OmniEdge on iOS

1. N2N On iOS

There is no tuntap virtual device supported on iOS platform, so 'uip' is introduced here to provide 'tap' device.

Tun device is implementd in NetworkExtension:

class PacketTunnelProvider: NEPacketTunnelProvider {
    ...
    override func startTunnel(options: [String : NSObject]?, completionHandler: @escaping (Error?) -> Void) {
    }
    ...
}

1.1 Runloop

Because the runloop in n2n is based on either file descriptor of socket, a bridge between async message and fd is necessary on iOS system.

A pipe based bridge is introduced to solve this problem.

device.fd

a pipe is instroduced here, fd[0] is set to device.fd for select in n2n runloop. if tunnel packets comes from system statck, data will be written to fd[1] and the select will be activated and data can be read from device.fd.

udp_sock

udp_mgmt_sock

1.2 data transfer

Once data packets received on Tun device, they'd be transfered to remote(by udp socket shown as below).

...
/** Send a datagram to a socket defined by a n2n_sock_t */
static ssize_t sendto_sock(int fd, const void * buf,
			   size_t len, const n2n_sock_t * dest) {
  struct sockaddr_in peer_addr;
...
  fill_sockaddr((struct sockaddr *) &peer_addr,
		sizeof(peer_addr),
		dest);

  sent = sendto(fd, buf, len, 0/*flags*/,
		(struct sockaddr *)&peer_addr, sizeof(struct sockaddr_in));
  if(sent < 0) {
      ...
  } else {
      ...
    }
...

}
...

send data to supernode or remote peer:

1.2.1 send data to supernode

//loop up registration info
static void send_register_super(n2n_edge_t * eee,
				const n2n_sock_t * supernode) {
...
sendto_sock(eee->udp_sock, pktbuf, idx, supernode);
...
}

//loop up peer info
static void send_query_peer( n2n_edge_t * eee,
                             const n2n_mac_t dstMac) {
...
sendto_sock( eee->udp_sock, pktbuf, idx, &(eee->supernode) );
...
}

1.2.2 send data to remote edge

/** Send a REGISTER packet to another edge. */
static void send_register(n2n_edge_t * eee,
		   const n2n_sock_t * remote_peer,
		   const n2n_mac_t peer_mac) {
...
sendto_sock(eee->udp_sock, pktbuf, idx, remote_peer);
...
}

/** Send a REGISTER_ACK packet to a peer edge. */
static void send_register_ack(n2n_edge_t * eee,
			      const n2n_sock_t * remote_peer,
			      const n2n_REGISTER_t * reg) {
...
sendto_sock(eee->udp_sock, pktbuf, idx, remote_peer);
...                      
}

/** Send an ecapsulated ethernet PACKET to a destination edge or broadcast MAC
 *  address. */
static int send_packet(n2n_edge_t * eee,
		       n2n_mac_t dstMac,
		       const uint8_t * pktbuf,
		       size_t pktlen) {
}

Reference

https://kean.blog/post/packet-tunnel-provider