C99 compliant chat server (2.0)

server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>


#define INPUT_BUFFER_SIZE 2048 //2k buffer
#define PORT "9034"   // port we're listening on


/////global variables
fd_set master_fds; // master file descriptor list
fd_set read_fds; // temp file descriptor list for select()
int fdmax; // maximum file descriptor number

int masterSocket; // listening socket descriptor
int newfd; // newly accept()ed socket descriptor
struct sockaddr_storage remoteaddr; // client address
socklen_t addrlen;

char buf[INPUT_BUFFER_SIZE]; // buffer for client data
int nbytes;

char remoteIP[INET6_ADDRSTRLEN];

int opt = 1; // for setsockopt() SO_REUSEADDR, below
int i, j, rv, select_ret;

struct addrinfo server_addr, *ai, *p;

//end global variables

void safeShutdown(int code) {
    close(masterSocket);
    printf("[INFO] [SHUTDOWN] safely shutting down server...");
    exit(code);
}

void setup() {

    printf("[SERVER] starting server\n");
    FD_ZERO(&master_fds); // clear the master and temp sets
    FD_ZERO(&read_fds);

    // get us a socket and bind it
    memset(&server_addr, 0, sizeof server_addr); //bzero?
    server_addr.ai_family = AF_INET; //AF_UNSPEC
    server_addr.ai_socktype = SOCK_STREAM;
    server_addr.ai_flags = AI_PASSIVE;

    rv = getaddrinfo(NULL, PORT, &server_addr, &ai);
    if (0 != rv) {
        fprintf(stderr, "[ERROR]: %s\n", gai_strerror(rv));
        safeShutdown(EXIT_FAILURE);
    }
    

    for (p = ai; p != NULL; p = p->ai_next) {
        masterSocket = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
        if (masterSocket < 0) {
            printf("[DEBUG] socket creation failed; continue\n");
            continue;
        }

        //address already in use?
        setsockopt(masterSocket, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof (int));

        if (bind(masterSocket, p->ai_addr, p->ai_addrlen) < 0) {
            close(masterSocket);
            continue;
        }

        break;
    }

    // if we got here, it means we didn't get bound
    if (p == NULL) {
        fprintf(stderr, "[ERROR] [FATAL]: failed to bind\n");
        safeShutdown(EXIT_FAILURE);
    }

    freeaddrinfo(ai); // all done with this

    // listen
    if (listen(masterSocket, 10) == -1) {
        perror("listen");
        safeShutdown(EXIT_FAILURE);
    }

    // add the main socket to the master set
    FD_SET(masterSocket, &master_fds);

    // keep track of the biggest file descriptor
    fdmax = masterSocket; // so far, it's this one

    printf("[SERVER] setupinit completed.\n");
}


// get sockaddr, IPv4 or IPv6:

void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*) sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*) sa)->sin6_addr);
}

void handleConnection() {
    // handle new connections
    addrlen = sizeof remoteaddr;
    newfd = accept(masterSocket,
            (struct sockaddr *) &remoteaddr,
            &addrlen);

    if (newfd < 0) {
        perror("accept");
    } else {
        FD_SET(newfd, &master_fds); // add to master set
        if (newfd > fdmax) { // keep track of the max
            fdmax = newfd;
        }
        printf("[INFO]: new connection from '%s'; on socket '%d'\n", inet_ntop(remoteaddr.ss_family, get_in_addr((struct sockaddr*) &remoteaddr), remoteIP, INET6_ADDRSTRLEN), newfd);
    }
}

void handleInput() {
    // handle data from a client
    nbytes = recv(i, buf, sizeof buf, 0);
    if (nbytes <= 0) {
        // got error or connection closed by client
        if (nbytes == 0) {
            // connection closed
            printf("[INFO]: socket '%d' hung up (closed connection)\n", i);
        } else {
            perror("recv failed");
        }
        close(i); // bye!
        FD_CLR(i, &master_fds); // remove from master set
    } else {
        // we got some data from a client
        //send the data we've recv()'d to all clients
        //loop the fd_set socket fd's 
        for (j = 0; j <= fdmax; j++) {
            // send to everyone!
            if (FD_ISSET(j, &master_fds)) { //check for socket integrity
                // except the listener and the socket the data came from
                if (j != masterSocket && j != i) {
                    if (send(j, buf, nbytes, 0) == -1) {
                        perror("send failed");
                    }
                }
            }
        }


    }
}

int main(void) {
    
    //run server setup once
    setup();

    while (1) {
        read_fds = master_fds; // copy it
        select_ret = select(fdmax + 1, &read_fds, NULL, NULL, NULL); //blocking call, waits for activity on one of the sockets in the fd_set passed to it (read_fds)
        if (select_ret < 0) {
            perror("select failed");
            exit(EXIT_FAILURE);
        }

        //loop fd_set looking for new data (FD_ISSET)
        for (i = 0; i <= fdmax; i++) {
            if (FD_ISSET(i, &read_fds)) { //got activity on one of the sockets
                if (i == masterSocket) {
                    //new connection, master socket was select()'ed
                    handleConnection();
                } else {
                    //existing connection sending new data
                    handleInput();
                }
            }
        }
    }

    return 0;
}