server_udp.c

   1 /* Creates a datagram server.  The port
   2    number is passed as an argument.  This
   3    server runs forever */
   4
   5 #include <sys/types.h>
   6 #include <stdlib.h>
   7 #include <unistd.h>
   8 #include <sys/socket.h>
   9 #include <netinet/in.h>
  10 #include <string.h>
  11 #include <netdb.h>
  12 #include <stdio.h>
  13
  14 void error(const char *msg)
  15 {
  16     perror(msg);
  17     exit(0);
  18 }
  19
  20 int main(int argc, char *argv[])
  21 {
  22    int sock, length, n;
  23    socklen_t fromlen;
  24    struct sockaddr_in server;
  25    struct sockaddr_in from;
  26    char buf[1024];
  27
  28    if (argc < 2) {
  29       fprintf(stderr, "ERROR, no port provided\n");
  30       exit(0);
  31    }
  32
  33    sock=socket(AF_INET, SOCK_DGRAM, 0);
  34    if (sock < 0) error("Opening socket");
  35    length = sizeof(server);
  36    bzero(&server,length);
  37    server.sin_family=AF_INET;
  38    server.sin_addr.s_addr=INADDR_ANY;
  39    server.sin_port=htons(atoi(argv[1]));
  40    if (bind(sock,(struct sockaddr *)&server,length)<0)
  41        error("binding");
  42    fromlen = sizeof(struct sockaddr_in);
  43    while (1) {
  44        n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
  45        if (n < 0) error("recvfrom");
  46        write(1,"Received a datagram: ",21);
  47        write(1,buf,n);
  48        n = sendto(sock,"Got your message\n",17,
  49                   0,(struct sockaddr *)&from,fromlen);
  50        if (n  < 0) error("sendto");
  51    }
  52    return 0;
  53  }
  54