Chapter 03. 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_data[14]; }; 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_zero[8]; // always 0 }; typedef struct sockaddr_in SOCKADDR_IN;

6. 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;

7. 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)

8. 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 ...

9. 0x1000 0x1001 0x1002 0x1003 Big-endian    0x12 0x34 0x56 0x78    Little-endian    0x78 0x56 0x34 0x12    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

10. router End system router End system ? (a) ? (b) (c) IP address Port number ? data Byte ordering function calls (2/6) • What if byte ordering is not considered in the below?

11. 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

12. 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_long 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. SOCKADDR_IN{} sin_family (2) Host byte ordering sin_port (2) sin_addr (4) Network byte ordering sin_zero (8) 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.

17. 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

18. Function calls to convert IP address(3/4) • Use ① 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, ...);

19. Function calls to convert IP address (4/4) • Use ② 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 ofsocket address structure SOCKADDR_IN addr; // socket system call g((SOCKADDR *)&addr, ...); // print IP address and port number printf("IP address=%s, port number=%d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));

20. Byte ordering function calls (6/6) • IPAddr.cpp

21. 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) );

23. 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_list[0] // address, for backward compatibility }; typedef struct hostent HOSTENT;

24. coversion between domain name and IP address(4/6) • hostent struct (cont’d) HOSTENT{} h_name official domain name\0 h_aliases alias #1\0 h_addrtype AF_INET alias #2\0 h_length 4 NULL h_addr_list IN_ADDR{} IP address #1 IP address #2 NULL h_length = 4

25. coversion between domain name and IP address(5/6) • User defined function ① // domain name -> IP address BOOL GetIPAddr(char *name, IN_ADDR *addr) { HOSTENT *ptr = gethostbyname(name); if(ptr == NULL){ err_display("gethostbyname()"); return FALSE; } memcpy(addr, ptr->h_addr, ptr->h_length); return TRUE; }

26. coversion between domain name and IP address (6/6) • User defined function ② // IP address -> 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->h_name); return TRUE; }

27. Byte ordering function calls (6/6) • INameResolution.cpp