getaddrinfo : try to connect until success
On the Internet, hostnames often have multiple IP address. Sometimes both IPv4 and IPv6 address are resolved. It is very popular to try connecting until the connect system call succeeds. This document shows you how to resolve both IPv4 and IPv6 address, and try connecting until connect system call succeeds.
Simple sample code
#include <winsock2.h>
#include <ws2tcpip.h>
int
main()
{
char *hostname = "localhost";
char *service = "http";
struct addrinfo hints, *res0, *res;
int err;
SOCKET sock;
memset(&hints, 0, sizeof(hints));
hints.ai_socktype = SOCK_STREAM;
hints.ai_family = PF_UNSPEC;
WSAData data;
WSAStartup(MAKEWORD(2,0), &data);
if ((err = getaddrinfo(hostname, service, &hints, &res0)) != 0) {
printf("error %d\n", err);
return 1;
}
for (res=res0; res!=NULL; res=res->ai_next) {
sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (sock == INVALID_SOCKET) {
continue;
}
if (!connect(sock, res->ai_addr, res->ai_addrlen)) {
closesocket(sock);
continue;
}
break;
}
freeaddrinfo(res0);
// write transmission code here if sock is valid...
WSACleanup();
return 0;
}
