📄 uip.c
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goto drop;
UIP_STAT(++uip_stat.tcp.rst);
BUF->flags = TCP_RST | TCP_ACK;
uip_len = 40;
BUF->tcpoffset = 5 << 4;
/* Flip the seqno and ackno fields in the TCP header. */
c = BUF->seqno[3];
BUF->seqno[3] = BUF->ackno[3];
BUF->ackno[3] = c;
c = BUF->seqno[2];
BUF->seqno[2] = BUF->ackno[2];
BUF->ackno[2] = c;
c = BUF->seqno[1];
BUF->seqno[1] = BUF->ackno[1];
BUF->ackno[1] = c;
c = BUF->seqno[0];
BUF->seqno[0] = BUF->ackno[0];
BUF->ackno[0] = c;
/* We also have to increase the sequence number we are
acknowledging. If the least significant byte overflowed, we need
to propagate the carry to the other bytes as well. */
if(++BUF->ackno[3] == 0) {
if(++BUF->ackno[2] == 0) {
if(++BUF->ackno[1] == 0) {
++BUF->ackno[0];
}
}
}
/* Swap port numbers. */
tmp16 = BUF->srcport;
BUF->srcport = BUF->destport;
BUF->destport = tmp16;
/* Swap IP addresses. */
tmp16 = BUF->destipaddr[0];
BUF->destipaddr[0] = BUF->srcipaddr[0];
BUF->srcipaddr[0] = tmp16;
tmp16 = BUF->destipaddr[1];
BUF->destipaddr[1] = BUF->srcipaddr[1];
BUF->srcipaddr[1] = tmp16;
/* And send out the RST packet! */
goto tcp_send_noconn;
/* This label will be jumped to if we matched the incoming packet
with a connection in LISTEN. In that case, we should create a new
connection and send a SYNACK in return. */
found_listen:
/* First we check if there are any connections avaliable. Unused
connections are kept in the same table as used connections, but
unused ones have the tcpstate set to CLOSED. Also, connections in
TIME_WAIT are kept track of and we'll use the oldest one if no
CLOSED connections are found. Thanks to Eddie C. Dost for a very
nice algorithm for the TIME_WAIT search. */
uip_connr = 0;
for(c = 0; c < UIP_CONNS; ++c) {
if(uip_conns[c].tcpstateflags == CLOSED) {
uip_connr = &uip_conns[c];
break;
}
if(uip_conns[c].tcpstateflags == TIME_WAIT) {
if(uip_connr == 0 || uip_conns[c].timer > uip_connr->timer) {
uip_connr = &uip_conns[c];
}
}
}
if(uip_connr == 0) {
/* All connections are used already, we drop packet and hope that
the remote end will retransmit the packet at a time when we
have more spare connections. */
UIP_STAT(++uip_stat.tcp.syndrop);
UIP_LOG("tcp: found no unused connections.");
goto drop;
}
uip_conn = uip_connr;
/* Fill in the necessary fields for the new connection. */
uip_connr->rto = uip_connr->timer = UIP_RTO;
uip_connr->sa = 0;
uip_connr->sv = 4;
uip_connr->nrtx = 0;
uip_connr->lport = BUF->destport;
uip_connr->rport = BUF->srcport;
uip_connr->ripaddr[0] = BUF->srcipaddr[0];
uip_connr->ripaddr[1] = BUF->srcipaddr[1];
uip_connr->tcpstateflags = SYN_RCVD;
uip_connr->snd_nxt[0] = iss[0];
uip_connr->snd_nxt[1] = iss[1];
uip_connr->snd_nxt[2] = iss[2];
uip_connr->snd_nxt[3] = iss[3];
uip_connr->len = 1;
/* rcv_nxt should be the seqno from the incoming packet + 1. */
uip_connr->rcv_nxt[3] = BUF->seqno[3];
uip_connr->rcv_nxt[2] = BUF->seqno[2];
uip_connr->rcv_nxt[1] = BUF->seqno[1];
uip_connr->rcv_nxt[0] = BUF->seqno[0];
uip_add_rcv_nxt(1);
/* Parse the TCP MSS option, if present. */
if((BUF->tcpoffset & 0xf0) > 0x50) {
for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
opt = uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + c];
if(opt == 0x00) {
/* End of options. */
break;
}
else if(opt == 0x01) {
++c;
/* NOP option. */
}
else if(opt == 0x02 &&uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0x04) {
/* An MSS option with the right option length. */
tmp16 = ((u16_t)uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |
(u16_t)uip_buf[40 + UIP_LLH_LEN + 3 + c];
uip_connr->initialmss = uip_connr->mss =
tmp16 > UIP_TCP_MSS? UIP_TCP_MSS: tmp16;
/* And we are done processing options. */
break;
}
else {
/* All other options have a length field, so that we easily
can skip past them. */
if(uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0) {
/* If the length field is zero, the options are malformed
and we don't process them further. */
break;
}
c += uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c];
}
}
}
/* Our response will be a SYNACK. */
#if UIP_ACTIVE_OPEN
tcp_send_synack:
BUF->flags = TCP_ACK;
tcp_send_syn:
BUF->flags |= TCP_SYN;
#else /* UIP_ACTIVE_OPEN */
tcp_send_synack:
BUF->flags = TCP_SYN | TCP_ACK;
#endif /* UIP_ACTIVE_OPEN */
/* We send out the TCP Maximum Segment Size option with our
SYNACK. */
BUF->optdata[0] = 2;
BUF->optdata[1] = 4;
BUF->optdata[2] = (UIP_TCP_MSS) / 256;
BUF->optdata[3] = (UIP_TCP_MSS) & 255;
uip_len = 44;
BUF->tcpoffset = 6 << 4;
goto tcp_send;
/* This label will be jumped to if we found an active connection. */
found:
uip_conn = uip_connr;
uip_flags = 0;
/* We do a very naive form of TCP reset processing; we just accept
any RST and kill our connection. We should in fact check if the
sequence number of this reset is wihtin our advertised window
before we accept the reset. */
if(BUF->flags & TCP_RST) {
uip_connr->tcpstateflags = CLOSED;
UIP_LOG("tcp: got reset, aborting connection.");
uip_flags = UIP_ABORT;
UIP_APPCALL();
goto drop;
}
/* Calculated the length of the data, if the application has sent
any data to us. */
c = (BUF->tcpoffset >> 4) << 2;
/* uip_len will contain the length of the actual TCP data. This is
calculated by subtracing the length of the TCP header (in
c) and the length of the IP header (20 bytes). */
uip_len = uip_len - c - 20;
/* First, check if the sequence number of the incoming packet is
what we're expecting next. If not, we send out an ACK with the
correct numbers in. */
if(uip_len > 0 &&
(BUF->seqno[0] != uip_connr->rcv_nxt[0] ||
BUF->seqno[1] != uip_connr->rcv_nxt[1] ||
BUF->seqno[2] != uip_connr->rcv_nxt[2] ||
BUF->seqno[3] != uip_connr->rcv_nxt[3])) {
goto tcp_send_ack;
}
/* Next, check if the incoming segment acknowledges any outstanding
data. If so, we update the sequence number, reset the length of
the outstanding data, calculate RTT estimations, and reset the
retransmission timer. */
if((BUF->flags & TCP_ACK) && uip_outstanding(uip_connr)) {
uip_add32(uip_connr->snd_nxt, uip_connr->len);
if(BUF->ackno[0] == uip_acc32[0] &&
BUF->ackno[1] == uip_acc32[1] &&
BUF->ackno[2] == uip_acc32[2] &&
BUF->ackno[3] == uip_acc32[3]) {
/* Update sequence number. */
uip_connr->snd_nxt[0] = uip_acc32[0];
uip_connr->snd_nxt[1] = uip_acc32[1];
uip_connr->snd_nxt[2] = uip_acc32[2];
uip_connr->snd_nxt[3] = uip_acc32[3];
/* Do RTT estimation, unless we have done retransmissions. */
if(uip_connr->nrtx == 0) {
signed char m;
m = uip_connr->rto - uip_connr->timer;
/* This is taken directly from VJs original code in his paper */
m = m - (uip_connr->sa >> 3);
uip_connr->sa += m;
if(m < 0) {
m = -m;
}
m = m - (uip_connr->sv >> 2);
uip_connr->sv += m;
uip_connr->rto = (uip_connr->sa >> 3) + uip_connr->sv;
}
/* Set the acknowledged flag. */
uip_flags = UIP_ACKDATA;
/* Reset the retransmission timer. */
uip_connr->timer = uip_connr->rto;
}
}
/* Do different things depending on in what state the connection is. */
switch(uip_connr->tcpstateflags & TS_MASK) {
/* CLOSED and LISTEN are not handled here. CLOSE_WAIT is not
implemented, since we force the application to close when the
peer sends a FIN (hence the application goes directly from
ESTABLISHED to LAST_ACK). */
case SYN_RCVD:
/* In SYN_RCVD we have sent out a SYNACK in response to a SYN, and
we are waiting for an ACK that acknowledges the data we sent
out the last time. Therefore, we want to have the UIP_ACKDATA
flag set. If so, we enter the ESTABLISHED state. */
if(uip_flags & UIP_ACKDATA) {
uip_connr->tcpstateflags = ESTABLISHED;
uip_flags = UIP_CONNECTED;
uip_connr->len = 0;
if(uip_len > 0) {
uip_flags |= UIP_NEWDATA;
uip_add_rcv_nxt(uip_len);
}
uip_slen = 0;
UIP_APPCALL();
goto appsend;
}
goto drop;
#if UIP_ACTIVE_OPEN
case SYN_SENT:
/* In SYN_SENT, we wait for a SYNACK that is sent in response to
our SYN. The rcv_nxt is set to sequence number in the SYNACK
plus one, and we send an ACK. We move into the ESTABLISHED
state. */
if((uip_flags & UIP_ACKDATA) && BUF->flags == (TCP_SYN | TCP_ACK)) {
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