Getting an address IP and using a socket to connect to it - c

Question

I'm writing an HTTP client using UNIX sockets (as part of a homework assignment). I currently have this working code to connect to a given IP Address:
int sockfd = socket(AF_INET, SOCK_STREAM, 0);
char *server_address = "127.0.0.1";
struct sockaddr_in address;
if (sockfd < 0) {
printf("Unable to open socket\n");
exit(1);
}
// Try to connect to server_address on port PORT
address.sin_family = AF_INET;
address.sin_addr.s_addr = inet_addr(server_address);
address.sin_port = htons(PORT);
if (connect(sockfd, (struct sockaddr*) &address, sizeof(address)) < 0) {
printf("Unable to connect to host\n");
exit(1);
}
However, I now want to modify it so that server_address could also be something that is not an IP, such as "google.com". I've been trying to figure out how to do this using gethostbyname, but I am having trouble.
Will gethostbyname accept both an IP Address OR an address like "google.com" and have it work correctly? (or should I try and run a regex on the address first and do something else if it is an IP Address)?
I have tried the following code to try to get it working with something like "google.com", but I am getting a warning warning: assignment makes integer from pointer without a cast
struct hostent *host_entity = gethostbyname(server_address);
address.sin_addr.s_addr = host_entity->h_addr_list[0];
I know I am doing-it-wrong, but the gethostbyname documentation is atrocious.

Answer 1

What you want is maybe getaddrinfo(3):
#include <sys/socket.h>
#include <netdb.h>
static int
resolve(const char *host, const char *port)
{
struct addrinfo *aires;
struct addrinfo hints = {0};
int s = -1;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = 0;
#if defined AI_ADDRCONFIG
hints.ai_flags |= AI_ADDRCONFIG;
#endif /* AI_ADDRCONFIG */
#if defined AI_V4MAPPED
hints.ai_flags |= AI_V4MAPPED;
#endif /* AI_V4MAPPED */
hints.ai_protocol = 0;
if (getaddrinfo(host, port, &hints, &aires) < 0) {
goto out;
}
/* now try them all */
for (const struct addrinfo *ai = aires;
ai != NULL &&
((s = socket(ai->ai_family, ai->ai_socktype, 0)) < 0 ||
connect(s, ai->ai_addr, ai->ai_addrlen) < 0);
close(s), s = -1, ai = ai->ai_next);
out:
freeaddrinfo(aires);
return s;
}
This version gets you a socket from a host/port pair. It also takes IP addresses for host and service strings for port. It will, however, connect to the host in question already.