/*
 * The idea of this is to get a program that tries to resolve one name, 
 * to resolve another instead. This is just so that programs that do not support SRV yet
 * can be tricked into connecting properly. 
 *
 * compile with: gcc -Wall -shared -o libdivert.so libdivert.c -ldl -fPIC
 * usage: env LD_PRELOAD=libdivert.so LD_LIBRARY_PATH=. /path/to/program
 */

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

#define RTLD_NEXT ((void*)(-1l))

extern int h_errno;

static const char* divert(const char* name) {

	/* fprintf(stderr, "Resolving a name with getaddrinfo %s and service %s \n", node, service); */
	char* next;
	next = getenv(name);
	if (next != NULL) {
		return next;
	}

	return name;	
}

/* This hooks into any call to getaddrinfo by the target program
 * if it tries to resolve a trapped name, we have it resolve something else.
 */
int getaddrinfo(const char *node, const char *service,
                      const struct addrinfo *hints,
                      struct addrinfo **res) {

       int (*real_getaddrinfo)(const char*, const char*,
                       const struct addrinfo *,
                       struct addrinfo **);

	real_getaddrinfo = dlsym(RTLD_NEXT, "getaddrinfo");
	return (*real_getaddrinfo)(divert(node), service, hints, res);
}



int gethostbyname_r(const char *name, struct hostent *ret, char *buf, size_t buflen, struct hostent **result, int *h_errnop) {
	int (*real_gethostbyname_r)(const char*,
             struct hostent*, char *, size_t,
              struct hostent**, int*);

	real_gethostbyname_r = dlsym(RTLD_NEXT, "gethostbyname_r");
	return (*real_gethostbyname_r)(divert(name), ret, buf, buflen, result, h_errnop);
}

struct hostent* gethostbyname(const char *name) {
	struct hostent* (*real_gethostbyname)(const char*);

	real_gethostbyname = dlsym(RTLD_NEXT, "gethostbyname");
	return (*real_gethostbyname)(divert(name));
}

int getnameinfo(const struct sockaddr* sa, socklen_t salen,
                     char* host, socklen_t hostlen,
                     char* serv, socklen_t servlen, unsigned int flags) {

	int (*real_getnameinfo)(const struct sockaddr*, socklen_t,
                      char*, socklen_t,
                      char*, socklen_t, unsigned int);

	real_getnameinfo = dlsym(RTLD_NEXT, "getnameinfo");
	return (*real_getnameinfo)(sa, salen, host, hostlen, serv, servlen, flags);
}