Socket Server

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>

/* this is the port the server will listen on.  Telnet to this port
 *  to try it out.
 */
#define MYPORT 3490
#define MAXDATASIZE 100 /* max number of bytes we can get at once */

#define BACKLOG 10     /* how many pending connections queue will hold */

main()
{
    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 */
    int sin_size = sizeof(struct sockaddr_in);
    int pid;
    int i;
    int instance;
    int numbytes;
    char buf[MAXDATASIZE];
    char server_string[] = "Hello from server";

    /* give me a file descriptor for my socket that I will fill out
     */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror("in grabbing socket descriptor");
        exit(1);
    }
//  fcntl(sockfd, F_SETFL, O_NONBLOCK);

    my_addr.sin_family      = AF_INET;

    /* set the port, converting to network byte order
     *  (htons = host to network short - example, on Intel
     *    0x0da2 -> 0xa20d)
     */
    my_addr.sin_port        = htons(MYPORT);
    my_addr.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
    bzero(&(my_addr.sin_zero), 8);        /* zero the rest of the struct */

    /* Now bind the socket descriptor I just made to the port I want
     *  to listen to on my machine
     */
    if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1)
    {   perror("bind");
        exit(1);
    }

    /* Listen on the socket
     */
    if (listen(sockfd, BACKLOG) == -1)
    {   perror("listen");
        exit(1);
    }

    while(1)
    {
        printf("server: waiting for a connection()\n");
        new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);

        if (new_fd == -1)
        {   perror("accept");
            continue;
        }

        printf("server: got connection from %s\n",
                 inet_ntoa(their_addr.sin_addr));

        pid = fork();

    /* am I the child process?
     */
        if (pid == 0)
        {   instance = getpid();
            printf("server child %d: spawned\n", instance);
    /* send a message, close the connection and die.
     */
            for (i = 0; i < 2; i++)
            {
            if (send(new_fd, server_string, strlen(server_string), 0) == -1)
            {   perror("send");
            }
            if ((numbytes=recv(new_fd, buf, MAXDATASIZE, 0)) == -1) {
                perror("recv");
                exit(1);
            }
            buf[numbytes] = '\0';
            printf("Received: %s\n",buf);

            sleep(1);
            printf("server child %d: sent message\n", instance);
            }
            close(new_fd);
            printf("server child %d: closed connection\n", instance);
            exit(0);
        }
        printf("hi\n");
        close(new_fd);  /* parent doesn't need this */

        while(waitpid(-1, NULL, WNOHANG) > 0); /* clean up child processes */
    }
}

Socket Client

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

#define PORT 3490    /* the port client will be connecting to */

#define MAXDATASIZE 100 /* max number of bytes we can get at once */

int main(int argc, char *argv[])
{
    int sockfd, numbytes;
    char buf[MAXDATASIZE];
    struct hostent *he;
    struct sockaddr_in their_addr; /* connector's address information */
    char client_string[] = "Hello from client";

    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }

    if ((he=gethostbyname(argv[1])) == NULL) {  /* get the host info */
        herror("gethostbyname");
        exit(1);
    }

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    their_addr.sin_family = AF_INET;      /* host byte order */
    their_addr.sin_port = htons(PORT);    /* short, network byte order */
    their_addr.sin_addr = *((struct in_addr *)he->h_addr);
    bzero(&(their_addr.sin_zero), 8);     /* zero the rest of the struct */

    if (connect(sockfd, (struct sockaddr *)&their_addr, \
                                          sizeof(struct sockaddr)) == -1) {
        perror("connect");
        exit(1);
    }

    while (1)
    {
        if ((numbytes=recv(sockfd, buf, MAXDATASIZE, 0)) == -1) {
            perror("recv");
            exit(1);
        }
        if (send(sockfd, client_string, strlen(client_string),  0) == -1)
        {   perror("send");
        }
        if (numbytes == 0)
        {   break;
        }

        buf[numbytes] = '\0';

        printf("Received: %s\n", buf, numbytes);
    }
    close(sockfd);

    return 0;
}

-- MattWalsh - 31 Aug 2004