/*
NAME:        TCPServer 
SYNOPSIS:    TCPServer [port]

DESCRIPTION:  The program creates a TCP socket in the inet 
              listen for connections from TCPClients, 
              accept clients into private sockets, and 
              fork an echo process to ``serve'' the client.
              If [port] is not specified, the program uses any available port.

*/

#include "def"
void exit(int);

#define MAXHOSTNAME 80
void reusePort(int sock);   

main( argc, argv )
int argc;
char *argv[];
{
  int   sd, psd;
  struct   sockaddr_in server;
  struct  hostent *hp, *gethostbyname();
  struct  servent *sp;
  struct sockaddr_in from;
  int fromlen;
  int length;
  char ThisHost[80];
  int pn;
  int childpid;

  sp = getservbyname("echo", "tcp");
/* get TCPServer1 Host information, NAME and INET ADDRESS */

  gethostname(ThisHost, MAXHOSTNAME);
  /* OR strcpy(ThisHost,"localhost"); */

  printf("----TCP/Server running at host NAME: %s\n", ThisHost);
  if  ( (hp = gethostbyname(ThisHost)) == NULL ) {
    fprintf(stderr, "Can't find host %s\n", argv[1]);
    exit(-1);
  }
  bcopy ( hp->h_addr, &(server.sin_addr), hp->h_length);
  printf("    (TCP/Server INET ADDRESS is: %s )\n", inet_ntoa(server.sin_addr));


/** Construct name of socket */
  server.sin_family = AF_INET;
  /* OR server.sin_family = hp->h_addrtype; */
 
  server.sin_addr.s_addr = htonl(INADDR_ANY);
if (argc == 1)
        server.sin_port = htons(0);  
   else  {
        pn = htons(atoi(argv[1])); 
        server.sin_port =  pn;
   }
   /*OR    server.sin_port = sp->s_port; */

/** Create socket on which to send  and receive */

  sd = socket (AF_INET,SOCK_STREAM,IPPROTO_TCP); 
  /* OR sd = socket (hp->h_addrtype,SOCK_STREAM,0); */
  if (sd<0) {
    perror("opening stream socket");
    exit(-1);
  }
/** this allow the server to re-start quickly instead of fully wait
    for TIME_WAIT which can be as large as 2 minutes */
  reusePort(sd);
  if ( bind( sd, (SA *) &server, sizeof(server) ) < 0 ) {
    close(sd);
    perror("binding name to stream socket");
    exit(-1);
  }

/** get port information and  prints it out */
  length = sizeof(server);
  if ( getsockname (sd, (SA *)&server,&length) ) {
    perror("getting socket name");
    exit(0);
  }
  printf("Server Port is: %d\n", ntohs(server.sin_port));

/** accept TCP connections from clients and fork a process to serve each */
  listen(sd,4);
  fromlen = sizeof(from);
  for(;;){
    psd  = accept(sd, (SA *)&from, &fromlen);
    childpid = fork();
    if ( childpid == 0) {
      close (sd);
      EchoServe(psd, from);
    }
    else{
       printf("My new child pid is %d\n", childpid);
       close(psd);
    }
  }
}

EchoServe(psd, from)
int psd;
struct sockaddr_in from;
{
  char buf[512];
  int rc;
  struct  hostent *hp, *gethostbyname();

  printf("Serving %s:%d\n", inet_ntoa(from.sin_addr),
      ntohs(from.sin_port));
  if ((hp = gethostbyaddr((char *)&from.sin_addr.s_addr,
      sizeof(from.sin_addr.s_addr),AF_INET)) == NULL)
    fprintf(stderr, "Can't find host %s\n", inet_ntoa(from.sin_addr));
  else
    printf("(Name is : %s)\n", hp->h_name);

/**  get data from  clients and send it back */
  for(;;){
    printf("\n...server is waiting...\n");
    if( (rc=recv(psd, buf, sizeof(buf), 0)) < 0){
      perror("receiving stream  message");
      exit(-1);
    }
    if (rc > 0){
      buf[rc]=NULL;
      printf("Received: %s\n", buf);
      printf("From TCP/Client: %s:%d\n", inet_ntoa(from.sin_addr),
          ntohs(from.sin_port));
      printf("(Name is : %s)\n", hp->h_name);
      if (send(psd, buf, rc, 0) <0 )
        perror("sending stream message");
    }
    else {
      printf("TCP/Client: %s:%d\n", inet_ntoa(from.sin_addr),
          ntohs(from.sin_port));
      printf("(Name is : %s)\n", hp->h_name);
      printf("Disconnected..\n");
      close (psd);
      exit(0);
    }
  }
}
void reusePort(int s)
{
  int one=1;

  if ( setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *) &one,sizeof(one)) == -1 )
  {
    printf("error in setsockopt,SO_REUSEPORT \n");
    exit(-1);
  }
}