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px4_autopilot/nuttx/net/uip/uip_tcpinput.c

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/****************************************************************************
* net/uip/uip_tcpinput.c
* Handling incoming TCP input
*
* Copyright (C) 2007-2012 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Adapted for NuttX from logic in uIP which also has a BSD-like license:
*
* Original author Adam Dunkels <adam@dunkels.com>
* Copyright () 2001-2003, Adam Dunkels.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#if defined(CONFIG_NET) && defined(CONFIG_NET_TCP)
#include <stdint.h>
#include <string.h>
#include <debug.h>
#include <nuttx/net/uip/uipopt.h>
#include <nuttx/net/uip/uip.h>
#include <nuttx/net/uip/uip-arch.h>
#include "uip_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define BUF ((struct uip_tcpip_hdr *)&dev->d_buf[UIP_LLH_LEN])
/****************************************************************************
* Public Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: uip_tcpinput
*
* Description:
* Handle incoming TCP input
*
* Parameters:
* dev - The device driver structure containing the received TCP packet.
*
* Return:
* None
*
* Assumptions:
* Called from the interrupt level or with interrupts disabled.
*
****************************************************************************/
void uip_tcpinput(struct uip_driver_s *dev)
{
struct uip_conn *conn = NULL;
struct uip_tcpip_hdr *pbuf = BUF;
uint16_t tmp16;
uint16_t flags;
uint8_t opt;
uint8_t result;
int len;
int i;
dev->d_snddata = &dev->d_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN];
dev->d_appdata = &dev->d_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN];
#ifdef CONFIG_NET_STATISTICS
uip_stat.tcp.recv++;
#endif
/* Start of TCP input header processing code. */
if (uip_tcpchksum(dev) != 0xffff)
{
/* Compute and check the TCP checksum. */
#ifdef CONFIG_NET_STATISTICS
uip_stat.tcp.drop++;
uip_stat.tcp.chkerr++;
#endif
nlldbg("Bad TCP checksum\n");
goto drop;
}
/* Demultiplex this segment. First check any active connections. */
conn = uip_tcpactive(pbuf);
if (conn)
{
/* We found an active connection.. Check for the subsequent SYN
* arriving in UIP_SYN_RCVD state after the SYNACK packet was
* lost. To avoid other issues, reset any active connection
* where a SYN arrives in a state != UIP_SYN_RCVD.
*/
if ((conn->tcpstateflags & UIP_TS_MASK) != UIP_SYN_RCVD &&
(BUF->flags & TCP_CTL) == TCP_SYN)
{
goto reset;
}
else
{
goto found;
}
}
/* If we didn't find and active connection that expected the packet,
* either (1) this packet is an old duplicate, or (2) this is a SYN packet
* destined for a connection in LISTEN. If the SYN flag isn't set,
* it is an old packet and we send a RST.
*/
if ((pbuf->flags & TCP_CTL) == TCP_SYN)
{
/* This is a SYN packet for a connection. Find the connection
* listening on this port.
*/
tmp16 = pbuf->destport;
if (uip_islistener(tmp16))
{
/* We matched the incoming packet with a connection in LISTEN.
* We now need to create a new connection and send a SYNACK in
* response.
*/
/* First allocate a new connection structure and see if there is any
* user application to accept it.
*/
conn = uip_tcpaccept(pbuf);
if (conn)
{
/* The connection structure was successfully allocated. Now see if
* there is an application waiting to accept the connection (or at
* least queue it it for acceptance).
*/
conn->crefs = 1;
if (uip_accept(dev, conn, tmp16) != OK)
{
/* No, then we have to give the connection back and drop the packet */
conn->crefs = 0;
uip_tcpfree(conn);
conn = NULL;
}
else
{
/* TCP state machine should move to the ESTABLISHED state only after
* it has received ACK from the host. This needs to be investigated
* further.
*/
conn->tcpstateflags = UIP_ESTABLISHED;
}
}
if (!conn)
{
/* Either (1) all available connections are in use, or (2) there is no
* application in place to accept the connection. We drop packet and hope that
* the remote end will retransmit the packet at a time when we
* have more spare connections or someone waiting to accept the connection.
*/
#ifdef CONFIG_NET_STATISTICS
uip_stat.tcp.syndrop++;
#endif
nlldbg("No free TCP connections\n");
goto drop;
}
uip_incr32(conn->rcvseq, 1);
/* Parse the TCP MSS option, if present. */
if ((pbuf->tcpoffset & 0xf0) > 0x50)
{
for (i = 0; i < ((pbuf->tcpoffset >> 4) - 5) << 2 ;)
{
opt = dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + i];
if (opt == TCP_OPT_END)
{
/* End of options. */
break;
}
else if (opt == TCP_OPT_NOOP)
{
/* NOP option. */
++i;
}
else if (opt == TCP_OPT_MSS &&
dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i] == TCP_OPT_MSS_LEN)
{
/* An MSS option with the right option length. */
tmp16 = ((uint16_t)dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + i] << 8) |
(uint16_t)dev->d_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN + 3 + i];
conn->initialmss = conn->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 (dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i] == 0)
{
/* If the length field is zero, the options are malformed
* and we don't process them further.
*/
break;
}
i += dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i];
}
}
}
/* Our response will be a SYNACK. */
uip_tcpack(dev, conn, TCP_ACK | TCP_SYN);
return;
}
}
/* This is (1) an old duplicate packet or (2) a SYN packet but with
* no matching listener found. Send RST packet in either case.
*/
reset:
/* We do not send resets in response to resets. */
if ((pbuf->flags & TCP_RST) != 0)
{
goto drop;
}
#ifdef CONFIG_NET_STATISTICS
uip_stat.tcp.synrst++;
#endif
uip_tcpreset(dev);
return;
found:
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 within our advertised window
* before we accept the reset.
*/
if ((pbuf->flags & TCP_RST) != 0)
{
conn->tcpstateflags = UIP_CLOSED;
nlldbg("RESET - TCP state: UIP_CLOSED\n");
(void)uip_tcpcallback(dev, conn, UIP_ABORT);
goto drop;
}
/* Calculated the length of the data, if the application has sent
* any data to us.
*/
len = (pbuf->tcpoffset >> 4) << 2;
/* d_len will contain the length of the actual TCP data. This is
* calculated by subtracting the length of the TCP header (in
* len) and the length of the IP header (20 bytes).
*/
dev->d_len -= (len + UIP_IPH_LEN);
/* 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, unless we are in the SYN_RCVD state and
* receive a SYN, in which case we should retransmit our SYNACK
* (which is done further down).
*/
if (!((((conn->tcpstateflags & UIP_TS_MASK) == UIP_SYN_SENT) &&
((pbuf->flags & TCP_CTL) == (TCP_SYN | TCP_ACK))) ||
(((conn->tcpstateflags & UIP_TS_MASK) == UIP_SYN_RCVD) &&
((pbuf->flags & TCP_CTL) == TCP_SYN))))
{
if ((dev->d_len > 0 || ((pbuf->flags & (TCP_SYN | TCP_FIN)) != 0)) &&
memcmp(pbuf->seqno, conn->rcvseq, 4) != 0)
{
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
}
}
/* 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 ((pbuf->flags & TCP_ACK) != 0 && conn->unacked > 0)
{
uint32_t unackseq;
uint32_t ackseq;
/* The next sequence number is equal to the current sequence
* number (sndseq) plus the size of the oustanding, unacknowledged
* data (unacked).
*/
unackseq = uip_tcpaddsequence(conn->sndseq, conn->unacked);
/* Get the sequence number of that has just been acknowledged by this
* incoming packet.
*/
ackseq = uip_tcpgetsequence(pbuf->ackno);
/* Check how many of the outstanding bytes have been acknowledged. For
* a most uIP send operation, this should always be true. However,
* the send() API sends data ahead when it can without waiting for
* the ACK. In this case, the 'ackseq' could be less than then the
* new sequence number.
*/
if (ackseq <= unackseq)
{
/* Calculate the new number of oustanding, unacknowledged bytes */
conn->unacked = unackseq - ackseq;
}
else
{
/* What would it mean if ackseq > unackseq? The peer has ACKed
* more bytes than we think we have sent? Someone has lost it.
* Complain and reset the number of outstanding, unackowledged
* bytes
*/
nlldbg("ERROR: ackseq[%08x] > unackseq[%08x]\n", ackseq, unackseq);
conn->unacked = 0;
}
/* Update sequence number to the unacknowledge sequence number. If
* there is still outstanding, unacknowledged data, then this will
* be beyond ackseq.
*/
nllvdbg("sndseq: %08x->%08x unackseq: %08x new unacked: %d\n",
conn->sndseq, ackseq, unackseq, conn->unacked);
uip_tcpsetsequence(conn->sndseq, ackseq);
/* Do RTT estimation, unless we have done retransmissions. */
if (conn->nrtx == 0)
{
signed char m;
m = conn->rto - conn->timer;
/* This is taken directly from VJs original code in his paper */
m = m - (conn->sa >> 3);
conn->sa += m;
if (m < 0)
{
m = -m;
}
m = m - (conn->sv >> 2);
conn->sv += m;
conn->rto = (conn->sa >> 3) + conn->sv;
}
/* Set the acknowledged flag. */
flags |= UIP_ACKDATA;
/* Reset the retransmission timer. */
conn->timer = conn->rto;
}
/* Do different things depending on in what state the connection is. */
switch (conn->tcpstateflags & UIP_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 UIP_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 ((flags & UIP_ACKDATA) != 0)
{
conn->tcpstateflags = UIP_ESTABLISHED;
conn->unacked = 0;
nllvdbg("TCP state: UIP_ESTABLISHED\n");
flags = UIP_CONNECTED;
if (dev->d_len > 0)
{
flags |= UIP_NEWDATA;
uip_incr32(conn->rcvseq, dev->d_len);
}
dev->d_sndlen = 0;
result = uip_tcpcallback(dev, conn, flags);
uip_tcpappsend(dev, conn, result);
return;
}
/* We need to retransmit the SYNACK */
if ((pbuf->flags & TCP_CTL) == TCP_SYN)
{
uip_tcpack(dev, conn, TCP_ACK | TCP_SYN);
return;
}
goto drop;
case UIP_SYN_SENT:
/* In SYN_SENT, we wait for a SYNACK that is sent in response to
* our SYN. The rcvseq is set to sequence number in the SYNACK
* plus one, and we send an ACK. We move into the ESTABLISHED
* state.
*/
if ((flags & UIP_ACKDATA) != 0 && (pbuf->flags & TCP_CTL) == (TCP_SYN | TCP_ACK))
{
/* Parse the TCP MSS option, if present. */
if ((pbuf->tcpoffset & 0xf0) > 0x50)
{
for (i = 0; i < ((pbuf->tcpoffset >> 4) - 5) << 2 ;)
{
opt = dev->d_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN + i];
if (opt == TCP_OPT_END)
{
/* End of options. */
break;
}
else if (opt == TCP_OPT_NOOP)
{
/* NOP option. */
++i;
}
else if (opt == TCP_OPT_MSS &&
dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i] == TCP_OPT_MSS_LEN)
{
/* An MSS option with the right option length. */
tmp16 =
(dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + i] << 8) |
dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 3 + i];
conn->initialmss =
conn->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 (dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i] == 0)
{
/* If the length field is zero, the options are
* malformed and we don't process them further.
*/
break;
}
i += dev->d_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + i];
}
}
}
conn->tcpstateflags = UIP_ESTABLISHED;
memcpy(conn->rcvseq, pbuf->seqno, 4);
nllvdbg("TCP state: UIP_ESTABLISHED\n");
uip_incr32(conn->rcvseq, 1);
conn->unacked = 0;
dev->d_len = 0;
dev->d_sndlen = 0;
result = uip_tcpcallback(dev, conn, UIP_CONNECTED | UIP_NEWDATA);
uip_tcpappsend(dev, conn, result);
return;
}
/* Inform the application that the connection failed */
(void)uip_tcpcallback(dev, conn, UIP_ABORT);
/* The connection is closed after we send the RST */
conn->tcpstateflags = UIP_CLOSED;
nllvdbg("Connection failed - TCP state: UIP_CLOSED\n");
/* We do not send resets in response to resets. */
if ((pbuf->flags & TCP_RST) != 0)
{
goto drop;
}
uip_tcpreset(dev);
return;
case UIP_ESTABLISHED:
/* In the ESTABLISHED state, we call upon the application to feed
* data into the d_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 ((pbuf->flags & TCP_FIN) != 0 && (conn->tcpstateflags & UIP_STOPPED) == 0)
{
if (conn->unacked > 0)
{
goto drop;
}
/* Update the sequence number and indicate that the connection has
* been closed.
*/
uip_incr32(conn->rcvseq, dev->d_len + 1);
flags |= UIP_CLOSE;
if (dev->d_len > 0)
{
flags |= UIP_NEWDATA;
}
(void)uip_tcpcallback(dev, conn, flags);
conn->tcpstateflags = UIP_LAST_ACK;
conn->unacked = 1;
conn->nrtx = 0;
nllvdbg("TCP state: UIP_LAST_ACK\n");
uip_tcpsend(dev, conn, TCP_FIN | TCP_ACK, UIP_IPTCPH_LEN);
return;
}
/* Check the URG flag. If this is set, the segment carries urgent
* data that we must pass to the application.
*/
if ((pbuf->flags & TCP_URG) != 0)
{
#ifdef CONFIG_NET_TCPURGDATA
dev->d_urglen = (pbuf->urgp[0] << 8) | pbuf->urgp[1];
if (dev->d_urglen > dev->d_len)
{
/* There is more urgent data in the next segment to come. */
dev->d_urglen = dev->d_len;
}
uip_incr32(conn->rcvseq, dev->d_urglen);
dev->d_len -= dev->d_urglen;
dev->d_urgdata = dev->d_appdata;
dev->d_appdata += dev->d_urglen;
}
else
{
dev->d_urglen = 0;
#else /* CONFIG_NET_TCPURGDATA */
dev->d_appdata = ((uint8_t*)dev->d_appdata) + ((pbuf->urgp[0] << 8) | pbuf->urgp[1]);
dev->d_len -= (pbuf->urgp[0] << 8) | pbuf->urgp[1];
#endif /* CONFIG_NET_TCPURGDATA */
}
/* If d_len > 0 we have TCP data in the packet, and we flag this
* by setting the UIP_NEWDATA flag. If the application has stopped
* the dataflow using uip_stop(), we must not accept any data
* packets from the remote host.
*/
if (dev->d_len > 0 && (conn->tcpstateflags & UIP_STOPPED) == 0)
{
flags |= UIP_NEWDATA;
}
/* 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 = ((uint16_t)pbuf->wnd[0] << 8) + (uint16_t)pbuf->wnd[1];
if (tmp16 > conn->initialmss || tmp16 == 0)
{
tmp16 = conn->initialmss;
}
conn->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 d_len field
* contains the length of the incoming data. The application can
* access the incoming data through the global pointer
* d_appdata, which usually points UIP_IPTCPH_LEN + UIP_LLH_LEN
* bytes into the d_buf array.
*
* If the application wishes to send any data, this data should be
* put into the d_appdata and the length of the data should be
* put into d_len. If the application don't have any data to
* send, d_len must be set to 0.
*/
if ((flags & (UIP_NEWDATA | UIP_ACKDATA)) != 0)
{
/* Clear sndlen and remember the size in d_len. The application
* may modify d_len and we will need this value later when we
* update the sequence number.
*/
dev->d_sndlen = 0;
len = dev->d_len;
/* Provide the packet to the application */
result = uip_tcpcallback(dev, conn, flags);
/* If the application successfully handled the incoming data,
* then UIP_SNDACK will be set in the result. In this case,
* we need to update the sequence number. The ACK will be
* send by uip_tcpappsend().
*/
if ((result & UIP_SNDACK) != 0)
{
/* Update the sequence number using the saved length */
uip_incr32(conn->rcvseq, len);
}
/* Send the response, ACKing the data or not, as appropriate */
uip_tcpappsend(dev, conn, result);
return;
}
goto drop;
case UIP_LAST_ACK:
/* We can close this connection if the peer has acknowledged our
* FIN. This is indicated by the UIP_ACKDATA flag.
*/
if ((flags & UIP_ACKDATA) != 0)
{
conn->tcpstateflags = UIP_CLOSED;
nllvdbg("UIP_LAST_ACK TCP state: UIP_CLOSED\n");
(void)uip_tcpcallback(dev, conn, UIP_CLOSE);
}
break;
case UIP_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 (dev->d_len > 0)
{
uip_incr32(conn->rcvseq, dev->d_len);
}
if ((pbuf->flags & TCP_FIN) != 0)
{
if ((flags & UIP_ACKDATA) != 0)
{
conn->tcpstateflags = UIP_TIME_WAIT;
conn->timer = 0;
conn->unacked = 0;
nllvdbg("TCP state: UIP_TIME_WAIT\n");
}
else
{
conn->tcpstateflags = UIP_CLOSING;
nllvdbg("TCP state: UIP_CLOSING\n");
}
uip_incr32(conn->rcvseq, 1);
(void)uip_tcpcallback(dev, conn, UIP_CLOSE);
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
}
else if ((flags & UIP_ACKDATA) != 0)
{
conn->tcpstateflags = UIP_FIN_WAIT_2;
conn->unacked = 0;
nllvdbg("TCP state: UIP_FIN_WAIT_2\n");
goto drop;
}
if (dev->d_len > 0)
{
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
}
goto drop;
case UIP_FIN_WAIT_2:
if (dev->d_len > 0)
{
uip_incr32(conn->rcvseq, dev->d_len);
}
if ((pbuf->flags & TCP_FIN) != 0)
{
conn->tcpstateflags = UIP_TIME_WAIT;
conn->timer = 0;
nllvdbg("TCP state: UIP_TIME_WAIT\n");
uip_incr32(conn->rcvseq, 1);
(void)uip_tcpcallback(dev, conn, UIP_CLOSE);
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
}
if (dev->d_len > 0)
{
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
}
goto drop;
case UIP_TIME_WAIT:
uip_tcpsend(dev, conn, TCP_ACK, UIP_IPTCPH_LEN);
return;
case UIP_CLOSING:
if ((flags & UIP_ACKDATA) != 0)
{
conn->tcpstateflags = UIP_TIME_WAIT;
conn->timer = 0;
nllvdbg("TCP state: UIP_TIME_WAIT\n");
}
default:
break;
}
drop:
dev->d_len = 0;
}
#endif /* CONFIG_NET && CONFIG_NET_TCP */