IPv6 connect error WSAEAFNOSUPPORT - c++

Question

I code a small client for IPv4 / IPv6 with a hostname resolver.
For IPv4 and resolver it's fine but not with IPv6 when connect() I have a problem WSAGetLastError() say WSAEAFNOSUPPORT.
I have a switch all structures (AF_INET -> AF_INET6, SOCKADDR_IN -> SOCKADDR_IN6) to IPv6 versions.
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")
int main()
{
printf("Simple_Client IPv4 & IPv6\n\n");
// Initiates Winsock
WSADATA WSAData;
WSAStartup(MAKEWORD(2, 0), &WSAData);
// Get Parameters IP/PORT and request
std::string str_HOSTNAME = "mirror.neostrada.nl";
int PORT = 21;
// RESOLVE IP
BOOL is_IPv6 = FALSE;
std::string str_dest_ip = "";
addrinfo hints = { 0 };
hints.ai_flags = AI_ALL;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
addrinfo * pResult;
getaddrinfo(str_HOSTNAME.c_str(), NULL, &hints, &pResult);
if (pResult == NULL)
{
printf("pResult error\n");
return -1;
}
if (pResult->ai_family == AF_INET)
{
printf("getaddrinfo = AF_INET (IPv4)\n");
is_IPv6 = FALSE;
}
if (pResult->ai_family == AF_INET6)
{
printf("getaddrinfo = AF_INET6 (IPv6)\n");
is_IPv6 = TRUE;
}
char str[128];
memset(str, 0, sizeof(str));
if (is_IPv6 == FALSE) // IPv4
{
if (inet_ntop(AF_INET, &(*((ULONG*)&(((sockaddr_in*)pResult->ai_addr)->sin_addr))), str, INET_ADDRSTRLEN))
str_dest_ip = char_to_string(str, strlen(str)); // Copy char in std::string
else
printf("inet_ntop error\n");
}
if (is_IPv6 == TRUE) // IPv6
{
if (inet_ntop(AF_INET6, &(*((ULONG*)&(((sockaddr_in6 *)pResult->ai_addr)->sin6_addr))), str, INET6_ADDRSTRLEN))
str_dest_ip = char_to_string(str, strlen(str)); // Copy char in std::string
}
printf("%s : %s | Port : %i\n", is_IPv6 ? "IPv6" : "IPv4", str_dest_ip.c_str(), PORT);
// Connect to the HOSTNAME
SOCKET sock;
if (is_IPv6 == TRUE)
{
SOCKADDR_IN6 sin;
sin.sin6_family = AF_INET6;
if(inet_pton(sin.sin6_family, str_dest_ip.c_str(), &sin) != 1)
printf("ERROR inet_pton %i\n", WSAGetLastError());
sin.sin6_port = htons(PORT);
sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
if (sock == INVALID_SOCKET)
return -2;
if (connect(sock, (struct sockaddr *)&sin, sizeof(sin)) != SOCKET_ERROR)
{
printf("Connect Success to %s | PORT : %i\n", str_dest_ip.c_str(), PORT);
}
else
{
printf("ERROR connect to %s | PORT : %i : %i\n", str_dest_ip.c_str(), PORT, WSAGetLastError());
Sleep(10000);
return -2;
}
}
char buf[1024] = { 0 };
int size_recv = recv(sock, buf, sizeof(buf), 0);
printf("SIZE RECV = %i | DATA RECV = %s\n", size_recv, char_to_string(buf, size_recv).c_str());
WSACleanup();
getchar();
return 0;
}
If somebody have a idea, thanks for reading.

Answer 1

The problem is here:
inet_pton(sin.sin6_family, str_dest_ip.c_str(), &sin)
This writes the IPv6 address on top of the sin6_family field, damaging the whole structure.
It should be:
inet_pton(sin.sin6_family, str_dest_ip.c_str(), &sin.sin6_addr)
It's also a good idea to zero-initialize the whole sin structure in the beginning because it has more fields than you're filling in.

Answer 2

You are not using getaddrinfo() correctly.
For one thing, getaddrinfo() returns an error code that you are ignoring.
For another thing, getaddrinfo() returns a linked list that potentially contains multiple addresses in a mix of IPv4 and/or IPv6, due to your use of AF_UNSPEC. If you are only interested in IPv6, set hints.ai_family to AF_INET6 rather than AF_UNSPEC.
But either way, a given hostname may have multiple IPs associated with it, and they might not all be reachable from your location, so you should be connect()'ing to each address in the list, either one at a time or in parallel, until one of them succeeds.
Also, there is no need to use inet_pton() in this situation at all (which you are not using correctly, as explained by #rustyx's answer). getaddrinfo() returns fully populated sockaddr_in(6) structs that you can pass as-is to connect().
Try something more like this instead:
#include <winsock2.h>
#include <ws2tcpip.h>
#include <iostream>
#include <string>
#pragma comment(lib, "ws2_32.lib")
std::string addr_to_str(addrinfo *addr)
{
char str[128];
switch (addr->ai_family)
{
case AF_INET: // IPv4
{
if (inet_ntop(AF_INET, &(((sockaddr_in*)(addr->ai_addr))->sin_addr), str, INET_ADDRSTRLEN))
return str;
ret = WSAGetLastError();
break;
}
case AF_INET6: // IPv6
{
if (inet_ntop(AF_INET6, &(((sockaddr_in6*)(addr->ai_addr))->sin6_addr), str, INET6_ADDRSTRLEN))
return str;
ret = WSAGetLastError();
break;
}
default:
ret = WSAEAFNOSUPPORT;
break;
}
std::cerr << "inet_ntop error: " << ret << std::endl;
return "";
}
int main()
{
std::cout << "Simple_Client IPv4 & IPv6" << std::endl << std::endl;
// Initiates Winsock
WSADATA WSAData;
int ret = WSAStartup(MAKEWORD(2, 0), &WSAData);
if (ret != 0)
{
std::cerr << "WSAStartup error: " << ret << std::endl;
return -1;
}
// Get Parameters IP/PORT and request
std::string str_HOSTNAME = "mirror.neostrada.nl";
int PORT = 21;
// RESOLVE IP
addrinfo hints = { 0 };
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
addrinfo *pResult = NULL;
ret = getaddrinfo(str_HOSTNAME.c_str(), std::to_string(PORT).c_str(), &hints, &pResult);
if (ret != 0)
{
std::cerr << "getaddrinfo error: " << ret << std::endl;
WSACleanup();
return -1;
}
// Log the IPs
bool has_IPv4 = false;
bool has_IPv6 = false;
for (addrinfo *addr = pResult; addr != NULL; addr = addr->ai_next)
{
switch (addr->ai_family)
{
case AF_INET: // IPv4
{
has_IPv4 = true;
std::cout << "IPv4 : " << addr_to_str(addr);
break;
}
case AF_INET6: // IPv6
{
has_IPv6 = true;
std::cout << "IPv6 : " << addr_to_str(addr);
break;
}
}
}
// Connect to the HOSTNAME
SOCKET sock = INVALID_SOCKET;
if (has_IPv6)
{
// try IPv6 first...
for (addrinfo *addr = pResult; addr != NULL; addr = addr->ai_next)
{
if (addr->ai_family != AF_INET6)
continue;
std::cout << "Connecting to IPv6 : " << addr_to_str(addr) << " | Port : " << PORT << std::endl;
sock = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
if (sock == INVALID_SOCKET)
{
ret = WSAGetLastError();
std::cerr << "socket error: " << ret << std::endl;
continue;
}
if (connect(sock, addr->ai_addr, addr->ai_addrlen) == SOCKET_ERROR)
{
ret = WSAGetLastError();
std::cerr << "connect error: " << ret << std::endl;
closesocket(sock);
sock = INVALID_SOCKET;
continue;
}
break;
}
}
if ((sock == INVALID_SOCKET) && (has_IPv4))
{
// try IPv4 next...
for (addrinfo *addr = pResult; addr != NULL; addr = addr->ai_next)
{
if (addr->ai_family != AF_INET)
continue;
std::cout << "Connecting to IPv4 : " << addr_to_str(addr) << " | Port : " << PORT << std::endl;
sock = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
if (sock == INVALID_SOCKET)
{
ret = WSAGetLastError();
std::cerr << "socket error: " << ret << std::endl;
continue;
}
if (connect(sock, addr->ai_addr, addr->ai_addrlen) == SOCKET_ERROR)
{
ret = WSAGetLastError();
std::cerr << "connect error: " << ret << std::endl;
closesocket(sock);
sock = INVALID_SOCKET;
continue;
}
break;
}
}
freeaddrinfo(pResult);
if (sock == INVALID_SOCKET)
{
WSACleanup();
return -2;
}
std::cout << "Connect Successful" << std::endl;
char buf[1024];
int size_recv = recv(sock, buf, sizeof(buf), 0);
if (size_recv == SOCKET_ERROR)
{
ret = WSAGetLastError();
std::cerr << "recv error: " << ret << std::endl;
}
else
{
std::cout << "SIZE RECV = " << size_recv;
if (size_recv > 0)
{
std::cout << " | DATA RECV = ";
std::cout.write(buf, size_recv);
}
std::cout << std::endl;
}
closesocket(sock);
WSACleanup();
std::cin.get();
return 0;
}