Miscellany

        #include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <sys/wait.h>#include <signal.h>#define MYPORT 3490    // the port users will be connecting to#define BACKLOG 10     // how many pending connections queue will holdvoid sigchld_handler(int s){    while(waitpid(-1, NULL, WNOHANG) > 0);}int main(void){    int sockfd, new_fd;  // listen on sock_fd, new connection on new_fd    struct sockaddr_in my_addr;    // my address information    struct sockaddr_in their_addr; // connector's address information    socklen_t sin_size;    struct sigaction sa;    int yes=1;    if ((sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1) {        perror("socket");        exit(1);    }    if (setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {        perror("setsockopt");        exit(1);    }    my_addr.sin_family = AF_INET;         // host byte order    my_addr.sin_port = htons(MYPORT);     // short, network byte order    my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP    memset(&(my_addr.sin_zero), '\0', 8); // zero the rest of the struct    if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr))                                                                   == -1) {        perror("bind");        exit(1);    }    if (listen(sockfd, BACKLOG) == -1) {        perror("listen");        exit(1);    }    sa.sa_handler = sigchld_handler; // reap all dead processes    sigemptyset(&sa.sa_mask);    sa.sa_flags = SA_RESTART;    if (sigaction(SIGCHLD, &sa, NULL) == -1) {        perror("sigaction");        exit(1);    }    int bufsize = 1024;    char buffer[bufsize];    while(1) {  // main accept() loop        sin_size = sizeof(struct sockaddr_in);        if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr,                                                       &sin_size)) == -1) {            perror("accept");            continue;        }        printf("server: got connection from %s\n",                                           inet_ntoa(their_addr.sin_addr));        if (!fork()) { // this is the child process            close(sockfd); // child doesn't need the listener            send(new_fd, "Hello, world!\n", 14, 0);            while(1) {            recv(new_fd, buffer, bufsize, 0);            send(new_fd, "Paketti vastaanotettu\n", 22, 0);                }            }            close(new_fd);            exit(0);        }        close(new_fd);  // parent doesn't need this    return 0;}