Intel Threading Building Blocks

Class translator : public tbb::filter

The filter class translator (Example 11-46) performs the NAT function. In this simple example, it separates inbound packets from outbound packets. For outbound packets, it maps the local device (IP, Port) to the router port by hashing into the mapped_ports_table, creating a mapping if one is needed. It also inserts the router’s IP into the packet source IP slot in case the destination will send a packet back. For inbound packets, it does the reverse by looking up the router port to local device (IP, Port).

Example 11-46. Filter that does the actual NAT

class translator : public tbb::filter { const ip_t outgoing_ip; const nic_t outgoing_nic; // port => address, where port={router mapped port | home device port} // and address = {home device port | pair(IP, router mapped port)} mapped_ports_table& mapped_ports; static tbb::atomic<int> spare_port; // Previous spare port number public: translator (ip_t& _outgoing_ip, nic_t& _outgoing_nic, mapped_ports_table& _mapped_ports) : outgoing_ip(_outgoing_ip), outgoing_nic(_outgoing_nic), mapped_ports(_mapped_ports), filter (true /* is_serial*/) { spare_port = 2002; } void* operator() (void* item) { packet_trace* packet = static_cast<packet_trace*> (item); if (packet->packetNic == outgoing_nic) { // this is an external incoming packet ip_t app_ip; port_t app_port; if (get_port_mapping (packet->packetDestPort, app_ip, app_port)) { packet->packetDestIp = app_ip; packet->packetDestPort = app_port; } else cerr ...