Boost library consists of asio which is a free, cross-platform C++ library for network and low-level I/O programming that provides a consistent asynchronous model using a modern C++ approach. This article will help to develop a client-server synchronous chatting application using boost::asio. We are explicitly mentioning "synchronous" because in the synchronous model one of our client or server has to wait for another.

Server-Side Application: Below are the various steps to create the Server Side application:

• Importing boost/asio.hpp (Version: 1.65.1.0)

  #include <boost/asio.hpp>

• Creating object of io_service (for server) which is mandatory for using boost::asio.

  boost::asio::io_service io_service_object;

• Creating object of acceptor, passing io_service object and endpoint of connection i.e. IPv4 and port number 9999 (IPv6 protocol is also supported in boost::asio, also note that port 0 - 1233 are reserved).

  boost::asio::ip::tcp::acceptor 
    acceptor_object(
      io_service_object, 
      tcp::endpoint(boost::asio::ip::tcp::v4(), 
                    9999));

• Creating tcp::socket object for our server.

  boost::asio::ip::tcp::socket socket_object(io_service_object) 
  

• Invoking accept method of acceptor object to establish connection.

  acceptor_server.accept(server_socket);
  

• read_until() method fetches message from the buffer which stores data during communication. Here we are using "\n" as out delimiter, which means we shall keep reading data from the buffer until we encounter "\n" and store it.

  // Create buffer for storing
  boost::asio::streambuf buf;
  
  boost::asio::read_until(socket, buf, "\n");
  string data = boost::asio::buffer_cast(buf.data());
  

• write() method writes data to the buffer taking socket object and message as parameter.

  boost::asio::write(
    socket, 
    boost::asio::buffer(message + "\n"));
  

Client-Side Application: Below are the various steps to create the Client Side application:

• Importing boost/asio.hpp.

  #include <boost/asio.hpp>

• Creating object of io_service for client.

  boost::asio::io_service io_service_object;

• Creating tcp::socket object for client.

  boost::asio::ip::tcp::socket
    socket_object(io_service_object) 

• Invoking connect method of socket object to initiate connection with server using localhost (IP 127.0.0.1) and connecting to same port 9999.

  client_socket.connect(
    tcp::endpoint(
      address::from_string("127.0.0.1"), 
      9999 ));

• read_until() and write() will remain same for our client application as well, as the Server side.

Below is the implementation of the above approach: Program:

// Client-side Synchronous Chatting Application

// using C++ boost::asio

  

#include <boost/asio.hpp>

#include <iostream>

using namespace std;

using namespace boost::asio;

using namespace boost::asio::ip;

  

string getData(tcp::socket& socket)

{

    streambuf buf;

    read_until(socket, buf, "\n");

    string data = buffer_cast<const char*>(buf.data());

    return data;

}

  

void sendData(tcp::socket& socket, const string& message)

{

    write(socket,

          buffer(message + "\n"));

}

  

int main(int argc, char* argv[])

{

    io_service io_service;

    // socket creation

    ip::tcp::socket client_socket(io_service);

  

    client_socket

        .connect(

            tcp::endpoint(

                address::from_string("127.0.0.1"),

                9999));

  

    // Getting username from user

    cout << "Enter your name: ";

    string u_name, reply, response;

    getline(cin, u_name);

  

    // Sending username to another end

    // to initiate the conversation

    sendData(client_socket, u_name);

  

    // Infinite loop for chit-chat

    while (true) {

  

        // Fetching response

        response = getData(client_socket);

  

        // Popping last character "\n"

        response.pop_back();

  

        // Validating if the connection has to be closed

        if (response == "exit") {

            cout << "Connection terminated" << endl;

            break;

        }

        cout << "Server: " << response << endl;

  

        // Reading new message from input stream

        cout << u_name << ": ";

        getline(cin, reply);

        sendData(client_socket, reply);

  

        if (reply == "exit")

            break;

    }

    return 0;

}




OUTPUT:













The above socket programming explains our simple synchronous TCP server and client chatting application. One of the major drawbacks of the synchronous client-server application is that one request has to be served before we request for another one, thus blocking our later requests. In case we want our program to perform multiple operations simultaneously, we can use multi-threaded TCP client-server to handle the situation. However, the multi-threaded application is not recommended because of various complexities involved in creating threads. Another option can come handy, and that is the asynchronous server. This is where boost::asio shines, we shall understand this in the next article.