cube-game-plus-plus/server/network/Server.cpp

#include <iostream>
#include <cstring>

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <poll.h>

#include "server/network/Server.h"

// the empty function ensures the thread is joinable
Server::ConnectedClient::ConnectedClient() : th([]() {}), socket(-1)
{
}

Server::Server(uint16_t port, uint16_t maxClients, const IServerListener& listener) : 
    shouldRun(false), port(port), maxClients(maxClients), serverListener(listener), 
    listenerSocket(-1), clientAmount(0), clients(nullptr)
{
    // create socket for incoming connections
    // domain - AF_INET - IPv4 Internet protocols
    // type - SOCK_STREAM - two-way, connection-based byte streams
    // protocol - 0 - use standard protocol for the given socket type
    listenerSocket = socket(AF_INET, SOCK_STREAM, 0);
    if(listenerSocket == -1)
    {
        printError("cannot create listener socket");
        return;
    }
    
    // prevents clients from blocking the port if the server exits
    // this is useful if server and client run on the same system
    struct linger sl;
    sl.l_onoff = 1; // nonzero to linger on close
    sl.l_linger = 0; // time to linger
    // sockfd - listenerSocket - modified socket
    // level - SOL_SOCKET - manipulate options at the sockets API level
    // optname - SO_LINGER - identifier of the option
    if(setsockopt(listenerSocket, SOL_SOCKET, SO_LINGER, &sl, sizeof(struct linger)) == -1)
    {
        printError("cannot set non lingering");
        return;
    }
    
    // specify binding data
    struct sockaddr_in connectSocketData;
    // clear padding
    memset(&connectSocketData, 0, sizeof(struct sockaddr_in));
    // IPv4 Internet protocols
    connectSocketData.sin_family = AF_INET; 
    // port in network byte order
    connectSocketData.sin_port = htons(port); 
    // address in network byte order, accept any incoming messages
    connectSocketData.sin_addr.s_addr = htons(INADDR_ANY); 
    // bind the socket
    if(bind(listenerSocket, (struct sockaddr*) &connectSocketData, sizeof(struct sockaddr_in)) == -1)
    {
        printError("cannot bind listener socket");
        return;
    }
    
    // mark the socket as handler for connection requests
    // backlog - 5 - max queue length of pending connections
    if(listen(listenerSocket, 5) == -1)
    {
        printError("cannot start listening on socket");
        return;
    }
    
    shouldRun = true;
    listenerThread = std::thread(&Server::listenForClients, this);
    
    clients = new ConnectedClient[maxClients];
}

Server::~Server()
{
    shouldRun = false;
    listenerThread.join();
    
    if(listenerSocket != -1)
    {
        if(close(listenerSocket) == -1)
        {
            printError("cannot close listener socket");
        }
    }
    
    if(clients != nullptr)
    {
        for(uint16_t i = 0; i < maxClients; i++)
        {
            if(clients[i].socket != -1)
            {
                if(shutdown(clients[i].socket, SHUT_RDWR))
                {
                    printError("cannot shutdown client socket");
                }
                if(close(clients[i].socket) == -1)
                {
                    printError("cannot close client socket");
                }
            }
            if(clients[i].th.joinable())
            {
                clients[i].th.join();
            }
            else
            {
                std::cout << "cannot join client connection thread " << std::endl;
            }
        }
        delete[] clients;
    }
}

bool Server::isRunning() const
{
    return shouldRun;
}

void Server::printError(const char* message) const
{
    std::cout << message << ": " << strerror(errno) << std::endl;
}

void Server::listenForClients()
{
    while(shouldRun)
    {
        // wait until a connection arrives with timeout, this prevents being 
        // stuck in accept
        struct pollfd fds;
        fds.fd = listenerSocket; // file descriptor for polling
        fds.events = POLLIN; // wait until data is ready to read
        fds.revents = 0; // return events - none
        // nfds_t - 1 - amount of passed in structs
        // timeout - 100 - milliseconds to wait until an event occurs
        // returns 0 on timeout, -1 on error, and >0 on success
        int pollData = poll(&fds, 1, 100);
        if(pollData > 0)
        {
            struct sockaddr_in clientSocketData;
            // accepts an incoming client connection and stores the data in the
            // given struct, returns a nonnegative file descriptor on success
            socklen_t addrlen = sizeof(struct sockaddr_in);
            int clientSocket = accept(listenerSocket, (struct sockaddr*) &clientSocketData, &addrlen);
            if(clientSocket >= 0)
            {
                //std::cout << inet_ntoa(clientSocketData.sin_addr) << ":" << (int) ntohs(clientSocketData.sin_port) << std::endl;
                if(addClient(clientSocket))
                {
                    if(close(clientSocket) == -1)
                    {
                        printError("cannot close client socket");
                    }
                }
            }
            else
            {
                printError("accept error");
                break;
            }
        }
        else if(pollData == -1)
        {
            printError("poll error");
            break;
        }
    }
}

bool Server::addClient(int clientSocket)
{
    std::lock_guard<std::mutex> lg(clientMutex);
    if(clientAmount >= maxClients)
    {
        serverListener.onFullServerClientConnect(clientSocket);
        return true;
    }
    else
    {
        // search for free slot
        uint16_t index = 0;
        while(index < maxClients)
        {
            if(clients[index].socket == -1)
            {
                break;
            }
            index++;
        }
        
        if(index >= maxClients)
        {
            std::cout << "cannot find free slot - even if there should be one" << std::endl;
            return true;
        }

        //ensure old thread has ended
        if(!clients[index].th.joinable())
        {
            std::cout << "cannot join thread of non used client connection" << std::endl;
            return true;
        }
        clients[index].th.join();

        clients[index].socket = clientSocket;
        clients[index].th = std::thread(&Server::listenOnClient, this, std::ref(clients[index]));

        clientAmount++;

        return false;
    }
}

void Server::listenOnClient(ConnectedClient& cc)
{
    // poll data
    struct pollfd fds;
    fds.fd = cc.socket; // file descriptor for polling
    fds.events = POLLIN; // wait until data is ready to read
    fds.revents = 0; // return events - none
    
    serverListener.onClientConnect(cc.socket);
    
    Stream st;
    while(shouldRun)
    {
        // nfds_t - 1 - amount of passed in structs
        // timeout - 100 - milliseconds to wait until an event occurs
        // returns 0 on timeout, -1 on error, and >0 on success
        int pollData = poll(&fds, 1, 100);
        if(pollData > 0)
        {
            st.readSocket(cc.socket);
            if(st.hasData())
            {
                serverListener.onClientPackage(cc.socket, st);
            }
            else
            {
                // client closed connection
                break;
            }
        }
        else if(pollData == -1)
        {
            printError("cannot poll from client");
            break;
        }
    }
    
    serverListener.onClientDisconnect(cc.socket);
    
    // reset slot for another client
    if(shouldRun)
    {
        std::lock_guard<std::mutex> lg(clientMutex);
        if(close(cc.socket) == -1)
        {
            printError("cannot close socket of client");
        }
        cc.socket = -1;
        clientAmount--;
    }
}