Create socket when have DNS name - c++

Question

Bellow is peace of code that I use to connect to socket in Windows. Sometimes I don't have IP dress, but have DNS name in inetAddr. Probably I must resolve address from host name, or it is possible create socket with DNS name? What is the best way to create socket when have DNS name?
commStatus communicate( const char * tx, char * rx, const int bufSize , const char * inetAddr, const int port )
{
...
SOCKET s;
struct sockaddr_in server;
server.sin_addr.s_addr = inet_addr(inetAddr);
server.sin_family = AF_INET;
server.sin_port = htons( port );
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
FILELOGL("Could not create socket : " << WSAGetLastError(),Level::Error );
} else
{
if (connect(s , (struct sockaddr *)&server , sizeof(server)) < 0)
{
FILELOGL("connect error", Level::Error);
r= commStatus::COMM_NO_TRANSMIT ;
} else
{
...
}
}
...
}

Answer 1

There is only one way: Resolve the host name.
Here's a part of my code that I've modified and haven't tested, but it should work:
WSADATA wsdata;
const char * inetAddr
addrinfo hints, *res;
WSAStartup (MAKEWORD (2, 2), &wsdata);
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
if (getaddrinfo("someaddress.com", NULL, &hints, &res) != 0)
return false;
inetAddr = inet_ntoa(((sockaddr_in *) res -> ai_addr) -> sin_addr);

Answer 2

You need to resolve the DNS name. Use getaddrinfo() for that. Just note that a DNS name can resolve to multiple IPs, both IPv4 and IPv6, so you have to call getaddrinfo() first in order to know how many IPs are reported, and what type of socket to create for each IP.
For example:
commStatus communicate( const char * tx, char * rx, const int bufSize , const char * inetAddr, const int port )
{
...
SOCKET s = INVALID_SOCKET;
struct addrinfo hint = {0};
hint.ai_flags = AI_NUMERICHOST;
hint.ai_family = AF_UNSPEC;
hint.ai_socktype = SOCK_STREAM;
hint.ai_protocol = IPPROTO_TCP;
struct addrinfo *addrs = NULL;
int ret = getaddrinfo(inetAddr, NULL, &hint, &addrs);
if (ret == EAI_NONAME)
{
hint.ai_flags = 0;
ret = getaddrinfo(inetAddr, NULL, &hint, &addrs);
}
if (ret != 0)
{
FILELOGL("Could not resolve inetAddr: " << ret, Level::Error);
}
else
{
for (struct addrinfo *addr = addrs; addr != NULL; addr = addr->ai_next)
{
s = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
if (s == INVALID_SOCKET)
{
FILELOGL("Could not create socket : " << WSAGetLastError(), Level::Error);
break;
}
if (connect(s, addr->ai_addr, addr->ai_addrlen) == 0)
break;
closesocket(s);
s = INVALID_SOCKET;
if (addr->ai_next == NULL)
{
FILELOGL("connect error", Level::Error);
}
}
freeaddrinfo(addrs);
if (s != INVALID_SOCKET)
{
...
}
}
...
}