Send GET Request in C to IPv6 web server on windows - c

Question

I am trying to make a simple GET request to a webserver that has an IPv6 address, and it does not work. My code has to be available on Windows, so I use the Windows libraries, e.g.
#include <stdio.h>
#include <winsock2.h>
#pragma comment (lib, "Ws2_32.lib")
#include <windows.h>
#include <winuser.h>
#include <string.h>
Here is the part of the code that establishes the connection :
int portno = 825;
//yes, strange port number...
const char *adress = "[2a02:842a:86d1:d001:26dd:8d7a:8202:d9a3]";
WSADATA wsa;
SOCKET sockfd;
char message[4096] = "GET //page//index.php?data=somedata HTTP/1.1\r\nHost: [2a02:842a:86d1:d001:26dd:8d7a:8202:d9a3]\r\nUser-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0\r\nAccept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8\r\n\r\n");
struct hostent *server;
struct sockaddr_in6 serv_addr;
int bytes, sent, received, total;
char response[4096];
int iResult = WSAStartup(MAKEWORD(2,2),&wsa);
sockfd = socket(AF_INET6 , SOCK_STREAM , 0 );
//while debugging i noticed that this line does not work
server = gethostbyname(adress);
memset(&serv_addr,0,sizeof(serv_addr));
printf("1\n");
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portno);
memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);
connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
If anybody knows how to change this code so that it will allow IPv6 connections, please tell me :)

Answer 1

Your call to gethostbyname() cannot possibly work, as this function only works with IPv4 addresses or hostnames, while you are providing an IPv6 address in URI notation ([addr]). Furthermore, gethostbyname() is obsolete and should not be used in new code.
Since you already have an IPv6 address, you don't need to perform a lookup. You could use getaddrinfo(), but you're better off just transforming that in binary form through the much simpler inet_pton(). Remember that you need to remove the enclosing [] brackets as they are only needed for URIs, not for literal addresses.
Here's an example:
const char *address = "2a02:842a:86d1:d001:26dd:8d7a:8202:d9a3";
if (inet_pton(AF_INET6, address, &serv_addr.sin6_addr.s6_addr) != 1) {
// invalid address, handle the error somehow
}
Also, note that the correct sockaddr_in6 has the following fields (see man 7 ipv6):
struct sockaddr_in6 {
sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* port number */
uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* Scope ID (new in 2.4) */
};
struct in6_addr {
unsigned char s6_addr[16]; /* IPv6 address */
};
While you are using sin_addr, sin_family, etc, as if it were a sockaddr_in structure. What you want instead is:
serv_addr.sin6_family = AF_INET6;
serv_addr.sin6_port = htons(portno);