📄 uip.c
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/* Parse the TCP MSS option, if present. */
if((BUF->tcpoffset & 0xf0) > 0x50) {
for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
opt = uip_buf[40 + 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 = (uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |
uip_buf[UIP_TCPIP_HLEN + 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];
}
}
}
uip_connr->tcpstateflags = ESTABLISHED;
uip_connr->rcv_nxt[0] = BUF->seqno[0];
uip_connr->rcv_nxt[1] = BUF->seqno[1];
uip_connr->rcv_nxt[2] = BUF->seqno[2];
uip_connr->rcv_nxt[3] = BUF->seqno[3];
uip_add_rcv_nxt(1);
uip_flags = UIP_CONNECTED | UIP_NEWDATA;
uip_connr->len = 0;
uip_len = 0;
uip_slen = 0;
UIP_APPCALL();
goto appsend;
}
goto reset;
#endif /* UIP_ACTIVE_OPEN */
case ESTABLISHED:
/* In the ESTABLISHED state, we call upon the application to feed
data into the uip_buf. If the UIP_ACKDATA flag is set, the
application should put new data into the buffer, otherwise we are
retransmitting an old segment, and the application should put that
data into the buffer.
If the incoming packet is a FIN, we should close the connection on
this side as well, and we send out a FIN and enter the LAST_ACK
state. We require that there is no outstanding data; otherwise the
sequence numbers will be screwed up. */
if(BUF->flags & TCP_FIN) {
if(uip_outstanding(uip_connr)) {
goto drop;
}
uip_add_rcv_nxt(1 + uip_len);
uip_flags = UIP_CLOSE;
if(uip_len > 0) {
uip_flags |= UIP_NEWDATA;
}
UIP_APPCALL();
uip_connr->len = 1;
uip_connr->tcpstateflags = LAST_ACK;
uip_connr->nrtx = 0;
tcp_send_finack:
BUF->flags = TCP_FIN | TCP_ACK;
goto tcp_send_nodata;
}
/* Check the URG flag. If this is set, the segment carries urgent
data that we must pass to the application. */
if(BUF->flags & TCP_URG) {
#if UIP_URGDATA > 0
uip_urglen = (BUF->urgp[0] << 8) | BUF->urgp[1];
if(uip_urglen > uip_len) {
/* There is more urgent data in the next segment to come. */
uip_urglen = uip_len;
}
uip_add_rcv_nxt(uip_urglen);
uip_len -= uip_urglen;
uip_urgdata = uip_appdata;
uip_appdata += uip_urglen;
}
else {
uip_urglen = 0;
#endif /* UIP_URGDATA > 0 */
uip_appdata += (BUF->urgp[0] << 8) | BUF->urgp[1];
uip_len -= (BUF->urgp[0] << 8) | BUF->urgp[1];
}
/* If uip_len > 0 we have TCP data in the packet, and we flag this
by setting the UIP_NEWDATA flag and update the sequence number
we acknowledge. If the application has stopped the dataflow
using uip_stop(), we must not accept any data packets from the
remote host. */
if(uip_len > 0 && !(uip_connr->tcpstateflags & UIP_STOPPED)) {
uip_flags |= UIP_NEWDATA;
uip_add_rcv_nxt(uip_len);
}
/* Check if the available buffer space advertised by the other end
is smaller than the initial MSS for this connection. If so, we
set the current MSS to the window size to ensure that the
application does not send more data than the other end can
handle.
If the remote host advertises a zero window, we set the MSS to
the initial MSS so that the application will send an entire MSS
of data. This data will not be acknowledged by the receiver,
and the application will retransmit it. This is called the
"persistent timer" and uses the retransmission mechanim.
*/
tmp16 = ((u16_t)BUF->wnd[0] << 8) + (u16_t)BUF->wnd[1];
if(tmp16 > uip_connr->initialmss || tmp16 == 0) {
tmp16 = uip_connr->initialmss;
}
uip_connr->mss = tmp16;
/* If this packet constitutes an ACK for outstanding data (flagged
by the UIP_ACKDATA flag, we should call the application since it
might want to send more data. If the incoming packet had data
from the peer (as flagged by the UIP_NEWDATA flag), the
application must also be notified.
When the application is called, the global variable uip_len
contains the length of the incoming data. The application can
access the incoming data through the global pointer
uip_appdata, which usually points 40 bytes into the uip_buf
array.
If the application wishes to send any data, this data should be
put into the uip_appdata and the length of the data should be
put into uip_len. If the application don't have any data to
send, uip_len must be set to 0. */
if(uip_flags & (UIP_NEWDATA | UIP_ACKDATA)) {
uip_slen = 0;
UIP_APPCALL();
appsend:
if(uip_flags & UIP_ABORT) {
uip_slen = 0;
uip_connr->tcpstateflags = CLOSED;
BUF->flags = TCP_RST | TCP_ACK;
goto tcp_send_nodata;
}
if(uip_flags & UIP_CLOSE) {
uip_slen = 0;
uip_connr->len = 1;
uip_connr->tcpstateflags = FIN_WAIT_1;
uip_connr->nrtx = 0;
BUF->flags = TCP_FIN | TCP_ACK;
goto tcp_send_nodata;
}
/* If uip_slen > 0, the application has data to be sent. */
if(uip_slen > 0) {
/* If the connection has acknowledged data, the contents of
the ->len variable should be discarded. */
if((uip_flags & UIP_ACKDATA) != 0) {
uip_connr->len = 0;
}
/* If the ->len variable is non-zero the connection has
already data in transit and cannot send anymore right
now. */
if(uip_connr->len == 0) {
/* The application cannot send more than what is allowed by
the mss (the minumum of the MSS and the available
window). */
if(uip_slen > uip_connr->mss) {
uip_slen = uip_connr->mss;
}
/* Remember how much data we send out now so that we know
when everything has been acknowledged. */
uip_connr->len = uip_slen;
}
else {
/* If the application already had unacknowledged data, we
make sure that the application does not send (i.e.,
retransmit) out more than it previously sent out. */
uip_slen = uip_connr->len;
}
}
else {
uip_connr->len = 0;
}
uip_connr->nrtx = 0;
apprexmit:
uip_appdata = uip_sappdata;
/* If the application has data to be sent, or if the incoming
packet had new data in it, we must send out a packet. */
if(uip_slen > 0 && uip_connr->len > 0) {
/* Add the length of the IP and TCP headers. */
uip_len = uip_connr->len + UIP_TCPIP_HLEN;
/* We always set the ACK flag in response packets. */
BUF->flags = TCP_ACK | TCP_PSH;
/* Send the packet. */
goto tcp_send_noopts;
}
/* If there is no data to send, just send out a pure ACK if
there is newdata. */
if(uip_flags & UIP_NEWDATA) {
uip_len = UIP_TCPIP_HLEN;
BUF->flags = TCP_ACK;
goto tcp_send_noopts;
}
}
goto drop;
case LAST_ACK:
/* We can close this connection if the peer has acknowledged our
FIN. This is indicated by the UIP_ACKDATA flag. */
if(uip_flags & UIP_ACKDATA) {
uip_connr->tcpstateflags = CLOSED;
uip_flags = UIP_CLOSE;
UIP_APPCALL();
}
break;
case FIN_WAIT_1:
/* The application has closed the connection, but the remote host
hasn't closed its end yet. Thus we do nothing but wait for a
FIN from the other side. */
if(uip_len > 0) {
uip_add_rcv_nxt(uip_len);
}
if(BUF->flags & TCP_FIN) {
if(uip_flags & UIP_ACKDATA) {
uip_connr->tcpstateflags = TIME_WAIT;
uip_connr->timer = 0;
uip_connr->len = 0;
} else {
uip_connr->tcpstateflags = CLOSING;
}
uip_add_rcv_nxt(1);
uip_flags = UIP_CLOSE;
UIP_APPCALL();
goto tcp_send_ack;
} else if(uip_flags & UIP_ACKDATA) {
uip_connr->tcpstateflags = FIN_WAIT_2;
uip_connr->len = 0;
goto drop;
}
if(uip_len > 0) {
goto tcp_send_ack;
}
goto drop;
case FIN_WAIT_2:
if(uip_len > 0) {
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