NETWORK PROGRAMMING
CSC- 341
Instructor:
Junaid Tariq,
Lecturer,
Department of Computer Science
Lecture
11
PART 2
SOCKETS INTRODUCTION
CHAPTER 3
SOCKET ADDRESS STRUCTURE




Socket = IP address + TCP or UDP port number
Used in a socket function as a argument (as
pointer).
Socket Address Structure includes: IP address,
TCP or UDP port number, length of structure .....
Each protocol define its own Socket Address
Structure(IPv4, IPv6....)
IPV4 SOCKET
struct in_addr{
in_addr_t
};
ADDRESS STRUCTURE
s_addr;
struct sockaddr_in {
uint8_t
sin_len;
sa_family_t
sin_family;
in_port_t
sin_port;
struct
in_addr sin_addr;
char
sin_zero[8];
}; /* included in <netinet/in.h> */
/*32bit IPv4 address*/
/*network byte ordered*/
/* length of structure(16) */
/* AF_INET */
/* 16bit TCP or UDP port number */
/*network byte ordered*/
/* 32bit IPv4 address */
/*network byte ordered*/
/* unused */
IPV4 SOCKET ADDRESS STRUCTURE
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


The length member, sin_len, was added with 4.3BSD-Reno
Even if the length field is present, we never need to examine it,
unless we are dealing with routing sockets (Chapter 17). It is used
within the kernel by the routines that deal with socket address
structures from various protocol families
The four socket functions that pass a socket address structure
from the process to the kernel, bind, connect, sendto, and sendmsg,
This function copies the socket address structure from the process
and explicitly sets its sin_len member to the size of the structure.
The five socket functions that pass a socket address structure
from the kernel to the process, accept, recvfrom, recvmsg,
getpeername, and getsockname, all set the sin_len member before
returning to the process.
IPV4 SOCKET ADDRESS STRUCTURE

The 32-bit IPv4 address can be accessed in two different ways.
serv.sin_addr references the 32-bit IPv4 address as an in_addr
structure,


if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
err_quit("inet_pton error for %s", argv[1]);
serv.sin_addr.s_addr references the same 32-bit IPv4 address as
an in_addr_t (typically an unsigned 32-bit integer). We must be
certain that we are referencing the IPv4 address correctly,
especially when it is used as an argument to a function, because
compilers often pass structures differently from integers.

servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
GENERIC SOCKET ADDRESS STRUCTURE

<sys/socket.h> : Generic Socket address structure
struct sockaddr {
uint8_t sa_len;
sa_family_t sa_family;
char sa_data[14];
}
/*address family: AF_xxx value*/
/*protocol specific address*/
Generic Socket address structure
 int
bind(int sockfd, struct sockaddr * , socklen_t);
struct sockaddr_in serv; /*IPv4 socket address structure*/
/* fill in serv{} */
bind(sockfd, (struct sockaddr *) &serv, sizeof(serv));
bind(sockfd, (SA *) &servaddr, sizeof(servaddr));
IPV6 SOCKET
ADDRESS STRUCTURE
struct in6_addr{
uint8_t
s6_addr[16];
};
/*128bit IPv6 address*/
/*network byte ordered*/
struct sockaddr_in6 {
uint8_t
sin6_len;
/* length of structure(24) */
sa_family_t
sin6_family;
/* AF_INET6*/
in_port_t
sin6_port;
/* Transport layer port# */
/*network byte ordered*/
uint32_t
sin6_flowinfo;
/* priority & flow label */
/*network byte ordered*/
struct
in6_addr sin6_addr;
/* IPv6 address */
/*network byte ordered*/
}; /* included in <netinet/in.h> */
COMPARISON OF SOCKET ADDRESS STRUCTURE
VALUE-RESULT ARGUMENT
 socket
address structure is always
passed by reference to socket functions.
 The length of the structure is also
passed.
 The way the length is passed depends on
which direction the structure is being
passed
Socket address structure pass.
int
User
length
Socket
Address
structure
value
process
Protocol address
Kernel
Bind, connect, sendto
Socket address structure pass.
int *
length
User
value
result
Socket
Address
structure
process
Protocol address
Kernel
Accept, recvfrom, getsockname,
getpeername
Process to Kernel
Kernel to Process
struct sockaddr_in
serv
/* fill in serv{} */
struct sockaddr_in cli
connect(sockfd, (SA
*)&serv, sizeof(serv));
socklen_t len;
len = sizeof(cli);
accept(listenfd, (SA *)
&cli, &len);
/* len is filled in by the
kernel. */
BYTE ORDERING FUNCTION
Increasing memory
address
Little-endian byte order:
Address A+1
High-order byte
MSB
big-endian byte order:
Address A
low-order byte
16bit value
High-order byte
LSB
low-order byte
Address A
Address A+1
Increasing memory
address
FIGURE3.9 DETERMINE HOST BYTE ORDER
int main(int argc, char **argv)
{
union {
short s;
char c[sizeof(short)];
} un;
un.s = 0x0102;
if (sizeof(short) == 2) {
if (un.c[0] == 1 && un.c[1] == 2)
printf("big-endian\n");
else if (un.c[0] == 2 && un.c[1] == 1)
printf("little-endian\n");
else printf("unknown\n");
}
else
printf("sizeof(short) = %d\n", sizeof(short));
exit(0);
}