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Socket Introduction 1

Sockets Introduction

Socket Address Structure

• Socket = IP address + TCP or UDP port

number

• Used in a socket function as a argument

(as pointer).

• IP address, TCP or UDP port number,

length of structure .....

• Each protocol define its own Socket

Address Structure(IPv4, IPv6....)

Generic Socket address structure

• <sys/socket.h> : Generic Socket address structure

struct sockaddr { uint8_t sa_len; sa_family_t sa_family; /address family: AF_xxx value/ char sa_data[14]; /protocol specific address/ }**

• int bind(int , struct sockaddr * , socklen_t);

struct sockaddr_in serv; /IPv4 socket address structure/ /* fill in serv{} */ bind(sockfd, (struct sockaddr *) &serv, sizeof(serv));

Generic Socket address structure

Comparison of socket address structure

IPv4 Header

IPv

Address

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.

Accept, recvfrom, getsockname, getpeername

length Socket Address structure

Kernel

int *

User

process

value result

Protocol address

• Process to kernel

struct sockaddr_in serv

/* fill in serv{} */

connect(sockfd, (SA *)&serv,

sizeof(serv));

• Kernel to process

struct sockaddr_un cli

socklen_t len;

len = sizeof(cli);

getpeername(unixfd,

(SA*)&cli,&len);

/* len is filled in by the kernel. */

Figure3.9 determine host byte order

**int main(int argc, char argv) { union {short s; char c[sizeof(short)]; } un; un.s = 0x0102; printf("%s: ", CPU_VENDOR_OS); 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); }

Byte Manipulation Functions

• #include <strings.h>

void bzero(void dest, size_t nbytes); / sets the specified no of bytes to zero */

void bcopy(const void *src, void dest, size_t nbytes); / byte by byte copy from source to destination */

int bcmp(const void *ptr1, const void ptr2, size_t nbytes); / return 0 if equal, nonzero if unequal */

inet_aton,inet_addr, inet_ntoa

functions

• Convert internet address between ASCII string

and network byte ordered binary values(as stored

in socket address structure)

• Used for IPv4 addresses conversion
• For both IPv4 and IPv6 we have : inet_pton ,

inet_ntop

• #include<arpa/inet.h>

For ASCII to network binary:

int inet_aton(const char *strptr, struct in_addr *addrptr);

/* return : 1 if string was valid,0 on error */

For ASCII to network binary:

in_addr_t inet_addr(const char *strptr);

/* deprecated. return : 32bit binary network byte ordered IPv4 address; INADDR_NONE if error */

For network binary to ASCII:

char *inet_ntoa(struct in_addr inaddr);

/return pointer to dotted-decimal string/