/**
* Process one IP packet. Change buffer and set length to get a packet sent back. called from
* Net.loop().
*/
public void receive(Packet p) {
int i;
int[] buf = p.buf;
int len;
i = buf[0];
len = i & 0xffff; // length from IP header
// NO options are assumed in ICMP/TCP/IP...
// => copy if options present
// but we just drop it now - too lazy
if (len > p.len || (i >>> 24 != 0x45)) {
if (Logging.LOG) Logging.wr("IP options -> discard");
ejip.returnPacket(p); // packet to short or ip options => drop it
return;
} else {
p.len = len; // correct for to long packets
}
// TODO fragmentation
if (Ip.chkSum(buf, 0, 20) != 0) {
ejip.returnPacket(p);
if (Logging.LOG) Logging.wr("wrong IP checksum ");
return;
}
int prot = (buf[2] >> 16) & 0xff; // protocol
if (prot == PROT_ICMP) {
doICMP(p);
ip.doIp(p, prot);
} else if (prot == Tcp.PROTOCOL) {
if (Ejip.TCP_ENABLED) {
// that's the new TCP processing
tcp.process(p);
} else {
ejip.returnPacket(p); // mark packet free
}
} else if (prot == Udp.PROTOCOL) {
udp.process(p); // Udp generates the reply
} else {
ejip.returnPacket(p); // mark packet free
}
}
/** the famous ping. */
private void doICMP(Packet p) {
int type_code = p.buf[5] >>> 16;
if (Logging.LOG) Logging.wr('P');
if (Logging.LOG) Logging.hexVal(type_code);
if (type_code == 0x0800) {
// TODO check received ICMP checksum
p.buf[5] = 0; // echo replay plus clear checksum,
p.buf[5] = Ip.chkSum(p.buf, 5, p.len - 20); // echo replay (0x0000)
// plus checksum
} else {
p.len = 0;
}
}
/**
* Look for received packets and invoke receive. Mark them to be sent if returned with len!=0 from
* TcpIp layer.
*/
public void run() {
Packet p;
PacketQueue rxQ = ejip.llRxQueue;
if (rxQ == null) {
if (Logging.LOG) Logging.wr("No link layer registered");
return;
}
// get one received packet from the receive queue
p = rxQ.deq();
if (p != null) {
receive(p);
} else {
udp.run();
if (Ejip.TCP_ENABLED) tcp.run();
}
}