WINSOCK 2.pdf

WINSOCK 2WINDOWS SOCKET: PROGRAM EXAMPLESPART 8Machine’s OS is standalone Windows Xp Pro with SP2 except whenevermentioned. Compiler used was Visual C++ 2003 .Net 1.1. Beware the codes thatspan more than one line. Program examples have been tested for NonDestructive Test. All information compiled for Windows 2000 (NT5.0) aboveand...1.The story was discussed at Winsock introduction story.2.Related functions, structures and macros used in the program exampleshave been dumped at Winsock structure & function 1 and Winsockstructure & function 2.3.Other related and required information (if any) not available in no. 2 canbe found at MSDN & Visual C++ online reference.AbilitiesAble to understand more 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 programminglanguage and Winsock APIs.sockaddrItem DescriptionStructure sockaddr.Info Contains socket address information. The sockaddr structure varies depending on the protocol selected. It is better to use SOCKADDR_STORAGE instead.Definition struct sockaddr_in {short sin_family;u_short sin_port;struct in_addr sin_addr; char sin_zero[8];};struct sockaddr_in6 {short sin6_family;u_short sin6_port;u_long sin6_flowinfo;struct in6_addr sin6_addr; u_long sin6_scope_id; };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.RemarkThe sockaddr structure varies depending on the protocol selected. Except for thesin*_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 1Program ExampleThe following example demonstrates the use of the sockaddr structure.#include <stdio.h>#include "winsock2.h"int main(){// Declare variablesWSADATA wsaData;SOCKET ListenSocket;sockaddr_in service;// Initialize Winsock, request the Winsock 2.2int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);if(iResult != NO_ERROR)printf("Error at WSAStartup().\n");elseprintf("WSAStartup() is OK.\n");// Create a listening socketListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (ListenSocket == INVALID_SOCKET){printf("Error at socket().\n");WSACleanup();return 0;}elseprintf("socket() is OK.\n");// Bind the socket to the local IP address and port 55555hostent* 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;}elseprintf("bind() is OK.\n");WSACleanup();return 0;}Figure 1hostentem Descriptioncture hostentUsed by functions to store information about a given host, such as host name, IP address, and so forth. An application should never attempt to modify this structure or to free any of its components. Furthermore, only copy of the hostent structure is allocated per thread, and an application should therefore copy any informatiothat it needs before issuing any other Windows Sockets API calls.nition typedef struct hostent {char FAR* h_name;char FAR FAR** h_aliases; short h_addrtype;short h_length;char FAR FAR** h_addr_list; } hostent;mbers h_name - Official name of the host (PC). If using the DNS or similar resolution system, it is the Fully Qualified Domain Name (FQDN) that caused the server to return a reply. If using a local hosts file, it is the first entry a the IP address.h_aliases - Null-terminated array of alternate names.h_addrtype - Type of address being returned.h_length - Length of each address, in bytes.h_addr_list - Null-terminated list of addresses for the host. Addresses are returned in network byte order. Th macro h_addr is defined to be h_addr_list[0] for compatibility with older software.der<winsock2.h>mark-Table 2gethostbyaddr()Item Descriptionction gethostbyaddr()Retrieves the host information corresponding to a network address. The gethostbyaddr function hasbeen deprecated by the introduction of the getnameinfo() function. Developers creating WindowsSockets 2 applications are urged to use the getnameinfo() function instead of the gethostbyaddr()function.otype struct HOSTENT* FAR gethostbyaddr( const char* addr, int len, int type);ameters addr - [in] Pointer to an address in network byte order.len - [in] Length of the address, in bytes.type - [in] Type of the address, such as the AF_INET address family type (defined as TCP, UDP, and other associated Internet protocols). Address family types and their corresponding values are defined the winsock2.h header file.urn value See below. ude file<winsock2.h> ary ws2_32.lib.mark The gethostbyaddr() function returns a pointer to the hostent structure that contains the name and address corresponding to the given network address. Although gethostbyaddr is deprecated by the getnameinfo() function, gethostbyaddr is capable of returning a NetBIOS name; getnameinfo is not. Developers requiring NetBIOS name resolution may need to use gethostbyaddr() until their applicatio are completely independent of NetBIOS names. Note The capability to perform reverse lookups usin the gethostbyaddr function is convenient, but such lookups are considered inherently unreliable, and should be used only as a hint.Table 3Return ValuesIf 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().Error code MeaningWSANOTINITIALISED A successful WSAStartup() call must occur before using this function.WSAENETDOWN The network subsystem has failed. WSAHOST_NOT_FOUND Authoritative answer host not found.WSATRY_AGAIN Non-authoritative host not found, or server failed.WSANO_RECOVERY A non-recoverable error occurred.WSANO_DATA Valid name, no data record of requested type.WSAEINPROGRESS A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.WSAEAFNOSUPPORT The type specified is not supported by the Windows Sockets implementation.WSAEFAULT The addr parameter is not a valid part of the user address space, or the len parameter is too small.WSAEINTR A blocking Windows Socket 1.1 call was canceled through WSACancelBlockingCall().Table 4For program sample, see the following example.gethostbyname()Item Description nction gethostbyname().e Retrieves host information corresponding to a host name from a host database. The gethostbyname( function has been deprecated by the introduction of the getaddrinfo() function. Developers creating Windows Sockets 2 applications are urged to use the getaddrinfo() function instead of gethostbynamtotype struct hostent* FAR gethostbyname(const char* name);ameters name - [in] Pointer to the null-terminated name of the host to resolve. urn value See below.ude file<winsock2.h>rary ws2_32.lib.mark The gethostbyname() function returns a pointer to a hostent structure - a structure allocated by Windows Sockets. The hostent structure contains the results of a successful search for the host specified in the name parameter.The application must never attempt to modify this structure or to free any of its components. Furthermore, only one copy of this structure is allocated per thread, so the application should copy an information it needs before issuing any other Windows Sockets function calls.The gethostbyname() function cannot resolve IP address strings passed to it. Such a request is treate exactly as if an unknown host name were passed. Use inet_addr to convert an IP address string the string to an actual IP address, then use another function, gethostbyaddr(), to obtain the contents of th hostent structure. If null is provided in the name parameter, the returned string is the same as the stri returned by a successful gethostname() function call. The gethostbyname() function does not check t size of the name parameter before passing the buffer. In improperly sized name parameters, heap corruption can occur.Table 5Return ValuesIf no error occurs, gethostbyname() returns a pointer to the hostent structuredescribed above. Otherwise, it returns a null pointer and a specific error numbercan be retrieved by calling WSAGetLastError().Error code MeaningWSANOTINITIALISEDA successful WSAStartup() call mustoccur before using this function.WSAENETDOWN The network subsystem has failed.WSAHOST_NOT_FOUND Authoritative answer host not found.WSATRY_AGAINNon-authoritative host not found, orserver failure.WSANO_RECOVERY A non-recoverable error occurred.WSANO_DATAValid name, no data record ofrequested type.WSAEINPROGRESSA blocking Windows Sockets 1.1 call isin progress, or the service provider isstill processing a callback function.WSAEFAULTThe name parameter is not a valid partof the user address space.WSAEINTRA blocking Windows Socket 1.1 callwas canceled throughWSACancelBlockingCall().Table 6Program ExampleThe following examples demonstrates the use of the gethostbyname() and gethostbyaddr() functions.#include <stdio.h>#include <winsock2.h>int main(){// Declare variablesWSADATA wsaData;// Initialize Winsock, request the Winsock 2.2int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);if(iResult != NO_ERROR)printf("Error at WSAStartup().\n");elseprintf("WSAStartup() is OK.\n");// Declare and initialize variableshostent* remoteHost;char* ip;char* host_name;unsigned int addr;// User inputs name of hostprintf("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 nameif (isalpha(host_name[0])){printf("\nUsing gethostbyname()...\n");// NULL terminatedhost_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");}elseprintf("error #: %ld\n", WSAGetLastError());// The remoteHost structure can now be used to// access information about the hostWSACleanup();return 0;}Figure 2Figure 3。