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) {
}
...
}
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
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:
//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) );
...
}
/** 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) {
}
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