net/tcp/tcp_appsend.c

/****************************************************************************
 * net/tcp/tcp_appsend.c
 *
 *   Copyright (C) 2007-2010, 2014 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 <inttypes.h>
#include <stdint.h>
#include <assert.h>
#include <debug.h>

#include <nuttx/net/netconfig.h>
#include <nuttx/net/netdev.h>
#include <nuttx/net/tcp.h>

#include "devif/devif.h"
#include "tcp/tcp.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: tcp_appsend
 *
 * Description:
 *   Handle application or TCP protocol response.  If this function is called
 *   with dev->d_sndlen > 0, then this is an application attempting to send
 *   packet.
 *
 * Input Parameters:
 *   dev    - The device driver structure to use in the send operation
 *   conn   - The TCP connection structure holding connection information
 *   result - App result event sent
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *   The network is locked.
 *
 ****************************************************************************/

void tcp_appsend(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
                 uint16_t result)
{
  uint8_t hdrlen;

  ninfo("result: %04x d_sndlen: %d conn->tx_unacked: %" PRId32 "\n",
        result, dev->d_sndlen, (uint32_t)conn->tx_unacked);

  /* Need to update the recv window? */

  if (tcp_should_send_recvwindow(conn))
    {
      result |= TCP_SNDACK;
#ifdef CONFIG_NET_TCP_DELAYED_ACK
      conn->rx_unackseg = 0;
#endif
    }

#ifdef CONFIG_NET_TCP_DELAYED_ACK
  /* Did the caller request that an ACK be sent? */

  else if ((result & TCP_SNDACK) != 0)
    {
      /* Yes.. Handle delayed acknowledgments */

      /* Reset the ACK timer in any event. */

      conn->rx_acktimer = 0;

      /* Per RFC 1122:  "...in a stream of full-sized segments there
       * SHOULD be an ACK for at least every second segment."
       *
       * NOTES:
       * 1. If there is a data payload or other flags to be sent with the
       *    outgoing packet, then we may as well include the ACK too.
       * 2. The RFC refers to full-size segments.  It is not clear what
       *    "full-size" means.  Does that mean that the payload is the size
       *    of the MSS?  Payload size is not considered other there being
       *    a payload or or not.  Should there be some special action for
       *    small payloads of size < MSS?
       * 3. Experimentation shows that Windows and Linux behave somewhat
       *    differently; they delay the ACKs for many more segments (6 or
       *    more).  Delaying for more segments would provide less network
       *    traffic and better performance but seems non-compliant.
       */

      if (conn->rx_unackseg > 0 || dev->d_sndlen > 0 ||
          result != TCP_SNDACK)
        {
          /* Reset the delayed ACK state and send the ACK with this packet. */

          conn->rx_unackseg = 0;
        }
      else
        {
          /* This is only an ACK and there is no pending delayed ACK and
           * no TX data is being sent.  Indicate that there is one un-ACKed
           * segment and don't send anything now.
           */

          conn->rx_unackseg = 1;
          return;
        }
    }

  /* If there are data to be sent in the same direction as the ACK before
   * the second data packet is received and the delay timer expires, the ACK
   * is piggybacked with the data segment and sent immediately.
   */

  else if (dev->d_sndlen > 0 && conn->rx_unackseg > 0)
    {
      result |= TCP_SNDACK;
      conn->rx_unackseg = 0;
    }
#endif

  /* Get the IP header length associated with the IP domain configured for
   * this TCP connection.
   */

  hdrlen = tcpip_hdrsize(conn);

  /* Check If the device went down */

  if ((result & NETDEV_DOWN) != 0)
    {
      /* If so, make sure that the connection is marked closed
       * and do not try to send anything.
       */

      dev->d_sndlen = 0;
      conn->tcpstateflags = TCP_CLOSED;
      ninfo("TCP state: NETDEV_DOWN\n");
    }

  /* Check for connection aborted */

  else if ((result & TCP_ABORT) != 0)
    {
      dev->d_sndlen = 0;
      conn->tcpstateflags = TCP_CLOSED;
      ninfo("TCP state: TCP_CLOSED\n");

      tcp_send(dev, conn, TCP_RST | TCP_ACK, hdrlen);
    }

  /* Check for connection closed */

  else if ((result & TCP_CLOSE) != 0)
    {
      conn->tcpstateflags = TCP_FIN_WAIT_1;
      conn->tx_unacked    = 1;
      conn->nrtx          = 0;
#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
      conn->sndseq_max    = tcp_getsequence(conn->sndseq) + 1;
#endif
      ninfo("TCP state: TCP_FIN_WAIT_1\n");

      dev->d_sndlen       = 0;
      tcp_send(dev, conn, TCP_FIN | TCP_ACK, hdrlen);
    }

  /* None of the above */

  else
    {
      /* The application cannot send more than what is allowed by the
       * MSS (the minimum of the MSS and the available window).
       */

      DEBUGASSERT(dev->d_sndlen <= conn->mss);

#if !defined(CONFIG_NET_TCP_WRITE_BUFFERS) || defined(CONFIG_NET_SENDFILE)

#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
      if (conn->sendfile)
        {
#endif

      /* If d_sndlen > 0, the application has data to be sent. */

      if (dev->d_sndlen > 0)
        {
          /* Remember how much data we send out now so that we know
           * when everything has been acknowledged.  Just increment the
           * amount of data sent.  This will be needed in sequence number
           * calculations and we know that this is not a re-transmission.
           * Retransmissions do not go through this path.
           */

          conn->tx_unacked += dev->d_sndlen;
        }

      conn->nrtx = 0;

#ifdef CONFIG_NET_TCP_WRITE_BUFFERS
        }
#endif

#endif

      /* Then handle the rest of the operation just as for the rexmit case */

      tcp_rexmit(dev, conn, result);
    }
}

/****************************************************************************
 * Name: tcp_rexmit
 *
 * Description:
 *   Handle application retransmission
 *
 * Input Parameters:
 *   dev    - The device driver structure to use in the send operation
 *   conn   - The TCP connection structure holding connection information
 *   result - App result event sent
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *   The network is locked.
 *
 ****************************************************************************/

void tcp_rexmit(FAR struct net_driver_s *dev, FAR struct tcp_conn_s *conn,
                uint16_t result)
{
  uint8_t hdrlen;

  ninfo("result: %04x d_sndlen: %d conn->tx_unacked: %" PRId32 "\n",
        result, dev->d_sndlen, (uint32_t)conn->tx_unacked);

  /* Get the IP header length associated with the IP domain configured for
   * this TCP connection.
   */

  hdrlen = tcpip_hdrsize(conn);

  /* 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 defined(CONFIG_NET_TCP_WRITE_BUFFERS) && defined(CONFIG_NET_SENDFILE)
  if (conn->sendfile)
#endif
    {
#if !defined(CONFIG_NET_TCP_WRITE_BUFFERS) || defined(CONFIG_NET_SENDFILE)
      if ((result & TCP_REXMIT) != 0 &&
          dev->d_sndlen > 0 && conn->tx_unacked > 0 &&
          conn->rexmit_seq > 0)
        {
          uint32_t saveseq;

          /* According to RFC 6298 (5.4), retransmit the earliest segment
           * that has not been acknowledged by the TCP receiver.
           */

          saveseq = tcp_getsequence(conn->sndseq);
          tcp_setsequence(conn->sndseq, conn->rexmit_seq);

          tcp_send(dev, conn, TCP_ACK | TCP_PSH, dev->d_sndlen + hdrlen);

          tcp_setsequence(conn->sndseq, saveseq);

          return;
        }
#endif
    }

#if defined(CONFIG_NET_TCP_WRITE_BUFFERS)
  if (dev->d_sndlen > 0)
#else
  if (dev->d_sndlen > 0 && conn->tx_unacked > 0)
#endif
    {
      uint32_t seq;

      /* We always set the ACK flag in response packets adding the length of
       * the IP and TCP headers.
       */

      tcp_send(dev, conn, TCP_ACK | TCP_PSH, dev->d_sndlen + hdrlen);

      /* Advance sndseq */

      seq = tcp_getsequence(conn->sndseq);
      tcp_setsequence(conn->sndseq, seq + dev->d_sndlen);
    }

  /* If there is no data to send, just send out a pure ACK if one is
   * requested.
   */

  else if ((result & TCP_SNDACK) != 0)
    {
      tcp_send(dev, conn, TCP_ACK, hdrlen);
    }

  /* There is nothing to do -- drop the packet */

  else
    {
      dev->d_len = 0;
    }
}
#endif /* CONFIG_NET && CONFIG_NET_TCP */