#include <sys/types.h&  /**********  Multi-Client Fifo Server!  **********/
#include <sys/stat.h&
#include <stdio.h&
#include <signal.h&  
#include <sys/fcntl.h&
#include <errno.h&
#include <stdlib.h&
#include <unistd.h& 
#include <string.h&
main()
{
     int readfifo, writefifo, dummyfd;
     pid_t client_pid;
     char buf[80], outbuf[80], filename[80], *fifoid, *message, client[80];
     void handler(int signum);
   
     signal(SIGPIPE, handler);   /******  In case client disappears ******/
     signal(SIGTTOU, handler);   /******  To keep server alive on printf *****/

     sprintf(filename, "%s/sysprog/demos/server", getenv("HOME"));
     if ((mkfifo(filename, S_IRUSR | S_IWUSR) < 0) && (errno != EEXIST)) 
     {
          printf("Cannot make server fifo!");
          exit(1);
     }

     if ((readfifo = open(filename, O_RDONLY)) < 0)
     {
         printf("Cannot open server fifo!");
         exit(2);
     }
     if ((dummyfd = open(filename, O_WRONLY)) < 0)
     {
         printf("Cannot open server fifo dummy!");
         exit(3);
     }

     while (read(readfifo, buf, 80) == 80)
     {
         fifoid  = strtok(buf, "\040");
         message = strtok(NULL, "\n");
         printf("Got %s from client\n", buf);
         if ((writefifo = open(fifoid, O_WRONLY)) < 0)
         {
              printf("Cannot open fifo to client!"); 
              continue;
         }
         memset(outbuf, 0, 80);
         sprintf(outbuf, "%s\n", message);
         write(writefifo, outbuf, 80);
         close(writefifo);
     }
}

void handler(int signum)
{
     printf("Fifo has been closed in reader!");
     exit(0);
}
#include <sys/types.h&  /**********  Fifo Client  ***********/
#include <sys/stat.h&
#include <stdio.h&
#include <signal.h&  
#include <sys/fcntl.h&
#include <errno.h&
#include <stdlib.h&
#include <unistd.h& 
#include <string.h&
int main()
{
      int clientfifo, serverfifo, dummyfd;
      char buf[80], filename[80], outbuf[256], inbuf[80], fifoname[80];

      sprintf(filename, "%s/sysprog/demos/server", getenv("HOME"));
      if ((serverfifo = open(filename, O_WRONLY)) < 0)
      {
           perror("Cannot open server's fifo!");
           exit(3);
      }

      sprintf(fifoname, "fifo.%ld", getpid());
      if ((mkfifo(fifoname, S_IRUSR | S_IWUSR) < 0) && (errno != EEXIST))
      {
          perror("mkfifo error!");
          exit(1);
      }

      memset(buf, 0, 80);
      printf("Enter string: ");
      while(fgets(buf, 80, stdin) && strcmp(buf, "quit\n") != 0)
      {
/*************  Tell server who we are
 *************/
           memset(outbuf, 0, 256);
           sprintf(outbuf, "fifo.%ld %s", getpid(), buf);
           write(serverfifo, outbuf, 80);

/*************  Open must be done here!  It blocks if done above loop
 *************  because opens for read block until data arrives!!
 *************/
           memset(inbuf, 0, 80);
           if ((clientfifo = open(fifoname, O_RDONLY, 0)) < 0)
           {
                perror("Could not open client fifo!");
                exit(2);
           }
           read(clientfifo, inbuf, 80);
           printf("From server: %s", inbuf);
           memset(buf, 0, 80);
           printf("Enter string: ");
           close(clientfifo);
      }  
      unlink(fifoname);   /******  Get rid of filesystem entry.  ******/
}
/************************   A Multi-Client Session  **********************/

$ ms&            /******  Server in background.  ******/
[1]     25815

$ mc
Enter string: hello
Got fifo.25816 from client
From server: hello

Enter string: goodbyte
Got fifo.25816 from client
From server: goodbyte      /*******  Here, I CTRL-Z'ed this client! *******/
Enter string: [2] + Stopped                  mc

$ mc       /*******  New client!!  *******/
Enter string: what's happening?
Got fifo.25817 from client
From server: what's happening?   /*****  Now I CTRL-Z this client, too! *****/
Enter string: [3] + Stopped                  mc

$ mc
Enter string: who's on first?
Got fifo.25818 from client
From server: who's on first?
Enter string: quit       /******  A normal exit.  ******/

$ fg        /********  I revive one of the two suspended clients. ********/
mc
I am back!!
Got fifo.25817 from client
From server: I am back!!
Enter string: quit

$ fg        /*********  Here comes the other suspended client!!  **********/
mc
I am also back
Got fifo.25816 from client
From server: I am also back
Enter string: quit

$ ls -l fifo.*    /********  Any fifo.pid files left??  ********/

-rw-------    1 jwp2286  staff       1590 Nov 15 00:27 fifo.demo