C++ Event driven TCP socket server (multi client, single threaded)

Server.cpp

/*
 * Server.cpp
 *
 * EventServer is a simple C++ TCP socket server implementation,
 * to serve as an example to anyone who wants to learn it.
 * It can interface with the rest of your program using three callback functions.
 * - onConnect, which fires when a new client connects. the client's fd is passed.
 * - onDisconnect, which fires when a client disconnects. passes fd.
 * - onInput, fires when input is received from a client. passes fd and char*
 *
 * define SERVER_DEBUG to spew out some juicy debug data!
 *
 * Original work by Gydo194, BSD 3-clause license below applies.
 * 
 * For an usage example, see the following project: https://github.com/Gydo194/server
 *
 * Use with neccesary caution, this code has not been audited or tested for performance problems, security holes, memory leaks etc.
 * 
 */

/*
Copyright 2018-2021 Gydo194

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include "Server.hpp"

Server::Server()
{
    setup(DEFAULT_PORT);
}

Server::Server(int port)
{
    setup(port);
}

Server::Server(const Server& orig)
{
}

Server::~Server()
{
	#ifdef SERVER_DEBUG
	std::cout << "[SERVER] [DESTRUCTOR] Destroying Server...\n";
	#endif
	close(mastersocket_fd);
}

void Server::setup(int port)
{
    mastersocket_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (mastersocket_fd < 0) {
        perror("Socket creation failed");
    }

    FD_ZERO(&masterfds);
    FD_ZERO(&tempfds);

    memset(&servaddr, 0, sizeof (servaddr)); //bzero
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htons(INADDR_ANY);
    servaddr.sin_port = htons(port);

    bzero(input_buffer,INPUT_BUFFER_SIZE); //zero the input buffer before use to avoid random data appearing in first receives
}

void Server::initializeSocket()
{
	#ifdef SERVER_DEBUG
	std::cout << "[SERVER] initializing socket\n";
	#endif
	int opt_value = 1;
	int ret_test = setsockopt(mastersocket_fd, SOL_SOCKET, SO_REUSEADDR, (char *) &opt_value, sizeof (int));
	#ifdef SERVER_DEBUG
	printf("[SERVER] setsockopt() ret %d\n", ret_test);
    	#endif
	if (ret_test < 0) {
        	perror("[SERVER] [ERROR] setsockopt() failed");
		shutdown();
    	}
}

void Server::bindSocket()
{
	#ifdef SERVER_DEBUG
	std::cout << "[SERVER] binding...\n";
	#endif
	int bind_ret = bind(mastersocket_fd, (struct sockaddr*) &servaddr, sizeof (servaddr));
	#ifdef SERVER_DEBUG
	printf("[SERVER] bind() ret %d\n", bind_ret);
	#endif
	if (bind_ret < 0) {
		perror("[SERVER] [ERROR] bind() failed");
	}
	FD_SET(mastersocket_fd, &masterfds); //insert the master socket file-descriptor into the master fd-set
	maxfd = mastersocket_fd; //set the current known maximum file descriptor count
}

void Server::startListen()
{
	#ifdef SERVER_DEBUG
	std::cout << "[SERVER] listen starting...\n";
	#endif
	int listen_ret = listen(mastersocket_fd, 3);
	#ifdef SERVER_DEBUG
	printf("[SERVER] listen() ret %d\n", listen_ret);
	#endif
	if (listen_ret < 0) {
		perror("[SERVER] [ERROR] listen() failed");
	}

}

void Server::shutdown()
{
	int close_ret = close(mastersocket_fd);
	#ifdef SERVER_DEBUG
	printf("[SERVER] [DEBUG] [SHUTDOWN] closing master fd..  ret '%d'.\n",close_ret);
	#endif
}

void Server::handleNewConnection()
{
	#ifdef SERVER_DEBUG
  	 std::cout << "[SERVER] [CONNECTION] handling new connection\n";
    	#endif
    	socklen_t addrlen = sizeof (client_addr);
    	tempsocket_fd = accept(mastersocket_fd, (struct sockaddr*) &client_addr, &addrlen);
    	
	if (tempsocket_fd < 0) {
        	perror("[SERVER] [ERROR] accept() failed");
	} else {
        	FD_SET(tempsocket_fd, &masterfds);
		//increment the maximum known file descriptor (select() needs it)
        	if (tempsocket_fd > maxfd) {
            		maxfd = tempsocket_fd;
			#ifdef SERVER_DEBUG
            		std::cout << "[SERVER] incrementing maxfd to " << maxfd << std::endl;
			#endif
        	}
        	#ifdef SERVER_DEBUG
        	printf("[SERVER] [CONNECTION] New connection on socket fd '%d'.\n",tempsocket_fd);
		#endif
    }
    newConnectionCallback(tempsocket_fd); //call the callback
}

void Server::recvInputFromExisting(int fd)
{
    int nbytesrecv = recv(fd, input_buffer, INPUT_BUFFER_SIZE, 0);
    if (nbytesrecv <= 0)
    {
        //problem
        if (0 == nbytesrecv)
	{
        	disconnectCallback((uint16_t)fd);
		close(fd); //well then, bye bye.
        	FD_CLR(fd, &masterfds);
        	return;
        } else 
	{
        	perror("[SERVER] [ERROR] recv() failed");
        }
        close(fd); //close connection to client
        FD_CLR(fd, &masterfds); //clear the client fd from fd set
        return;
    }
    #ifdef SERVER_DEBUG
    printf("[SERVER] [RECV] Received '%s' from client!\n", input_buffer);
    #endif
    receiveCallback(fd,input_buffer);
    //memset(&input_buffer, 0, INPUT_BUFFER_SIZE); //zero buffer //bzero
    bzero(&input_buffer,INPUT_BUFFER_SIZE); //clear input buffer
}

void Server::loop()
{
    tempfds = masterfds; //copy fd_set for select()
    #ifdef SERVER_DEBUG
    printf("[SERVER] [MISC] max fd = '%hu' \n", maxfd);
    std::cout << "[SERVER] [MISC] calling select()\n";
    #endif
    int sel = select(maxfd + 1, &tempfds, NULL, NULL, NULL); //blocks until activity
    //printf("[SERVER] [MISC] select() ret %d, processing...\n", sel);
    if (sel < 0) {
        perror("[SERVER] [ERROR] select() failed");
        shutdown();
    }

    //no problems, we're all set

    //loop the fd_set and check which socket has interactions available
    for (int i = 0; i <= maxfd; i++) {
        if (FD_ISSET(i, &tempfds)) { //if the socket has activity pending
            if (mastersocket_fd == i) {
                //new connection on master socket
                handleNewConnection();
            } else {
                //exisiting connection has new data
                recvInputFromExisting(i);
            }
        } //loop on to see if there is more
    }


}

void Server::init()
{
    initializeSocket();
    bindSocket();
    startListen();
}

void Server::onInput(void (*rc)(uint16_t fd, char *buffer))
{
    receiveCallback = rc;
}

void Server::onConnect(void(*ncc)(uint16_t))
{
    newConnectionCallback = ncc;
}

void Server::onDisconnect(void(*dc)(uint16_t))
{
    disconnectCallback = dc;
}

uint16_t Server::sendMessage(Connector conn, char *messageBuffer) {
    return send(conn.source_fd,messageBuffer,strlen(messageBuffer),0);
}

uint16_t Server::sendMessage(Connector conn, const char *messageBuffer) {
    return send(conn.source_fd,messageBuffer,strlen(messageBuffer),0);
}

Server.hpp

/*
 * Server.hpp
 *
 * EventServer is a simple C++ TCP socket server implementation,
 * to serve as an example to anyone who wants to learn it.
 * It can interface with the rest of your program using three callback functions.
 * - onConnect, which fires when a new client connects. the client's fd is passed.
 * - onDisconnect, which fires when a client disconnects. passes fd.
 * - onInput, fires when input is received from a client. passes fd and char*
 *
 * define SERVER_DEBUG to spew out some juicy debug data!
 *
 * Original work by Gydo194, BSD 3-clause license below applies.
 * 
 * For an usage example, see the following project: https://github.com/Gydo194/server
 *
 * Use with neccesary caution, this code has not been audited or tested for performance problems, security holes, memory leaks etc.
 * 
 */

/*
Copyright 2018-2021 Gydo194

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifndef SERVER_HPP
#define SERVER_HPP


#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h> //sockaddr, socklen_t
#include <arpa/inet.h>
#include <netdb.h>
#include <iostream>

#define INPUT_BUFFER_SIZE 100 //test: 100 bytes of buffer
#define DEFAULT_PORT 9034

class Server
{
public:
    Server();
    Server(int port);
    Server(const Server& orig);
    virtual ~Server();
    
    struct Connector {
        uint16_t source_fd;
    };
    
    void shutdown();
    void init();
    void loop();

    //callback setters
    void onConnect(void (*ncc)(uint16_t fd));
    void onInput(void (*rc)(uint16_t fd, char *buffer));
    void onDisconnect(void (*dc)(uint16_t fd));

    uint16_t sendMessage(Connector conn, const char *messageBuffer);
    uint16_t sendMessage(Connector conn, char *messageBuffer);

private:
    //fd_set file descriptor sets for use with FD_ macros
    fd_set masterfds;
    fd_set tempfds;

    //unsigned integer to keep track of maximum fd value, required for select()
    uint16_t maxfd;

    //socket file descriptors
    int mastersocket_fd; //master socket which receives new connections
    int tempsocket_fd; //temporary socket file descriptor which holds new clients

    //client connection data
    struct sockaddr_storage client_addr;
    //server socket details
    struct sockaddr_in servaddr;
    //input buffer
    char input_buffer[INPUT_BUFFER_SIZE];

    char remote_ip[INET6_ADDRSTRLEN];
    //int numbytes;

    void (*newConnectionCallback) (uint16_t fd);
    void (*receiveCallback) (uint16_t fd, char *buffer);
    void (*disconnectCallback) (uint16_t fd);


    //function prototypes
    void setup(int port);
    void initializeSocket();
    void bindSocket();
    void startListen();
    void handleNewConnection();
    void recvInputFromExisting(int fd);

    //void *getInetAddr(struct sockaddr *saddr);


};

#endif /* SERVER_HPP */

How do I use this in my int main()?

Hi,
Please see this file in my project, which sets this up and uses it.

Please be very careful about using this though; i must admit I'm not sure about the stability and security of this code as i've never thoroughly tested this for either.

Thanks a lot for your implementation!