DATA TYPES
==========


// Socket Address
struct sockaddr {
    unsigned short    sa_family;    // address family, AF_xxx
    char              sa_data[14];  // 14 bytes of protocol address
}; 

// Socket Address Internet
struct sockaddr_in {
    short int          sin_family;  // Address family
    unsigned short int sin_port;    // Port number
    struct in_addr     sin_addr;    // Internet address
    unsigned char      sin_zero[8]; // Same size as struct sockaddr
};

sizeof(sockadd_in) == sizeof(sockaddr)

// Internet address (a structure for historical reasons)
struct in_addr {
    unsigned long s_addr; // that's a 32-bit long, or 4 bytes
};








CONVERSIONS
===========

   Byte Order:
   ----------
      htons() -- "Host to Network Short"
      htonl() -- "Host to Network Long"
      ntohs() -- "Network to Host Short"
      ntohl() -- "Network to Host Long"

   IP to Text:
   ----------
      ina.sin_addr.s_addr = inet_addr("10.12.110.57"); 
          +-> PROBLEM: fail == -1 == (unsigned) -1 == 
		       255.255.255.255 ( broadcast )

      if (inet_aton("10.12.110.57", &(my_addr.sin_addr)))
          printf("error converting address.\n");
	  +-> PROBLEM: not available in every plataform.

      printf("address: %s\n", inet_ntoa(my_addr.sin_addr));









FUNCTIONS
=========

   socket():  Get the file descriptor.

   bind(): What port am I on?
	   -> Associate a socket with a port.

	TIP:
	   my_addr.sin_port = htons(0); // choose an unused port at random
	   my_addr.sin_addr.s_addr = htonl(INADDR_ANY);  // use my IP
	   address 

	REUSE ADDRESS:
	   int yes=1;

	   // lose the pesky "Address already in use" error message
	   if (setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
              perror("setsockopt");
              exit(1);
           }
	   
	DON'T CALL IT:
           When you don't mind the local port, just remote one, as telnet.


   connect(): Start the connection.
       INFO: will call bind() if socket was not binded.
   
   listen(): Wait for a connection.
       INFO: backlog: how many connections will wait before they're
             accept()'ed.
       INFO: sequence is socket() -> bind() -> listen() -> accept()

   accept(): removes the pending connection from queue and assign a
             new file descriptor to it.
       INFO: new fd will be ready to send() and recv().
       INFO: old fd will still listen to new connections.