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WINSOCK 2

WINDOWS SOCKET: PROGRAM EXAMPLES PART 8

 

 

 

What do we have in this chapter?

1. sockaddr Structure

2. SOCKADDR_STORAGE Structure

3. Members

4. Program Example Using sockaddr

5. hostent Structure

6. gethostbyaddr()

7. Return Values

8. gethostbyname()

9. Return Values

10. gethostbyname() and gethostbyaddr() Program Example

 

Winsock Tutorial   Winsock: Story 1 Winsock: Story 2 Winsock: Story 3 Winsock: Example 1 Winsock: Example 2 Winsock: Example 3 Winsock: Example 4 Winsock: Example 5 Winsock: Example 6 Winsock: Example 7 Winsock: Example 8 Winsock: Example 9 Winsock: Example 10 Winsock: Example 11 Winsock: Example 12 Winsock: Reference 1 Winsock: Reference 2 Winsock: Reference 3 Winsock: Reference 4 Another Complete and Advanced C & Winsock2 Programming Tutorial

My Training Period:          hours   Machine’s OS is standalone Windows Xp Pro with SP2 except whenever mentioned.  Compiler used was Visual C++ 2003 .Net 1.1. Beware the codes that span more than one line.  Program examples have been tested for Non Destructive Test.  All information compiled for Windows 2000 (NT5.0) above and...   The story was discussed at Winsock introduction story. Related functions, structures and macros used in the program examples have been dumped at Winsock structure & function 1 and Winsock structure & function 2. Other related and required information (if any) not available in no. 2 can be found at MSDN & Visual C++ online reference.   Abilities: Able to understand more Winsock implementation and operations through the APIs and program examples. Able to gather, understand and use the Winsockfunctions, structures and macros in your programs. Able to build programs that use Microsoft C/Standard C programming language and Winsock APIs. sockaddr Structure   Item Description Structure sockaddr. Info Contains socket address information. The sockaddr structure varies depending on the protocol selected. It is better to use SOCKADDR_STORAGE instead. Definition For IPv4:   struct sockaddr { ushort sa_family; char sa_data[14]; };   struct sockaddr_in {         short   sin_family;         u_short sin_port;         struct  in_addr sin_addr;         char    sin_zero[8]; };   The sockaddr_in6 and sockaddr_in6_old structures below are used with IPv6.   struct sockaddr_in6 {         short   sin6_family;         u_short sin6_port;         u_long  sin6_flowinfo;         struct  in6_addr sin6_addr;         u_long  sin6_scope_id; };   typedef struct sockaddr_in6 SOCKADDR_IN6; typedef struct sockaddr_in6 *PSOCKADDR_IN6; typedef struct sockaddr_in6 FAR *LPSOCKADDR_IN6;     struct sockaddr_in6_old {         short   sin6_family;         u_short sin6_port;         u_long  sin6_flowinfo;         struct  in6_addr sin6_addr;  }; Members As mentioned above. Header file <winsock2.h> for IPv4; <ws2tcpip.h> for IPv6. Remark The sockaddr structure varies depending on the protocol selected. Except for the sin*_family parameter, sockaddr contents are expressed in network byte order. Winsock functions using sockaddr are not strictly interpreted to be pointers to a sockaddr structure. The structure is interpreted differently in the context of different address families. The only requirements are that the first u_short is the address family and the total size of the memory buffer in bytes is namelen.  Other protocols use similar structures.   Table 1

Except for the sinX_family parameter, sockaddr contents are expressed in network byte order.

 

SOCKADDR_STORAGE Structure

 

The SOCKADDR_STORAGE structure also stores socket address information and the structure is sufficiently large to store IPv4 or IPv6 address information. The use of the SOCKADDR_STORAGE structure promotes protocol-family and protocol-version independence, and simplifies development. It is recommended that the SOCKADDR_STORAGE structure be used in place of the sockaddr structure. The SOCKADDR_STORAGE structure is supported on Windows Server 2003 and later.

The SOCKADDR_STORAGE structure stores socket address information. Since the SOCKADDR_STORAGE structure is sufficiently large to store address information for IPv4, IPv6, or other address families, its use promotes protocol-family and protocol-version independence and simplifies cross-platform development. So, use the SOCKADDR_STORAGE structure in place of the sockaddr structure. The syntax for SOCKADDR_STORAGE is:

typedef struct sockaddr_storage {

short ss_family;

char __ss_pad1[_SS_PAD1SIZE];

__int64 __ss_align;

char __ss_pad2[_SS_PAD2SIZE];

} SOCKADDR_STORAGE,

*PSOCKADDR_STORAGE;

Members

 

ss_family - Address family of the socket, such as AF_INET. On Windows Vista and later, the datatype for this member is defined as an ADDRESS_FAMILY.

1. __ss_pad1 - Reserved. Defined as a 48-bit pad that ensures SOCKADDR_STORAGE achieves 64-bit alignment.

2. __ss_align - Reserved. Used by the compiler to align the structure.

3. __ss_pad2 - Reserved. Used by the compiler to align the structure.

 

Keep in mind that in the Microsoft Windows Software Development Kit (SDK), the version of this structure for use on Windows Vista and later is defined as SOCKADDR_STORAGE_LH. In the Windows SDK, the version of this structure to be used on earlier systems including Windows XP and later is defined as SOCKADDR_STORAGE_XP. When compiling an application if the target platform is Windows Vista and later (NTDDI_VERSION >= NTDDI_LONGHORN, _WIN32_WINNT >= 0x0600, or WINVER >= 0x0600), the SOCKADDR_STORAGE_LH structure is typedefed to the SOCKADDR_STORAGE structure. When compiling an application if the target platform is not Windows Vista and later, the SOCKADDR_STORAGE_XP structure is typedefed to the SOCKADDR_STORAGE structure. The SOCKADDR_STORAGE_LH structure defines the data type of first member of the structure as an ADDRESS_FAMILY.Application developers normally use only the ss_family member of the SOCKADDR_STORAGE. The remaining members ensure that the SOCKADDR_STORAGE can contain either an IPv6 or IPv4 address and the structure is padded appropriately to achieve 64-bit alignment. Such alignment enables protocol-specific socket address data structures to access fields within a SOCKADDR_STORAGE structure without alignment problems. With its padding, the SOCKADDR_STORAGE structure is 128 bytes in length. The first member field of the SOCKADDR_STORAGE structure is isomorphic with the sockaddr structure to enable a simplified transition from the sockaddr structure to the SOCKADDR_STORAGE structure. For more information about platform-independent SOCKADDR_STORAGE implementation recommendations, refer to RFC 2553, available at www.ietf.org.On the Windows SDK released for Windows Vista and later, the organization of header files has changed and the SOCKADDR_STORAGE structure is defined in the Ws2def.h header file. Note that the Ws2def.h header file is automatically included in Winsock2.h, and should never be used directly.

 

Program Example Using sockaddr

 

The following example demonstrates the use of the sockaddr structure.

#include <stdio.h>

#include "winsock2.h"

 

int main()

{

  // Declare variables

  WSADATA wsaData;

  SOCKET ListenSocket;

  sockaddr_in service;

 

  // Initialize Winsock, request the Winsock 2.2

  int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);

  if(iResult != NO_ERROR)

    printf("Error at WSAStartup().\n");

  else

    printf("WSAStartup() is OK.\n");

 

  // Create a listening socket

  ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

  if (ListenSocket == INVALID_SOCKET)

  {

    printf("Error at socket().\n");

    WSACleanup();

    return 0;

  }

  else

     printf("socket() is OK.\n");

 

  // Bind the socket to the local IP address and port 55555

  hostent* thisHost;

  char* ip;

  u_short port;

  port = 55555;

  thisHost = gethostbyname("");

  ip = inet_ntoa(*(struct in_addr *)*thisHost->h_addr_list);

 

  printf("\nIP address is: %s.\n", ip);

  printf("Hostname is: %s.\n", thisHost->h_name);

  printf("Address type: %i.\n\n", thisHost->h_addrtype);

 

  service.sin_family = AF_INET;

  service.sin_addr.s_addr = inet_addr(ip);

  service.sin_port = htons(port);

 

  if (bind(ListenSocket,(SOCKADDR*) &service, sizeof(service)) == SOCKET_ERROR)

  {

    printf("bind() failed lol!\n");

    closesocket(ListenSocket);

    return 0;

  }

  else

    printf("bind() is OK.\n");

 

  WSACleanup();

  return 0;

}

 

Sample output:

 

 

 

 

 

 

---------------------------------------------

 

 

Figure 1

 

hostent Structure

 

 

gethostbyaddr()

 

 

Return Values

 

If no error occurs, gethostbyaddr() returns a pointer to the hostent structure. Otherwise, it returns a null pointer, and a specific error code can be retrieved by calling WSAGetLastError().

 

 

For program sample, see the following example.

 

gethostbyname()

 

 

Return Values

 

If no error occurs, gethostbyname() returns a pointer to the hostent structure described above. Otherwise, it returns a null pointer and a specific error number can be retrieved by calling WSAGetLastError().

 

 

 

gethostbyname() and  gethostbyaddr() Program Example

 

The following examples demonstrates the use of the gethostbyname() and  gethostbyaddr() functions.

 

 

 

 

#include <stdio.h>

#include <winsock2.h>

 

int main()

{

  // Declare variables

  WSADATA wsaData;

 

  // Initialize Winsock, request the Winsock 2.2

  int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);

  if(iResult != NO_ERROR)

    printf("Error at WSAStartup().\n");

  else

    printf("WSAStartup() is OK.\n");

 

// Declare and initialize variables

hostent* remoteHost;

char* ip;

char* host_name;

unsigned int addr;

 

// User inputs name of host

printf("Input name/IP of host: ");

host_name = (char*) malloc(sizeof(char*)*128);

fgets(host_name, 128, stdin);

 

// If the user input is an alpha name for the host, use gethostbyname()

// else, gethostbyaddr() (assume IPv4) host address is a name

if (isalpha(host_name[0]))

{

  printf("\nUsing gethostbyname()...\n");

  // NULL terminated

  host_name[strlen(host_name)-1] = '\0';

  remoteHost = gethostbyname(host_name);

  ip = inet_ntoa(*(struct in_addr *)*remoteHost->h_addr_list);

  printf("IP address is: %s.\n", ip);

  printf("Address type: %i.\n\n", remoteHost->h_addrtype);

 }

else

{

  printf("\nUsing gethostbyaddr()...\n");

  addr = inet_addr(host_name);

  remoteHost = gethostbyaddr((char *)&addr, 4, AF_INET);

  printf("Hostname is: %s.\n", remoteHost->h_name);

  printf("Address type: %i.\n\n", remoteHost->h_addrtype);

}

 

if (WSAGetLastError() != 0)

{

  if (WSAGetLastError() == 11001)

  printf("Host not found...\nExiting.\n");

}

else

  printf("error #: %ld\n", WSAGetLastError());

 

// The remoteHost structure can now be used to access information about the host

  WSACleanup();

  return 0;

}

 

Sample output:

 

Figure 2

 

 

Figure 3

 

 

 

 

 

Further reading and digging:

 

1. Linux Sockets: Story and program examples.

2. Linux and TCP/IP.

3. Structure, enum, union and typedef story can be found struct, enum, union & typedef tutorial.

4. For Multibytes, Unicode characters and Localization please refer to Multibyte, Unicode and wide characters (Story) and Win32 Windows & Users tutorial (Implementation).

5. Windows data type information is Win32 - Windows data types.

6. A complete info on Windows socket reference from MSDN which include managed and unmanaged API doc.

7. Check the best selling C / C++ and Windows books at Amazon.com.

 

 

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Tenouk C & C++ |< Winsock Prog. Example 7 | Main | Winsock Prog. Example 9 >| Site Index | Download | Linux Socket | Winsock in .NET