Conversion of IPv6 to IPv4 gives 0.0.0.1 only - c++

Question

I am writing a Java interposer (using LD_PRELOAD method) that modifies the recipient information in network communication system calls (connect/sendto).
Whenever Java tries to connect to another socket, I modify the intended recipient IP and port. Java uses IPv4-mapped-IPv6 addresses. So, I need to extract the IPv4 part of it. I achieve this using the method prescribed by Nicolas Bachschmidt at link.
The problem I am facing is that for every IPv4-mapped-IPv6 address, the result string (IPv4 part) I obtain is always 0.0.0.1. Instead it should be 10.0.0.1 (for ::ffff:10.0.0.1). I have tried this with different IP addresses. The result is always the same.
Two things I would like to mention that I think may be related:
When I tested the same program a month ago on my local network (that has 192.168.1.XXX IP addresses), the program worked correctly. Point being (I don't think) there is any problem with code. To verify this, I asked a question on stackoverflow to convert IPv4-mapped-IPv6 addresses to IPv4, the link of which is mentioned earlier).
I am trying to test this program now on my university network (that has 10.XXX.XXX.XXX IP addresses) and VirtualBox (NAT mode that also gives 10.XXX.XXX.XXX addresses). However, I have tried to connect to 10.0.0.1 and 12.0.0.1 in these cases. Both give 0.0.0.1.
What am I doing wrong?
UPDATE: In Java, socket connection is done by the usual method:
Socket conn = new Socket("10.0.0.1", 50021);
The code to interpose this connect() system call is as follows:
int connect(int fd, const struct sockaddr *sk, socklen_t sl)
{
struct sockaddr_in *lsk_in = (struct sockaddr_in *) sk;
struct sockaddr_in6 *lsk_in6 = (struct sockaddr_in6 *) sk;
struct sockaddr_in addr4;
unsigned int len;
int nbytes, oport, tport, ret, i;
char ip_address[30];
char buffer[1024];
char tempBuffer[1024];
if((lsk_in->sin_family == AF_INET) || (lsk_in->sin_family == AF_INET6))
{
if(lsk_in->sin_family == AF_INET)
{
oport = ntohs(lsk_in->sin_port);
memcpy(&addr4.sin_addr.s_addr, &lsk_in->sin_addr.s_addr, sizeof(addr4.sin_addr.s_addr));
}
else if(lsk_in->sin_family == AF_INET6)
{
oport = ntohs(lsk_in6->sin6_port);
//This is where the problem is. I always get 0.0.0.1
memcpy(&addr4.sin_addr.s_addr, lsk_in6->sin6_addr.s6_addr+12, sizeof(addr4.sin_addr.s_addr));
}
memset(buffer, '\0', sizeof(buffer));
sprintf(buffer, "%s%c%s%c%i", NAT_VM_CONNECT_RULE, NAT_VM_DELIMITER, (char *)inet_ntoa(addr4.sin_addr), NAT_VM_DELIMITER, oport);
nbytes = send(sock, buffer, strlen(buffer), 0);
if(DEBUG_MODE)
fprintf(stdout, "[LD_INTERPOSER] Sent[%s]\n", buffer);
memset(buffer, '\0', sizeof(buffer));
nbytes = recv(sock, buffer, sizeof(buffer), 0);
fprintf(stderr, "[LD_INTERPOSER] Received CONNECT [%s]\n", buffer);
memset(ip_address, '\0', sizeof(ip_address));
int pos = strrchr(buffer, NAT_VM_DELIMITER) - buffer;
strncpy(ip_address, buffer, pos);
ip_address[pos] = '\0';
tport = atoi(buffer + pos + 1);
if(lsk_in->sin_family == AF_INET)
{
lsk_in->sin_addr.s_addr = inet_addr(ip_address + 7);
lsk_in->sin_port = htons(tport);
}
else if(lsk_in->sin_family == AF_INET6)
{
inet_pton(AF_INET6, ip_address, &(lsk_in6->sin6_addr));
lsk_in6->sin6_port = htons(tport);
}
fprintf(stderr, "[LD_INTERPOSER] IP[%s], Port[%d] for VM[%s]\n", ip_address, tport, vm_ip);
}
return real_connect(fd, sk, sl);
}

Answer 1

Thanks to #ugoren hex dump technique (in comments), I was able to figure out that the IPv6 structure itself contained a 0.0.0.1 address. I realized that the problem may be due to different JDKs. The Java project was built using OpenJDK 7 while the PC I was using had OpenJDK 6. When I updated the JDK to version 7, the error disappeared. However, it has landed me to another error which is documented at a new stackoverflow question which I am still unable to resolve.