5.1 Source Program

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1. Establish the connection in loopback, using a single process:

   
     #include <stdio.h>
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <sys/stat.h>
     #include <sys/in.h>
     #include <sys/errno.h>
     #include <fcntl.h>
     #include <unistd.h>
   
     main()
     {
       int sock;
       int peer1;
       int struc_len;
       int fret;
       int sock2;
       struct sockaddr_in sockaddr;
           

2. Create the two sockets:

   
       sock=socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
       if (sock == -1) 
         printf ("Error creating socket.\n");
   
       peer1 = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
       if (peer1 == -1) 
         printf ("Error creating socket.\n");
           

3. Create the socket structure to bind the socket. The IP address used is 0 (loopback), and the SAP is set to an arbitrary constant (4444). This structure is used for both the bind and the connect:

   
       sockaddr.sin_family = AF_INET;
       sockaddr.sin_addr.s_addr = INADDR_THISHOST;
       sockaddr.sin_port = 4444;
      
       struc_len = 16;
      
       if (bind (sock, (struct sockaddr *)&sockaddr,
           sizeof (sockaddr)) < 0 ) 
         printf ("Bind failed\n");
         listen (sock,10);
           

4. Set the socket initiating the connection to be nonblocking. This allows the connect to return to the user without blocking and waiting for accept:

   NOTE: The sfcntl function should be used until the fcntl is provided by the operating system.

   
       sfcntl (peer1, F_SETFL, O_NONBLOCK);
   
       fret = connect (peer1, (struct sockaddr *) &sockaddr,
         struc_len);
       if (fret == -1)
         printf ("Connect failed with error %d\n",errno);
       else 
         printf ("Connect succeeded\n");
   
       sock2 = accept (sock, (struct sockaddr *) &sockaddr,
         &struc_len);
       if (sock2 == -1)
         printf ("Accept failed\n");
       else
         printf ("Accept succeeded\n");
           

5. Call recv to complete the connection:

   
       recv (peer1, 0,0,0);
     }   /* end main */