), 13);
    thread thr(boost::bind(rev,&socket));
    while(1)
    {
        std::string str;
        std::cout << "Input string: ";
        std::cin >> str;
        // mutex.lock()
        socket.send_to(boost::asio::buffer(str),endpoint);
        // mutex.unlock()
    }
    thr.join();
}
*/

/* two sockets, from the result, we know the data supposed to receive is sent to socket1 not socket2
void rev(udp::socket * socket)
{
    while(1)
    {
        char rec_buf[128];
        udp::endpoint sender_point;
        std::cout << socket->local_endpoint().address() <<" : " << socket->local_endpoint().port()
            << std::endl;
        size_t len = socket->receive_from(boost::asio::buffer(rec_buf), sender_point);
        std::cout.write(rec_buf,len) << std::endl;
    }
}

int main()
{
    boost::asio::io_service io;
    udp::socket socket(io);
    udp::socket socket2(io);
    socket.open(udp::v4());
    socket2.open(udp::v4());
    udp::endpoint endpoint(boost::asio::ip::address::from_string("127.0.0.1"), 13);
    thread thr(boost::bind(rev,&socket2));
    while(1)
    {
        std::string str;
        std::cout << "Input string: ";
        std::cin >> str;
        socket.send_to(boost::asio::buffer(str),endpoint);
        std::cout << socket.local_endpoint().address() << " : " << socket.local_endpoint().port();
    }
    thr.join();
}
*/

char rec_buf[];
udp::endpoint endpoint(boost::asio::ip::address::from_string("127.0.0.1"), );

void rev(udp::socket * socket);
void on_rec(udp::socket * socket) {
    std::cout<<rec_buf<<std::endl;
    rev(socket);
}

void rev(udp::socket * socket) {
    udp::endpoint sender_point;
    socket->async_receive_from(boost::asio::buffer(rec_buf), sender_point, boost::bind(on_rec,socket));
}

void send(udp::socket *);
void on_send(udp::socket * socket, const boost::system::error_code & error) {
    if(!error) {
        std::cout << "send the message successfully" << std::endl;
    }
    send(socket);
}
void send(udp::socket * socket) {

    std::string str;
    std::cout << "Input string: ";
    std::cin >> str;
    socket->async_send_to(boost::asio::buffer(str),endpoint,boost::bind(on_send, socket, boost::asio::placeholders::error));
}

int main()
{
    boost::asio::io_service io;
    udp::socket socket(io);
    socket.open(udp::v4());
    io.post(boost::bind(rev,&socket));
    send(&socket);

    thread thr(boost::bind(&boost::asio::io_service::run,&io));
    thr.join();
}

to build it:

g++ -o tcp-client tcp-client.cpp -lboost_system -lpthread
g++ -o server server.cpp -lboost_system -lpthread
g++ -o udp-client udp.cpp -lboost_system -lpthread -lboost_thread