getnameinfo() function on a dualstack socket returning incorrect IP address?

Question

I am using TCP accept() function on a dualstack socket. Next I am trying to print IPV4 mapped Ipv6 client address using getnameinfo(). For the first connection to accept(), getnameinfo() is correctly returning IPv4-Ipv6 client source address. But for second clients on wards it is returning the same IPv4 mapped Ipv6 address as first. Can any one help me in this ?

Pseudo Code:

struct sockaddr_storage client_ip;
socklen_t sock_len = sizeof(client_ip);
char buffer[INET6_ADDRSTRLEN];
struct sockaddr_in sa4;
static char *pclient_ipv4_addr = NULL;

while(1)
{
  fd = accept(master_fd, (struct sockaddr*)&client_ip, &sock_len);

  if (!getnameinfo((struct sockaddr*)&client_ip, sock_len, buffer,
          sizeof(buffer),0,0,NI_NUMERICHOST))
  {
    pclient_ipv4_addr = buffer;
    if (client_ip.ss_family==AF_INET6)
    {
      struct sockaddr_in6 *sa6=(struct sockaddr_in6*)&client_ip;
      if (IN6_IS_ADDR_V4MAPPED(&sa6->sin6_addr))
      {
        memset(&sa4,0,sizeof(sa4));
        sa4.sin_family=AF_INET;
        sa4.sin_port=sa6->sin6_port;
        memcpy(&sa4.sin_addr.s_addr, sa6->sin6_addr.s6_addr+12, 4);
        memcpy(&client_ip, &sa4,sizeof(sa4));
        sock_len=sizeof(sa4);
        pclient_ipv4_addr = inet_ntoa(sa4.sin_addr);
        printf("IPV4 add is %s\n", pclient_ipv4_addr );
      }
    }

  }

  memset(buffer, 0 , INET6_ADDRSTRLEN);
}

For eg: For First client pclient_ipv4_addr is "192.168.208.13", then for next client also
pclient_ipv4_addr is printing the same address. Is non reentrant of getnameinfo(0 any issue? How can solve this?

Answer 1

Try something more like this:

struct sockaddr_storage client_ip;
socklen_t sock_len;

while(1)
{
  sock_len = sizeof(client_ip);
  fd = accept(master_fd, (struct sockaddr*)&client_ip, &sock_len);

  if (fd == -1)
    break;

  if (client_ip.ss_family==AF_INET)
  {
    struct sockaddr_in *sa4 = (struct sockaddr_in*) &client_ip;
    printf("IPv4 add is %s\n", inet_ntoa(sa4->sin_addr) );
  }
  else if (client_ip.ss_family==AF_INET6)
  {
    struct sockaddr_in6 *sa6 = (struct sockaddr_in6*) &client_ip;
    if (IN6_IS_ADDR_V4MAPPED(&sa6->sin6_addr))
    {
      struct in_addr a4;
      memcpy(&a4, sa6->sin6_addr.s6_addr+12, 4);
      printf("IPv4 add is %s\n", inet_ntoa(a4) );
    }
    else
    {
      char buffer[INET6_ADDRSTRLEN];
      if (getnameinfo((struct sockaddr*)&client_ip, sock_len, buffer, sizeof(buffer), 0, 0, NI_NUMERICHOST) == 0)
        printf("IPv6 add is %s\n", buffer );
    }
  }
}