Socket Address Structures

1
Chapter 03. Socket Address Structures
2
Goal

• Socket address structures
• Byte ordering
• IP address conversion
• Domain name conversion

3
Def. of socket address structures (1/6)

• Socket address structures
• Sockets use the socket address structure to pass
  and to receive addresses
• Several types depending on address family
• example) TCP/IP ? SOCKADDR_IN, IrDA ?
  SOCKADDR_IRDA
• Basic type is SOCKADDR structure

4
Def. of socket address structures (2/6)

• SOCKADDR structure
• sa_family
• 16-bit integer value identifying the protocol
  family being used
• e.g.) TCP/IP ? AF_INET
• sa_data
• Address information used in the protocol family
• e.g.) TCP/IP ? IP address and port number

struct sockaddr u_short sa_family
char sa_data14 typedef struct sockaddr
SOCKADDR
5
Def. of socket address structures (3/6)

• SOCKADDR_IN structure
• sin_addr
• 32-bit in_addr structure

struct sockaddr_in short
sin_family // AF_INET u_short
sin_port // port number struct in_addr
sin_addr // IP address char
sin_zero8 // always 0 typedef struct
sockaddr_in SOCKADDR_IN
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Def. of socket address structures (4/6)

• IN_ADDR structure

struct in_addr union struct
u_char s_b1,s_b2,s_b3,s_b4 S_un_b
struct u_short s_w1,s_w2 S_un_w
u_long S_addr S_un define s_addr
S_un.S_addr typedef struct in_addr IN_ADDR
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Def. of socket address structures (5/6)

• comparison of socket address structures

SOCKADDR
SOCKADDR_IN
SOCKADDR_IRDA
sa_family (2)
sin_family (2)
irdaAddressFamily (2)
sa_data (14)
sin_port (2)
irdaDeviceID (4)
sin_addr (4)
irdaServiceName (25)
sin_zero (8)
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Def. of socket address structures (6/6)

• Use of socket address structure
• example1)
• Example 2)

SOCKADDR_IN addr1 // initialize socket address
structure ... f((SOCKADDR )addr1, ...)
SOCKADDR_IN addr2 g((SOCKADDR )addr2,
...) // use socket address structure ...
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Byte ordering function calls (1/6)

• byte ordering
• Two ways to store data in their memories
• big-endian the high-order octet is stored in the
  lowest memory location
• little-endian the high-order octet is stored in
  the highest memory location

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Byte ordering function calls (2/6)

• What if byte ordering is not considered in the
  below?

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Byte ordering function calls (3/6)

• Cases that byte ordering must be considered in
  network applications
• Address information for protocol
• (a) IP address ? big-endian
• (b) port number ? big-endian
• Data that applications send and receive
• (c) big-endian or little-endian

Ref.
? network byte ordering big-endian ?
host byte ordering byte ordering that
system uses
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Byte ordering function calls (4/6)

• Byte ordering functions(unix compatible)
• Byte ordering functions(Winsock extended)

u_short htons (u_short hostshort) //
host-to-network-short u_long htonl (u_long
hostlong) // host-to-network-long u_short ntohs
(u_short netshort) // network-to-host-short u_lon
g ntohl (u_long netlong) // network-to-host-long
int WSAHtons (SOCKET s, u_short hostshort,
u_short lpnetshort) int WSAHtonl (SOCKET s,
u_long hostlong, u_long lpnetlong) int WSANtohs
(SOCKET s, u_short netshort, u_short
lphostshort) int WSANtohl (SOCKET s, u_long
netlong, u_long lphostlong)
13
Byte ordering function calls (5/6)

• Use of byte ordering functions

Data to pass
Use data in application
hton( )
ntoh( )
Data from socket call
Socket system call
Socket system call
14
Byte ordering function calls (6/6)

• Byte ordering of SOCKADDR_IN structure

15
Byte ordering function calls (6/6)

• ByteOrder.cpp

16
Function calls to convert IP address (1/4)

• Example.

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Function calls to convert IP address(2/4)

• IP address coversion function calls
• Converts an IP address in ASCII dotted-decimal
  format to 32-bit binary format (network byte
  ordering)
• Converts 32-bit binary format (network byte
  ordering) to an IP address in ASCII
  dotted-decimal format

unsigned long inet_addr (const char cp)
char inet_ntoa (struct in_addr in) //
network-to-ascii
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Function calls to convert IP address(3/4)

• Use ? of byte ordering and IP address conversion
  function calls
• Case that address information is passed to socket
  system call after socket address structure
  initialization (usually sender side)
• f( ) is socket system call

// initialize socket address structure SOCKADDR_IN
addr ZeroMemory(addr, sizeof(addr)) //
initialize to 0 addr.sin_family
AF_INET addr.sin_addr.s_addr
inet_addr("147.46.114.70") addr.sin_port
htons(9010) // socket system call f((SOCKADDR
)addr, ...)
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Function calls to convert IP address (4/4)

• Use ? of byte ordering and IP address conversion
  function calls
• Case that application prints address information
  after socket system call (usually receiver side)
• g( ) is socket system call

// declaration of socket address
structure SOCKADDR_IN addr // socket system
call g((SOCKADDR )addr, ...) // print IP
address and port number printf("IP addresss,
port numberd\n", inet_ntoa(addr.sin_addr),
ntohs(addr.sin_port))
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Byte ordering function calls (6/6)

• IPAddr.cpp

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coversion between domain name and IP address
(1/6)

• Example Domain name ? IP address

22
coversion between domain name and IP address
(2/6)

• Domain name ? IP address

/ domain name ? IP address(network byte
ordering) / struct hostent gethostbyname (
const char name // domain name ) /
address(network byte ordering) ? domain name
/ struct hostent gethostbyaddr ( const
char addr, // network byte ordered IP address
int len, // length of IP
address(e.g. 4) int type //
address family(e.g. AF_INET) )
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coversion between domain name and IP address(3/6)

• hostent struct

struct hostent char h_name
// official name of host char
h_aliases // alias list short
h_addrtype // host address type short
h_length // length of address
char h_addr_list // list of
addresses define h_addr h_addr_list0 //
address, for backward compatibility typedef
struct hostent HOSTENT
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coversion between domain name and IP address(4/6)

• hostent struct (contd)

HOSTENT
official domain name\0
h_name
h_aliases
alias 1\0
AF_INET
h_addrtype

alias 2\0
4
h_length
NULL
h_addr_list
IN_ADDR
IP address 1

IP address 2
NULL
h_length 4
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coversion between domain name and IP address(5/6)

• User defined function ?

// domain name -gt IP address BOOL GetIPAddr(char
name, IN_ADDR addr) HOSTENT ptr
gethostbyname(name) if(ptr NULL)
err_display("gethostbyname()") return
FALSE memcpy(addr, ptr-gth_addr,
ptr-gth_length) return TRUE
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coversion between domain name and IP address
(6/6)

• User defined function ?

// IP address -gt domain name BOOL
GetDomainName(IN_ADDR addr, char name)
HOSTENT ptr gethostbyaddr((char )addr,
sizeof(addr), AF_INET) if(ptr NULL)
err_display("gethostbyaddr()")
return FALSE strcpy(name,
ptr-gth_name) return TRUE
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Byte ordering function calls (6/6)

• INameResolution.cpp