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WINSOCK 2

WINDOWS SOCKET: PROGRAM EXAMPLES PART 9

 

 

What do we have in this chapter?

1. getnameinfo()

2. Remarks

3. getnameinfo() Program Example

4. getaddrinfo()

5. Return Values

6. Remarks

7. getaddrinfo() Program Example

8. Use of ai_flags in the hints parameter

9. Freeing Address Information from Dynamic Allocation

 

 

 

 

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.   Skills to be acquired: Able to understand Winsock implementation and operations through the APIs and program examples. Able to gather, understand and use the Winsock functions, structures and macros in your programs. Able to build programs that use Microsoft C/Standard C programming language and Winsock APIs. getnameinfo()   Item Description Function getnameinfo() Use Provides name resolution from an address to the host name. Prototype int getnameinfo( const struct sockaddr* sa,   socklen_t salen,   char* host,   DWORD hostlen,   char* serv,   DWORD servlen,   int flags); Parameters sa - [in] Pointer to a socket address structure containing the address and port number of the socket. For IPv4, the sa parameter points to a sockaddr_in structure; for IPv6, the sa parameter points to a sockaddr_in6 structure. salen - [in] Length of the structure pointed to in the sa parameter, in bytes. host - [out] Pointer to the host name. The host name is returned as a Fully Qualified Domain Name (FQDN) by default. hostlen - [in] Length of the buffer pointed to by the host parameter, in bytes. The caller must provide a buffer large enough to hold the host name, including terminating NULL characters. A value of zero indicates the caller does not want to receive the string provided in host. serv - [out] Pointer to the service name associated with the port number. servlen - [in] Length of the buffer pointed to by the serv parameter, in bytes. The caller must provide a buffer large enough to hold the service name, including terminating null characters. A value of zero indicates the caller does not want to receive the string provided in serv. flags - [in] Flags used to customize processing of the getnameinfo() function. Return value Success returns zero. Any nonzero return value indicates failure. Use the WSAGetLastError() function to retrieve error information. Include file <winsock2.h >, <ws2tcpip.h> Library - Remark Declared in ws2tcpip.h; include <wspiapi.h> for Windows 95/98/Me, Windows 2000 and Windows NT.   Table 1

Remarks

 

To simplify determining buffer requirements for the host and serv parameters, the following values for maximum host name length and maximum service name are defined in the ws2tcpip.h header file:

#define NI_MAXHOST  1025

#define NI_MAXSERV    32

The flags parameter can be used to customize processing of the getnameinfo function. The following flags are available:

1. NI_NOFQDN

2. NI_NUMERICHOST

3. NI_NAMEREQD

4. NI_NUMERICSERV

5. NI_DGRAM

 

When the NI_NAMEREQD flag is set, host names that cannot be resolved by Domain Name System (DNS) result in an error. Setting the NI_NOFQDN flag results in local hosts having only their Relative Distinguished Name (RDN) returned in the host parameter. Setting the NI_NUMERICHOST flag returns the numeric form of the host name instead of its name. The numeric form of the host name is also returned if the host name cannot be resolved by DNS. Setting the NI_NUMERICSERV flag returns the port number of the service instead of its name. If NI_NUMERICSERV is not specified and the port number contained in sa does not resolve to a well known service, the getnameinfo() function fails. When NI_NUMERICSERV is specified, the port number is returned as a numeric string. Setting the NI_DGRAM flag indicates that the service is a datagram service. This flag is necessary for the few services that provide different port numbers for UDP and TCP service. The capability to perform reverse lookups using the getnameinfo() function is convenient, but such lookups are considered inherently unreliable, and should be used only as a hint. Macros in the Winsock header file define the mixed-case function name GetNameInfo() to getnameinfo(); either spelling is acceptable.

 

getnameinfo() Program Example

 

The following example demonstrates the use of the getnameinfo() function.

// Run on Windows Xp Pro, Visual C++ .Net 1.1

#include <stdio.h>

#include <winsock2.h>

#include <ws2tcpip.h>

#define NI_MAXHOST  1025

#define NI_MAXSERV    32

 

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;

struct sockaddr_in saGNI;

char *hostName;

char servInfo[256];

int retVal;

u_short port;

port = 55555;

 

// Input name of host

printf("Input name of host: ");

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

fgets(hostName, 128, stdin);

 

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

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

remoteHost = gethostbyname(hostName);

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);

 

// Set up sockaddr_in structure which is passed

// to the getnameinfo() function

saGNI.sin_family = AF_INET;

// saGNI.sin_addr.s_addr = inet_addr(ip);

saGNI.sin_addr.s_addr = inet_addr(ip);

saGNI.sin_port = htons(port);

 

// Call getnameinfo

if ((retVal = getnameinfo((SOCKADDR *)&saGNI,

  sizeof(sockaddr),

  hostName,

  256,

  servInfo,

  256,

  NI_NUMERICSERV)) != 0)

{

  printf("getnameinfo() failed.\n");

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

}

else

  printf("getnameinfo() is OK.\n");

 

  WSACleanup();

  return 0;

}

 

Sample output:

 

Figure 1

 

getaddrinfo()

 

 

Return Values

 

Success returns zero. Failure returns a nonzero Windows Sockets error code, as found in the Windows Sockets Error Codes. Nonzero error codes returned by the getaddrinfo() function also map to the set of errors outlined by IETF recommendations. The following table shows these error codes and their WSA* equivalents. It is recommended that the WSA* error codes be used, as they offer familiar and comprehensive error information for Winsock programmers.

 

 

 

1. A value of PF_UNSPEC for ai_family indicates the caller will accept any protocol family.

2. A value of zero for ai_socktype indicates the caller will accept any socket type.

3. A value of zero for ai_protocol indicates the caller will accept any protocol.

4. ai_addrlen must be zero or a null pointer.

5. ai_canonname must be zero or a null pointer.

6. ai_addr must be zero or a null pointer.

7. ai_next must be zero or a null pointer.

 

Other values in the addrinfo structure provided in the hints parameter indicate specific requirements. For example, if the caller handles only TCP and does not handle UDP, the ai_socktype member should be set to SOCK_STREAM. For another example, if the caller handles only IPv4 and does not handle IPv6, the ai_family member should be set to PF_INET. If the hints parameter is a null pointer, the getaddrinfo() function treats it as if the addrinfo structure in hints were initialized with its ai_family member set to PF_UNSPEC and all other members set to zero. Macros in the Winsock header file define the mixed-case function name GetAddrInfo() to getaddrinfo(); either spelling is acceptable.

 

getaddrinfo() Program Example

 

The following example demonstrates the use of the getaddrinfo() function.

// Run on Windows Xp Pro, Visual C++ .Net 1.1

#include <stdio.h>

#include <winsock2.h>

#include <ws2tcpip.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.

char* ip = "127.0.0.1";

char* port = "55555";

struct addrinfo aiHints;

struct addrinfo *aiList = NULL;

int retVal;

 

// Setup the hints address info structure

// which is passed to the getaddrinfo() function

memset(&aiHints, 0, sizeof(aiHints));

aiHints.ai_family = AF_INET;

aiHints.ai_socktype = SOCK_STREAM;

aiHints.ai_protocol = IPPROTO_TCP;

 

// Call getaddrinfo(). If the call succeeds,

// the aiList variable will hold a linked list

// of addrinfo structures containing response

// information about the host

if ((retVal = getaddrinfo(ip, port, &aiHints, &aiList)) != 0)

{

  printf("getaddrinfo() failed.\n");

}

else

  printf("getaddrinfo() is OK.\n");

 

  freeaddrinfo(aiList);

  WSACleanup();

  return 0;

}

 

Sample output:

 

Figure 2

 

Ensure that the development environment targets the newest version of ws2tcpip.h which includes structure and function definitions for addrinfo() and getaddrinfo(), respectively.

 

Use of ai_flags in the hints parameter

 

Flags in the ai_flags member of the optional addrinfo structure provided in the hints parameter are as follows:

1. AI_PASSIVE

2. AI_CANONNAME

3. AI_NUMERICHOST

 

Setting the AI_PASSIVE flag indicates the caller intends to use the returned socket address structure in a call to the bind() function. When the AI_PASSIVE flag is set and nodename is a null pointer, the IP address portion of the socket address structure is set to INADDR_ANY for IPv4 addresses and IN6ADDR_ANY_INIT for IPv6 addresses. When the AI_PASSIVE flag is not set, the returned socket address structure is ready for a call to the connect() function for a connection-oriented protocol, or ready for a call to either the connect(), sendto(), or send() functions for a connectionless protocol. If the nodename parameter is a null pointer in this case, the IP address portion of the socket address structure is set to the loopback address. If neither AI_CANONNAME nor AI_NUMERICHOST is used, the getaddrinfo() function attempts resolution. If a literal string is passed getaddrinfo() attempts to convert the string, and if a host name is passed the getaddrinfo() function attempts to resolve it.

When the AI_CANONNAME bit is set and the getaddrinfo() function returns success, the ai_canonname member in the hints parameter points to a NULL-terminated string that contains the canonical name of the specified node. The getaddrinfo() function can return success when the AI_CANNONNAME flag is set, yet the ai_canonname member in the associated addrinfo structure is null. Therefore, the recommended use of the AI_CANONNAME flag includes testing whether the ai_canonname member in the associated addrinfo structure is null. When the AI_NUMERICHOST bit is set, the nodename parameter must contain a non-NULL numeric host address string, otherwise the EAI_NONAME error is returned. This prevents a name resolution service from being called; all information returned by the getaddrinfo() function is dynamically allocated.

 

Freeing Address Information from Dynamic Allocation

 

All information returned by the getaddrinfo() function is dynamically allocated, including all addrinfo structures, socket address structures, and canonical host name strings pointed to by addrinfo structures. To return that information to the system, call the freeaddrinfo() function.

 

 

 

 

 

 

 

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 8 | Main | Winsock Prog. Example 10 >| Site Index | Download | Linux Socket | Winsock in .NET