socketServerWIthSelect01.cpp

//Example code: A simple server side code, which echos back the received message.
//Handle multiple socket connections with select and fd_set on Linux
#include <stdio.h>
#include <string.h> //strlen
#include <stdlib.h>
#include <errno.h>
#include <iostream>
#include <string>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")
#pragma warning( disable : 4996)
using namespace std;

#define TRUE 1
#define FALSE 0
#define PORT 5555

int main(int argc, char *argv[])
{
    int opt = TRUE;
    int master_socket, addrlen, new_socket, client_socket[30], max_clients = 30, activity, i, valread, sd;
    int max_sd;
    struct sockaddr_in address;
    WSADATA WSAData;
    WSAStartup(MAKEWORD(2, 0), &WSAData);

    char buffer[1024]; //data buffer of 1K

    //set of socket descriptors
    fd_set readfds;

    //a message
    const char *message = "ECHO Daemon v1.0";

    //initialise all client_socket[] to 0 so not checked
    for (i = 0; i < max_clients; i++)
    {
        client_socket[i] = 0;
    }

    //create a master socket
    if ((master_socket = socket(AF_INET, SOCK_STREAM, 0)) == 0)
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
    //int Socketerror = WSAGetLastError();
    //cout << Socketerror << endl;



    //set master socket to allow multiple connections ,
    //this is just a good habit, it will work without this
    if (setsockopt(master_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0)
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    //type of socket created
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    //bind the socket to localhost port 5555
    if (bind(master_socket, (struct sockaddr *)&address, sizeof(address)) < 0)
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    printf("Listener on port %d \n", PORT);

    //try to specify maximum of 3 pending connections for the master socket
    if (listen(master_socket, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    //accept the incoming connection
    addrlen = sizeof(address);
    puts("Waiting for connections ...");

    while (TRUE)
    {
        //clear the socket set
        FD_ZERO(&readfds);

        //add master socket to set
        FD_SET(master_socket, &readfds);
        max_sd = master_socket;

        //add child sockets to set
        for (i = 0; i < max_clients; i++)
        {
            //socket descriptor
            sd = client_socket[i];

            //if valid socket descriptor then add to read list
            if (sd > 0)
                FD_SET(sd, &readfds);

            //highest file descriptor number, need it for the select function
            if (sd > max_sd)
                max_sd = sd;
        }

        //wait for an activity on one of the sockets , timeout is NULL ,
        //so wait indefinitely
        activity = select(max_sd + 1, &readfds, NULL, NULL, NULL);

        if ((activity < 0) && (errno != EINTR))
        {
            printf("select error");
        }

        //If something happened on the master socket ,
        //then its an incoming connection
        if (FD_ISSET(master_socket, &readfds))
        {
            if ((new_socket = accept(master_socket, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0)
            {
                perror("accept");
                exit(EXIT_FAILURE);
            }

            //inform user of socket number - used in send and receive commands
            printf("New connection , socket fd is %d , ip is : %s , port : %d\n" , new_socket , inet_ntoa(address.sin_addr) , ntohs (address.sin_port));

            //send new connection greeting message
            if (send(new_socket, message, strlen(message), 0) != strlen(message))
            {
                perror("send");
            }

            puts("Welcome message sent successfully");

            //add new socket to array of sockets
            for (i = 0; i < max_clients; i++)
            {
                //if position is empty
                if (client_socket[i] == 0)
                {
                    client_socket[i] = new_socket;
                    printf("Adding to list of sockets as %d\n", i);

                    break;
                }
            }
        }

        //else its some IO operation on some other socket
        for (i = 0; i < max_clients; i++)
        {
            sd = client_socket[i];

            if (FD_ISSET(sd, &readfds))
            {
                //Check if it was for closing , and also read the
                //incoming message
                if ((valread = recv(sd, buffer, 1024,0)) < 0)//get data here
                {
                    //Somebody disconnected , get his details and print
                    getpeername(sd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
                    printf("Host disconnected , ip %s , port %d \n", inet_ntoa(address.sin_addr), ntohs(address.sin_port));

                    //Close the socket and mark as 0 in list for reuse
                    closesocket(sd);//close
                    client_socket[i] = 0;
                }

                //Echo back the message that came in
                else
                {
                    //set the string terminating NULL byte on the end
                    //of the data read
                    //here we can use the data sent by client
                    buffer[valread] = '\0';
                    send(sd, buffer, strlen(buffer), 0);
                }
            }
        }
    }

    system("pause");
    //return 0;
}