Windows Socket Programming 网络编程系列 信息获取

Structure Introduction

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, *PHOSTENT, FAR *LPHOSTENT;

struct sockaddr { 
   unsigned short sa_family; 
   char sa_data[14]; 
};
struct sockaddr_in{ 
   short sin_family; 
   unsigned short sin_port; 
   struct in_addr sin_addr; 
   char sin_zero[8]; 
};
typedef struct addrinfo {
  int             ai_flags;
  int             ai_family;
  int             ai_socktype;
  int             ai_protocol;
  size_t          ai_addrlen;
  char            *ai_canonname;
  struct sockaddr  *ai_addr;
  struct addrinfo  *ai_next;
} ADDRINFOA, *PADDRINFOA;
typedef 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;
} IN_ADDR, *PIN_ADDR, FAR *LPIN_ADDR;

Retrieving Functions

For getting struct hostent, using gethostbyaddr or gethostbyname. However both gethostbyname and gethostbyaddr are deprecated on Windows Socket 2. we suggest to use getnameinfo or getaddrinfo to retrieve name of the host or ip info. Here is a sample for using gethostbyaddr and getshotbyname.

char * tgrIP = "192.168.1.107";//"192.168.1.107";
struct hostent* rmtHost = nullptr;
if (!isalpha(tgrIP[0]))
{
    t1 = time(nullptr);
    unsigned int naddr = inet_addr(tgrIP);
    rmtHost = gethostbyaddr((char *)&naddr, 4, AF_INET);
    if (rmtHost == nullptr)
    {
        int errcode = ::WSAGetLastError();
        cerr<<errcode<<endl;
        return -1;
    }
    cout<<"Using "<<time(nullptr) - t1<<" seconds"<<endl;
    cout<<"Official name:"<<rmtHost->h_name<<endl;
    char ** pAlias;
    for (pAlias = rmtHost->h_aliases; *pAlias != nullptr; pAlias++)
    cout<<"length:"<<rmtHost->h_length<<endl;
    cout<<"aliases:"<<rmtHost->h_aliases<<endl;
    cout<<"addrtype:"<<rmtHost->h_addrtype<<endl;
    if (rmtHost->h_addrtype == AF_INET)
    {
        int i = 0;
        while (rmtHost->h_addr_list[i] != nullptr)
        {
            struct in_addr addr;
            addr.S_un.S_addr = *(u_long *)rmtHost->h_addr_list[i];
            cout<<"IP:"<<inet_ntoa(addr)<<endl;
            i++;
        }
    }
}

char * tgrName = www.baidu.com;//"192.168.1.107";
rmtHost = nullptr;
if (!isalpha(tgrIP[0]))
{
    t1 = time(nullptr);
    
    rmtHost = gethostbyname(tgrName);
    if (rmtHost == nullptr)
    {
        int errcode = ::WSAGetLastError();
        cerr<<errcode<<endl;
        return -1;
    }
    cout<<"Using "<<time(nullptr) - t1<<" seconds"<<endl;
    cout<<"Official name:"<<rmtHost->h_name<<endl;
    char ** pAlias;
    for (pAlias = rmtHost->h_aliases; *pAlias != nullptr; pAlias++)
    cout<<"length:"<<rmtHost->h_length<<endl;
    cout<<"aliases:"<<rmtHost->h_aliases<<endl;
    cout<<"addrtype:"<<rmtHost->h_addrtype<<endl;
    if (rmtHost->h_addrtype == AF_INET)
    {
        int i = 0;
        while (rmtHost->h_addr_list[i] != nullptr)
        {
            struct in_addr addr;
            addr.S_un.S_addr = *(u_long *)rmtHost->h_addr_list[i];
            cout<<"IP:"<<inet_ntoa(addr)<<endl;
            i++;
        }
    }
}

For gethostbyaddr, it only supports AF_INET, AF_INET6 and AF_NETBIOS. For gethostbyname, it only returns IPv4 decimal-dot format.

MSDN recommands using getnameinfo to instead of gethostbyaddr. Here is using getnameinfo sample.

char hostname[NI_MAXHOST] = {0};
char servInfo[NI_MAXSERV] = {0};
unsigned short port = 3389;
struct sockaddr_in sa;
ZeroMemory(&sa, sizeof(sockaddr_in));
sa.sin_family = AF_INET;
sa.sin_addr.S_un.S_addr = inet_addr(tgrIP);
sa.sin_port = ::htons(port);
t1 = time(nullptr);
int iret = ::getnameinfo((sockaddr*)&sa, sizeof(sockaddr), 
                        hostname, NI_MAXHOST,
                        servInfo, NI_MAXSERV,
                        NI_NOFQDN); 
if (iret != 0)
{
    iret = ::WSAGetLastError();
    cerr<<"Failed to GetAddrInfo: "<<gai_strerror(iret)<<" (ErrCode: "<<iret<<")."<<endl;
    return -1;
}
cout<<"Using "<<time(nullptr) - t1<<" seconds"<<endl;
cout<<hostname<<endl;
cout<<servInfo<<endl;

MSDN recommands using getaddrinfo to instead of gethostbyname. Here is using getaddrinfo sample.

int hname2ip(const char * pname)
{
    struct addrinfo hints, * result = nullptr;
    memset(&hints, 0, sizeof(struct addrinfo));

    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_CANONNAME; 

    int ret = getaddrinfo(pname, nullptr, &hints, &result);
    if (ret != 0)
    {
        cerr<<"Error:"<<gai_strerror(ret)<<endl;
        return 1;
    }

    cout<<"Host Name: "<<pname<<endl;
    struct addrinfo * curInfo = nullptr;
    for (curInfo = result; curInfo != nullptr; curInfo = curInfo->ai_next)
    {
        cout<<"IP: "<<inet_ntoa(((struct sockaddr_in *)(curInfo->ai_addr))->sin_addr)<<endl;
    }

    return 0;
}