Workaround getaddrinfo(3) from the dumb AIX C library performing DNS requests on numeric IP addresses

no-lookup-for-numeric-name.c

/*	Copyright 2015-2022 Rivoreo

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	a copy of this software and associated documentation files (the
	"Software"), to deal in the Software without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Software, and to
	permit persons to whom the Software is furnished to do so, subject to
	the following conditions:

	The above copyright notice and this permission notice shall be
	included in all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	NONINFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE
	FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
	CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
	WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include <dlfcn.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>

static void *get_libc() {
	static void *libc;
	if(!libc) libc = dlopen("/usr/lib/libc.a(shr.o)", RTLD_NOW | RTLD_LOCAL | RTLD_MEMBER | RTLD_NOAUTODEFER);
	return libc;
}

static int (*get_libc_getaddrinfo())(const char *, const char *, const struct addrinfo *, struct addrinfo **) {
	static int (*f)(const char *, const char *, const struct addrinfo *, struct addrinfo **);
	if(f) return f;
	void *libc = get_libc();
	if(!libc) {
		perror("dlopen");
		abort();
	}
	*(void **)&f = dlsym(libc, "getaddrinfo");
	if(!f) {
		perror("dlsym: getaddrinfo");
		abort();
	}
	return f;
}

int getaddrinfo(const char *host, const char *serv, const struct addrinfo *hints, struct addrinfo **result) {
	int (*libc_getaddrinfo)(const char *, const char *, const struct addrinfo *, struct addrinfo **) = get_libc_getaddrinfo();
	if(!host) return libc_getaddrinfo(host, serv, hints, result);
	if(hints && (hints->ai_flags & AI_ADDRCONFIG)) return libc_getaddrinfo(host, serv, hints, result);
	int family = hints ? hints->ai_family : AF_INET;
	switch(family) {
		case AF_UNSPEC:
			family = AF_INET;
			break;
		case AF_INET:
		case AF_INET6:
			break;
		default:
			return EAI_FAMILY;
	}
	unsigned int port;
	if(serv) {
		char *end_p;
		port = strtoul(serv, &end_p, 0);
		if(*end_p) {
			return hints && (hints->ai_flags & AI_NUMERICSERV) ?
				EAI_NONAME : libc_getaddrinfo(host, serv, hints, result);
		}
	}
	union {
		struct in_addr inet4_address;
		struct in6_addr inet6_address;
	} address;
	//if(host) {
		if(inet_pton(family, host, &address) < 1) {
			return hints && (hints->ai_flags & AI_NUMERICHOST) ?
				EAI_NONAME : libc_getaddrinfo(host, serv, hints, result);
		}
	//}
	*result = malloc(sizeof(struct addrinfo));
	if(!*result) return EAI_MEMORY;
	memset(*result, 0, sizeof(struct addrinfo));
	(*result)->ai_family = family;
	switch(family) {
		case AF_INET:
			(*result)->ai_addrlen = sizeof(struct sockaddr_in);
			(*result)->ai_addr = malloc((*result)->ai_addrlen);
			if(!(*result)->ai_addr) {
				free(*result);
				return EAI_MEMORY;
			}
			memset((*result)->ai_addr, 0, (*result)->ai_addrlen);
			((struct sockaddr_in *)(*result)->ai_addr)->sin_addr = address.inet4_address;
			if(serv) ((struct sockaddr_in *)(*result)->ai_addr)->sin_port = htons(port);
			break;
		case AF_INET6:
			(*result)->ai_addrlen = sizeof(struct sockaddr_in6);
			(*result)->ai_addr = malloc((*result)->ai_addrlen);
			if(!(*result)->ai_addr) {
				free(*result);
				return EAI_MEMORY;
			}
			memset((*result)->ai_addr, 0, (*result)->ai_addrlen);
			((struct sockaddr_in6 *)(*result)->ai_addr)->sin6_addr = address.inet6_address;
			if(serv) ((struct sockaddr_in6 *)(*result)->ai_addr)->sin6_port = htons(port);
			break;
	}
	(*result)->ai_addr->sa_family = family;
	(*result)->ai_socktype = hints ? hints->ai_socktype : SOCK_STREAM;
	if(hints) (*result)->ai_protocol = hints->ai_protocol;
	return 0;
}